WO2009117796A1

WO2009117796A1 - Refrigeration system

Info

Publication number: WO2009117796A1
Application number: PCT/BR2009/000083
Authority: WO
Inventors: Dietmar Erich Bernhard Lilie
Original assignee: Whirlpool S.A.
Priority date: 2008-03-27
Filing date: 2009-03-25
Publication date: 2009-10-01
Also published as: BRPI0801109A2

Abstract

The refrigeration system of the present invention comprises: a compressor (10); a condenser (30) connected to the compressor (10); a separating means (50) connected to the condenser (30) and to the compressor (10); at least one evaporator (100) in heat exchange contact with a respective medium (M) to be cooled and being connected to the separating means (50); and a flow accelerating means (200) which is operatively associated with a respective evaporator (100) so as to provide a refrigerant fluid mass flow through the evaporator (100), greater than that passing through the compressor (10) and which is calculated as a function of the dimensioning of the heat exchange area of the evaporator (100) and also of the thermal load to be removed from the medium (M) to be cooled.

Description

REFRIGERATION SYSTEM Field of the Invention

The present invention refers to a small refrigeration system to be used, for example, in compact electronic devices, particularly for cooling components of said devices, such as microprocessors in general and integrated circuits. Background of the Invention The development of manufacturing technology for the increasingly faster computers that are being demanded is facing limitations regarding the removal of the heat generated by said equipment under operation. Electronic equipment in general, and particularly computers, present determined electronic components, such as microprocessors and integrated circuits which, for a good functioning, require their temperature to be maintained within a certain temperature range, which is previously determined and mainly lower than its superior limit, and which also guarantees the maintenance of the operational properties of these electronic components.

Due to the technological advances, mainly regarding the processing speed of these electronic components, problems, such as superheating and heat dissipation in equipment using such electronic components, have been more and more a limitation factor for the good performance of these electronic components and represent one of the great obstacles to the improvement of such equipment. Traditional refrigeration systems (radiation or convection) do not lead to an efficient refrigeration of the more sensitive electronic components, neither to an efficient dissipation of the heat generated by operation of the equipment containing such electronic components . Several alternatives to reduce, at maximum, the heat generation have been object of studies, but in some cases, in which the processing requirements demand very high speeds, the processor is taken to its thermal limit. If more heat can be extracted, it is possible to increase the processing speed even more, shortening the time for processing very complex operations.

Cooling a processor or computer chip is a great challenge, as a result of the heat liberation concentrated in a very small area. Nevertheless, heat exchangers are usually constructed with large areas to permit an efficient heat exchange. Another complicating fact is the geometry of the surface to be cooled, which generally cannot be modified to facilitate the removal of heat, due to problems in the chip manufacturing process. The most traditional solution for cooling these processors (chips) removes heat by thermal contact by using, to be in contact with the device to be cooled, a heat exchange body having a heat exchanger, said body being constructed to present a more suitable area for removing the heat. This heat exchanger can be a simple fin system, or an exchanger using refrigerant fluid with or without phase change. This technique brings limitations, such as thermal contact deficiency and low thermal conductivity of this heat exchange body. Another solution for cooling processors or chips uses a technique known as spray cooling. This technique uses the phase change of a fluid to remove the heat and solves one of the problems presented by micro-channel exchangers regarding the removal of bubbles from the evaporated fluid, said bubbles resulting from the refrigeration process itself. The fluid evaporation causes the formation of bubbles which occupy space in the heat exchanger, reducing the efficiency of the latter. The size of the heat exchanger is important, but the expulsion of the bubbles in contact with the heat surface is mandatory. The "spray cooling" provides this removal through the collision of fluid drops with the formed bubbles. The drawback of this method is the high load loss in the spray generation, as well as in the liquid or vapor collection to allow the fluid to be reused. Using household refrigeration systems for cooling processors and similar equipment presents some barriers regarding not only the miniaturization of the compressor, but also the efficiency of the known evaporators when their size is reduced to the usual dimensions of the processors, and the like.

