Abstract:
A hydraulic power generation system is provided for generating power using a pseudo-osmosis process which efficiently exploits the osmotic energy potential between two bodies of water having different salinity concentrations. The method and apparatus of the present invention does not require the use of a semi-permeable membrane or other specially formulated material, nor does it require heating or cooling of the fresh water or salt water solution. Moreover, the device may be used to recover energy from a wide variety of fresh water sources, including treated or untreated river run-off, treated waste-water run-off or effluent, storm-drain run-off, partly contaminated fresh water run-off, and a wide variety of other fresh water sources. The device is well suited to power production in a wide variety of geographic locations and under a wide variety of conditions. The invention has particular advantage for use in remote regions where electrical power generation by conventional means may be commercially infeasible or impractical.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/415,170 filed Oct. 8, 1999, now U.S. Pat. No. ______, which is incorporated herein. Ser. No. 09/415,170 itself claims the benefit of Provisional Patent Applications Nos. 60/123,596 and 60/141,349, both of which are incorporated herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to hydraulic power generation systems and, in particular, to an apparatus and method for generating power using a novel pseudo-osmosis process which efficiently exploits the osmotic energy potential between two bodies of water having different salinity concentrations.  
           [0004]    2. Description of the Related Art  
           [0005]    About 20% of the world&#39;s electricity is generated using hydropower. In the United States alone this resource accounts for about 12% of the nation&#39;s supply of electricity, producing more than 90,000 megawatts of electricity annually and meeting the needs of approximately 28.3 million consumers each year. Hydropower is a clean source of natural energy. Not only is it environmentally friendly (and even beneficial in terms of flood control, etc.), but it is also extremely cost-efficient. In the Northwest, for example, electricity from hydropower plants typically costs about $10 per megawatt hour to produce. This compares to about $60, $45 and $25 per megawatt hour to produce electricity at nuclear, coal and natural gas power plants, respectively.  
           [0006]    However, current hydroelectric power plants are configured to recover only the energy component of water that is released as a result of elevational changes. In particular, hydroelectric power is typically generated by dropping 200-300 feet-head (61-91 m-head) of fresh water from a higher elevation to a lower elevation across a rotating turbine coupled to an electrical generator. The exhaust water flow is discharged at the lower elevation as energy-depleted fresh water run-off. But, as will be explained in more detail below, this fresh water run-off is not completely depleted of energy. In fact, the amount of remaining recoverable energy in the discharged fresh water can be as great as the equivalent of 950 feet-head (290 m-head) of water or more. To understand the nature and origin of this additional recoverable energy component it is helpful to look at how fresh water is created.  
           [0007]    Fresh water begins as water vapor that is evaporated from the oceans by solar energy. This water vapor rises into the atmosphere whereupon it cools. Cooling causes the water vapors to condense into clouds, ultimately resulting in precipitation. Some of this precipitation occurs over land masses forming fresh-water lakes, accumulated snow-fall and an extensive network of associated rivers, streams, aquifers and other forms of water run-off. Ultimately, all or virtually all of this fresh water run-off makes its way back to the oceans, thus completing the cycle. In fact, throughout the world enormous quantities of fresh water is freely washed into the ocean each year as part of the naturally occurring water cycle and/or as part of various human interventions such as hydro-power facilities, municipal waste water treatment facilities, and the like.  
           [0008]    The overall driving force behind the water cycle is solar energy radiating from the sun over millions of square miles of exposed ocean waters each day. It is this solar energy that causes evaporation of fresh water vapors from the relatively high-saline ocean waters. The amount of radiant solar energy absorbed in this process is enormous, representing approximately 2,300 kJ/kg (0.64 kW-hr/kg) of water evaporated. This absorbed energy causes a concomitant increase in the latent energy or enthalpy of the evaporated water. The vast majority of this latent energy (approximately 99%) is dissipated as heat energy into the atmosphere upon re-condensing of the water vapors into clouds. However, a small but significant portion of this latent energy (approximately 0.13%) remains stored within the resulting fresh-water precipitation. This remaining non-dissipated stored energy represents the so-called “free energy of mixing” (or “heat of mixing”) of fresh water into sea water. Specifically, it is the additional incremental energy (beyond the energy of evaporation of pure water) that is required to separate the fresh water (or other solvent) from the salt water solution (or other solvent/solute solution).  
           [0009]    The free energy of mixing reflects an increase in entropy of water (or other solvent) when it is transformed from its pure (fresh-water) state to its diluted (salt-water) state. It is a physical property of solvents, such as water, that they have a natural tendency to migrate from an area of relatively low solute concentration (lower entropy) to an area of relatively high solute concentration (higher entropy). Thus, an entropy gradient is created whenever two bodies of water or other solvent having differing solute concentrations are brought into contact with one another and begin to mix. This entropy gradient can be physically observed and measured in the well-known phenomena known as osmosis.  
           [0010]    Osmosis is the flow of water through a selectively permeable membrane (i.e., permeable to water, but impermeable to dissolved solutes) from a lower concentration of solute to a higher one. It is a colligative phenomenon—that is, it is not dependent on the nature of the solute, only on the total molar concentration of all dissolved species. Pure water is defined as having an osmotic potential of zero. All water-based solutions have varying degrees of negative osmotic potential. Many references discuss osmotic potential in terms of pressure across a semi-permeable membrane since the easiest way to measure the effect is to apply pressure to the side of the membrane with higher negative osmotic potential until the net flow is canceled. “Reverse osmosis” is the phenomena that occurs when additional pressure is applied across a selectively permeable membrane to the point of reversing the natural flow-direction there-through, resulting in separation of the solvent from the solute.  
           [0011]    But, just as it takes energy to separate an amount of fresh water from a body of salt water, such as through solar evaporation or using the well-known reverse-osmosis desalinization process, remixing the fresh water back into the ocean waters results in the release of an equal amount of stored energy (approximately 2.84 kJ/kg) of fresh water. If this source of latent stored energy could somehow be efficiently exploited, it could result in the production of enormous amounts of inexpensive electrical power from a heretofore untapped and continually renewable energy resource.  
           [0012]    For example, if 30% of the average flow from the Columbia River could be diverted into a device that recovered this latent free energy of mixing or osmotic energy potential at 100% efficiency, it would generate 6,300 megawatts of power. To put this in perspective, the current hydroelectric facility of the Grand Coulee Dam on the Columbia River (the largest hydroelectric power plant in the United States and the third largest in the world) generates a peak output of 6,800 megawatts. See, http://www.cqs.washington.edu/crisp/hydro/gcl.html. If the flow from the Weber River into the Great Salt Lake could be diverted through such a device, it would generate 400 megawatts of power. See, e.g., http://h20.usgs.gov/public/realtime.html for a statistical survey of other U.S. hydrographic data. Such a device would be of enormous benefit to people throughout the world, particularly those in remote regions where electrical power generation by conventional means may be difficult or impractical.  
           [0013]    Various proposals have been made over the years for possible ways of commercially exploiting this attractive source of natural, renewable energy. For example, Jellinek (U.S. Pat. No. 3,978,344) proposed to pass fresh water through a semi-permeable membrane into a salt or brine solution. The resulting osmotic pressure differential across the membrane would then be used to eject a stream of salt water through an outlet orifice to drive a water wheel coupled to an electrical power generator to generate electrical power. Similarly, Loeb (U.S. Pat. No. 3,906,250) describes a method and apparatus for generating power utilizing pressure retarded osmosis through a semi-permeable membrane.  
           [0014]    Each of the above approaches, like many others heretofore advocated, rely on a forward osmosis process utilizing a semi-permeable membrane to obtain useful work from the difference in osmotic potential exerted across the membrane. While such systems may have useful application on a small scale under certain limited conditions, full-scale commercial development and exploitation of such power-generation systems is hampered by the large membrane surface area required to achieve adequate flow rates and the expense and difficulty of maintaining such semi-permeable membranes. Although modern advances in synthetic materials have produced membranes that are very efficient at rejecting brine solutes and are tough enough to withstand high pressures, such membranes are still susceptible to clogging, scaling and general degradation over time. For example, river water used as a fresh-water source would likely carry a variety of solutes and other suspended sediment or contaminants which could easily clog the membrane, requiring filtering and/or periodic cleaning. Treated effluent from a municipal waste-water treatment plant used as a fresh water source would present similar and possibly additional complications, making such approach commercially impractical.  
           [0015]    Urry (U.S. Pat. No. 5,255,518) proposed an alternative method and apparatus for exploiting osmotic energy potential in a manner that does not utilize a semi-permeable membrane. In particular, Urry proposed the use of a specially formulated bio-elastomer. The bio-elastomer is selected such that it alternately and reversibly contracts or expands when exposed to different concentrations of a brine solution. A mechanical engine is proposed for converting the expansion and contraction motion of individual bio-elastomer elements into useful work. While such a system demonstrates the usefulness of the general approach, the proposed system utilizing bio-elastomer elements or the like is not readily suited for large-scale, low cost energy production. To produce useful energy on a commercial scale such a system would require a vast number of bio-elastic elements having very large surface area. Again, the exposed surface area would be subject to contamination and degradation over time, as with the membranes discussed above, making such a system prohibitively expensive to construct and maintain.  
           [0016]    Assaf (U.S. Pat. No. 4,617,800) proposed another alternative apparatus for producing energy from concentrated brine in a manner that does not utilize a semi-permeable membrane or specially formulated bio-elastomer. In particular, Assaf proposed using a system of steam evaporation and re-condensation. In this approach steam is first generated by heating fresh water in an evaporator and passing the steam through a turbine to drive an electric generator. The condensed steam is then passed to a condenser wherein it is contacted with a flow of concentrated brine, generating heat from the heat of dilution of the brine. It is proposed that the evolved heat would then be transmitted though a heat-exchanger element back to the evaporator to generate steam from the fresh water. While this approach generally avoids the membrane and large surface area contamination problems discussed above, it is not ideally suited for large-scale, low cost energy production. This is because of the number and complexity of components involved and the need to heat and cool the fresh water in pressure sealed evaporator and condenser units. Such a system would be expensive to construct and operate on a commercial scale.  
           [0017]    Thus, there remains a need for a method and apparatus for efficiently exploiting the osmotic energy potential between fresh water and sea water (and/or other solutions).  
