BACKGROUND OF THE INVENTION Fig. 1 is a block diagram of a conventional refrigeration system, generally denoted at 10. The 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 such as indicated at 20 to form a closed loop system through which a refrigerant such as R-12, R-22, R-134a, R-407c, R-410a, ammonia, carbon dioxide or natural gas is cycled.

The main steps in the refrigeration cycle are compression of the refrigerant by compressor 12, heat extraction from the refrigerant to the environment by condenser 14, throttling of the refrigerant in the expansion device 16, and heat absorption by the refrigerant from the space being cooled in evaporator 18. This process, sometimes referred to as a 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.

Fig. 2 shows the temperature-entropy curve for the vapor compression refrigeration cycle illustrated in Fig. 1. The refrigerant exits evaporator 18 as a saturated vapor (Point 1), and is compressed by compressor 12 to a very high pressure. The temperature of the refrigerant also increases during compression, and it leaves the compressor as superheated vapor (Point 2).

A typical condenser comprises a single conduit formed into a serpentine-like shape with a plurality of rows of conduit lying in a spaced parallel relationship. Metal fins or other structures which provide high heat conductivity are usually attached to the serpentine conduit to maximize the transfer of heat between the refrigerant passing through the condenser and the ambient air. As the superheated refrigerant gives up heat in the upstream portion of the condenser, the superheated vapor becomes a saturated vapor (Point 2a), and after losing further heat as it travels through the remainder of condenser 14, the refrigerant exits as saturated liquid (Point 3).

As the saturated liquid refrigerant passes through expansion device 16, its pressure is reduced, and it becomes a liquid-vapor mixture comprised of approximately 20% vapor and 80% liquid. Also, its temperature drops below the temperature of the ambient air as it goes through the expansion device (Point 4 in Fig. 2).

Evaporator 18 physically resembles the serpentine-shaped conduit of the condenser. Air to be cooled is exposed to the surface of the evaporator where heat is transferred to the refrigerant. As the refrigerant absorbs heat in evaporator 18, it becomes a saturated or slightly superheated vapor at the suction pressure of the compressor and reenters the compressor thereby completing the cycle (Point 1 in Fig. 2).

The injection of liquid refrigerant to the discharge line of the compressor or the inlet of the condenser in a conventional refrigeration system such as illustrated in Fig. 1 has been used to make the condenser more efficient. Referring to Fig. 3 (in which parts corresponding to those of Fig. 1 are given the same reference numerals), to provide liquid injection according to known practice, in addition to the above-described components, a bypass circuit 22 is coupled across condenser 14. This includes a pump 24, the inlet of which is coupled by a tube 26 to the outlet of condenser 14 through a suitable diverter valve (not shown). The outlet of pump 24 is coupled by a tube 28 and a suitable check valve (also not shown) to a further

tube 30 which connects the outlet of compressor 12 and the inlet of condenser 14.

Liquid refrigerant is injected into tube 30 to cool the superheated vapor exiting compressor 12 before it reaches the condenser. As the liquid refrigerant and the superheated vapor mix, the liquid flashes to a superheated vapor, and its temperature drops substantially. As a result, the superheated vapor can enter the condenser at a temperature close to its saturation temperature. This is illustrated in the modified temperature-entropy curve of Fig. 4 between Points 2 and 2a.

As will be understood, the liquid pressure at the condenser exit is slightly lower than the vapor pressure at the condenser inlet. Accordingly pump 24 must be used to pressurize the liquid. Generally, however, the cost of the pump does not justify the benefit gained by the liquid injection, so the concept of liquid injection has not been widely utilized in the air-conditioning and refrigeration industry.

Nevertheless, Fig. 4 demonstrates that with liquid injection, the portion of condenser 14 in which the superheated vapor is converted from superheated vapor to (lower temperature) saturated vapor (between Points 2 and 2a in Fig. 2) may be eliminated, thus reducing the manufacturing cost.

Alternatively, for a condenser of a particular size, greater supercooling can be achieved (as indicated at Point 3 in Fig. 4). This results in increased cooling capacity.