When used in household refrigeration, such refrigeration systems present the evaporator dimensioned to define a large heat exchange area. In such constructions, during the compressor operation, the refrigerant fluid comprises a vapor portion and a liquid portion in the inlet of the evaporator. This generated vapor, upon passing in the evaporator together with the liquid, practically does not act in the heat exchange, resulting in an almost null heat exchange efficiency. This causes a certain inefficiency in the refrigeration system, since the compressor consumes energy to move this refrigerant fluid along the whole evaporator and, afterwards, to compress it, without said refrigerant fluid, in the form of vapor, carrying out heat exchange. The compressor wastes energy to compress the vapor from a very low pressure to a higher condensation pressure. The amount of the refrigerant fluid in the vapor phase and present in the evaporator, acts as a gas dead volume being continuously pumped and drawn, without producing refrigeration work and consuming energy of the compressor to move said fluid. In some known prior art solutions, this energy loss is minimized through a refrigeration system using a separating means in the refrigeration circuit and which executes a process for extracting part of this vapor, so as to provide the circuit with a process for expanding refrigerant fluid in two pressure stages. Since in conventional refrigeration systems the heat exchange of the evaporator is large, the efficiency losses in heat exchange are compensated by the dimensioning of said evaporator. However, in small heat exchange areas, in which the evaporator size needs to be reduced, the presence of gas in the interior of the latter, without carrying out heat exchange, is an obstacle to the application of such refrigeration circuits in miniaturized systems. Objects of the Invention

It is an object of the present invention to provide a refrigeration system, by vapor mechanical compression, particularly to be used for refrigerating electronic systems, but which does not present the deficiencies existing in the known prior art solutions regarding refrigeration of small electronic equipment. It is another object of the present invention to provide a refrigeration system which can efficiently remove heat from the small heat production areas, independently of the geometry of said areas and without requiring modifying the characteristics thereof. It is a further object of the present invention to provide a system of the type cited above and which allows obtaining the maximum yield from the refrigeration system, independently of the type of refrigerant fluid used. It is also a further object of the present invention to provide a system, such as cited above and which reduces the presence of dead volume of refrigerant fluid, in the form of vapor, in the evaporator outlet, allowing great amounts of heat to be removed in a very small space. It is yet another object to provide a system, such as cited above and which presents a heat exchanger with high energy density.

These and other objects of the present invention are attained by providing a refrigeration system which comprises: a compressor having an inlet and an outlet of refrigerant fluid in the form of gas; a condenser having a gas inlet, connected to the outlet of the compressor, and a gas-liquid mixture outlet; a separating means having a first gas-liquid mixture inlet, connected to the gas-liquid mixture outlet of the condenser, a second gas- liquid mixture inlet, a gas outlet connected to the inlet of the compressor; and a liquid outlet; at least one evaporator in heat exchange contact with a respective medium to be cooled, and having a liquid inlet connected, by a liquid duct, to the liquid outlet of the separating means, and a gas-liquid mixture outlet connected, by a mixture duct, to the second inlet of the separating means. The refrigeration system of the present invention further comprises a flow accelerating means, which is operatively associated with a respective evaporator, to accelerate the refrigerant fluid flow being circulated through the separating means, through the liquid duct, through the evaporator and through the mixture duct, so as to provide a refrigerant fluid mass flow, through the evaporator, greater than that passing through the compressor and which is calculated as a function of the dimensioning of the heat exchange area of the evaporator and also of the thermal load to be removed from the medium to be cooled.

It should be observed that the mass flow in the gas outlet of the separating means will be always the same as that pumped by the compressor, otherwise the mass balance of the compressor would not be achieved. The mass flow in the evaporator will be always greater than the mass flow of the compressor, as a function of the actuation of the flow accelerating means of the refrigeration system of the present invention. According to a way of carrying out the present invention, the refrigerant fluid flow passing through the liquid duct is divided, in the interior of the evaporator, in a plurality of flows parallel to one another and converging, at the gas-liquid mixture outlet of the evaporator, towards the mixture duct.

According to a particular constructive form of the present invention, the parallel refrigerant fluid flows, in the interior of the evaporator, are contained in respective ducts, each connected to both the liquid inlet and to the gas-liquid mixture outlet of the evaporator.