         SUMMARY OF THE INVENTION  
         [0018]    Accordingly, it is an aspect to provide an improved apparatus and method for generating power using a novel forward osmosis process which efficiently exploits the osmotic energy potential between two bodies of water having different salinity concentrations.  
           [0019]    Advantageously, the method and apparatus of the present invention does not require the use of a semi-permeable membrane or other specially formulated material, nor does it require heating or cooling of the fresh water or salt water solution. Moreover, the present invention may recover energy from a wide variety of fresh water sources, including treated or untreated river run-off, treated waste-water run-off or effluent, storm-drain run-off, partly contaminated fresh water run-off, and a wide variety of other fresh water sources. Thus, the present invention is well suited to large scale power production in a wide variety of geographic locations and under a wide variety of conditions. The invention has particular advantage for use in remote regions where electrical power generation by conventional means may be commercially infeasible or impractical.  
           [0020]    In accordance with one embodiment the present invention provides a method for generating power from the differences in osmotic potential between a source of relatively low salinity water and a source of relatively high salinity water. Relatively low salinity water is conducted through a first tube. The relatively low salinity water is then directly contacted with the relatively high salinity water in an enclosed second tube to form a mixture. The second tube is in fluid communication with the source of relatively high salinity water through one or more openings. The contacting of the two different salinity waters causes upwelling of the mixture within the second tube. This mixture is passed through a power generation unit to generate mechanical and/or electrical power.  
           [0021]    In accordance with another embodiment the present invention provides a method for generating power from the osmotic energy potential of fresh water. A source of relatively low salinity water is conducted to a predetermined depth in a body of relatively high salinity water through a down tube having a first cross-sectional area. The relatively low salinity water is directly contacted with the relatively high salinity water from the predetermined depth in an up tube having a second cross-sectional area, forming a mixture. The mixture is allowed to upwell within the up tube upward to a depth less than the predetermined depth. The upwelling mixture is passed through a power generation unit to generate useful power.  
           [0022]    In accordance with another embodiment the present invention provides a system for generating power from differences in osmotic potential between a source of relatively low salinity water and a source of relatively high salinity water. The system comprises an up tube located in the source of relatively high salinity water. The up tube is fluidly connected to the source of relatively high salinity water through one or more openings in the up tube at a first depth. The up tube terminates at a depth in the source of relatively high salinity water at a second depth less than the first depth. A down tube is provided having a first end connected to the source of relatively low salinity water and a second end which discharges the low salinity water from the source of relatively low salinity water into the up tube such that the relatively low salinity water and the relatively high salinity water form a mixture which upwells within the up tube. A means is provided for generating power from the rising mixture.  
           [0023]    In accordance with another embodiment, the present invention provides a system for generating power from differences in osmotic potential between a source of relatively low salinity water and a source of relatively high salinity water. The system comprises a first tube for conducting a flow of relatively high salinity water from a first depth to a second depth, the first tube having a first cross-sectional area. A second tube is provided fluidly connected to the source of relatively low salinity water at a first end and to the first tube at a second end at or near the first depth, where the second tube has a second cross-sectional area. A third tube is provided for conducting a flow of relatively high salinity water from the second depth at or near a first end of the third tube to the first tube at the second end, where the relatively low salinity water and the high salinity water form a mixture in the first tube. The mixture is caused to flow in the first tube, increasing the recoverable energy of the relatively high salinity water in the third tube. A power generator is provided, disposed between the first and third tubes for generating power from the increase in recoverable energy.  
           [0024]    In accordance with another embodiment, the present invention provides a method for generating power from the difference in osmotic potential between a source of relatively low salinity water and a source of relatively high salinity water. A source of relatively low salinity water is conducted through a first tube, where the first tube has a first cross-sectional area. The relatively low salinity water is directly contacted with water from the source of relatively high salinity in an enclosed second tube to form a mixture, where the second tube has a second cross-sectional area. The second tube is in fluid communication with the source of relatively high salinity water through one or more openings in a third tube. The contacting causes an increase in recoverable energy of the relatively low salinity water in the first tube. The relatively high salinity water in the third tube is conducted through a power generation unit to generate mechanical and/or electrical power.  
           [0025]    For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.  
           [0026]    All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    Having thus summarized the general nature of the invention and its essential features and advantages, certain preferred embodiments and modifications thereof will become apparent to those skilled in the art from the detailed description herein having reference to the figures that follow, of which:  
         [0028]    [0028]FIG. 1A is a schematic diagram representation of a conventional forward osmosis process through a semi-permeable membrane;  
         [0029]    [0029]FIG. 1B is a schematic diagram representation of a conventional reverse osmosis process through a semi-permeable membrane;  
         [0030]    [0030]FIG. 2 is a schematic representation of an experimental up tube upwelling apparatus for use in accordance with the present invention;  
         [0031]    [0031]FIG. 3 is a graph of theoretical power recovery for different sized down-tubes and fresh water flow rates using the experimental upwelling device of FIG. 2;  
         [0032]    [0032]FIG. 4 is a schematic representation of one embodiment of a hydrocratic generator having features and advantages in accordance with the present invention;  
         [0033]    [0033]FIG. 5 is a schematic representation of an alternative embodiment of a hydrocratic generator having features and advantages in accordance with the present invention;  
         [0034]    [0034]FIG. 6 is a schematic representation of a further alternative embodiment of a hydrocratic generator having features and advantages in accordance with the present invention;  
         [0035]    [0035]FIG. 7A is a schematic representation of a further alternative embodiment of a hydrocratic generator having features and advantages in accordance with the present invention;  
         [0036]    [0036]FIG. 7B is a side view of the up tube of FIG. 7A, showing the slots in the side of the up tube;  
         [0037]    [0037]FIG. 7C is a sectional view from below of the shaft support of FIG. 7A;  
         [0038]    [0038]FIG. 7D is a sectional view from above of the vane drum of FIG. 7A;  
         [0039]    [0039]FIG. 8A is a schematic representation of a further alternative embodiment of a hydro-osmotic generator having features and advantages in accordance with the present invention;  
         [0040]    [0040]FIG. 8B is a side view of the up tube of FIG. 8A showing two sets of slots in the side of the up tube;  
         [0041]    [0041]FIG. 8C is a sectional view from below of the shaft support of FIG. 8A;  
         [0042]    [0042]FIG. 8D is a sectional view from above of the vane drum of FIG. 8A;  
         [0043]    [0043]FIG. 9A is a schematic view of an up tube with an open lower end with an alternative embodiment of a down tube having a plurality of holes in the sides and the outlet end, having features and advantages in accordance with the present invention;  
         [0044]    [0044]FIG. 9B is a sectional view from below of the up tube and the outlet end of the down tube of FIG. 9A;  
         [0045]    [0045]FIG. 10A is a schematic view of an up tube with an open lower end with an alternative embodiment of the down tube with a plurality of secondary down tubes having holes in the sides and the outlet end, having features and advantages in accordance with the present invention;  
         [0046]    [0046]FIG. 10B is a sectional view from below of the up tube and the outlet end of the down tube of FIG. 10A showing the plurality of secondary down tubes and the holes on the outlet ends of the secondary down tubes;  
         [0047]    [0047]FIG. 11 is a schematic view of an up tube with an open lower end with an alternative embodiment of the down tube with a plurality of secondary down tubes, having features and advantages in accordance with the present invention;  
         [0048]    [0048]FIG. 12 is a schematic view of a down tube with a rotating hub and spoke outlets with no up tube;  
         [0049]    [0049]FIG. 13 is a schematic view of a down tube with a rotating hub and spoke outlets with an up tube, having features and advantages in accordance with the present invention;  
         [0050]    [0050]FIG. 14 is a schematic view of a portion of an up tube comprising a plurality of concentric up tubes, having features and advantages in accordance with the present invention;  
         [0051]    [0051]FIG. 15 is a schematic representation of a modified up tube having features and advantages in accordance with the present invention;  
         [0052]    [0052]FIG. 16 is a schematic illustration of a possible large-scale commercial embodiment of a hydro-osmotic generator having features and advantages in accordance with the present invention;  
         [0053]    [0053]FIG. 17 is a cutaway view of the turbine and generator assembly of the hydro-osmotic generator of FIG. 12;  
         [0054]    [0054]FIG. 18 is a schematic view of an up tube with an open lower end, with an alternative embodiment of the rotating down tube, extending substantially into the up tube, and having holes and turbines mounted thereon, having features and advantages in accordance with the present invention;  
         [0055]    [0055]FIG. 19A is a schematic view of an up tube with a closed lower end, with an alternative embodiment of the rotating downtube, extending substantially into the up tube, and having holes and turbines mounted thereon, having features and advantages in accordance with the present invention;  
         [0056]    [0056]FIG. 19B is a side view of the up tube shown in FIG. 19A;  
         [0057]    [0057]FIG. 20 is a schematic view of an up tube with an open lower end, with an alternative embodiment of the rotating downtube, extending substantially into the up tube, and having holes and turbines mounted thereon, with rotating up tube and down tube, having features and advantages in accordance with the present invention;  
         [0058]    [0058]FIG. 21 is a schematic view of an up tube upwelling apparatus in accordance with the present invention wherein a rotating helical screw is used to generate the power instead of a plurality of fan blades, having features and advantages in accordance with the present invention;  
         [0059]    [0059]FIG. 22A is a side view of an alternative embodiment of a fan blade used in accordance with the present invention; and  
         [0060]    [0060]FIG. 22B is a schematic view showing the under portion of the fan blade illustrated in FIG. 22A of the drawings.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0061]    As discussed in the Background section above, when solvent fluids having differing osmotic potentials are contacted and mixed with each other energy is released. This released energy results from an increase in entropy of water (or other solvent) when it is transformed from its pure (fresh-water) state to its diluted (salt-water) state. Thus, an entropy gradient is created whenever two bodies of water or other solvents having differing solute concentrations are brought into contact with one another and begin to mix. This entropy gradient can be physically observed and measured in the well-known phenomena known as osmosis.  
         [0062]    Because the term “osmosis” is associated with a membrane, the term “hydrocrasis” is used as a term for the situation when solvent fluids having differing osmotic potentials are contacted and mixed with each other in the absence of a membrane.  