An additional benefit which can be achieved by use of liquid injection, assuming that the negative effect on cost resulting from the need for pump 24 can be overcome, is an improved energy-efficiency ratio (EER).

This is defined as Qv/Wc, where Qv is the heat absorption by the evaporator of the system and Wc is the work done by the compressor. As liquid injection increases supercooling, it also results in a greater quantity of liquid in the refrigerant entering the evaporator. This increases the cooling capacity Qv, thus the EER also increases.

Therefore a need exists for a cost-effective way to provide injection of liquid refrigerant at the inlet side of the condenser.

SUMMARY OF THE INVENTION According to the present invention, it has been found that a vacuum generating device with no moving parts can be used instead of a pump for the liquid injection. Such devices rely on geometry and fluid dynamics to create pressure differentials. Known devices of this type include venturi tubes and ejectors or syphons. Also, it has been found that the so-called"vortex tube" which is conventionally used to create two fluid steams of differing temperature from a single high pressure input stream can be adapted to function as a vacuum generating device, and may be used for that purpose according to the present invention. Such a vortex generator is the subject of a copending U. S. provisional patent application entitled USE OF A VORTEX GENERATOR TO GENERATE VACUUM, filed in the names of Young Cho, Cheolho Bai, and Joong-Hyoung Lee on February 11,2002, the contents of which are hereby incorporated by reference.

The concepts of this invention are applicable to conventional single-refrigerant systems, and also to mixed-refrigerant systems using a combination of refrigerants selected to provide the desired combination of thermal and flammability characteristics. Such mixed-refrigerant systems may also include regenerative features which provide higher evaporator efficiency by increasing the percentage of liquid in the refrigerant as it enters the evaporator. Regenerative mixed refrigerant systems are disclosed, for example, in our U. S. Patents 6,250, 086 and 6,293, 108, the contents of which are hereby incorporated by reference.

According to a first feature of the invention, there is provided a refrigeration system including refrigerant compressing means, refrigerant condensing means, expansion means and evaporation means connected together to form a closed loop system with a refrigerant circulating therein,

and vacuum generating means for receiving liquid refrigerant from an outlet of the condensing means and for injecting the liquid refrigerant into the closed loop between the outlet of the compressing means and an inlet of the condensing means.

According to a second feature of the invention, there is provided a refrigeration system including refrigerant compressing means, refrigerant condensing means, expansion means and evaporation means connected together to form a closed loop system, vacuum generating means, means for coupling an outlet of the condensing means to an inlet of the vacuum generating means, and means for coupling an outlet of the vacuum generating means to an inlet of the condensing means.

According to a third feature of the invention, there is provided a refrigeration system including a compressor, a condenser, an expansion device and an evaporator connected together to form a closed loop system with a refrigerant circulating therein, and a vacuum generating device operative to inject a liquid portion of the refrigerant exiting the condenser into the closed loop between an outlet of the compressor and an inlet of the condenser.

According to a fourth feature of the invention, there is provided a refrigeration system including a compressor, a condenser, an expansion device and an evaporator connected together to form a closed loop system with a refrigerant circulating therein, a vacuum generating device coupled to an outlet of the condenser and operative to inject a liquid portion of the refrigerant exiting the condenser into the closed loop between an outlet of the compressor and an inlet of the condenser.

According to a fifth feature of the invention, a vacuum generating device injects liquified refrigerant into the inlet of the condenser of a refrigeration system employing a vapor-compression refrigeration cycle.

According to a sixth feature of the invention, and with respect to each of the above-described other features, the vacuum generator is a device

without moving parts which generates a pressure differential as a result of the geometry of the device and the fluid flow therethrough. Such devices include a modified vortex tube, venturis, ejectors or siphons, etc.

Also with respect to each of the above-described features of the invention, the refrigeration system may employ a single refrigerant, or a mixture of refrigerants selected to provide the desired combination of thermal and flammability characteristics and may include regenerative features which provide higher evaporator efficiency by increasing the percentage of liquid in the refrigerant as it enters the evaporator.

According to a seventh feature of the invention, there is provided a novel vortex generator which functions as a vacuum generating device without moving parts.

