High efficiency refrigeration system

[0002] The present invention relates generally to a high efficiency refrigeration system and, more specifically, to a refrigeration system utilizing one or more vortex tubes for increasing the overall efficiency of a refrigeration system.

[0003] A refrigeration system typically consists of four major components connected together via a conduit (preferably copper tubing) to form a closed loop system. The four major components are a compressor, a condenser, expansion device and an evaporator. A refrigerant circulates through the four major components and will have its pressure either increased or decreased and its temperature increased or decreased.

[0004] The refrigerant is continuously cycled through the refrigeration system. The main steps in the refrigeration cycle are compression of the refrigerant by the compressor, heat rejection of the refrigerant in the condenser, throttling of the refrigerant in the expansion device, and heat absorption of the refrigerant in the evaporator. This process is sometimes referred to as a vapor-compression refrigeration cycle.

[0005] The vapor-compression refrigeration cycle is used in air conditioning systems, which cool and dehumidify air in a living space, in a moving vehicle (e.g., automobile, airplane, train, etc.), refrigerators and heat pumps.

[0006] In an ideal refrigeration cycle, the refrigerant enters the compressor as saturated vapor and is compressed to a very high pressure. The temperature of the refrigerant increases during this compression step. The refrigerant leaves the compressor as superheated vapor and enters the condenser. A typical condenser comprises a single conduit formed into a serpentine-like shape so that a plurality of rows of conduit is formed parallel to each other. Metal fins or other aids are usually attached to the serpentine conduit in order to increase the transfer of heat between the refrigerant passing through the condenser and the ambient air. As heat is rejected from the superheated vapor as it passes through the condenser, the refrigerant exits the condenser as saturated liquid.

[0007] The expansion device reduces the pressure of the saturated liquid thereby turning it into saturated liquid-vapor mixture, which is throttled to the evaporator. The temperature of the refrigerant drops below the temperature of the ambient air as it goes through the expansion device. The refrigerant enters the evaporator as a low quality saturated mixture comprised of approximately 20% vapor and 80% liquid. Note that the quality is defined as the mass fraction of vapor in the liquid-vapor mixture.

[0008] The evaporator physically resembles the serpentine-shaped conduit of the condenser. The refrigerant completely evaporates by absorbing heat from the refrigerated space and leaves the evaporator as saturated vapor at the suction pressure of the compressor and reenters the compressor thereby completing the cycle.

[0009] The efficiency of a refrigeration cycle is traditionally described by an energy-efficiency ratio (EER). It is defined as the ratio of the heat absorption from an evaporator to the work done by a compressor. $\mathrm{EER}=\frac{\mathrm{Heat}\mathrm{absorption}\mathrm{from}\mathrm{evaporator}}{\mathrm{Work}\mathrm{done}\mathrm{by}\mathrm{compressor}}$

[0010] The present invention is designed to increase the efficiency of a refrigeration system by increasing the efficiency of the refrigeration cycle. The increase in the efficiency is achieved by assisting in the conversion of the refrigerant from vapor to liquid at specific points in the refrigeration cycle. In the present invention, a vortex tube is placed between the expansion device and the evaporator in order to increase the percentage of refrigerant entering the evaporator as a liquid. Since the heat absorption from the evaporator occurs through the evaporation of the liquid refrigerant, the increase in the percentage of the liquid refrigerant entering the evaporator increases the efficiency of the refrigeration cycle and reduces the size of the evaporator.

[0011] Another way the present invention increases the efficiency of the refrigeration cycle is by placing a vortex tube in the serpentine tubing of the condenser. In the preferred embodiment, the vortex tube is placed approximately one-quarter of the way in from the inlet of the condenser where desuperheating is completed. Once again, the vortex tube produces liquid refrigerant and further increases the temperature of the vapor refrigerant thereby reducing the size of the condenser and decreasing the head pressure of the compressor. As a result, the compression ratio decreases, and the work required by the compressor is reduced, thus increasing the efficiency of the refrigeration cycle.

[0012] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention.

