Patent Application
20120260673
1. Field of the Invention
The present invention generally relates to cooling via a supersonic fluid flow cycle. More specifically, the present invention is related to cooling systems that establish a supersonic cooling cycle using a reciprocating piston.
2. Description of the Related Art
Vapor compression systems are used in many cooling applications such as air conditioning and industrial refrigeration. A vapor compression system generally includes a compressor, a condenser, an expansion device, and an evaporator. In a prior art vapor compression system, a gas in a saturated vapor state is compressed to raise the temperature of that gas, the gas then being in a superheated vapor state. The compressed gas is then run through a condenser and turned into a liquid, and heat is rejected from the system. 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, with the refrigerant absorbing heat. The saturated vapor is then returned to the compressor.
A corresponding drop in temperature accompanies the drop in pressure, which is reflected as a temperature drop to (approximately) 34° F. in
The cycle carried out by the system 100 of
A system like that illustrated in
Haloalkane refrigerants such as tetrafluoroethane (CH2FCF3) are inert gases that are commonly used as refrigerants in refrigerators and automobile air conditioners. Tetrafluoroethane has also been used to cool over-clocked computers. These gases are referred to as R-134 gases. The volume of an R-134 gas can be 600-1000 times greater than its corresponding liquid form. This multiplier shows that the theoretical efficiency of a system utilizing an R-134 gas is much higher than is currently being realized, and evidences the need for an improved cooling system that more fully recognizes system potential and overcomes technical barriers related to compressor performance.
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. There is a further need for a cooling system that operates without the use of a conventional mechanical pump.
A first claimed embodiment is for a cooling system. The system includes a fluid flow path with a converging/diverging nozzle positioned therein. A reciprocating piston is positioned in the converging/diverging nozzle, and a driving mechanism is coupled to the reciprocating piston to impart linear motion to the reciprocating piston. The motion of the reciprocating piston accelerates a fluid in the fluid flow path so that the fluid flows in the critical flow regime. The fluid undergoes a pressure change so that the temperature of the fluid is reduced, thereby allowing heat to be exchanged with an element to be cooled.
A supersonic cooling method is also claimed. The method includes driving a reciprocating piston positioned within a converging/diverging nozzle to impart linear motion to the piston. The motion of the piston accelerates the fluid to a velocity equal to or greater than the speed of sound in the fluid. The acceleration also creates a low pressure region in which the fluid undergoes a phase change and a decrease in temperature. Heat may be exchanged either directly though the walls of the converging/diverging nozzle or via a heat exchange mechanism.
Embodiments of the present invention implement a supersonic cooling cycle that increases efficiency as compared to prior art cooling systems. A system utilizing the present invention may operate at a COP of 2 or greater, 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, 9 or greater, 10 or greater, 20 or greater, or 50 or greater. Embodiments of the present invention do not require a compressor or a conventional mechanical pump to operate. In place of these components is an electric motor or other driving mechanism that imparts a driving force. The elimination of the need for a conventional mechanical pump is beneficial in that the supersonic cooling system includes cavitation as part of the cooling cycle. Since cavitation is typically detrimental to the operation of a conventional mechanical pump, the elimination of the conventional mechanical pump benefits the operation of the system.
Part of the increase in COP for systems utilizing the supersonic cooling cycle with a reciprocating piston is due to the fact that such systems do not need to compress a gas as otherwise occurs at compressor 110 in a prior art vapor compression system 100 like the one shown in
A ‘converging/diverging’ configuration is generally representative of a nozzle design that includes an inlet, throat, and exit with a continuous flow path in fluid communication with each section. The inlet section receives a fluid, which is ultimately expeller at the exit portion. The diameter of the flow path decreases (i.e., converges) from the inlet portion to the throat portion of the nozzle. The nozzle then expands (i.e., diverges) from the throat to the exit portion of the nozzle. The converging/diverging nozzle 305 may be advantageously positioned in the vertical orientation shown in
Because the supersonic cooling system 300 utilizes the converging/diverging nozzle 305 to generate a cooling effect as further described herein, the system 300 does not require the use of a condenser 120 as does the prior art compression system 100 of
The working fluid is accelerated in the converging/diverging nozzle 305 by a reciprocating piston 310. The reciprocating piston 310 is coupled to a driving mechanism that imparts reciprocating linear motion to the piston. The driving mechanism may be a crankshaft, a linear actuator, or a cam system. The driving mechanism may be powered by any suitable driving device, such as an electric motor.
