Patent Publication Number: US-2011048062-A1

Title: Portable Cooling Unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part and claims the priority benefit of U.S. patent application Ser. No. 12/732,171, filed Mar. 25, 2010, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to cooling systems. The present invention more specifically relates to portable cooling units. 
     2. Description of the Related Art 
     A vapor compression system as known in the art generally includes a compressor, a condenser, and an evaporator. These systems also include an expansion device. In a prior art vapor compression system, a gas is compressed whereby the temperature of that gas is increased beyond that of the ambient temperature. The compressed gas is then run through a condenser and turned into a liquid. The condensed and liquefied gas is then taken through an expansion device, which drops the pressure and the corresponding temperature. The resulting refrigerant is then boiled in an evaporator. This vapor compression cycle is generally known to those of skill in the art. 
       FIG. 1  illustrates a vapor compression system  100  as might be found in the prior art. In the prior art vapor compression system  100  of  FIG. 1 , compressor  110  compresses the gas to (approximately) 238 pounds per square inch (PSI) and a temperature of 190° F. Condenser  120  then liquefies the heated and compressed gas to (approximately) 220 PSI and 117° F. The gas that was liquefied by the condenser  120  is then passed through the expansion valve  130  of  FIG. 1 . By passing the liquefied gas through expansion valve  130 , the pressure is dropped to (approximately) 20 PSI. A corresponding drop in temperature accompanies the drop in pressure, which is reflected as a temperature drop to (approximately) 34° F. in  FIG. 1 . The refrigerant that results from dropping the pressure and temperature at the expansion valve  130  is boiled at evaporator  140 . Through boiling of the refrigerant by evaporator  140 , a low temperature vapor results, which is illustrated in  FIG. 1  as having (approximately) a temperature of 39° F. and a corresponding pressure of 20 PSI. 
     The cycle related to the system  100  of  FIG. 1  is sometimes referred to as the vapor compression cycle. Such a cycle generally results in a coefficient of performance (COP) between 2.4 and 3.5. The coefficient of performance, as reflected in  FIG. 1 , is the evaporator cooling power or capacity divided by compressor power. It should be noted that the temperature and pressure references that are reflected in  FIG. 1  are exemplary and illustrative. 
       FIG. 2  illustrates the performance of a vapor compression system like that illustrated in  FIG. 1 . The COP illustrated in  FIG. 2  corresponds to a typical home or automotive vapor compression system—like that of FIG.  1 —operating in an ambient temperature of (approximately)  900 F. The COP shown in  FIG. 2  further corresponds to a vapor compression system utilizing a fixed orifice tube system. 
     Such a system  100 , however, operates at an efficiency rate (i.e., COP) that is far below that of system potential. To compress gas in a conventional vapor compression system  100  like that illustrated in  FIG. 1  typically takes 1.75-2.5 kilowatts for every 5 kilowatts of cooling power generated. This exchange rate is less than optimal and directly correlates to the rise in pressure times the volumetric flow rate. Degraded performance is similarly and ultimately related to performance (or lack thereof) by the compressor  110 . 
     Haloalkane refrigerants such as tetrafluoroethane (CH 2 FCF 3 ) are inert gases that are commonly used as high-temperature refrigerants in refrigerators and automobile air conditioners. Haloalkane refrigerants have also been used to cool over-clocked computers. These inert, refrigerant gases are more commonly referred to as R-134 gases. The volume of an R-134 gas can be 600-1000 times greater than the corresponding liquid. 
     In light of the theoretical efficiencies of systems using haloalkanes or other fluids, there is a need in the art for an improved cooling system that more fully recognizes system potential and overcomes technical barriers related to compressor performance. 
     SUMMARY OF THE CLAIMED INVENTION 
     The portable cooling unit disclosed herein includes a pump that maintains a circulatory fluid flow through a flow path. The unit also includes an evaporator that operates in the critical flow regime of the circulatory fluid. The evaporator generates a compression wave that shocks the maintained fluid flow, thereby changing the pressure of the maintained fluid flow and exchanging heat introduced into the circulatory fluid flow. No heat is added to the circulatory fluid flow before the circulatory fluid flow passes through the evaporator. The evaporator may use one or more tubes/nozzles, and may generate 20-80 watts of cooling power. 