[0013] In the drawings:

[0014] FIG. 1 is a block diagram of a typical refrigeration system;

[0015] FIG. 2 shows a temperature entropy diagram of the refrigeration system illustrated in FIG. 1;

[0016] FIG. 3 is a block diagram of a refrigeration system in accordance with the present invention utilizing a vortex tube proximate the evaporator;

[0017] FIG. 4A illustrates a side cut-away view of a conventional vortex tube;

[0018] FIG. 4B is a top cut-away view of the vortex tube shown in FIG. 4A;

[0019] FIG. 5 is a block diagram of a refrigeration system in accordance with the present invention utilizing a vortex tube in the condenser;

[0020] FIG. 6 is a pictorial representation of the phase change in the refrigerant in a condenser and vortex tube of the type used in the refrigeration system of FIG. 5;

[0021] FIG. 7 is a block diagram of another embodiment of refrigeration system in accordance with the present invention which utilizes two vortex tubes;

[0022] FIG. 8 is a block diagram of the refrigeration system of FIG. 7 in which the refrigerant vapor bypasses the evaporator and the liquid refrigerant bypasses the condenser;

[0023] FIG. 9 is a block diagram of another embodiment of a refrigeration system in accordance with the present invention which utilizes a liquid/vapor separator and/or a third vortex tube; and

[0024] FIG. 10 is a block diagram of another embodiment of a refrigeration system in accordance with the present invention which utilizes three vortex tubes and a pump.

[0025] In describing a preferred embodiment of the invention, specific terminology will be selected for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.

[0026] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings in which a refrigeration system in accordance with the present invention is generally indicated at 10.

[0027] A typical refrigeration system is illustrated in FIG. 1. The refrigeration system includes a compressor 12, a condenser 14, an expansion device 16 and an evaporator 18. The various components are connected together via copper tubing 19.

[0028] The refrigeration system is a closed loop system that circulates a refrigerant through the various elements. Some common types of refrigerant include R-12, R-22, R-134A, R-410A, ammonia, carbon dioxide and natural gas. A refrigerant is continuously cycled through the refrigeration system. The main steps in the refrigeration cycle are compression of the refrigerant by the compressor, heat rejection of the refrigerant in the condenser, throttling of the refrigerant in the expansion device, and heat absorption of the refrigerant in the evaporator. As indicated previously, this process is referred to as the vapor compression refrigeration cycle.

[0029] The temperature entropy curve of a typical refrigeration cycle is illustrated is FIG. 2. Point 2 is where the refrigerant exists as a superheated vapor. As the superheated vapor cools inside the condenser, the superheated vapor becomes a saturated vapor (point 2a). As heat transfer to the ambient air continues in the condenser, the refrigerant becomes a saturated liquid at point 3. After going through the expansion device, the refrigerant becomes a mixture of approximately 20% vapor and 80% liquid at point 4. As the refrigerant absorbs heat in the evaporator, the refrigerant becomes a saturated vapor at the suction pressure at point 1.

[0030] The efficiency of a refrigeration cycle (and by analogy a heat pump cycle) depends primarily on the heat absorption from the evaporator and the efficiency of the compressor. The former depends on the percentage of liquid in the liquid-vapor refrigerant mixture before the evaporator, whereas the latter depends on the magnitude of the head or discharge pressure. The pressure of the refrigerant as it enters the compressor is referred to as the suction pressure level and the pressure of the refrigerant as it leaves the compressor is referred to as the head pressure level. Depending on the type of refrigerant used, the head pressure can range from about 170 PSIG to about 450 PSIG.

[0031] Compression ratio is the term used to express the pressure difference between the head pressure and the suction pressure. Compression ratio is calculated by converting the head pressure and the suction pressure onto an absolute pressure scale and dividing the head pressure by the suction pressure. When the compression ratio increases, the compressor efficiency drops thereby increasing energy consumption. (In most cases, the energy is used by the electric motor that drives the compressor.) In addition, the temperature of the refrigerant vapor increases to the point that oil for lubrication may be overheated which may cause corrosion in the refrigeration system.

[0032] When a compressor runs at a high compression ratio, it no longer has the capability to keep a refrigerated space or living space at the designated temperature. As the compressor efficiency drops, more electricity is used for less refrigeration. Furthermore, running the compressor at a high compression ratio increases the wear and tear on the compressor and decreases its operating life.

[0033] An evaporator is made of a long coil or a series of heat transfer panels which absorb heat from a volume of air that is desired to be cooled. In order to absorb heat from this ambient volume, the temperature of the refrigerant must be lower than that of the volume. The refrigerant exiting the expansion device consists of low quality vapor, which is approximately 20% vapor and 80% liquid.

