EP1519127A1

EP1519127A1 - Cooling cycle

Info

Publication number: EP1519127A1
Application number: EP04022914A
Authority: EP
Inventors: Kenji Zexel Valeo Climate Control Corp. Lijima
Original assignee: Valeo Climatisation SA; Valeo Systemes Thermiques SAS
Current assignee: Valeo Systemes Thermiques SAS
Priority date: 2003-09-26
Filing date: 2004-09-27
Publication date: 2005-03-30
Also published as: JP2005098635A

Abstract

Theme : To provide a cooling cycle having a structure such that rises in the coolant discharge temperature of a compressor are prevented, increases in pressure losses in the internal heat exchanger are avoided, and reductions in size, weight and cost of the necessary components are enabled.

Means of Resolution : A Cooling cycle 1, comprising compressor 2 which increases the pressure of the coolant, radiator 3 which cools the coolant compressed by the compressor, expansion device 4 which reduces the pressure of the coolant cooled by radiator 3, evaporator 5 which evaporates the coolant whose pressure is reduced in expansion device 4, accumulator 6 which in addition to separating out the gas and liquid in the coolant passing through evaporator 5 separates out the oil mixed in with the coolant, and internal heat exchanger 7 which exchanges heat between the low-pressure coolant conducted from accumulator 6 to compressor 2 and the high-pressure coolant conducted from radiator 3 to expansion device 4, is provided with recovery path 10 which bypasses internal heat exchanger 7 enabling recovery of the liquid coolant or oil in accumulator 6 between said internal heat exchanger 7 and compressor 2, and regulator valve 11 which regulates the quantity recovered via this recovery path 10.