         [0063]    [0063]FIG. 1A schematically illustrates conventional forward osmosis through a semi-permeable membrane. Forward osmosis results in the flow of water  10  (or other solvent) through a selectively permeable membrane  12  from a lower concentration of solute  14  to a higher concentration of solute  14 . Many references discuss osmotic potential or osmotic pressure in terms of pressure drop Π across a semi-permeable membrane since the easiest way to measure the effect is to measure the difference in height or feet (meters) of head between the high concentration side and the low concentration side of the membrane  12 . Forward osmosis results in the release of work energy.  
         [0064]    [0064]FIG. 1B illustrates the condition of reverse osmosis whereby water (or other solvent)  10  under the influence of external pressure is forced through a selectively permeable membrane  12  from a higher concentration of solute  14  to a lower concentration of solute  14 , thus squeezing out or extracting the pure solvent  10  from the solute  14 . Reverse osmosis is widely used in water purification and desalinization plants throughout the world. Reverse osmosis consumes work energy.  
         [0065]    To illustrate the amount of work energy dissipated or released in the osmotic process consider a hypothetical example where a large container of salt water is supported just under the surface of a large open container of fresh water. Moreover, there is an osmotic membrane separating the two containers of water. Attached to the vessel of salt water and extending up out of the fresh water is a slender, tall tube with a volume of exactly one cubic meter. This slender, tall tube is open at the top, and this is the only opening to the salt water vessel. At the start of the hypothetical experiment the water level and pressure in both containers is identical and is at the bottom of the slender, tall tube. However, osmosis will cause the fresh water to flow into the container of salt water through the membrane and raise the level of salt water in the slender tall tube until the pressure exerted by the column of salt water is sufficient to just cancel or oppose the osmotic pressure across the membrane.  
         [0066]    Now, if the top of the tube is cut just below the highest level of water therein, then salt water will begin spilling over and dropping from the top of the tube as fresh water continues to flow through the membrane into the salt water solution at an equal rate. Now, for each cubic centimeter of fresh water that flows through the membrane, an equal volume of salt water solution will be displaced from the top of the tube and drop a certain distance. Clearly, work is being done through the mechanism of osmosis, but how much work is being done? How much pressure is exerted by the column of salt water and what is the height of the column? 
         [0067]    For small concentrations of an ideal solution, van&#39;t Hoff&#39;s formula for osmotic pressure (Π) is:  
         [0068]    Π=−CRT  
         [0069]    where C=Molar Concentration, R=Gas Constant and T=Absolute temperature. For salt water there are two ions per molecule and:  
         [0070]    wt(NaCl)=58.5 g  
         [0071]    T=20° C.=293° K  
         [0072]    R=8.3144 J/mole° K  
         [0073]    C=35 ppt=35,000 g/m 3    
         [0074]    =(35,000×2/58.5 moles)/m 3    
         [0075]    =1200 moles/m 3    
         [0076]    Π=−(1200 moles/m 3 ) (8.3144 J/mole° K) (293° K)  
         [0077]    =−2.9&#39;10 6  N/m 2    
         [0078]    =−2.9×10 6  Pa  
         [0079]    =−29 atm.  
         [0080]    Pascal&#39;s Law says:  
         [0081]    p=ρgh  
         [0082]    Setting p (pressure due to the height of a column of liquid) equal to Π (the osmotic pressure) and solving for the height of the column (h) gives:  
         [0083]    p=1034 kg/m 3    
         [0084]    g=9.8 m/s 2    
         [0085]    h=(2.9×10 6  N/m 2 )/((1034 kg/m 3 ) (9.8 m/s 2 ))  
         [0086]    =290 m  
         [0087]    The incremental work done to displace 1 kg of water is:  
         [0088]    W=½ mgh  
         [0089]    =(0.5)(1 kg)(9.8 m/s 2 ) (290 m)  
         [0090]    =1.4 kJ  
         [0091]    Thus, the osmotic energy potential to be gained from remixing fresh water into saline ocean water is significant—about 1.4 kJ/kg of fresh water, or the equivalent of about 290 m-head of water for a conventional hydropower system. If this source of stored energy could somehow be efficiently exploited, it could result in the production of enormous amounts of inexpensive electrical power from a heretofore untapped and continually renewable energy resource.  
         [0092]    Let us now cut the tall tube just below the maximum height of the salt water (290 meters) and attach a spigot. The salt solution would continuously flow out of the spigot. What force is generated when a kilogram of water flows through the tube and falls back to the original water level? 
         [0093]    W=Mgh  
         [0094]    =(1 Kg)(9.8 m/s 2 ) (290 m)  
         [0095]    2.8×10 3  Joules  
         [0096]    If the osmotic membrane had a sufficiently large surface area to allow a flow of one kilogram per second, then the system would be generating 1.4×10 3  Joules per second which is the same as 1.4 Kilowatts.  
         [0097]    If a penstock was attached to the end of the spigot and that in turn was attached to a hydroelectric generator placed at the original water level, then that generator (at 100% efficiency) would deliver 1.4 kilowatts of electrical power.  
         [0098]    There actually would be no need for either the tall tube or the penstock. The generator would not care if the head pressure was generated by gravity or osmotic pressure. The same electricity would be generated if the opening in the salt water vessel was directly connected to the inlet of the generator.  
         [0099]    This is, of course, not a practical system for generating electricity since it relies on an infinitely large rigid vessel and an infinitely large osmotic membrane.  
         [0100]    While many systems have been proposed for harnessing this osmotic energy potential, few if any have been commercially successful. One problem is that most osmotic energy recovery systems rely on a conventional forward osmosis process utilizing a semi-permeable membrane. Full-scale commercial development and exploitation of such power-generation systems is hampered by the large membrane surface area required to achieve adequate flow rates and the expense and difficulty of maintaining such semi-permeable membranes. Other systems require the use of exotic bio-elastic materials and/or the use of evaporators, condensers and/or heat exchangers to extract useful work energy from osmotic energy potential.  
         [0101]    However, in the unrelated field of ocean mariculture it is known to use the buoyancy effect of fresh water mixed with saline water to provide artificial ocean upwelling for purposes of enriching the waters in the upper photic zone of the ocean with nutrient rich waters from the lower aphotic zones. For example, U.S. Pat. No. 5,106,230, incorporated herein by reference, describes a method for the controlled generation of artificial oceanographic upwelling. The method includes introducing a relatively fresh-water input stream to a predetermined depth, where the fresh-water mixes with the nutrient-rich deep-sea water so as to form a mixture. The mixture is lifted upward by a buoyancy effect brought about by its reduced density, whereby the mixture is conducted towards the surface through an up pipe. The method results in upwelling of cold, nutrient rich water from the lower aphotic regions of the ocean to the upper photic regions where the nutrients may be beneficially used by aquatic sea life.  
         [0102]    During recent prototype testing of a similar upwelling device it was discovered, surprisingly, that the amount of upwelling flow achieved in terms of kinetic energy of the overall mass flow was in excess of the input energy into the system in terms of the buoyancy effect and kinetic energy resulting from the fresh water introduced into the up tube. Subsequent experiments using a modified upwelling device have confirmed that the total hydraulic energy output of such system significantly exceeds the total hydraulic energy input.  
         [0103]    While an exact explanation for this observed phenomena is not fully appreciated at this time, it is believed that the excess energy output is somehow attributable to the release of osmotic energy potential upon remixing of the fresh water and the salt water in the up tube. This result is particularly surprising since the modified upwelling device incorporated no semi-permeable membrane or other specialized system components heretofore thought necessary to recover such osmotic energy potential. Because no membrane is present, the term hydrocratic generator is applied to the apparatus. For completeness of disclosure and understanding of the invention, the experimental design used in making this discovery is described and discussed below:  
         [0104]    Experimental Design  
         [0105]    An experimental upwelling apparatus similar to that illustrated in FIG. 2 was constructed using suitable corrosion resistant materials. The ocean was simulated by dissolving 1800 kilograms (2 tons) of sea salt in a 50,000 liter (15,000 gallon) swimming pool. The up tube  40  was a 15 cm (6 inch) inside diameter (i.d.) polyvinylchloride (PVC) tube 1.5 meters long. In some experiments discussed herein, the top of the up tube  40  was left open and unobstructed, as illustrated. In other experiments discussed herein, a turbine was attached to the top of the up tube  40  to convert kinetic flow energy into mechanical work energy. The down tube  20  was a 1.8 cm (½ inch) i.d. (PVC) tube 1 meter long. Two 90° elbows and a short piece of pipe were attached to the end of the down tube  20  so that the fresh water was caused to exit upwards into the up tube  40  from the down tube  20 . The apparatus was attached to a float  48  by nylon support cables  50 , and the outlet end  44  of the up tube  40  was positioned about 15 cm below the surface of the salt water.  
         [0106]    The down tube  20  was connected to a reservoir  25  of fresh water. The reservoir  25  was kept at a constant level by continually filling with tap water and allowing the excess to flow out the spill-way  27  so that the flow rate of fresh water through the down tube  20  was kept essentially constant. According to measurements the water in the reservoir  25  contained about 300 ppm of dissolved solids at all times, and the salt water in the swimming pool contained between 34,000 and 36,000 ppm of dissolved solids. The temperature of both the water in the reservoir  25  and the salt water was the same in any individual experiment (18-20° C.), because the salt water tank was set into the ground, and the fresh water in the reservoir came from buried pipes.  
         [0107]    The experiment was started by filling the down tube  20  with water to eliminate air bubbles. The height of the reservoir was then adjusted to establish a pressure head that determined the rate of flow of fresh water in the down tube  20 . The reservoir  25  was then filled with fresh water which was then allowed to flow from the reservoir  25  through the down tube  20  whereupon it was introduced into the lower portion of the up tube  40 .  
         [0108]    The experiment was monitored by periodically measuring the salinity at the outlet end  44  of the up tube  40  using a Myron L., DS Meter (model 512T5). The flow rate out of the outlet end  44  of the up tube  40  was calculated by measuring the salinity at the outlet end  44  of the up tube  40 . In particular, FIG. 2 shows four reference points in the experimental apparatus: Point  1  is the fresh water reservoir; Point  2  is at the outlet end  44  of the up tube  40  where the salinity was measured; Point  3  is immediately above the outlet end  24  of the down tube  20 ; and Point  4  is inside the up tube  40  below the outlet end  24  of the down tube  20 . The following salinities and densities were used in the analysis of the data.  