[0034] The liquid portion of the refrigerant is used to absorb heat from the desired volume as the liquid refrigerant evaporates inside the evaporator. The vapor portion of the refrigerant is not utilized to absorb heat from the ambient volume. In other words, the vapor portion of the refrigerant does not contribute to cooling the ambient volume and decreases the efficiency of the refrigeration cycle.

[0035] Referring to FIG. 3, the present invention uses a vortex tube 20 between the expansion device 16 and the evaporator 18. Vortex tube 20 converts at least a portion of the refrigerant vapor that exits the expansion device into liquid so that it can be used in the evaporator to absorb heat from the ambient volume. Vortex tubes are well-known in other areas of art but are not commonly found in refrigeration systems.

[0036] As illustrated in FIG. 4A, the vortex tube 20 is a device which converts a flow of compressed gas into two streams—one stream hotter than and the other stream colder than the temperature of the gas supplied to the vortex tube. A vortex tube does not contain any moving parts.

[0037] Referring now to FIG. 4B, a high pressure gas stream is shown entering the vortex tube 20 tangentially at one end (i.e., the inlet 22). The high pressure gas stream produces a strong vortex flow in the tube 20. The vortex flow is similar in shape to a helix. The high pressure gas separates into two streams having different temperatures, one along the outer wall and one along the axis of the tube. In the outer stream, the circumferential velocity is inversely proportional to the radial position. The pressure within a vortex tube is lowest at the center of the tube and increases to a maximum at the wall.

[0038] The high pressure gas that enters a vortex tube will be the refrigerant in a refrigeration cycle. Since vapor refrigerant is a compressible medium, the pressure distribution within the vortex tube causes a temperature difference between the inner and outer streams.

[0039] Referring again to FIG. 3, in the preferred embodiment, the vortex tube 20 is preferably placed proximate the evaporator 18. In order to reduce manufacturing costs, the vortex tube 20 may be placed immediately before the evaporator 18. However, other positions of the vortex tube proximate the evaporator including a percentage of the distance from the inlet of the evaporator may be desirable.

[0040] A condenser 14 in the refrigeration cycle is used to convert superheated refrigerant vapor to liquid by rejecting heat to the surroundings. The condenser is a long heat transfer coil or series of heat rejecting panels similar in appearance to the evaporator. Referring again to FIG. 1, as refrigerant enters the condenser 14, the superheated vapor first becomes saturated vapor in the approximately first quarter-section of the condenser, and the saturated vapor undergoes phase change in the remainder of the condenser at approximately constant pressure.

[0041] Since the heat rejection from the condenser to the surroundings can occur only when the temperature of the refrigerant is greater than that of the surroundings, the refrigerant temperature has to be raised well above that of the surroundings. This is accomplished by raising the pressure of the refrigerant vapor, a task that is done by the compressor 12. Since vapor temperature is closely related to vapor pressure, it is critically important that the condenser efficiently rejects heat from the refrigerant to the surroundings. If the condenser 14 is not efficient, the compressor 12 has to further increase the head pressure in an attempt to assist the condenser in dumping heat to the surroundings.

[0042] As illustrated in FIG. 5, another embodiment of the present invention utilizes a vortex tube 29 in the condenser to convert saturated refrigerant vapor to liquid thus increasing the condenser's efficiency. The first approximately one-quarter of the condenser is represented by 14A and the remaining three-quarters of the condenser is represented by 14B.

[0043] Referring to FIG. 6, in the preferred embodiment the vortex tube 29 is inserted approximately one-quarter of the way into the condenser (i.e., at the point where the superheated vapor becomes saturated vapor in full or in part). By inserting the vortex tube 29 in an existing condenser, manufacturing costs may be minimized. However, for all intents and purposes two separate condensers, each about the respective size of condenser portions 14A and 14B, may be used.

[0044] When a vortex tube 29 is placed approximately one-fourth of the way from the inlet of the condenser, the temperature of the refrigerant does not have to be raised well over that of the surroundings thus allowing the compressor to run at a lower head pressure than would be the case without the vortex tube 29.