     The unit further includes a storage compartment, the storage compartment receiving items to be cooled or maintained at a temperature below ambient. The storage compartment may form a housing for the pump and the evaporator. An external surface of the storage compartment may effectuate convection and further exchange heat introduced into the unit. 
     The unit may be powered by an adapter such as for a vehicle battery. Moreover, the unit may be powered by a self-contained battery pack. The unit may use a solar cell as a direct power source or as a means of charging a battery pack. 
     Operating conditions within the unit may include the pump raising the pressure of the circulatory fluid flow from approximately 20 PSI to approximately 100 PSI. In certain embodiments, the pressure may be raised to pressures in excess of 100 PSI, such as 300 or 500 PSI. 
     A portable cooling system according to the technology disclosed herein may include a storage compartment that receives items to be cooled or maintained at a temperature below ambient. The system may also include a pump that maintains a fluid flow of a compressible fluid through the system, and an evaporator that effects a phase change in the compressible fluid. The system may establish a compression wave in the compressible fluid by passing the compressible fluid from a high pressure region to a low pressure region, the velocity of the fluid being greater than or equal to the speed of sound in the compressible fluid. The compressible fluid is cooled during a phase change so that heat may be transferred from the system by thermally coupling one or more fins between the compressible fluid and the ambient atmosphere. 
     Operating conditions in the evaporator may include a pressure drop in the cooling liquid to approximately 5.5 PSI. A corresponding phase change results in a lowered temperature of the cooling liquid. The pressure change may occur within a range of approximately 20 PSI to 100 PSI, or the increased pressure may be in excess of 100 PSI, such as 300 or 500 PSI. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a vapor compression system as might be found in the prior art. 
         FIG. 2  illustrates the performance of a vapor compression system like that illustrated in  FIG. 1 . 
         FIG. 3  illustrates an exemplary cooling system in accordance with an embodiment of the present invention. 
         FIG. 4  illustrates an exemplary cooling system in accordance with another embodiment of the present invention. 
         FIG. 5  illustrates performance of a cooling system like that illustrated in  FIGS. 3 and 4 . 
         FIG. 6  illustrates the operation of a single tube cooling system. 
         FIG. 7  illustrates a method of operation for a portable cooling unit. 
         FIG. 8  illustrates an exemplary embodiment of the portable cooling unit. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 3  illustrates an exemplary cooling system  300  in accordance with an embodiment of the present invention. The cooling system  300  does not need to compress a gas as otherwise occurs at compressor  110  in a prior art vapor compression system  100  like that shown in  FIG. 1 . Cooling system  300  operates by pumping liquid. Because cooling system  300  pumps liquid, the compression cooling system  300  does not require the use of a condenser  120  as does the prior art compression system  100  of  FIG. 1 . Compression cooling system  300  instead utilizes a compression wave. The evaporator of cooling system  300  operates in the critical flow regime where the pressure in an evaporator tube will remain almost constant and then ‘jump’ or ‘shock up’ to the ambient pressure. 
     The cooling system  300  of  FIG. 3  recognizes a heightened degree of efficiency in that the pump  320  of the system  300  is not required to draw as much power as the compressor  110  in a prior art compression system  100  like that illustrated in  FIG. 1 . A compression system designed according to an embodiment of the presently disclosed invention may recognize exponential performance efficiencies. For example, a prior art compression system  100  as illustrated in  FIG. 1  may require 1.75-2.5 kilowatts to generate 5 kilowatts of cooling power. Prior art compression system  100  therefore may operate at a coefficient of performance (COP) of less than 3. A system  300  like that illustrated in  FIG. 3  may pump fluid from approximately 14.7 to approximately 120 PSI with the pump drawing power at approximately 500 W (0.5 kilowatts), with the system  300  also generating 5 kilowatts of cooling power. The system  300  may therefore operate with a COP of 10. As a result of the cycle illustrated in  FIG. 3 , and the resultant increased efficiencies, system  300  may utilize many working fluids, including but not limited to water. 