         [0109]    Salinity of Salt Water=35,000 ppm  
         [0110]    Salinity of Fresh Water=300 ppm  
         [0111]    Density of Salt Water=1.035  
         [0112]    Flow rates were calculated using the following analysis. Since there was a continuous tube from Point  1  to Point  3 , the salinity and flow rate must be the same at Points  1  and  3 . Since the only inlets to the up tube  40  are from Point  3  and Point  4 , the flow at Point  2  must equal the sum of the flows at Point  3  and Point  4 . The equation for the flow at Point  4  is derived from the following analysis:  
         [0113]    If:  
         [0114]    Q i =Flow at point i  
         [0115]    =W T /ρ per second  
         [0116]    S i =Salinity at point i  
         [0117]    =(W S /W T )  
         [0118]    W S =Weight of Salt in a Solution  
         [0119]    W T =Total Weight of Solution  
         [0120]    ρ=Density of Solution  
         [0121]    Then:  
         [0122]    S 2 =W S2 /W T2    
         [0123]    And since the flow past Point  2  comes from either Point  3  or Point  4 :  
           S   2 =( W   S3   +W   S4 )/( W   T3   +W   T4 )  
         [0124]    Substituting in:  
         [0125]    W S =S W T    
         [0126]    Results in:  
           S   2 =( S   3    W   T3   +S   4    W   T4 )/( W   T3   +W   T4 )  
         [0127]    Substituting in:  
         [0128]    W T =Q ρ seconds  
         [0129]    Results in:  
           S   2 =( S   3    Q   3    ρ   3   +S   4    Q   4  ρ 4 )/( Q   3  ρ 3   +Q   4  ρ 4 )  
         [0130]    Which gives an equation that has one unknown variable (Q 4 ).  
           Q   4   =Q   3 (ρ 3 /ρ 4 ) ( S   2   −S   3 )/( S   4   −S   2 )  
         [0131]    It can be assumed, within the accuracy of this experiment, that:  
         [0132]    S 3 =0  
         [0133]    ρ 3 =ρ 4    
         [0134]    Which leaves:  
           Q   4   =Q   3    S   2 /( S   4   −S   2 )  
         [0135]    The following Examples 1-4 report the results of several experiments which were conducted using the experimental design described above and as illustrated in FIG. 2:  
       EXAMPLE 1  
       [0136]    The apparatus shown in FIG. 2 was used to measure observed flow rates in the up tube  40  with different fresh water flow rates introduced into the down tube  20 . Table 1 is a compilation of the results for flow rates at various points in the up tube  40  with two different flow rates of fresh water in the down tube  20 . The flow rate at Point  1 , the flow rate of fresh water from the reservoir, and the salinity at Point  2  at the outlet end  44  of the up tube  40  were measured parameters. The flow rate at Point  3 , the outlet end  24  of the down tube  20 , was the same as the flow rate at Point  1 . The remaining flow rates were calculated using the equations discussed above.  
                                                       TABLE 1                           Flow Rates at Various Locations in the Up Tube            Height of   Salinity           Reservoir   at Point   Flow (10 −4  m 3 /sec)            (meters)   2 (ppt)   Point 1   Point 2   Point 3   Point 4               0.23   34   1.3   45.5   1.3   44.2       0.55   34   2.4   84.0   2.4   81.6                  
 
         [0137]    The results indicate that the flow rate of the mixed salt-water/fresh-water solution at Point  2  at the outlet end  44  of the up tube  40  far exceeded the flow rate of fresh water at Point  1  and Point  3 . Introducing fresh water into the down tube  20  and allowing the salt water to flow into the up tube  40  therefore generated higher flow rates at Point  2 , at the top of the up tube  40 .  
         [0138]    In order to demonstrate that this higher flow rate at Point  4  was not due to transfer of kinetic energy from the fresh water flow coming from the down tube  20 , the following experiment was performed.  
       EXAMPLE 2  
       [0139]    Flow Rates Through the Up Tube with Salt Water vs. Fresh Water Introduced Into the Down Tube  
         [0140]    For this experiment, a 6″ turbine roof vent was attached to the outlet end  44  of the up tube  40 . One of the vanes was painted to allow for the counting of rotations. The reservoir was filled with fresh water having a salinity of 300 ppm in one experiment and with salt water having a salinity of 36,000 ppm in a second experiment. The reservoir was placed at a height of 0.55 meters above the water level of the salt water in the pool. The fresh water was then allowed to flow through the down tube  20 , and the rate at which the turbine rotated was determined. Then, salt water from the salt water pool was allowed to flow through the down tube  20 , and the rate at which the turbine rotated was again determined. The results are shown in Table 2 below.  
                                               TABLE 2                           Turbine Speed with Fresh Water vs. Salt Water in Down Tube                Down Tube Water               Flow   Turbine Speed           (10 −4 m 3 /sec)   (rpm)                            Fresh Water (0.3 ppt)   2.4   5.6           Salt Water (36 ppt)   2.3   2.3                      
 
         [0141]    As illustrated in Table 2, above, the turbine rotated 2.4 times more rapidly when fresh water was introduced into the down tube  20  than when salt water was used. The higher turbine speed when fresh water was introduced into the down tube  20  is a direct indication that the water flow in the up tube  40  was higher when fresh water rather than salt water was introduced into the down tube  20  and that the higher observed water flow rates from the top of the up tube  40  in Example 1 were not due solely to kinetic energy transfer from the fresh water flow out of the down tube  20 .  
         [0142]    The kinetic energy transferred from the salt water in the down tube  20  to the salt water in the up tube  40  would be at least as great (if not slightly greater due to increased density of salt water) as the kinetic energy transferred from the fresh water in the down tube  20 . The results shown in Table 2 indicate that some, but not all, of the upwelling of water in the up tube  40  is due to kinetic energy transfer from the water introduced into the down tube  20 .  
         [0143]    The power which is available from the kinetic energy of the water flow at various locations in the up tube  40  can be calculated as follows:  
         [0144]    P k =Power from Kinetic Energy  
         [0145]    =½ M q v 2    
         [0146]    =½(η Q) (16Q 2 /Π 2 d 4 )  
         [0147]    =8Q 3  ρ/Π 2 d 4    
         [0148]    where:  
         [0149]    A=Cross Sectional Area  
         [0150]    =Πd/4  
         [0151]    d=Tube Diameter  
         [0152]    M q =Mass Flow  
         [0153]    =Q×ρ 
         [0154]    ρ=1+(S 1 /1000)  
         [0155]    v=Velocity  
         [0156]    =Q/A  
         [0157]    Table 3 shows the calculated power attributable to kinetic energy at the three points in the up tube  40 .  
                                                   TABLE 3                           Kinetic Energy at Various Points in the Up Tube                Salinity at           Height of   Point 2   Kinetic Power (watts)            Reservoir (meters)   (ppt)   Point 2   Point 3   Point 4               0.23   34   0.16   0.02   0.14       0.55   34   0.98   0.11   0.90                  
 
         [0158]    In the following series of experiments, the diameter of the down tube  20  and the rate of flow of the fresh water which was introduced into the down tube  20  were varied to determine the dependence of the rate of upwelling in the up tube  40  on these parameters.  
       EXAMPLE 3  
       [0159]    A series of experiments were carried out using the experimental design described above and as illustrated in FIG. 2, but with down tubes  20  having different diameters. With each down tube  20 , the flow rates of the fresh water in the down tube  20  were varied to determine the effect of different fresh water flow rates on available power. The salinity at the outlet end  44  of the up tube  40  was measured, and the water flow rates were calculated from the salinity as before. The water flow rates were used to calculate the available power at Point  2 , the outlet end  44  of the up tube  40 . The available power was then normalized by dividing the available power by the fresh water flow rate in the down tube  20 . The results are shown in Table 4 below.  
                                                                                                 TABLE 4                           Normalized Power Production vs. Diameter of Up Tube and Fresh Water       Flow Rates                        Ratio of Up           Salinity   Flow (× 0.0001 m 3 )       Tube Area of   Power/Fresh            at Point 2   Point   Point   Point   Down Tube   Down Tube   Water Flow       (ppt)   1   4   2   Area (m 2 )   Area   (Watts/m 3 )                    31.8   22   259   281   0.000254   69.7   1312       32.6   18   309   327   0.000071   249   2715       33.4   5.2   158   163   0.000018   983   1256       31.4   33   334   367   0.000254   69.7   1877       32.6   26   446   472   0.000071   249   5664       33.3   7.6   211   218   0.000018   983   2047       35.0   5   168   173   0.000010   1770   1559                  
 
         [0160]    In all cases, the power per unit volume of fresh water introduced into a down tube  20  of a given diameter increased as the flow rate of fresh water through the down tube  20  increased. Thus, for the down tube  20  with an area of 0.000254 m 2 , the power/m 3  of fresh water flow increased from 1312 watts/m 3  with a fresh water flow rate of 22×10 −4  m 3  to 1877 watts/m 3  with a fresh water flow rate of 33×10 −4  m 3 . The same trend was maintained for the down tubes having areas of 0.000071 and 0.000018 m 2 . Thus, the data illustrates that increasing the fresh water flow rate in a down tube  20  having a given area increased the normalized available power output of the device.  
         [0161]    Second, although the power per unit volume of fresh water introduced into the down tube  20  increased with increased volume of fresh water introduced into the down tube  20  in all cases, the percent increase in the power with increase in fresh water flow rate was less for the largest down tube  20  (0.000254 m 2  area) than for the other down tubes  20 . When the fresh water flow rate increased from 22×10 −4  m 3  to 33×10 −4  m 3 , or by 50%, with the largest down tube  20 , the power/fresh water flow rate increased from 1312 watts/m 3  to 1877 watts/m 3 , or 40%. By comparison, when the fresh water flow rate for the down tube  20  with an area of 0.000018 m 2  was increased from 5.2 to 7.6×10 −4  m 3 , or 46%, the power/fresh water flow rate increased from 1256 watts/m 3  to 2047 watts/m 3 , or 62%, more than 1.5 times as much as for a comparable percent change in the fresh water flow rate with the larger down tube  20 .  
         [0162]    Similarly, when the fresh water flow rate for the down tube  20  with an area of 0.000071 m 3  increased from 18 to 26×10 −4  m 3 , or 44%, the power/fresh water flow rate increased from 2715 watts/m 3  to 5664 watts/m 3  or 108%, more than 2.5 times as much as for the largest down tube  20 . The efficiency of power production declined with the largest diameter down tube  20 .  