Brief Description of the Drawings The invention will be described below with reference to the enclosed drawings, given by way of example of an embodiment of the invention and in which:

Figure 1 schematically represents a refrigeration system by mechanical vapor compression, constructed according to the present invention and further illustrating, in dashed lines, a possible constructive variant for the positioning of the flow accelerating means in relation to the evaporator;

Figure 2 schematically represents a simplified partially- sectioned perspective view of a possible construction for the evaporator mounted on a body to be cooled;

Figure 3 schematically represents a horizontal sectional view of the evaporator, taken according to line III-III in figure 2; Figure 4 schematically represents a vertical sectional view of the evaporator, taken according to line IV-IV in figure 2; and

Figure 5 schematically represents a vertical sectional view of the evaporator, taken according to line V-V in figure 2.

Description of the Invention

The present invention will be described for a refrigeration system of the type which operates by mechanical vapor compression, said refrigeration system comprising: a compressor 10, having an inlet 11 and an outlet 12 of refrigerant fluid in the form of gas, said outlet 12 being connected, by a first gas duct 20, to a condenser 30.

The condenser 30 presents a gas inlet 31 connected to the outlet 12 of the compressor 10 and a gas-liquid mixture outlet 32 connected, by a condensate duct 60, to a first gas-liquid mixture inlet 51 of a separating means 50. The separating means 50 further presents: a second gas- liquid mixture inlet 52 connected, by a mixture duct 70, to an evaporator 100 operatively associated with a medium M to be cooled; a gas outlet 53 connected to the inlet 11 of the compressor 10 through a second gas duct 40; and a liquid outlet 54 connected, by a liquid duct 80, to the evaporator 100.

The evaporator 100 presents a liquid inlet 101 connected, by the liquid duct 80, to the liquid outlet 54 of the separating means 50 and a gas-liquid mixture outlet 102 connected, by the mixture duct 70, to the second inlet 52 of the separating means 50.

In these known prior art refrigeration systems, the operation mass flow of the compressor is the same along the whole refrigeration circuit.

Such refrigeration system circuits present the deficiencies commented above and which impair their use for refrigerating electronic elements, which present a small heat exchange area to interact with the evaporator of the refrigeration system.

In order to allow reducing the dimensions of the evaporator 100, the present invention provides the refrigeration system with a flow accelerating means 200, which is operatively associated with the evaporator 100, to accelerate the refrigerant fluid flow being circulated through the separating means 50, through the liquid duct 80, through the evaporator 100 and through the mixture duct 70, so as to provide a mass flow of said refrigerant fluid, through the evaporator 100, greater than that passing through the compressor 10 and which is calculated as a function of the dimensioning of the heat exchange area of the evaporator 100 and also of the thermal load to be removed from the medium M to be cooled. The mass flow passing through the reduced heat exchange area in the evaporator corresponds to a multiple, not necessarily an integer, of the mass flow of the compressor, so as to minimize the amount of gas in the gas-liquid mixture outlet 102 of the evaporator 100, compensating the reduced heat exchange area in the latter. In conventional evaporators, 100% of gas comes out from the gas outlet of the evaporator. Exemplifying, in a constructive option of the present invention, the acceleration of the refrigerant fluid by the flow accelerating means 200 can correspond to 20% of gas in the gas-liquid mixture outlet 102 of the evaporator 100. In this case, the mass flow in the evaporator 100 is five times the mass flow of the compressor.

In another constructive option, the flow accelerating means 200 provides an acceleration of the mass flow through the evaporator 100, which is calculated to provide a determined non-null amount of gas in the gas- liquid mixture outlet 102 of said evaporator 100. For any of the present solutions, the amount of gas in the gas-liquid mixture outlet 102 of the evaporator 100 is inversely proportional to the acceleration of refrigerant fluid through the evaporator 100.

