Abstract:
Closed system heat engines can be used to deliver useful electrical power by harvesting ambient energy in the environment. The present invention provides a means of harvesting these low temperature differences in to useful energy and provides while providing rectification and regulation features.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional Patent Application Ser. No. 60/975,99, which was filed on Sep. 27, 2007. This application is incorporated entirely by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to heat engine devices such as those used for harvesting thermal energy in to another form of energy such as mechanical energy or electrical energy. Specifically the present invention relates to closed cycle (Carnot cycle) heat engines and their practical implementation. 
         [0004]    2. Prior Art 
         [0005]    Closed cycle heat engines are governed by various types of heat cycles derived from Carnot&#39;s law of efficiency and the laws of thermodynamics. Much ambient energy in the form of small temperature differentials exist for harvesting around the planet. However typically simple closed cycle heat engines are inefficient at small temperature differences in typical temperature ranges found on earth (e.g. around 250-320K). For example if a small heat engine is employed with a cold side temperature of 300K and a hot side temperature of 305K then the efficiency is given by Eff=1−[Thot/(Tcold+Thot)]=0.017 or about 1.7% efficient. This has made the use of simple heat engines to harvest even moderate amounts of energy impractical. In addition areas where there are larger temperature differences to exploit, such as around sub ocean volcanic features, are impractical to set up traditional heat engines due to constraints of access. 
         [0006]    Heat engines can come in both solid state forms such as shown in  FIG. 1  which is a typical implementation of a mechanical closed cycle Stirling engine. Here heat is applied to the displacer piston  105 . As the gas of the system (typically air) heats up it pushes the piston in to the region with the cooling fins  110 . The action of the piston turns the wheel  115  which also pushes a second compressor piston  120 . This piston pushes air back in to the displacer piston which in turn, after enough cooling returns to the heated area of the piston to repeat the cycle. The rotational energy of the such an engine can be used to turn the armature of an electrical generator creating electricity. As noted the maximum efficiency for small temperature differences will be low (much lower than the Carnot limit). Another approach to creating electricity from heat differences is to use solid-state means such as depicted in  FIG. 2 . Here  200  represents the hot side of a Peltier device and  205  represents a the cold side. Individually there may be hundreds of small junctions comprising the device. The output is a voltage developed across the electrical leads  210 . Many types of solid state thermopiles exist for converting heat directly to electricity without mechanical steps. 
       OBJECTS AND ADVANTAGES 
       [0007]    The present invention allows the use of multiple small thermal differences to create a larger stabilized electric voltage which is both fixed in polarity and magnitude across an entire day. The present invention also presents simple cost effective ways to harvest ambient energy which is not typically accessible such as that in the deep ocean with traditional mechanical machinery and minimizes impact to the environment. 
     
    
     
       LIST OF FIGURES 
         [0008]      FIG. 1  a typical mechanical Stirling type heat engine. 
           [0009]      FIG. 2  depicts a solid state thermopile such as a Peltier junction. 
           [0010]      FIG. 3  shows a simple embodiment of the present invention 
           [0011]      FIG. 4  shows an enhancement of the present invention using circulating fluids 
           [0012]      FIG. 5  shows an embodiment of the present invention used outdoors 
           [0013]      FIG. 6  shows an embodiment of the present invention used in conjunction with a large body of water. 
           [0014]      FIG. 7  depicts an array of implementation of the present invention. 
           [0015]      FIG. 8  depicts an embodiment of the present invention used in a large body of water such as an ocean or deep lake. 
           [0016]      FIG. 9  depicts an embodiment of the present invention used in a large body of water which contains a thermal feature such as volcanic activity 
           [0017]      FIG. 10  depicts a diagrams for thermal switches as are used in  FIG. 7  and in later figures. 
           [0018]      FIG. 11  depicts a close up view of the present invention with a thermal switch. 
           [0019]      FIG. 12  depicts a type of thermal switch based on gas pistons 
           [0020]      FIG. 13  depicts alternative types of gas piston based switches 
           [0021]      FIG. 14  depicts a thermal switch which is completely solid-state (electronic) in nature 
           [0022]      FIG. 15  depicts a block diagram of a 2:1 combiner for use in array type applications of the present invention 
           [0023]      FIG. 16  depicts the combiner in action 
           [0024]      FIG. 17  depicts the combiner in action 
           [0025]      FIG. 18  depicts the combiner in action 
           [0026]      FIG. 19  depicts the combiner in action 
           [0027]      FIG. 20  depicts issues of paralleling voltage sources 
           [0028]      FIG. 21  depicts a 3-way version of the combiner 
           [0029]      FIG. 22  depicts the use of combiners to achieve regulation 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0030]    The basic unit of the present invention is presented in  FIG. 3 . Here two thermal temperature differences are presented at each side of the device. Heat sink  305  is attached to heat spreader plate  325  via a heat conducting path  315 . The same is true on the opposite side heat sink  350  is attached to heat spreader plate  340  via heat conducting pat  345 . A series of thermopile junctions in series  335  and separated by thermal insulators  330 , which force heat flow through the junctions are in the center. Electrodes  325  and  355  provide electrical output whose polarity is dependant on which side of the apparatus is hotter. 
         [0031]      FIG. 4  depicts extra heat pipes  360 ,  365  in the heat conduction paths which can be filled with a fluid and may or may not be actively pumped or can be passively pumped via valves. This can help increase the efficiency of the heat transfer to the thermopile core. 