         [0163]    These results are shown graphically in FIG. 3. The graphs depicted therein appear to show that there is an optimum ratio (about 250:1) of the area of the up tube  40  relative to the area of the down tube  20  that maximizes normalized power production. At ratios higher or lower than about 250 the normalized power per unit volume of fresh water declines.  
         [0164]    Although a ratio of the area of the up tube  40  relative to the area of the down tube  20  of approximately 250 appears to be optimal, the ratio may range from approximately 5 to 50,000, more preferably from 50 to 2000.  
         [0165]    The previous examples and discussions illustrate that a suitably constructed upwelling apparatus as illustrated in FIG. 2 has the potential of generating useful power by mixing aqueous liquids having different osmotic potentials. The simple experimental apparatus illustrated in FIG. 2 generates 0.98 watts with a fresh water flow of 2.4×10 −4  cubic meters per second. This is equivalent to 4 kilowatts per cubic meter of fresh water per second, indicating an efficiency of about 0.15%. The actual efficiency and capacity of a commercial-scale power production facility will depend on a number of factors, including the size of the up tube, the ratio of the flow area of the fresh water down tube  20  to the flow area of the up tube  40 , and the rate of fresh water flow. Those skilled in the art will recognize that the experimental apparatus disclosed and discussed herein-above may be modified and improved in other obvious ways to achieve even greater power production and/or efficiency of operation.  
         [0166]    The remaining detailed discussion and corresponding figures illustrate various possible embodiments of a commercial hydrocratic generator utilizing the principles discussed above and having features and advantages in accordance with the present invention. Although the various embodiments of the apparatus depicted and described herein vary somewhat in design and operation, certain common features and advantages will become readily apparent and, thus, the descriptions thereof will not be repeated.  
         [0167]    [0167]FIG. 4 is a simple schematic illustration of one possible embodiment of a hydrocratic generator  100  utilizing the principles discussed above and having features and advantages in accordance with the present invention. The device  100  generally comprises a down tube  20 , an up tube  40 , and a power plant generator  60 . The particular device illustrated in FIG. 4 may be adapted for either large-scale deep water applications or for relatively small-scale or intermediate-scale power generation facilities in shallow coastal waters, as desired. For example, the depth of water illustrated in FIG. 4 may be 10 to 50 meters or more, with the up tube  40  being 1-5 meters in diameter.  
         [0168]    In a preferred embodiment, fresh water is introduced into the down tube  20  in order to power the device. The term “fresh” water as used herein is to be interpreted in a broad sense as water having an osmotic potential relative to sea water. Thus, it may be used to describe the input stream a river discharge, a mountain run-off, a treated sewage discharge, a melting iceberg, or even runoff from a city storm drainage system.  
         [0169]    The fresh-water input stream may be conducted though the down tube  20  by applying pressure at the inlet end  22  of the down tube  20 . The pressure may be provided by a pumping station or with a hydrostatic head pressure resulting from a fluid reservoir at a higher elevation. The pressure applied at the inlet end  22  of the down tube  20  need only be high enough to overcome the hydrostatic head at the outlet end  24  of the down tube  20 .  
         [0170]    It has been found that, when fresh water is introduced into the down tube  20 , sea water flows into the up tube  40 , causing upwelling in the up tube  40  that can be used to generate power with the power generator  60 . Some of this upwelling effect is due to the increased buoyancy of the mixed water in the up tube  20 , because fresh water has a lower density than sea water. However, far more upwelling of sea water is observed than would be expected from this phenomenon alone. It is believed that the apparatus and the method is able to harness the energy available from the different osmotic potentials of fresh water and sea water. The amount of upwelling and the amount of power that is generated in the device depend in part on the particular dimensions of the up tube  40  and the down tube  20  and the flow rate of fresh water in the down tube  20 .  
         [0171]    As shown in FIG. 4, the down tube  20  has an inlet end  22  and an outlet end  24 . The inlet end  22  is connected to a supply  25  of relatively fresh water. For example, this fresh water supply  25  may comprise a reservoir, pump or other source as desired or expedient. The outlet end  24  of the down tube  20  is open such that the fresh water discharges through the outlet end  24  of the down tube  20  into the up tube  40 . In alternative embodiments the outlet end  24  of the down tube  20  may be connected to an intermediate mixing chamber (not shown) which then discharges into the up tube  40 .  
         [0172]    Although the down tube  20  may be any of a variety of diameters, one criterion is to choose a diameter for the down tube  20  which minimizes the resistance to fluid flow through the down tube  20 . Resistance to flow through a tube decreases as the diameter of the tube increases. Choosing a large diameter for the down tube  20  therefore minimizes the resistance of the tube for a given flow rate.  
         [0173]    Another criterion in choosing the diameter of the down tube  20  is to maximize the amount and efficiency of power generated by the power generator  60 . When the diameter of the down tube  20  exceeds a certain value relative to the up tube  40 , it has been discovered that the efficiency of power generation declines as the diameter of the down tube  20  is increased further. There is therefore an optimum in the ratio of the diameter of the down tube  20  relative to the diameter of the up tube  40 , and therefore the ratio of the area of the down tube  20  relative to the area up tube  40 , in order to maximize the efficiency of power generation. When the ratio of the area of the down tube  20  to the up tube  40  increases beyond the optimal value, the increase in efficiency of power generation with increased fresh water flow in the down tube  20  is less than with a down tube  20  having a smaller area relative to the up tube  40  area. Choosing the diameter of the down tube  20  to maximize power production therefore involves tradeoffs to choose the maximum diameter possible without losing power efficiency.  
         [0174]    In the embodiment of the apparatus shown in FIG. 4, the outlet end  24  of the down tube  20  is located inside the up tube  40 . In this embodiment, the outlet end  24  of the down tube  20  is preferably oriented so that the outlet end  24  of the down tube  20  points upward.  
         [0175]    The up tube  40  has an lower end  42  and an outlet end  44 . In the embodiment of FIG. 4 both the lower end  42  and the outlet end  44  of the up tube  40  are open. In other embodiments, the lower end  42  of the up tube  40  may contain vanes or other means of directing water flow. Some of these alternative embodiments of the up tube  40  are illustrated in other figures herein.  
         [0176]    Although the diameters of the lower end  42  and the outlet end  44  of the embodiment of the up tube  40  shown in FIG. 4 are equal, the lower end  42  and the outlet end  44  of the up tube  40  may have different diameters in other embodiments. For example, the up tube may be positively or negatively tapered to form a nozzle or diffuser. Alternatively, the up tube  40  can have a necked-down portion to form an accelerated flow there-through.  
         [0177]    In the embodiment of FIG. 4 the outlet end  44  of the up tube  40  is attached to a flotation system for locating the up tube  40  at a predetermined depth. Other means of locating the up tube  40  at a predetermined depth may also used in place of the flotation system, and the invention is not limited to the embodiment shown in FIG. 4. The flotation system shown in FIG. 4 comprises one or more floats  48  and one or more support cables  50 . The float  48  may be formed of Styrofoam, or it may comprise a plurality of individual air bags, drums, or any other suitable material capable of producing buoyancy.  
         [0178]    In some embodiments, the lower end  42  of the up tube  40  is attached to mooring cables  52 . The mooring cables  52  extend from the lower end  42  of the up tube  40  to anchors  56  fixed on the sea floor. The mooring cables  52  and the anchors  56  retain the up tube  40  in a predetermined location on the sea floor. The lifting force of the float  48  transmitted through support cables  50  retains the up tube  40  at a desired predetermined vertical orientation.  
         [0179]    In the embodiment shown in FIG. 4, the down tube  20  is also attached to mooring cables  52  which extend to anchors  56  on the ocean floor. The mooring cables  52  and anchors  56  hold the down tube  20  in place. The down tube  20  is arranged so that it discharges the fresh water into the up tube  40 .  
         [0180]    Just as choosing an optimal diameter for the down tube  20  involves tradeoffs, choosing the diameter of the up tube  40  also involves optimization. Increasing the diameter of the up tube  40  increases the amount of upwelling in the up tube  40  and therefore increases power production. However, increasing the diameter of the up tube  40  increases both the size and the cost of the apparatus. Further, increasing the area of the up tube  40  allows the use of a down tube  20  with a greater area without losing efficiency in generating power. The ratio of the area of the down tube  20  to the area of the up tube  40  is therefore the parameter which is to be optimized rather than the diameter of either the up tube  40  or the down tube  20  alone The optimal diameters for the up tube  40  and the down tube  20  are interdependent on one another, because the ratio of the areas of the two tubes is a more important parameter in optimizing power production than the area, and therefore the diameter, or either the up tube  40  or the down tube  20  alone.  
         [0181]    Advantageously the down tube  20  and the up tube  40  are not subjected to excessively high pressures. In the embodiment shown in FIG. 4, the up tube  40  contains the sea water entering from the lower end  42  of the up tube  40  and the fresh water coming out of the outlet end  24  of the down tube  20 . Because the up tube  40  is operated at low pressures, the up tube  40  can be constructed of relatively inexpensive and lightweight materials such as plastic, PVC, lightweight concrete, and the like.  
         [0182]    Although the down tube  20  is subjected to higher pressures than the up tube  40 , the pressures in the down tube  20  are typically small. Thus, inexpensive materials can therefore generally be used for both the up tube  40  and the down tube  20 . Suitable materials for constructing the down tube  20  and the up tube  40  include, but are not limited to, polyvinyl chloride (PVC), fiberglass, polyethylene (PE), polypropylene (PP), concrete, gunite, and the like. Alternatively, other materials such as stainless steel or titanium may also be used. Because the up tube  20  and the down tube  40  are generally exposed to water of relatively high salinity, it is preferable to form the down tube  20  and the up tube  40  from materials which are resistant to corrosion from salt water. Although the materials listed above are, in general, resistant to corrosion, some alloys of stainless steel are not suitable for extended use in salt water. If stainless steel is chosen as a material of construction, it is preferable to select an alloy of stainless steel which is resistant to corrosion by salt water.  
         [0183]    The outlet end  44  of the up tube  40  may extend to or above the surface of the sea or may be located at any depth beneath the surface of the sea. In one embodiment, the outlet end  44  of the up tube  40  is located in the photic zone so as to bring nutrient-rich deep-sea water to the photic zone to enhance growth of the organisms in the photic zone through mariculture.  