Description

This invention relates to a cooling cycle which employs a supercritical fluid such as carbon dioxide (CO₂) as the coolant.
As the temperature of the coolant discharged from the compressor becomes extremely high at times of high load, there is a danger with this type of cooling cycle that the durability of the components which make up the cooling cycle can deteriorate significantly. In particular the temperature range within which the durability of rubber or resin parts can be maintained is low compared to other components, and during times of high load the discharge temperature of the coolant can exceed this temperature range leading to potential damage.
In a supercritical vapour compression cooling cycle which uses carbon dioxide or the like as the coolant, an internal heat exchanger which exchanges heat between the high-pressure coolant passing through the radiator and the low-pressure coolant introduced into the compressor is provided with the purpose of increasing cooling performance, and also to prevent compression of the liquid by the compressor.
For this reason proposals have been made in prior art, as shown in Japanese laid-open patent application 2002-228282, to recover the liquid coolant or oil separated out by the accumulator at the inlet side of the internal heat exchanger, which is designed to prevent overheating with the very high temperatures of the coolant introduced into the compressor, or as shown in Japanese laid-open patent applications 11-193967 or 11-201568, to recover gas coolant within the accumulator between the outlet side of the internal heat exchanger and the inlet side of the compressor.
However, with the structure cited in Patent application N°2002-228282, whilst it is possible to reduce the temperature of the coolant introduced into the compressor and even to reduce the temperature of the coolant discharged from the compressor, there is the disadvantage that there will be more pressure lost within the internal heat exchanger as the liquid coolant and oil pass through the internal heat exchanger, due to the fact that liquid coolant and oil cooled within the accumulator become mixed with coolant from which heat has been absorbed in the evaporator.
Moreover, with the structure cited in Japanese laid-open patent applications 11-193967 or 11-201568, as the gas coolant within the accumulator is supplied after bypassing the internal heat exchanger, being mixed with the gas coolant flowing out from the internal heat exchanger, effective recovery of the gas coolant requires a large regulator valve to regulate the diameter of the tubing of the diversion path and the amount recovered, which negates the requirement for reduced size, weight and cost.
Thus the main purpose of the invention is to provide a cooling cycle which, with a structure which prevents a rise of temperature in the coolant discharged from the compressor, avoids increased pressure loss in the internal heat exchanger and enables a reduction in the size, weight and cost of the necessary components which make up the structure in question.
In order to achieve this aim, in a cooling cycle having a compressor which raises the pressure of a coolant, a radiator which cools the coolant compressed in said compressor, an expansion device which reduces the pressure of the coolant cooled by said radiator, an evaporator which evaporates the coolant whose pressure has been reduced by said expansion device, an accumulator which in addition to separating out the gas and liquid in the coolant which has passed through said evaporator, separates out the oil in the coolant, and an internal heat exchanger which exchanges heat between the low-pressure coolant conducted from said accumulator to said compressor and the high-pressure coolant conducted from said radiator to said expansion device, the cooling cycle of the invention is characterized in that a recovery path is provided which bypasses said internal heat exchanger, enabling recovery of the liquid coolant or oil inside said accumulator between said internal heat exchanger and compressor, and a regulator valve which enables regulation of the quantity of said liquid coolant or oil recovered via this recovery path.
Thus as it is arranged that the liquid coolant or oil separated in the accumulator is recovered between the internal heat exchanger and the compressor and mixed with the gas coolant that has passed through the internal heat exchanger, it is possible to reduce the temperature of the coolant introduced into the compressor, and even to reduce the temperature of the coolant discharged from the compressor. Moreover, as it is arranged that the liquid coolant or oil separated in the accumulator is made to bypass the internal heat exchanger and is recovered between the internal heat exchanger and the compressor, it is possible to avoid pressure losses within the internal heat exchanger, and as the liquid coolant or oil are recovered via the recovery path, it is possible to make the diameter of the tubing of the recovery path smaller than with gas coolant passing through, thus enabling reductions in size and weight.
The above structure may also be realized by providing a coolant discharge temperature sensor which detects the temperature of the coolant discharged from said compressor, and a control means which controls said regulator valve in accordance with the coolant discharge temperature detected by said coolant discharge temperature sensor, or a control means which controls said regulator valve where it is expected that the discharge temperature will rise with a high cycle load due to the outside temperature, pressure within the cycle, room temperature or the like. The internal heat exchanger and regulator valve may also be built into the accumulator to enable reductions in the size, weight and cost of the cooling cycle.
The structure of the above cycle is suited to a supercritical vapour compression cooling cycle which uses carbon dioxide as a coolant, in which the coolant discharge temperature of the compressor becomes extremely high at times of high load.