[0045] Since the refrigerant vapor becomes saturated liquid at the output of the condenser, the size of the condenser in prior art refrigeration systems is often chosen larger than necessary in order to ensure the exchange of heat. The present method allows the size of the condenser 14 to be reduced because the substantial amount of saturated refrigerant vapor is converted to liquid by the vortex tube. The present invention allows the use of a smaller condenser than is the case without a vortex tube thereby reducing the size of air conditioning systems, refrigerators and heat pumps.

[0046] A further embodiment of the present invention utilizes two vortex tubes, one before the evaporator and the second in the condenser, as illustrated in FIG. 7.

[0047] The vortex tubes operate in a similar fashion as described in a refrigeration system when only one vortex tube is used. However, the efficiency of the refrigeration system illustrated in FIG. 7 is greater than the efficiency of the refrigeration illustrated in either FIG. 3 or FIG. 5.

[0048] FIG. 8 illustrates a variation of the two vortex tube refrigeration systems illustrated in FIG. 7. Instead of the vapor that exits vortex tube 20 being recombined with the liquid before entering the evaporator 18, a separate path for the vapor, bypassing the evaporator, is shown. This variation should be slightly more efficient than recombining the liquid with the vapor because the vapor does not absorb any heat as it passes through the evaporator. Accordingly, only liquid refrigerant enters evaporator 18.

[0049] Referring again to FIG. 8, the liquid portion of the refrigerant is drawn off from vortex tube 29 and bypasses condenser 14B. In this manner, the heat in the vapor refrigerant is rejected by condenser 14B. Since there is very little heat stored in the refrigerant liquid, it does not need to be passed through condenser 14B.

[0050] Referring to FIG. 9, another embodiment of the present invention is illustrated. In this embodiment, a liquid/vapor separator 35 may be utilized before a refrigerant enters the vortex tube 20. Liquid/vapor separators are known in other art areas. The liquid/vapor separator 35 ensures that only compressed vapor enters the vortex tube 20. Liquid from the liquid/vapor separator 35 is combined with the liquid that is output by vortex tube 20 and enters the evaporator 18. Any refrigerant vapor that is still present bypasses the evaporator and is directed to the compressor 12.

[0051] Also illustrated in FIG. 9 is another variation in which a third vortex tube 31 is inserted in a refrigeration system before condenser 14A. Vortex tube 31 separates the superheated refrigerant into a hot vapor component and a cool vapor component. The hot vapor from vortex tube 31 is directed to condenser 14A. The output of condenser 14A is combined with the cool vapor output from vortex tube 31. The liquid refrigerant from vortex tube 29 bypasses condenser 14B. The liquid refrigerant output from condenser 14B is mixed with the liquid refrigerant output from vortex tube 29.

[0052] The variations illustrated in FIG. 9 (i.e., a liquid/vapor separator and a third vortex tube proximate the condenser) may be used together or independently of each other.

[0053] Referring now to FIG. 10, another embodiment of the present invention is illustrated. This refrigeration system includes the compressor 12, first condenser 14A, vortex tube 29, second condenser 14B, expansion device 16, vortex tube 20, evaporator 18, a third vortex tube 21 and a pump 40. The vapor that exits vortex tube 20 and evaporator 18 is combined and input into third vortex tube 21.

[0054] The third vortex tube 21 again separates the refrigerant into a liquid component and a vapor component. The vapor component from vortex tube 21 is directed to the compressor 12. The liquid refrigerant from vortex tube 21 is combined with the liquid component from vortex tube 20 and enters the evaporator 18. Since the liquid portion of the refrigerant from vortex tube 21 is sent back to the inlet of the evaporator, an increase in the heat absorption is achieved as the liquid passes through evaporator 18 and the efficiency of the refrigeration cycle is improved. Pump 40 is used to move the liquid refrigerant from vortex tube 21 via tubing or conduit 19 to the input of the evaporator 18 because the liquid refrigerant that exits vortex tube 21 may not have the velocity or pressure to be directed back to the inlet of the evaporator 18.

[0055] Pump 40 somewhat offsets the gain in refrigeration efficiency because typical refrigeration systems do not include this pump. However, it is believed that the increased efficiency in the evaporation step is greater than the energy needed to drive a small pump such as used in this embodiment.

[0056] Although this invention has been described and illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made which clearly fall within the scope of this invention. The present invention is intended to be protected broadly within the spirit and scope of the appended claims.