     The cooling system  300  of  FIG. 3  may include a housing  310 . Housing  310  of  FIG. 3  is akin to that of a pumpkin. The particular shape or other design of housing  310  may be a matter of aesthetics with respect to where or how the system  300  is installed. The design of the housing  310  may be influenced by the facility in which the system  300  is installed, or by the equipment or machinery to which the system  300  is coupled. Functionally, housing  310  encloses pump  330 , evaporator  350 , and the attendant accessory equipment or flow paths (e.g., pump inlet  340  and evaporator tube  360 ). Housing  310  also contains the cooling fluid to be used by the system  300 . 
     Housing  310 , in an alternative embodiment, may also encompass a secondary heat exchanger (illustrated in  FIG. 4 ). A secondary heat exchanger may be excluded from being contained within the housing  310  and system  300 . In such an embodiment, the outer surface area of the system  300 —that is, the housing  310 —may be utilized in a cooling process through forced convection on the external surface of the housing  310 . 
     Pump  330  may be powered by a motor  320 , which is external to the system  300  and located outside the housing  310  in  FIG. 3 . Motor  320  may alternatively be contained within the housing  310  of system  300 . Motor  320  may drive the pump  330  of  FIG. 3  through a rotor drive shaft with a corresponding bearing and seal or magnetic induction, whereby penetration of the housing  310  is not required. Other motor designs may be utilized with respect to motor  320  and corresponding pump  330  including synchronous, alternating (AC), and direct current (DC) motors. Other electric motors that may be used with system  300  include induction motors; brushed and brushless DC motors; stepper, linear, unipolar, and reluctance motors; and ball bearing, homopolar, piezoelectric, ultrasonic, and electrostatic motors. 
     Pump  330  establishes circulation of a compressible fluid through the interior fluid flow paths of system  300 , the flow paths being contained within housing  310 . Pump  330  may circulate fluid throughout system  300  through use of vortex flow rings. Vortex rings operate as energy reservoirs whereby added energy is stored in the vortex ring. The progressive introduction of energy to a vortex ring via pump  330  causes the corresponding ring vortex to function at a level such that energy lost through dissipation corresponds to energy being input. 
     Pump  330  also operates to raise the pressure of a liquid being used by system  300  from, for example, 20 PSI to 100 PSI or more. Some systems may operate at an increased pressure of approximately 300 PSI. Other systems may operate at an increased pressure of approximately 500 PSI. 
     Pump inlet  340  introduces a liquid to be used in cooling and otherwise resident in system  300  (and contained within housing  310 ) into pump  330 . Fluid temperature may, at this point in the system  300 , be approximately 95 F. 
     The fluid introduced to pump  330  by inlet  340  traverses a primary flow path to nozzle/evaporator  350 . Evaporator  350  induces a pressure drop (e.g., to approximately 5.5 PSI) and phase change that results in a low temperature. The cooling fluid further ‘boils off’ at evaporator  350 , whereby the resident liquid may be used as a coolant. For example, the liquid coolant may be water cooled to 35-45° F. (approximately 37° F. as illustrated in  FIG. 3 ). 
     As noted above, the system  300  (specifically evaporator  350 ) operates in the critical flow regime, thereby generating a compression wave. The coolant fluid exits the evaporator  350  via evaporator tube  360  where the fluid is ‘shocked up’ to approximately 20 PSI because the flow in the evaporator tube  360  is in the critical regime. In some embodiments of system  300 , the nozzle/evaporator  350  and evaporator tube  360  may be integrated and/or collectively referred to as an evaporator. 
     The coolant fluid of system  300  (having now absorbed heat for dissipation) may be cooled at a heat exchanger to assist in dissipating absorbed heat, the temperature of the fluid being approximately 90-100° F. after having exited evaporator  350 . Instead of a heat exchanger, however, the housing  310  of the system  300  (as was noted above) may be used to cool via convection.  FIG. 5  illustrates an exemplary performance cycle of a cooling system like that illustrated in  FIGS. 3 and 4 . 