It is therefore an object of the invention to increase the efficiency of known refrigeration systems by providing a cost-effective way of injecting liquid refrigerant into the inlet of the condenser.

It is another object of the invention to increase the cooling capacity and EER of known refrigeration systems by providing a cost-effective way of injecting liquid refrigerant into the inlet of the condenser.

A related object of the invention to allow use of smaller condensers in known refrigeration systems by providing a cost-effective way of injecting liquid refrigerant into the inlet of the condenser.

An additional object of the invention is to provide improved liquid refrigerant injection apparatus which may be used in single-refrigerant systems and also in mixed-refrigerant systems, with and without regenerative features.

A further object of the invention is to provide an improved refrigeration system including a device for injecting liquid refrigerant into the inlet of the condenser without the need for a costly pump.

A related object of the invention is to provide an improved refrigeration system in which the device for injecting liquid refrigerant into

the inlet of the condenser is a vacuum generating device having no moving parts.

An additional related object of the invention is to provide an improved refrigeration system in which the device for injecting liquid refrigerant is a vacuum generating device which creates a pressure differential due to vortex flow, and which requires no moving parts.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a block diagram of a conventional refrigeration system.

Figure 2 shows a temperature-entropy curve for the conventional refrigeration system of Figure 1.

Figure 3 shows a block diagram of a conventional refrigeration system in which liquid refrigerant is injected into the condenser inlet using a pump.

Figure 4 shows a temperature-entropy curve for the refrigeration system of Figure 3.

Figure 5 shows a block diagram of an embodiment of the present invention in which a vortex generator is used to inject liquid refrigerant into the condenser inlet.

Figures 6A and 6B illustrate the construction of a vortex generator according to the invention.

Figure 7 illustrates the construction of a venturi which may be used instead of the vortex generator shown in Figures 6A and 6B.

Figure 8 shows a block diagram of a second embodiment in which the present invention applied to a mixed-refrigerant system.

Throughout the drawings, like parts are given the same reference numerals.

DETAILED DESCRIPTION

Fig. 5 illustrates in block diagram form, a first embodiment of the invention in which a vortex generator is used instead of a pump. The system of Fig. 5, generally denoted at 40, is similar to that of Fig. 3, except that in bypass circuit 42 coupled across condenser 14, pump 24 is replaced by a vortex generator (VG) 44, described in more detail below. A valve 46 is coupled by a tube 48 to the outlet of condenser 14, and by a second tube 50 to a first inlet 54 of VG 44. A second inlet 52 of VG 44 is coupled to the outlet of compressor 12 by a tube 56. The outlet 58 of VG 44 is coupled by tube 30 to the inlet of condenser 14.

The construction of VG 44 is shown schematically in Figs. 6A and 6B. The design of VG 44 is derived from the so-called vortex tube, a known device which converts an incoming flow of compressed gas into two outlet 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. The conventional version of a vortex tube, e. g., used for fluid separation in refrigeration systems, is illustrated in our U. S.

Patent 6,250, 086, which is hereby incorporated herein by reference.

As illustrated in Figs. 6A and 6B, a vortex generator according to this invention is comprised of a tubular body 60, with an axial inlet 52 and a tangential inlet 54 at an inlet end 62, and an outlet 58 at an opposite outlet end 64. The interior construction of tube 60 at the inlet end is such that a high pressure gas stream entering tangential inlet 54 travels along a helical path toward the outlet 58. This produces a strong vortex flow in tube 60, and a radial pressure differential due to the centrifugal force created by the vortex flow forces the vapor radially outward and produces high pressure at the periphery and low pressure at the axis. The low pressure allows fluid drawn in through axial inlet 52 to mix with the high pressure helical stream and to exit with it through outlet 58.

Further information concerning VG 44 may be found in the Cho, Bai, Lee Application mentioned above.

In the system illustrated in Fig. 5, the high pressure tangential flow is provided through tube 56 from compressor 12, and the incoming stream at axial inlet 52 is provided from the outlet of condenser 14 through valve 46 and tubes 48 and 50. Using a vacuum generating device based on the vortex tube makes it possible to provide injection of liquid refrigerant between the outlet of the compressor 12 and the inlet of condenser 14 without the need for a costly pump having moving parts.