The velocity of the linear travel and the size of the reciprocating piston 310 are selected based on factors unique to a particular installation. The factors may include, but are not limited to, the working fluid utilized in the installation and the amount of cooling power desired. The construction of the reciprocating piston 310 may be designed to ensure that the reciprocating piston 310 imparts sufficient suction on the working fluid to accelerate the fluid to at least the speed of sound in the fluid.
Fluid flow into and out of the converging/diverging nozzle 305 may be controlled by a pair of check valves. A first check valve 315 is positioned upstream of an inlet 320 of the converging/diverging nozzle 305. The first check valve 315 ensures that working fluid only enters the inlet 320 of the converging/diverging nozzle 305 with limited or no backflow. A second check valve 325 is positioned downstream of an outlet 330 of the converging/diverging nozzle 305. The second check valve 325 ensures that working fluid flows only outward through the outlet 330 with backflow eliminated or greatly limited. The outlet 330 may be installed at a position just below the lowest point of travel of the reciprocating piston 310.
As an alternative, the reciprocating piston 310 may be configured to impart a positive pressure on the working fluid to accelerate the fluid to a velocity greater than or equal to the speed of sound in the fluid. In such a case, the reciprocating piston may be disposed at the inlet 320 or upstream from the inlet 320 of the converging/diverging nozzle 305. In a first cycle the piston 310 may draw fluid into the inlet 320, and in a subsequent second cycle the piston 310 may drive the fluid through the converging/diverging nozzle 305. The positive pressure may be provided by the decreasing volume between the piston and the inlet 320 during the second cycle.
The working fluid may be introduced to the converging/diverging nozzle 305 from an accumulator 335 coupled to the inlet 320 of the converging/diverging nozzle 305. The accumulator 335 may be utilized to regulate the flow of the working fluid, and to reduce fluctuations in the flow. A pressure set valve 340 may be coupled to the accumulator to control the pressure of the working fluid in the accumulator 335, thereby controlling the pressure of the fluid entering the fluid flow path. The pressure in the accumulator 335 may be set to a pressure just above the vapor pressure of the working fluid.
The working fluid may contain certain non-condensable components such as air. To remove the non-condensable components, a trap 335 may be coupled to the fluid flow path. The trap 335 may be equipped with a bleed valve 355 to expel the non-condensable components from the fluid flow path. The trap 335 may be positioned at the highest point of the fluid flow path to increase its efficiency. The cooling system 300 may need to be periodically drained and/or recharged with working fluid. To this end, a charge/drain valve 345 is coupled to the fluid flow path.
The cooling cycle created by the system 300 is initiated with the reciprocating piston 310 at its lowest position in a cylindrical portion of the converging/diverging nozzle 305. The cooling cycle begins with an upward movement of the reciprocating piston 310 imparted by the driving mechanism. As the reciprocating piston 310 moves upward, working fluid may be drawn from the accumulator 335 through the first check valve 315. The working fluid is accelerated as it flows through the converging/diverging nozzle 305 and reaches its maximum velocity in the throat of the nozzle 305. At this point, the velocity of the working fluid will be equal to or greater than the speed of sound in the working fluid.