The flow accelerating means 200 forces the passage of the refrigerant fluid through the interior of the evaporator 100, with a greater speed than that presented by the refrigerant fluid through a conventional evaporator, usually used in refrigeration systems of a household refrigeration appliance, in which a large heat exchange area is available between the conventional evaporator and the medium or environment to be cooled. The increased speed of refrigerant fluid passing through the evaporator 100 is calculated so that the heat of the medium M to be cooled, which heat is removed by the evaporator 100, is received by the refrigerant fluid in liquid phase passing through the evaporator 100, producing a phase change in only part of said refrigerant fluid mass flow, whereby the permanence time of the gaseous phase of said refrigerant fluid in the interior of the evaporator 100 is considerably reduced. The refrigerant fluid is then conducted to the separating means 50 and the part of said refrigerant fluid still in liquid phase is returned to the evaporator 100 through the liquid duct 80. The speed of the refrigerant fluid through the evaporator 100 is calculated as a function of the heat exchange capacity of the evaporator 100, so that the refrigerant fluid flow coming out from said evaporator 100, containing only a gas fraction of the amount of the gaseous mass flow of the compressor operation, produces, per compressor operation time unit, the gaseous mass flow of the compressor normal operation.

In a way of carrying out the present invention, the smallest the heat exchange area available in the evaporator 100, the larger will be the refrigerant fluid mass flow through the evaporator 100.

According to a particular way of carrying out the present invention, the acceleration of refrigerant fluid through the evaporator - separating means system is inversely proportional to the amount of gas in the gas- liquid mixture outlet 102 of the evaporator 100. This relation is generally defined as a function of the thermal load to be removed from the medium M to be cooled, after removing the heat from the latter. Experimental models of the refrigeration system of the present invention indicate that the refrigerant fluid mass flow through the evaporator 100 is calculated to evaporate from about 2 to 30% of the liquid refrigerant fluid flow admitted in the evaporator 100 and, preferably, to evaporate from about 2% to 10% of said refrigerant fluid flow passing through evaporator 100.

According to the illustrated constructive form, the evaporator 100 is dimensioned to have a heat exchange area operatively associated with the medium M to be cooled (processor, chip, electronic board, etc.) and with a dimension corresponding to that of said medium M. The shape of the evaporator 100 can correspond to that of the medium M to be cooled or defined to have its heat exchange area covering at least a substantial part of the whole heated area of the medium M to be cooled. Although not illustrated, the evaporator 100 can be constructed to cover the area of different mediums to be cooled, each medium M to be cooled being operatively associated with a respective region of the evaporator 100.

According to a way of carrying out the present invention, illustrated in figure 1, the flow accelerating means 200 is provided in one of the liquid duct 80 (continuous line) and mixture duct 70 (dashed line) of the refrigeration system. Although not illustrated, the flow accelerating means 200 can be also provided in the interior of the evaporator 100. In a possible constructive form, as illustrated in figure 1, the flow accelerating means 200 can be defined, for example, by a centrifugal pump which imposes a constant acceleration speed of the refrigerant fluid flow through the evaporator 100, the mixture duct 70, the separating means 50 and the liquid duct 80.

It should be understood that the refrigeration system proposed by the present invention can comprise more than one evaporator 100, each presenting determined dimensional characteristics that are calculated as a function of a respective medium M to be cooled and being operatively associated with a respective flow accelerating means 200, and all the evaporators 100 being associated with a single assembly defined by a compressor 10, a condenser 30 and a separating means 50. Each flow accelerating means 200 can be specifically dimensioned and operated to produce a required determined mass flow through the respective evaporator 100.

According to the present invention, the refrigerant fluid flow passing through the liquid duct 80 is divided, in the interior of the evaporator 100, in a plurality of flows parallel to one another and converging, in the gas- liquid mixture outlet 102 of the evaporator 100, to the mixture duct 70.

In a way of carrying out the present invention, the parallel refrigerant fluid flows in the interior of the evaporator 100 are contained in respective ducts 110, provided in the interior of said evaporator 100, each duct 110 being connected to the liquid inlet 101 and to the gas-liquid mixture outlet 102 of the evaporator 100. Each duct 110 comprises: an inlet portion 111 connected to the liquid inlet 101 of the evaporator 100; an outlet portion 112 connected to the gas-liquid mixture outlet 102 of the evaporator 100; and a chamber portion 113, interconnecting the inlet portion 111 and the outlet portion 112 and maintained in heat exchange contact with an adjacent portion of the medium M to be cooled. In the construction illustrated in figures 2-5 of the enclosed drawings, the chamber portions 113 associated with each duct 110 form, together, a single common chamber C which is bounded, on one side, by a single outer wall which is heated, by conduction, by the medium M to be cooled.