       FIG. 6  shows the operation of a single evaporation tube or nozzle cooling system  600 . Single tube/nozzle cooling system  600  utilizes the supersonic cooling cycle illustrated in  FIGS. 3 and 4 , but may typically be implemented in an embodiment requiring a relatively low cooling power, for example 20-100 watts. The system  600  utilizes a small pump  610  and a single nozzle or tube  620 . The single tube  620  functions as the evaporator in the system  600 . A radiator  630  may be employed to remove heat from the system. 
     The pump  610  raises the pressure of a fluid in the system  600 . Various fluids, including water, may be used in the system. The pressure of the fluid may be raised from 20 PSI to in excess of 100 PSI. The fluid flows through the single tube  620  of the evaporator. Pressure drop and phase change result in a lower temperature of the fluid in the tube  620  and provide the cooling power for the system  600 . 
     Critical flow rate, which is the maximum flow rate that can be attained by a compressible fluid as that fluid passes from a high pressure region to a low pressure region (i.e., the critical flow regime), allows for a compression wave to be established and utilized in the critical flow regime. Critical flow occurs when the velocity of the fluid is greater or equal to the speed of sound in the fluid. 
     In critical flow, the pressure in the channel will not be influenced by the exit pressure and at the channel exit, the fluid will ‘shock up’ to the ambient condition. In critical flow the fluid will also stay at the low pressure and temperature corresponding to the saturation pressures. 
     In cooling system  600 , the cooled fluid is passed through radiator  630  to effectuate a heat transfer to the atmosphere. The operating steps of the system  600  are described in further detail below with reference to  FIG. 8 . 
       FIG. 7  shows an exemplary embodiment of a portable cooling unit  700 . Portable cooling unit  700  may be powered by a 12 volt power supply, such as a car battery. An adapter  710  that plugs into a power outlet such as those commonly found in vehicles may be provided with the unit  700 . Portable cooling unit  700  may also be powered by self-contained batteries or a solar cell. A solar cell may also be used to charge the self-contained batteries. Those skilled in the art will recognize that many power supply configurations may be utilized in the portable cooling unit  700 . 
     The housing  720  of unit  700  may include one or more fins  730 . The fins  730  may be coupled to the cooling fluid in the unit  700 , and may be open to the atmosphere. The fins  730  may therefore be used as the radiator to transfer heat from the interior of the unit  700  to the exterior atmosphere. 
       FIG. 8  illustrates a method of operation  800  for the cooling systems  300 ,  400 . In step  810 , a pump raises the pressure of a liquid. The pressure may, for example, be raised from 20 PSI to in excess of 100 PSI. As mentioned above, the increased pressure may be 300 PSI or even 500 PSI. In step  820 , fluid flows through the nozzle/evaporator tube(s). Pressure drop and phase change result in a lower temperature as fluid is boiled off in step  830 . 
     Critical flow rate, which is the maximum flow rate that can be attained by a compressible fluid as that fluid passes from a high pressure region to a low pressure region (i.e., the critical flow regime), allows for a compression wave to be established and utilized in the critical flow regime. Critical flow occurs when the velocity of the fluid is greater or equal to the speed of sound in the fluid. In critical flow, the pressure in the channel will not be influenced by the exit pressure and at the channel exit, the fluid will ‘shock up’ to the ambient condition. In critical flow the fluid will also stay at the low pressure and temperature corresponding to the saturation pressures. In step  740 , after exiting the evaporator tube, the fluid “shocks” up to 20 PSI. A heat exchanger may be used in optional step  850 . Cooling may also occur via convection on the surface of the housings of the systems  300 ,  400 . 
     While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. The descriptions are not intended to limit the scope of the invention to the particular forms set forth herein. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments. It should be understood that the above description is illustrative and not restrictive. To the contrary, the present descriptions are intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims and otherwise appreciated by one of ordinary skill in the art. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.