         [0032]      FIG. 5  depicts the present invention in use with one end in the ground  520  and the other in the air  505 . Depending on the temperature the either the ground or the surrounding air will be hotter. This forms a voltage on the thermopile  510  which can be tapped for energy  515 . This can be maximized by choosing places where the day to night temperature is most extreme such as the desert. During the day the air will increase in temperature and at night sharply decrease. Since the ground lags in temperature the difference can be tapped for energy. Note the this will result in a sinusoidal type voltage with a period of approximately one day. 
         [0033]      FIG. 6  depicts a similar setup over a large body of water. Here the air heat sink is  605 , the water heat sink is  620 , power is provide through interface  610 . In addition solar panels have been added  600  which can provide additional energy harvesting during the daylight hours. A cable  615  allows the combining of the two power sources in to a single power output. 
         [0034]      FIG. 7  depicts the entire setup as an array allowing greater voltage and current to be developed. 
         [0035]      FIG. 8  depicts the present invention harvesting thermal energy from the ocean or other large body of water. Water is taken in from the intake  820  and transported via path  805  to the thermal difference engine (TDE) apparatus  800 . There it is interface with another heat sink  825  which takes warmer water from the surface and then returns the water via path  810  to an outtake valve  815 . Electrical power is delivered through interface  830 . Note that since the output water can be delivered back the body of water at the thermocline which matches its temperature thereby reducing impact to the environment. Water can be actively pumped or if a suitable current can be found then it can be passively transported through the piping system. 
         [0036]      FIG. 9  depicts the present invention exploiting a volcanic feature on the ocean floor. Here feature  940  heats water at the intake  920  where it goes through transport pipe  905  and is delivered to the TDE apparatus  900 . The TDE is dissipating the heat through heat sink  925  and expels it through path  910  to exhaust vent  915 . Note that like in  FIG. 8  the exhaust outlet can be matched to a thermocline to minimize the effect of temperature on marine environments. Passive or active pumping may be used. 
         [0037]    The previous figures detail the invention and its use in many environments. However the need for fixed polarity of voltage and constant magnitude of the voltage also needs to be a achieved. This is also a portion of the invention and is detailed here in  FIGS. 10 to 21 . 
         [0038]      FIG. 10  shows a nomenclature for some thermal switches—either make before break (useful in parallel combiners discussed shortly) or break before make (discussed in series combiners discussed shortly). 
         [0039]      FIG. 11  depicts a thermal switch assembly, intended to be co-located with the thermal difference engine. Here the switches  1135  and  1130  switch the output polarity of the thermopile  1125  output electrodes by detecting the heat between plates  1110  and  115 . Each switch contains two plates (such as  1115  and  1120 ) which allows the switch to sense the temperature. No matter which plate is hotter the thermal switches allows the output voltage polarity of the thermopile to remain fixed. Hence rectification of the electrical output is accomplished using thermal switches. 
         [0040]      FIG. 12  depicts a gas-piston setup for implementing such a switch as symbolized by  FIG. 10  and used in  FIG. 11 . Two heat sink interfaces are at each end of the assembly as described by  1210  and  1205 . Two gas filled areas (typically a pressurized inert gas) occupy chambers  1235  and  1230 . Three electrodes  1252 ,  1242 , and  1222  form the contacts of an SPDT switch. A conductive plunger  1225  is pushed to make contact between the middle electrode and either one of the other two electrodes depending on the relative (not absolute) temperature difference. As depicted the switch is a break before make switch. 
         [0041]      FIG. 13  depicts variants of the switches. In  FIG. 13A  the plunger  1226  is larger to create a make before break switch. In  FIG. 13B  the plunger has been given bumpers to help provide mechanical relief if extreme temperature differences are encountered. In  FIG. 13C . The electrodes are re-arranged to provide an connection only when the temperate difference is zero (e.g. a zero temp detect switch). Without loss of generality it can be seen that many variants such as DPDT etc can be create with gas piston switches. 
         [0042]      FIG. 14  depicts a solid-state implementation of the switch diagram in  FIG. 11 . Here the thermopile outputs a voltage from  1405  and a detector  1410  drives a active bridge rectifier signified by the semiconductor switches shown in pairs  1412  and  1411  to maintain a fixed polarity output. A diode system can also be used but diodes may have large voltage drops which would unnecessarily lower efficiency. Note the use of active electronics requires power drive circuits not shown. 
         [0043]      FIG. 15  depicts a combiner where two thermal difference engines of fixed polarity (using the methods of  FIGS. 10 to 14 ) are combined to produce a new voltage. The combiner may include both the rectification and regulation methods can be accomplished via careful thermal switch layout design. Examples of the types of outputs of the combiner are shown in  FIG. 16  (summation),  FIG. 17  (minus V 1  plus V 2 ),  FIG. 18  (plus V 1  minus V 2 ).  FIG. 19  depicts a simple attempt at paralleling the voltages of the thermal difference engines. Note that this can cause a “fight” of the two voltage sources, hence if paralleling is desired careful balancing should be used as in  FIG. 20 .  FIG. 21  generalizes this concept to include 3 thermal difference engines. Now several switch configurations can be used to create a the desired output voltage and polarity, As the number of thermal difference engines is increased the precision of the control is also increased. 
         [0044]      FIG. 22  depicts the output of multiple combiners where a Set Voltage A from one configuration of thermal difference engines can be made in to another voltage B by recombining individual thermal difference engines. Here we see two sets in series  2205 ,  2210 . and  2215  paralleled with  2220 ,  2225 , and  2230 . If the temperature changes then to maintain the same output (for example if the temp rises) then the individual voltages produced by the thermopiles will increase. The same voltage can be delivered by reconfiguring the thermopiles in to a new orientation shown on the right. Here  2205  and  2210  are in series. This is repeated for  2215  plus  2220 , and  2225  and  2230 . This allows voltage B to be the same as voltage A even when the temperature changes.