Although not illustrated herein, the common chamber C can be provided in the form of a body separated from the evaporator 100 and from the medium M to be cooled, but hermetically mounted between said parts and in fluid communication therewith.

According to the present invention, each chamber portion 113 is bounded, on one side, by an outer wall which is heated, by conduction, through the medium M to be cooled. In a way of carrying out the present invention, the outer wall is a wall of the medium M to be cooled. In this case, the evaporator 100 is hermetically mounted to the medium M to be cooled.

In another way of carrying out the present invention (not illustrated) , the outer wall is a wall of the evaporator 100 seated against an adjacent surface of the medium M to be cooled. In this case, the common chamber C can be defined in a single piece with the evaporator 100. In a construction form of the evaporator 100, this presents the inlet portions 111 of the ducts 110 connected to the liquid inlet 101 of the evaporator 100, by means of an inlet channel 115, the outlet portions 112 of the ducts 110 being connected to the gas-liquid mixture outlet 102 of the evaporator 100, by means of an outlet channel 116. In a particular form of this construction, the inlet channel 115 and the outlet channel 116 are disposed spaced from the chamber portions 113, which can be bounded, on one side, as already described, by an outer wall which is heated, by conduction, through the medium M to be cooled. According to the present invention, the inlet portion 111 and the outlet portion 112 of the ducts 110 are interleaved and spaced from one another, along the inlet channel 115 and outlet channel 116. The inlet portion 111 and the outlet portion 112 of the ducts 110 present an elongated rectangular section, with the larger side having a length coinciding with one of the dimensions of the respective chamber portion 113.

In the illustrated construction, the evaporator 100 presents a prismatic body, particularly in a parallelepiped shape, in which the ducts 110 are provided interleaved and parallel to one another and open to a common chamber C having an outer wall defined by the adjacent surface of the medium M to be cooled. In this construction, the inlet channel 115 and outlet channel 116 are provided spaced from the common chamber C. The evaporator 100 is obtained in a material with high thermal conductivity and the inlet channel 115 and outlet channel 116, the ducts 110 and the common chamber C are defined by extracting material from the piece which will define the evaporator 100. In another way of carrying out the present invention (not illustrated) , the ducts 110 are disposed substantially coplanar to one another and parallel to the area of the medium M to be cooled. In the illustrated construction, the evaporator 100 presents the common chamber C with an area corresponding to the heat exchange surface of the medium M to be cooled. The ducts 110, the inlet channel 115 and the outlet channel 116 and the common chamber C are dimensioned so that the heat exchange time of the refrigerant fluid in the common chamber C is calculated so as to provide a certain heat exchange, without increasing the load loss. While the concept presented herein has been described mainly considering the illustrated circuit and evaporator constructions, it should be understood that these particular constructions do not restrict the applicability of the present invention. The intention is to protect the principle and not the specific application or particular constructive form.

Claims

1. A refrigeration system comprising:

- a compressor (10) having an inlet (11) and an outlet (12) of refrigerant fluid in the form of gas,- - a condenser (30) having a gas inlet (31) connected to the outlet (12) of the compressor (10) and a gas-liquid mixture outlet (32) ; a separating means (50) having a first gas-liquid mixture inlet (51) connected to the gas-liquid mixture outlet (32) of the condenser (30) , a second gas-liquid mixture inlet (52) , a gas outlet (53) connected to the inlet (11) of the compressor (10) ; and a liquid outlet

(54) ;

- at least one evaporator (100) in heat exchange contact with a respective medium (M) to be cooled and having a liquid inlet (101) connected, by a liquid duct (80) , to the liquid outlet (54) of the separating means (50) and a gas-liquid mixture outlet (102) connected, by a mixture duct (70) , to the second inlet (52) of the separating means (50) , characterized in that it comprises a flow accelerating means (200) , which is operatively associated with a respective evaporator (100) , to accelerate the refrigerant fluid flow being circulated through the separating means (50) , through the liquid duct (80) , through the evaporator (100) and through the mixture duct (70) , so as to provide a refrigerant fluid mass flow through the evaporator (100) greater than that passing through the compressor (10) and which is calculated as a function of the dimensioning of the heat exchange area of the evaporator (100) and also of the thermal load to be removed from the medium (M) to be cooled.