As has been described above, according to the invention, in a cooling cycle provided with an internal heat exchanger which exchanges heat between the low-pressure coolant conducted from the accumulator to the compressor and the high-pressure coolant conducted from the radiator to the expansion device, the liquid coolant or oil within the accumulator bypasses the internal heat exchanger via the recovery path, enabling recovery between the internal heat exchanger and the compressor, the quantity of liquid coolant or oil recovered via this recovery path being regulated by a regulator valve, thus enabling the temperature of the coolant introduced to the compressor to be reduced, and even enabling a reduction in the coolant discharge temperature. Moreover, in addition to preventing increases in pressure loss in the internal heat exchanger, it is possible to have a smaller diameter for the tubing of the recovery path than is possible with gas coolant passing through, thus permitting a smaller size of regulator valve, and allowing the cooling cycle to be of smaller size, weight and cost.
An optimal configuration of an embodiment of the invention will now be described with reference to the attached drawings :
Figure 1 is a diagram showing the overall structure of an example of the cooling cycle of the invention.
Figure 2 is an expanded diagram showing the vicinity of the accumulator and internal heat exchanger in Figure 1.
Figure 3 is a flow chart showing an example of the operation of the control unit from Figure 1.
Figure 4 is a Mollier diagram illustrating the operating mechanism of the cooling cycle.
Figure 5 is a graph showing the relationship between the quantity of oil recovered from the accumulator and the coolant discharge temperature of the compressor.
Figure 6 is a graph showing the relationship between the quantity of oil recovered from the accumulator and cooling performance.
In Figure 1, cooling cycle 1 has a structure comprising compressor 2 which increases the pressure of the coolant, radiator 3 which cools the coolant compressed by compressor 2, expansion device 4 which reduces the pressure of the coolant cooled by radiator 3, evaporator 5 which evaporates coolant whose pressure is reduced in expansion device 4, accumulator 6 which in addition to separating out the gas and liquid in the coolant passing through evaporator 5 separates the oil (lubricating oil) mixed in with the coolant, and internal heat exchanger 7 which exchanges heat between the low-pressure coolant conducted from accumulator 6 to compressor 2 and the high-pressure coolant conducted from radiator 3 to expansion device 4.
In other words, with cooling cycle 1 the discharge side of compressor 2 is connected to high-pressure duct 7a of internal heat exchanger 7 via radiator 3, the outlet side of this high-pressure duct 7a being connected to expansion device 4. Moreover, the outlet side of expansion device 4 is connected to the inlet port of accumulator 6 via evaporator 5, the outlet port of accumulator 6 being connected to the inlet side of compressor 2 via low-pressure duct 7b of internal heat exchanger 7. Thus high-pressure line 8 is comprised of the path which reaches expansion device 4 via radiator 3 and high-pressure duct 7a from the discharge side of compressor 2, and low-pressure line 9 is comprised of the path which reaches from expansion device 4 to compressor 2 via evaporator 5, accumulator 6 and low-pressure duct 7b.
The above described cooling cycle 1 uses carbon dioxide (CO₂) as the coolant, and the coolant whose pressure is increased in compressor 2 is introduced into radiator 3 as a high-temperature and high-pressure supercritical coolant, being cooled here by radiation. Thereafter it enters high-pressure duct 7a of internal heat exchanger 7 where it is further cooled by heat exchange with the low-temperature gas coolant flowing out from accumulator 6, and sent on without being liquefied to expansion device 4. In this expansion device 4 the pressure is then reduced, creating a low-temperature low-pressure wet vapour, which is vaporized by heat exchange with the air passing through evaporator 5, before flowing into accumulator 6 as a two-phase coolant in which gas and liquid are mixed.
Not only is the coolant which flows into accumulator 6 here separated out into gas and liquid, the oil which has become mixed into the coolant is also separated, the separated liquid coolant and oil remaining within the accumulator, and the gas coolant being sent to low-pressure duct 7b of internal heat exchanger 7, being returned to compressor 2 after complete conversion to a gas after absorbing more heat through heat exchange with the high-temperature coolant flowing out from radiator 3.
However, with this structure, as is shown in Figure 2, abovementioned cooling cycle 1 is provided with recovery path 10, one end of which has an opening at the bottom of accumulator 6, the other end being connected between low-pressure duct 7b of internal heat exchanger 7 and the inlet side of compressor 2, the degree of opening of this recovery path 10 being regulated by regulator valve 11, which comprises an electromagnetic valve.
Coming back to Figure 1, the reference 12 is a temperature sensor for the coolant discharge which detects temperature Td of the coolant discharged from compressor 2, and the temperature signal output from this coolant discharge temperature sensor 12 is input to control unit 13, said control unit 13 being part of the control means. This control unit 13 has a structure comprising a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), an input/output port and the like, and in addition a drive circuit which controls regulator valve 11, it being arranged that regulator valve 11 is controlled using the control routine shown in Figure 3 which is executed at prescribed intervals. In other words, the coolant discharge temperature Td is input at prescribed intervals (step 50), it is determined whether the coolant discharge temperature Td thus input is above a fixed temperature (step 52) and where determined that it is above the prescribed temperature, the degree of opening of regulator valve 11 is adjusted in accordance with the coolant discharge temperature Td (step 54) so that regulator valve 11 opens up more with rises in coolant discharge temperature Td (and a greater quantity of oil or liquid coolant is recovered via recovery path 10).