         [0184]    The length of the up tube  40  may vary, depending on a variety of factors. The length of the up tube is preferably sufficient to allow complete mixing of the fresh water with the salt water, but not so long as to cause unnecessary drag on the water flow. The optimal length will be determined as that which allows maximum output flow rate and power production for a given range of input fresh-water flow rates. The length of the up tube  40  may also be chosen based on a desire to facilitate mariculture, the promotion of growth of organisms in the sea by transfer of nutrients from nutrient-rich depths to the nutrient-poor water at lesser depths. If mariculture is practiced, the lower end  42  of the up tube  40  is preferably located at a depth of the sea where large concentrations of nutrients are available, and the outlet end  44  of the up tube  40  is preferably located in the photic zone. In this embodiment, the up tube  40  carries nutrient-rich water from the depth of the lower end  42  of the up tube  40  to the outlet end  44  of the up tube  40  in the photic zone, where few nutrients are available, thereby enhancing growth of the organisms in the photic zone. The length of the down tube  20  is relatively unimportant, provided that it is long enough to deliver the fresh water into the up tube.  
         [0185]    The power generator  60  generates electricity from the water flow inside the up tube  40 . FIG. 4 shows one simplified form of a power generator  60  suitable for use with the present invention. The power generator  60  comprises one or more turbines or propellers  62  attached to a shaft  64 . In a preferred embodiment, there are a plurality of propellers  62  attached to the shaft  64 . The shaft  64  is connected to an electrical generator  66 . When water upwells in the up tube  40 , the upwelling water turns the propellers  62 , which in turn rotate the shaft  64 . The rotating shaft  64  drives the electrical generator  66 , thereby generating power.  
         [0186]    Preferably, one or more shaft supports  68  are provided to support the shaft  64  to minimize wobbling of the shaft  64  while the upwelling water turns the one or more propellers  62  attached to the shaft  64 . In a preferred embodiment, a plurality of shaft supports  68  engage the shaft  64  to support the shaft  64  to minimize wobbling. In the embodiment shown in FIG. 4, three shaft supports  68  are present to support the shaft  64 , a lower shaft support  68 , a middle shaft support  68 , and an upper shaft support  68 . Further details on the shaft supports  68  are given in FIG. 7C, described later.  
         [0187]    The propellers  62  on the shaft  64  may be inside the up tube  40 , above the outlet end  44  of the up tube  40 , or both inside the up tube  40  and above the outlet end  44  of the up tube  40 . The propellers  62  on the shaft  64  may be located above the middle shaft support  68 , below the middle shaft support  68 , or both above and below the middle shaft support  68 . In the embodiment of FIG. 4, the propellers  62  are located inside the up tube  40  below the middle shaft support  68 . Similarly, the electrical generator  66  may be conveniently located above or below the surface of the water in which the up tube  40  is located. In the embodiment shown in FIG. 4, the electrical generator  66  is located above the surface of the water in order to minimize maintenance expense.  
         [0188]    [0188]FIG. 5 shows an alternative embodiment of a power generator  60 . In this case, the power generator  60  comprises propellers  62  attached to the shaft  64  both above and below the middle shaft support  68 . The shaft  64  is attached to the electrical generator  66 , which generates electrical power when the shaft  64  rotates due to the water flow in the up tube  40 . Again, the electrical generator  66  of FIG. 5 is located above the surface of the water. In alternative embodiments, the electrical generator  66  may be located below the surface of the water, if desired.  
         [0189]    [0189]FIG. 6 shows a further alternative embodiment of a power generator  60  in which one or more spiral fans  70  are mounted on the shaft  64 . Shaft supports  68  may optionally be provided to minimize wobbling of the shaft  64 . The one or more spiral fans  70  may be attached to the shaft  64  above the middle shaft support  68 , below the middle shaft support  68 , or both above and below the middle shaft support  68 . One or more spiral fans  70  may be mounted on the shaft  64  on the outlet end  44  of the up tube  40 . In an alternative embodiment, one or more spiral fans  70  may be mounted both inside the up tube  40  and on the outlet end  44  of the up tube  40 . In the embodiment of FIG. 6, the spiral fan  70  is attached to the outlet end  44  of the up tube  40 .  
         [0190]    The spiral fan  70  comprises a plurality of spiral vanes  72 . The water flow up the up tube  40  contacts the plurality of spiral vanes  72 , turning the one or more spiral fans  70  mounted on the shaft  64 . Turning the one or more spiral fans  70  rotates the shaft  64 . The rotating shaft  64  drives the electrical generator  66 , generating electrical power. Again, the electrical generator  66  may be conveniently located above or below the surface of the water, as desired.  
         [0191]    In the embodiment of the power generator  60  shown in FIG. 6, both propellers  62  and one spiral fan  70  are mounted on the shaft  64 . The propellers  62  and spiral fans  70  may be mounted on the shaft  64  in any order, above, below, or both above and below the middle shaft support  68 . The propellers  62  and spiral fans  70  may also be mounted on the shaft  64  inside the up tube  40  and/or above the outlet end  44  of the up tube  40 . In FIG. 6, propellers  62  are mounted on the shaft  64  inside the up tube  40  below the middle shaft support  68 , and the single spiral fan  70  is mounted on the outlet end  44  of the up tube  40 . The electrical generator  66  is located above the water.  
         [0192]    [0192]FIG. 7A shows a further alternative embodiment of the up tube  40  in which the lower end  42  of the up tube  40  is closed. The down tube  20  passes through the closed lower end  42  of the up tube  40 . Although FIG. 7A shows that the down tube  20  is attached to one or more mooring cables  52  which are attached to anchors  56  on the ocean floor, the down tube  20  may also be supported by the closed lower end  42  of the up tube  40 . The closed lower end  42  of the up tube  40  of FIG. 7A helps to keep the down tube  20  in position without the need for mooring cables  52  and anchors  56 .  
         [0193]    The up tube  40  of the embodiment of FIG. 7A comprises a plurality of slots  76 , as shown in FIG. 7B. The plurality of slots  76  are open to the surrounding sea and allow the sea water to enter the up tube  40 . One or more shaft supports  68  are attached to the up tube  40 . One possible embodiment of a suitable shaft support  68  is shown in FIG. 7C. The shaft support  68  comprises one or more hydrodynamic cross members  78  and a bearing  80 . The cross members  78  are attached to the up tube  40  at a first end and to the bearing  80  at a second end, thereby suspending the bearing  80  inside the up tube  40 . The bearing  80  can have a variety of designs such as ball bearings, compression bearings, and the like. The cross members  78  are preferably hydro-dynamically shaped so as to not slow down water flow in the up tube  40 . The shaft support  68  supports the shaft  64 , minimizing the wobbling of the shaft  64  when the shaft  64  rotates.  
         [0194]    The power generator  60  of the embodiment shown in FIG. 7A comprises a vane drum  90  inside the up tube  40 . The vane drum  90  comprises a plurality of rings  92  connected by a plurality of curved vanes  94 . FIG. 7D shows a sectional view of the vane drum  90 . Each curved vane  94  is attached by a first edge  96  to each of the plurality of rings  92 . The curved vanes  94  are attached to the plurality of rings  92  in a manner so that the curved vanes  94  form a helical curve when viewed from the side, as shown in FIG. 7A. The helical curved shape of the curved vanes  94  improve the efficiency of energy transfer from the water flow through the slots  76  on the up tube  40  compared to the efficiency of curved vanes  94  which are not oriented with a helical curve. FIG. 7D shows the curved vanes  94  attached to the ring  92  from above as illustrated in FIG. 7A. FIG. 7D also shows the preferred curved surface of the curved vanes  94  as well as the helical orientation of the curved vanes  94  as viewed from above.  
         [0195]    In one preferred embodiment, the vane drum  90  is attached to the shaft  64 . When the sea water is drawn into the up tube  40  through the slots  76 , the incoming water contacts the curved vanes  94 , rotating the vane drum  90 , which in turn rotates the shaft  64 . The rotating shaft  64  turns the electrical generator  66 , generating power from the upwelling water in the up tube  40 .  
         [0196]    [0196]FIG. 8A illustrates a further alternative embodiment of the power generator  60  comprising two vane drums  90 , a first vane drum  90  below the middle shaft support  68  and a second vane drum  90  above the middle shaft support  68 . In a preferred embodiment, both the first vane drum  90  and the second vane drum  90  are attached to the shaft  64  so that the shaft  64  rotates when the vane drums  90  rotate due to the flow of water through the slots  76  into the up tube  40 . The rotating shaft  64  rotates the shaft of the electrical generator  66 , generating electrical power.  
         [0197]    In the embodiment of the up tube  40  shown in FIG. 8B, there are preferably two sets of slots  76  in the up tube  40  and two vane drums  90 . In another embodiment, there are two vane drums  90  as in the embodiment shown in FIG. 8A, but the up tube  40  comprises only a single set of slots  76  in the up tube  40 , as in the embodiment of the up tube  40  shown in FIG. 7B.  
         [0198]    [0198]FIG. 9A shows an alternative embodiment of the down tube  20  in which a plurality of holes  110  are present in the side of the down tube  20 . FIG. 9B shows a view of the outlet end  24  of the down tube  20  of FIG. 9A. The outlet end  24  of the down tube  20  of FIG. 9A is sealed except for a single hole  110 . In alternative embodiments, a plurality of holes  110  may be provided in the outlet end  24  of the down tube  20 . The fresh water flowing through the down tube  20  of FIG. 9A flows out of the plurality of holes  110  and into the up tube  40 . Although the embodiment of the apparatus shown in FIG. 9A shows the alternative down tube  20  with the embodiment of the up tube  40  of FIGS.  4 - 6  with an open lower end  42 , the down tube  20  of FIG. 9A may also be used with the embodiment of the up tube  40  such as shown in FIGS. 7A or  8 A with a closed lower end  42 .  
         [0199]    [0199]FIGS. 10A and 10B show another embodiment of the down tube  20  in which the down tube  20  separates into a plurality of secondary down tubes  120  In the embodiment shown in FIG. 10A, there are a plurality of holes  110  in the secondary down tubes  120 , similar to the embodiment of the down tube  20  shown in FIG. 9A. FIG. 10B shows a sectional view of the down tube  20  of the embodiment of FIG. 10A from below. In the embodiment shown in FIG. 10B the outlet end  24  of each of the five secondary down tubes  120  is closed except for a single hole  110 . In the embodiment of the down tube  20  of FIGS. 10A and 10B, the fresh water that is introduced into the down tube  20  exits the holes  110  to enter the up tube  40 .  