2. The refrigeration system, as set forth in claim 1, characterized in that the refrigerant fluid mass flow through the evaporator (100) is calculated to evaporate from about 2 to 30% of the liquid refrigerant fluid flow admitted in the evaporator (100) .

3. The refrigeration system, as set forth in claim 1, characterized in that the flow accelerating means (110) is provided in one of the liquid duct (80) and mixture duct (70) .

4. The refrigeration system, as set forth in claim 3, characterized in that the refrigerant fluid flow passing through the liquid duct (80) is divided, in the interior of the evaporator (100) , in a plurality of flows parallel to one another and converging, in the gas-liquid mixture outlet (102) of the evaporator (100) , to the mixture duct (70) .

5. The refrigeration system, as set forth in claim 4, characterized in that the parallel refrigerant fluid flows in the interior of the evaporator (100) are contained in respective ducts (110) , each connected to the liquid inlet (101) and to the gas-liquid mixture outlet (102) of the evaporator (100) .

6. The refrigeration system, as set forth in claim 5, characterized in that each duct (110) comprises: an inlet portion (111) connected to the liquid inlet (101) of the evaporator (100) ; an outlet portion (112) connected to the gas-liquid mixture outlet (102) of the evaporator

(100) ; and a chamber portion (113) , interconnecting the inlet portion (111) and the outlet portion (112) and maintained in heat exchange contact with an adjacent portion of the medium (M) to be cooled.

7. The refrigeration system, as set forth in claim 6, characterized in that each chamber portion (113) is bounded, on one side, by an outer wall which is heated, by conduction, by the medium (M) to be cooled.

8. The refrigeration system, as set forth in claim 7, characterized in that the outer wall is a wall of the medium (M) to be cooled.

9. The refrigeration system, as set forth in claim 7, characterized in that the outer wall is a wall of the evaporator (100) seated against an adjacent surface of the medium (M) to be cooled.

10. The refrigeration system, as set forth in claim 6, characterized in that the chamber portions (113) associated with each duct (110) form, together, a single common chamber (C) bounded, on one side, by a single outer wall, which is heated, by conduction, by the medium (M) to be cooled.

11. The refrigeration system, as set forth in claim 6, characterized in that the inlet portions (111) of the ducts (110) are connected to the liquid inlet (101) of the evaporator (100) , by means of an inlet channel (115) , the outlet portions (112) of the ducts (110) being connected to the gas-liquid mixture outlet (102) of the evaporator (100) , by means of an outlet channel (116) .

12. The refrigeration system, as set forth in claim 11, characterized in that the inlet channel (115) and the outlet channel (116) are disposed spaced from the chamber portions (113) .

13. The refrigeration system, as set forth in claim 12, characterized in that the chamber portion (113) is bounded, on one side, by an outer wall, which is heated, by conduction, by the medium (M) to be cooled.

14. The refrigeration system, as set forth in claim 11, characterized in that the inlet portion (111) and the outlet portion (112) of the ducts (110) are interleaved and spaced from one another along the inlet channel (115) and outlet channel (116) .

15. The refrigeration system, as set forth in claim 14, characterized in that the inlet portion (111) and the outlet portion (112) present an elongated rectangular section, with the larger side having a length coinciding with one of the dimensions of the respective chamber portion (113) .

16. The refrigeration system, as set forth in claim 1, characterized in that the flow accelerating means (200) is a centrifugal pump.

17. The refrigeration system, as set forth in any of the previous claims, characterized in that the flow accelerating means (200) provides an acceleration of the mass flow through the evaporator (100) , which is calculated so as to provide a determined non-null amount of gas in the gas-liquid mixture outlet (102) of said evaporator (100) .

18. The refrigeration system, as set forth in claim 17, characterized in that the amount of gas in the gas-liquid mixture outlet (102) of the evaporator (100) is inversely- proportional to the acceleration of the refrigerant fluid through the evaporator (100) .