Other devices which rely on geometry and fluid dynamics may also be used to generate a vacuum which permits liquid refrigerant injection without use of a mechanical pump. For example, a device operating on the principle of a venturi tube may also be used. In such a device, as illustrated in Fig. 7, a high pressure fluid stream (here, the superheated vapor output of compressor 12), enters axially into an elongated tube 70 having an interior diameter 72 which decreases gradually to a point of minimum diameter 74 and thereafter increases gradually toward an outlet end 76. As the cross-sectional area decreases, the vapor stream is accelerated. According to Bernoulli's principle, the pressure decreases, and reaches a minimum at the so-called"throat corresponding to the point of minimum diameter 74 where a vacuum is created.

A radial inlet 78 is provided at the low-pressure point. This is connected by tubes 48 and 50, and valve 46 to the outlet of condenser 14 (see Fig. 5), thereby permitting mixture of the liquid refrigerant with the axial stream of superheated vapor from compressor 12.

Yet another possible device for creating a vacuum without reliance on a pump is the so-called ejector, sometimes also called a syphon or eductor.

In the constructions described above, it has been assumed that a single refrigerant circulates through the system. Liquid injection can also be used in conjunction with mixed refrigerants in regenerative systems to achieve highly beneficial results.

Fig. 8 illustrates use of liquid injection in a simple mixed-refrigerant system, employing, for example, a mixture of refrigerants R-32, R-125, and R-134a. This is a commonly used beneficial combination as the R-32 component is flammable, but possesses excellent thermal characteristics, while the R-125 and R-134a components exhibit less desirable thermal characteristics than R-32 but are non-flammable. In the interest of simplicity, various possible regenerative paths as illustrated in our above-identified U. S. Patents have been omitted from the illustrative system of Fig. 8.

The system, generally denoted at 86, comprises a compressor 12, an expansion device 16, and an evaporator 18. The condenser, however, is split into two stages designated 14a and 14b, and a liquid-vapor (LV) separator 88 of any suitable or desired type is provided between the two condenser stages.

LV separator 88 functions to separate the incoming vapor stream exiting from condenser stage 14a into a vapor component which passes through tube 90 to the inlet of condenser stage 14b, and a lower temperature liquid component which passes through a tube 92, a valve 46, and a second tube 50 to the axial inlet 52 of VG 44 (see Figs. 6A and 6B). The tangential inlet 54 of VG 44 is coupled to the outlet of compressor 12 by a tube 56, and the outlet 58 of VG 44 is coupled to the inlet of the first condenser stage 14a by a tube 30. In connection with the above description it should be understood that instead of VG 44, the venturi device 70 illustrated in Fig. 7, or other comparable device, may be used.

The liquid exiting from LV separator 88 is rich in the R-134a refrigerant component due to its high boiling point relative to the other refrigerant components. Aside from the advantages of liquid injection as described above, returning part of the R-134a to the condenser in liquid form has the added benefit of lowering the condenser pressure, thus further reducing the compressor work.

In summary, use of liquid injection in mixed refrigerant systems allows the refrigerant to enter the condenser as an almost saturated vapor which eliminates the need for a desuperheating section in the condenser and increases the supercooling of the refrigerant exiting the condenser. It also reduces the condenser pressure, and thus reduces the compressor work.

As indicated above, the system illustrated in Fig. 8 is representative of the application of the principles of this invention to mixed-refrigerant regenerative systems. It should therefore be understood, that liquid refrigerant injection to the condenser is applicable to other mixed-refrigerant regenerative system configurations as well.

In describing the invention, specific terminology has been employed for the sake of clarity. However, the invention is not intended to be limited to the specific descriptive terms, 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.

Similarly, the embodiments described and illustrated are also intended to be exemplary, and various changes and modifications, and other embodiments within the scope of the invention will be apparent to those skilled in the art in light of the disclosure. The scope of the invention is therefore intended to be defined and limited only by the appended claims, and not by the description herein.