         [0200]    In other embodiments the down tube  20  may separate into a plurality of secondary down tubes  120 , as in the embodiment of the down tube  20  of FIG. 10A, but there are no holes  110  in the secondary down tubes  120 , and the outlet ends  24  of the secondary down tubes  120  are open. In this embodiment of the down tube  20  (not shown), the fresh water which is introduced into the down tube  20  exits the open outlet ends  24  of the secondary down tubes  120  to enter the up tube  40 .  
         [0201]    [0201]FIG. 11 shows an alternative embodiment of the down tube  20  in which the down tube separates into a plurality of secondary down tubes  120 . In the embodiment shown in FIG. 11, the down tube  20  separates into a plurality of secondary down tubes  120  outside of the up tube  40 . In the embodiment shown in FIG. 11, there are no holes in the secondary down tubes  120 , as in the embodiments shown in FIGS. 9A and 10A. In other embodiments there are a plurality of holes  110  in the secondary down tubes  120 .  
         [0202]    Although the embodiment of the apparatus shown in FIG. 11 shows the alternative down tube  20  with the embodiment of the up tube  40  of FIGS.  4 - 6  with an open lower end  42 , the alternative down tube  20  of FIG. 11 may also be used with the embodiment of the up tube  40  such as shown in FIGS. 7A or  8 A with a closed lower end  42 .  
         [0203]    [0203]FIG. 12 shows another embodiment of the down tube  20  in which the down tube  20  terminates in a hub  122 . The hub  122  forms a cap on the down tube  20  and rotates freely on the down tube  20 . A plurality of spoke outlets  124  are fluidly connected to the hub  122 . The plurality of spoke outlets  124  emerge at approximately a right angle from the hub  124  and then bend at a second angle before terminating in a spoke discharge  126 . The spoke discharge  126  may have an open end or a partially closed end where the water from the down tube  20  discharges. The embodiment of the down tube  20  shown in FIG. 12 is similar to a rotating lawn sprinkler. The hub  122  is attached to the shaft  64 , which is in turn connected with the electrical generator  66 . In the embodiment shown in FIG. 12, there is no up tube  40 .  
         [0204]    When fresh water flows through the down tube  20  and is discharged out of the spoke outlets  124 , the hub  122 , shaft  64 , and electrical generator  66  rotate, generating electrical power. In the embodiment shown in FIG. 12, the energy generated by the electrical generator  66  comes almost exclusively from the kinetic energy from the water emerging from the plurality of spoke discharges  126 , because there is no up tube  40  or means of generating power from hydrocratic energy generated from the mixing of fresh water from the down tube  20  with water of high salinity.  
         [0205]    [0205]FIG. 13 shows another embodiment of the down tube  20  similar to the embodiment of FIG. 12, with a hub  122 , a plurality of spoke outlets  124 , and a plurality of spoke discharges  126  at the ends of the spoke outlets  124 . The embodiment of FIG. 13 differs from the embodiment of FIG. 12 in that the spoke discharges  126  discharge the fresh water from the down tube  20  into an up tube  40  with an open lower end  42  and a plurality of propellers  62  attached to the shaft  64 . The fresh water which exits the spoke discharges  126  into the up tube  40  causes upwelling in the up tube  40 , rotating the propellers, which in turn drive the shaft  64 . The shaft  64  drives a electrical generator  66  (not shown), generating electrical power.  
         [0206]    In the embodiment of the apparatus shown in FIG. 13, the shaft  64  is rotated both by the discharge of water from the spoke discharges  126  rotating the hub  122  and by the upwelling in the up tube  40  turning the propellers  62 , which in turn rotate the shaft  64 . The energy generated in the embodiment of the apparatus shown in FIG. 13 is therefore a combination of kinetic energy from the rotation of the hub  122 , shaft  64 , and electrical generator (not shown) from the fresh water ejected from the spoke discharges  126  and from hydrocratic energy generated from the upwelling in the up tube  40  from the mixing of fresh water from the spoke discharges  126  mixing with the water of high salinity entering the up tube  40  from the lower end  42 .  
         [0207]    [0207]FIG. 14 illustrates another embodiment of the up tube  40  in which there are a plurality of nested up tubes  40  having increasing diameters. The lower end  42  of each of the plurality of nested up tubes  40  is open. Fresh water is introduced into the down tube  20  causing upwelling in the plurality of up tubes  40  when the water of high salinity enters the open lower ends  42  of the nested up tubes  40 .  
         [0208]    Any of the embodiments of power generators  60  can be combined with the embodiment of the nested up tubes  40  of FIG. 14. For example, in one embodiment, the propellers  62  of FIGS. 4 and 5 may be used as a power generator  60  in combination with the nested up tubes  40  of FIG. 14. In another embodiment, the power generator  60  may comprise one or more spiral fans  70 , as shown in FIG. 6.  
         [0209]    [0209]FIG. 15 shows another embodiment of the up tube  40  and power generator  60 . In the embodiment of FIG. 15, a plurality of turbines  130  are mounted on a shaft  64  inter-spaced between a plurality of stators  132 . The stators  132  direct the water flow into the turbine blades of the turbines  130  to increase the efficiency thereof. The shaft  64  is connected to an electrical generator  66  (not shown). When water upwells in the up tube  40 , the upwelling water turns the turbines  130 , which in turn rotate the shaft  64  and the electrical generator  66 , generating power.  
         [0210]    In the embodiment shown in FIG. 15, the portion of the up tube  40  surrounding the turbines  130  and stators  132  comprises a nozzle  134  and an expander  136 . The nozzle  134  reduces the diameter of the up tube  40  in the portion of the up tube  40  around the turbines  130  and stators  132  from the diameter of the remainder of the up tube  40 . By reducing the diameter of the up tube  40  with the nozzle  134  in the portion of the up tube  40  surrounding the turbines  130 , the upwelling water is forced into a smaller area and is accelerated to a higher velocity water flow that can be harnessed more efficiently by the turbines  130 . Nozzles  134  and stators  132  can also be used with other embodiments of the power generator  60  illustrated herein.  
         [0211]    [0211]FIG. 16 is a schematic illustration of a possible large-scale commercial embodiment of a hydrocratic generator having features and advantages of the present invention. While a particular scale is not illustrated, those skilled in the art will recognize that the device  200  is advantageously suited for large-scale deep-water use 100-500 meters or more beneath sea level. The up tube  240  extends upward and terminates at any convenient point beneath sea level. The diameter of the up tube may be 3-20 meters or more, depending upon the desired capacity of the hydrocratic generator  200 . This particular design is preferably adapted to minimize environmental impact and, therefore, does not result in upwelling of nutrient rich water from the ocean depths.  
         [0212]    Sea water is admitted into the device from an elevated inlet tube  215  through a filter screen or grate  245 . The filter removes sea life and/or other unwanted objects or debris that could otherwise adversely impact the operation of generator  200  or result in injury to local sea life population. If desired, the inlet tube  215  may be insulated in order to minimize heat loss of the siphoned-off surface waters to colder water at or near full ocean depth. Advantageously, this ensures that the temperature and, therefore, the density of the sea water drawn into the generator  200  is not too cold and dense to prevent or inhibit upwelling in the up tube  240 .  
         [0213]    The sea water is passed through a hydraulic turbine power plant  260  of the type used to generate hydraulic power at a typical hydro-electric facility. The turbine and generator assembly is illustrated in more detail in the cutaway view of FIG. 16. Water enters the turbine  261  through a series of louvers  262 , called wicket gates, which are arranged in a ring around the turbine inlet. The amount of water entering the turbine  261  can be regulated by opening or closing the wicket gates  262  as required. This allows the operators to keep the turbine turning at a constant speed even under widely varying electrical loads and/or hydraulic flow rates. Maintaining precise speed is desirable since it is the rate of rotation which determines the frequency of the electricity produced.  
         [0214]    As illustrated in FIG. 16, the turbine is coupled to an electric generator  266  by a long shaft  264 . The generator  266  comprises a large, spinning “rotor”  267  and a stationary “stator”  268 . The outer ring of the rotor  267  is made up of a series of copper wound iron cells or “poles” each of which acts as an electromagnet. The stator  268  is similarly comprised of a series of vertically oriented copper coils disposed in the slots of an iron core. As the rotor  267  spins, its magnetic field induces a current in the stator&#39;s windings thereby generating alternating current (AC) electricity.  
         [0215]    Referring again to FIG. 16, the sea water is discharged from the turbine into the up tube  240 . Fresh water is introduced into the base of the up tube  240  by down tube  220 . The mixing of fresh water into saline sea water releases the hydrocratic or osmotic energy potential of the fresh water in accordance with the principles discussed above, resulting in a concomitant pressure drop (up to 190 meters of head) across the hydraulic turbine  260 . This pressure drop in conjunction with the induced water flow upwelling through the up tube  240  allows for generation of significant hydropower for commercial power production applications without adversely affecting surrounding marine culture.  
         [0216]    With reference to FIG. 18 of the drawings, this embodiment shows an up tube  40  having an open lower end  42  and an open outlet end  44 . A down tube  20  is provided which enters the up tube  40  through the lower end  42 , and extends to a point approximately midway along the length of the uptube, where it is sealed by a cap  302 . A shaft  64  extends upwardly from the cap  302 , extending to a generator, not shown in FIG. 18, but substantially similar to generators shown in some of the Figures described above.  
         [0217]    Although in the embodiment shown in FIG. 18, the down tube  20  is hown as extending to a point approximately midway up the length of the up tube  40 , this construction may, in practice, vary widely according to the conditions, length of the up tube  40 , and other apparatus parameters. Thus, the down tube  20  may extend only a short distance into the up tube  40 , or it may extend well beyond the midpoint thereof, to a selected height.  
         [0218]    The down tube  20  comprises an outside portion  304 , located outside of the up tube  40 , and an inside portion  306 , located within the up tube  40 . The outside portion  304  and inside portion  306  of the down tube  20  are connected to each other by a rotational connector  308 , which, in the embodiment shown in FIG. 18 is at the level of the open lower end  42 . However, this rotational connector  308  could be configured on the down tube  20  at any appropriate vertical position of the down tube  20 .  