As the fluid is accelerated through the converging/diverging nozzle 305, the static pressure of the fluid at the throat drops below the vapor pressure of the fluid. Cavitation occurs so that the working fluid in at least a part of the converging/diverging nozzle 305 is a dual phase fluid including the liquid phase and the vapor phase. The vapor phase mixing with the liquid working fluid reduces the speed of sound in the working fluid. As the working fluid continues to flow through the converging/diverging nozzle 305, still more vapor is formed through evaporation (boiling) of the fluid caused by supersonic flow in the expanding area of the converging/diverging nozzle 305. These factors may allow the formation of a compression wave that is utilized in the acceleration of the working fluid.
Because the working fluid flows in at least a portion of the converging/diverging nozzle 305 at a velocity equal to or greater than the speed of sound in the fluid, the cooling system 300 operates in the critical flow regime of the working fluid. In this regime, the pressure of the fluid in the system 300 may remain almost constant and then ‘jump’ or ‘shock up’ to the ambient pressure as the cooling cycle is completed.
Because cooling system 300 accelerates the working fluid and creates a pressure differential through the linear movement of the reciprocating piston 310, cooling system 300 does not require the use of a conventional mechanical pump. The reduced amount of hardware required to operate the cooling system 300—there is no need for either a compressor or a conventional mechanical pump—gives rise to a greatly improved coefficient of performance (COP) for the system.
When the reciprocating piston 310 reaches the top of its stroke in the cylindrical portion of the converging/diverging nozzle 305, the movement of the piston stops, and acceleration of the fluid is also stopped. The vapor bubbles in the fluid continue to rise in the converging/diverging nozzle 305 until the bubbles reach the lower surface of the reciprocating piston 310. The static pressure in the converging/diverging nozzle 305 increases until the bubbles collapse and the fluid flows out of the converging/diverging nozzle 305 through the outlet 330.
During the acceleration phase of the cooling cycle, the phase change and pressure differential in the converging/diverging nozzle 305 generate the cooling effect for the supersonic cooling system 300. The working fluid absorbs heat from the walls of the converging/diverging nozzle 305. Heat transfer to an object to be cooled may be facilitated by a heat exchanging mechanism 350. The heat exchanging mechanism 350 may include fins on the surface of the converging/diverging nozzle 305. A circulating fluid heated by the object to be cooled may be thermally coupled to the heat exchanging mechanism 350.
In the supersonic cooling system 300, the working fluid travels through the fluid flow path to generate a cooling effect via the method delineated in
In a further step 530, the fluid is accelerated through the converging/diverging nozzle 305. During the acceleration step 530, a cavitation effect is created in the converging/diverging nozzle 305. As the working fluid flows through the converging/diverging nozzle 305, the suction generated by the linear motion of the reciprocating piston 310 accelerates the working fluid. A decrease in pressure and a phase change in the working fluid result in a lowered temperature of the fluid to create a cooling effect in step 540.
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 established in the converging/diverging nozzle 305. Critical flow occurs when the velocity of the fluid is greater than or equal to the speed of sound in the fluid. In critical flow, the pressure in the converging/diverging nozzle 305 will not be influenced by the exit pressure. In step 550, the working fluid may ‘shock up’ to the ambient conditions as the fluid exits the converging/diverging nozzle 305.
The pressure change of the fluid in the system 300 may include a range of approximately 20 PSI in the low pressure region to 100 PSI in the high pressure region. In some instances, the pressure may be increased to more than 100 PSI or more than 150 PSI. In some embodiments, the low pressure region may be at a pressure of less than 1 PSI. For installations using water as the working fluid, an initial pressure of the fluid may be 30 PSI. Depending on the characteristics of any given application, the pressure change range may vary from that described immediately above.
The cooling effect of the system 300 may be realized in an object to be cooled by putting the object in direct contact with the converging/diverging nozzle 305. The transfer of heat from the object to be cooled into the system 300 may also be accomplished in an optional step 560. In optional step 560, the working fluid is thermally coupled to a heat exchange mechanism 350. The heat exchange mechanism 350 may be thermally coupled to a heated circulating fluid from the object to be cooled by the supersonic cooling system 300.
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.