         [0219]    The rotational connector  308  permits rotation of the inside portion  306  relative to the outside portion  304 , as will be described.  
         [0220]    The inside portion  306  has a plurality of radial apertures  310 , which may be randomly disposed on the inside portion  306 , or specifically located, such as beneath a turbine  62 , according to the selected configuration of the generator. Fresh water entering the down tube  20  from a supply source or reservoir passes through the rotational connector  308 , and into the inside portion  306 , where it must exit through one of the radial apertures. The cap  302  mounted at the top end of the inside portion  306  prevents any water or liquid from the down tube  20  from exiting the inside portion  306 , except through the radial apertures  310 .  
         [0221]    The inside portion  306  and shaft  64  are secured appropriately in position by shaft supports  68  to prevent wobbling or axial displacement thereof, as has already been described above in other embodiments.  
         [0222]    In operation, fresh water exiting the down pipe  20  through the radial apertures  310  is mixed with water of higher salinity entering the lower end  42  of the upper tube  40 . The energy produced by the mixing of the water of higher salinity and lower salinity drives turbine  62 , which in turn rotates the inside portion  306 , the cap  302 , and the shaft  64 . This embodiment permits accurate selection of apertures  310  for releasing of the fresh water into the up tube  40 , in a manner that is fixed with respect to the turbines  62 . Since the radial apertures  310  and turbines  62  are both rotating, the precise location of mixing, and the optimal effect thereof of driving the turbine  62 , can be exploited to improve the efficiency and hence the energy produced by the apparatus of the invention. This is achieved by the use of the rotational connector  308  which allows relative rotation of the inside portion  306 , but ensures no leakage or fresh water escape from the down tube  20  at the position of the rotational connector  308 .  
         [0223]    [0223]FIG. 19 shows a variation of the apparatus shown in FIG. 18, including the up tube  40 , the down tube  20  having an outside portion  304 , and an inside portion  306 , the outside and inside portions  304  and  306  respectively being connected by the rotational connector  308 . A cap  302  is provided at the top end of the inside portion  306 , and a series of turbines  62  are mounted on the inside portion  306 , which has a plurality of selectively placed radial apertures  310 . The apparatus in FIG. 19 differs from the embodiment shown in FIG. 18 by the existence of a closure piece  320  over the lower end  42  of the up tube  40 . Since the closure piece  320  prevents sea water from entering the lower end  42  of the up tube  40 , a plurality of holes  322  are provided at locations in the wall of the up tube  40 , as shown in FIG. 19B, through which the sea water is introduced to the interior of the up tube  40 . One advantage of the embodiment shown in FIGS. 19A and 19B is that the sea water can be introduced at the most efficient point, thereby facilitating control of the precise points or areas at which the sea water as well as the fresh water are first introduced and allowed to mix. This factor, coupled with the orientation of turbines  62  on the inside portion  306 , can be used to streamline the efficiency of the apparatus. As was the case with respect to FIG. 18, the fresh water is only allowed to exit through the radial apertures between the rotational connector  308  and the cap  302 , at a position, flow-rate and orientation which can be controlled and manipulated to advantage.  
         [0224]    In FIG. 20 of the drawings, a further embodiment showing a variation of those illustrated in FIGS. 18 and 19 of the drawings is illustrated. In this embodiment, an up tube  40  is provided, as well as a down tube  20  including an outside portion  304 , an inside portion  306  having a plurality of radial apertures  310 , and a cap  302 . At the lower end  42 , a closure piece  320  is provided. In the embodiment shown in FIG. 20, the rotational device  308  is positioned outside of the up tube  40  and closure piece  320  so as to permit rotation of both the inside portion  306  of the down tube  40 , and the up tube  20 , in response to energy production which causes rotation of the turbine  62 . Thus, rotation about the connector  308  as a result of forces on the turbines  62  thereby rotates the closure piece  320 , up tube  40  and the inside portion  306  of the down tube  20 .  
         [0225]    As was the case in the embodiment shown in FIGS. 19A and 19B, sea water will enter the up tube  40 , not through the lower end  42 , but through a series of holes  322  of the type shown in FIG. 19B. Alternatively, instead of having a plurality of holes  322 , one or more slits may be provided in the wall of the up tube  40 , such as those shown in FIGS. 7B or  8 B of the drawings.  
         [0226]    The embodiment of FIG. 20 is yet another variation by means of which the precise location of entry of the fresh water and sea water respectively into the up tube  40  can be controlled and exploited to derive maximum energy and power following hydrocrasis and the energy released thereby.  
         [0227]    [0227]FIG. 21 of the drawings shows a variation of the hydrocratic generator of the invention which uses neither vanes nor turbines on the shaft  64 , but rather a helical screw  330  mounted on the shaft, and which is caused to rotate in response to the energy released by mixing of the water with different salinities. Such forces acting on the helical screw  330  rotate the shaft  64 , which in turn transmits rotational forces to the generator for use as described above.  
         [0228]    [0228]FIG. 22A of the drawings shows an alternative embodiment for delivering fresh water from the down tube  20  to a precise location with respect to the fan blades. As shown in FIG. 22A, an inside portion  306  of the down tube  20  has a plurality of fan blades  62 , also referred to as turbines, mounted thereon. Instead of exiting the inside portion  306  through a plurality of apertures, the fresh water in the inside portion  306  is fed through a fan tube  336  which is mounted on the underside  338  of the fan blade  62 . Towards the outer extremity  340  of the fan blade  62 , the fan tube  336  includes a U-shaped section  342 , terminating in an outlet  344 . Thus, fresh water enters through the inside portion  306 , flows along the fan tube  336 , into the U-shaped section  342 , and exits through outlet  344 . In the embodiment shown in FIGS. 22A and 22B, the fresh water thus flows from the interior pipe through a series of smaller pipes located under the fan blades  62  (or helical screw, if this embodiment is used), to the outer edge of the fan blades  62 . The direction of flow is reversed so the fresh water exits in a flow direction which is towards the center of the up tube  40 .  
         [0229]    The embodiment shown in FIGS. 22A and 22B allows the apparatus to take advantage, once more, of controlling the exit areas for the saline and fresh water, thereby pinpointing the reaction location for maximum energy production and/or use of such energy in a manner which rotates the fan blades optimally. As with the other embodiments, the inside portion  306  of the down tube  20  is attached to a rotating shaft, which in turn attaches to a generator or power mechanism which uses or stores the energy so produced.  
       Other Applications/Embodiments  
       [0230]    In the preferred embodiments discussed above, the up tube  40  is located in a body of water of high salinity and high negative osmotic potential such as an ocean or a sea. The water of high salinity and high negative osmotic potential enters the up tube  40  in a ratio of greater than 8:1 salt water to fresh water, more preferably 30:1 salt water to fresh water, and most preferably about 34:1 or higher. The mixing of the fresh water of low negative osmotic potential with the sea water of high negative osmotic potential in the up tube  40  causes upwelling and draws sea water into the up tube  40  through the openings. The upwelling water in the up tube  40  rotates propellers  62 , spiral fans  70  or turbines  130 ,  261 , which are attached to a drive shaft  64 ,  264 . The rotating shaft  64 ,  264  turns the electrical generator  66 ,  266  generating electrical power from the difference in osmotic potential between the fresh water introduced into the down tube  20  and the water of high salinity which enters the up tube  40  through the openings in the up tube  40 .  
         [0231]    Because the method depends on having solutions of different osmotic potentials exiting the down tube  20  and entering the up tube  40 , it is preferable that the source of fresh water exiting the down tube  20  and the source of the water of high salinity entering the up tube  40  continue to have different osmotic potentials over time so that power generation continues over a long period of time. For example, if the body of water of high salinity surrounding the up tube  40  is small, the fresh water exiting the down tube  20  can dilute the water of high salinity after exiting the up tube  40 , reducing the difference in osmotic potential between the fresh water and the water of high salinity. Reducing the difference in osmotic potential between the fresh water exiting the down tube  20  and the water of high salinity entering the up tube  40  reduces the amount of energy available. It is therefore generally advantageous that the body of water of high salinity have a large volume. Locating the up tube  40  in a large body of water having high salinity such as the ocean or the Great Salt Lake is therefore a preferred embodiment.  
         [0232]    Alternatively, the invention can be operated between bodies of salt water having different salinity or between waters at different depths of the same body of water. For example, the salinity and temperature of sea water is known to vary with depth and location. In the Hawaiian islands, at a depth of 1000 meters, the ambient water temperature is approximately 35° F., with a salinity of approximately 34.6 ppt. The surface temperature is approximately 80° F. with a salinity of approximately 35.5 ppt. Thus, an osmotic energy potential (albeit small) exists between the surface waters and the waters at 100 meters depth.  
         [0233]    While the present invention is disclosed in the context of generating power by directly contacting and mixing fresh water with sea water in an apparatus located in the ocean, it is to be understood that the apparatus and method are not limited to this embodiment. The techniques and concepts taught herein are also applicable to a variety of other situations where aqueous solutions having differing osmotic potentials are available. For example, in one embodiment, the apparatus and method may be applied to a concentrated brine from a desalinization plant being mixed with the less-concentrated brine in sea water. In another embodiment, a treated sewage effluent, a fresh water stream, can be mixed with sea water. If desired, an osmotic membrane or osmotic water exchange plenum may be provided at the outlet end of the down tube and/or at the outlet (top) of the up tube in order to increase the efficiency of energy production. The apparatus and method may thus be applied to a wide range of applications in which two solutions of differing osmotic potential are available.  
         [0234]    The various embodiments of the invention disclosed and described herein are exemplary only. As such, these example embodiments are not intended to be exhaustive of all possible ways of carrying out the invention or even the most economical or cost-efficient ways of carrying out the invention on a commercial scale. Many of the example embodiments disclosed and discussed herein are based on experimental testing of small-scale models embodying certain features of the invention. These models and the test results reported herein may or may not be directly relevant to a full-scale power production facility utilizing the invention. However, those skilled in the art will readily recognize from the examples disclosed and discussed herein the utility of the invention in terms of its broader scope, and how it may be beneficially utilized in a commercial power production facility to efficiently harness the osmotic energy potential between fresh water run-off and sea water (or other convenient bodies of water/solvent having different solute concentrations).  
         [0235]    Thus, although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Accordingly, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.