Thus oil 20a separated within accumulator 6, as shown in Figure 2, sinks to a lower level than liquid coolant 20b as it has a higher specific gravity than liquid coolant 20b, and when recovery path 10 is opened up using regulator valve 11, recovery takes place between internal heat exchanger 7 and compressor 2 via recovery path 10 starting with the liquid coolant. After oil 20a has been recovered from inside accumulator 6, liquid coolant 20b is recovered between internal heat exchanger 7 and compressor 2 via recovery path 10, mixed in with the gas coolant passing through internal heat exchanger 7 and recovered to compressor 2. For this reason the temperature of the low-pressure gas coolant which has passed through internal heat exchanger 7 rises due to heat exchange with the high-temperature high-pressure gas coolant, but is then cooled again due to mixing with oil 20a or liquid coolant 20b cooled within accumulator 6, thus enabling the inlet temperature of compressor 2 to be reduced.
To describe the above mechanism using the Mollier diagram in Figure 4, in conventional structures which do not have recovery path 10 the changes proceed as shown in the Mollier diagram as A1 > B1 > C > D > E > A1, but with this structure since low temperature oil 20a or liquid coolant 20b recovered via recovery path 10 is mixed with the gas coolant passing through internal heat exchanger 7, the enthalpy momentarily increased by internal heat exchanger 7 is reduced from A1 to A2. Thus while in this cooling cycle the presence of oil 10a or liquid coolant 10b recovered via recovery path 10 has almost no influence on the cooling effect, the enthalpy on the discharge side of the compressor is reduced from B1 to B2. As a result in the above structure it is possible to reduce the temperature of the coolant introduced to compressor 2, and even to reduce the temperature of the coolant discharged from compressor 2.
In fact, where coolant discharge temperature Td is high the oil from accumulator 6 is made to bypass internal heat exchanger 7 and is recovered between the internal heat exchanger and the compressor, so that when considering changes in coolant discharge temperature, the greater the quantity of oil recovered the more it is possible to lower the coolant discharge temperature, as shown in Figure 5. Furthermore, changes in the cooling performance at this time, as shown in Figure 6 have been shown to remain almost the same regardless of the quantity of oil recovered.
Thus with the above structure, it is possible to prevent damage to components due to rises in the discharge coolant temperature Td of the compressor, and because of reductions in the coolant discharge temperature of compressor 2, oil 20a and liquid coolant 20b in accumulator 6 can be recovered while being made to bypass internal heat exchanger 7, thus preventing increases in pressure loss caused by flows of oil or liquid coolant into internal heat exchanger 7. Further, the liquid flowing through recovery path 10 is oil or liquid coolant, enabling the diameter of the tubing which makes up recovery path 10 to be made smaller than in the case of tubing through which a gas coolant flows, and also enabling the diameter of regulator valve 11 provided in recovery path 10 to be made smaller. For this reason a reduction in the size, weight and cost of components is feasible.
In the above described structure, it is arranged such that oil 20a or liquid coolant 20b within accumulator 6 is recovered with recovery path 10 connected to the bottom of accumulator 6, but as a structure for the recovery of oil or liquid coolant within accumulator 6 not limited to the above structure, the tubing which forms recovery path 10 may be inserted within the accumulator, and the regulator valve provided for recovering the oil or liquid coolant may be positioned within this inserted portion.
Furthermore, internal heat exchanger 7 may be built into accumulator 6, and the regulator valve, which regulates the quantity recovered and the recovery path for oil or liquid coolant, may also be provided within accumulator 6. With this kind of structure, there is no need to provide new tubing external to accumulator 6, thus making it easier to realize a reduction in size, weight and cost for cooling cycle 1.
Furthermore, with the above structure, it is arranged that the quantity recovered is regulated where the coolant discharge temperature is above a prescribed value, but where it is expected that a high coolant discharge temperature will result from a high cycle load due to external temperature, internal cycle pressure, room temperature or the like, said regulator valve may be controlled to allow the quantity recovered to be regulated. In practical terms, the quantity recovered may be regulated where the room temperature, the external temperature or the air temperature at the inlet of radiator 3 exceeds a prescribed temperature, where the air temperature at the exit of the evaporator 5 or the pressure of the low-pressure line is above a prescribed value, or where the flow of air blown from the air-conditioning unit is above a prescribed level.

Claims

Cooling cycle (1) having a compressor (2) which raises the pressure of a coolant, a radiator (3) which cools the coolant compressed in said compressor, an expansion device (4) which reduces the pressure of the coolant cooled by said radiator, an evaporator (5) which evaporates the coolant whose pressure has been reduced by said expansion device, an accumulator (6) which in addition to separating out the gas and liquid in the coolant which has passed through said evaporator, separates out the oil in the coolant, and an internal heat exchanger (7) which exchanges heat between the low-pressure coolant conducted from said accumulator to said compressor and the high-pressure coolant conducted from said radiator to said expansion device, characterized in that a recovery path (10) is provided which bypasses said internal heat exchanger, enabling recovery of the liquid coolant or oil inside said accumulator between said internal heat exchanger and the compressor, and a regulator valve (11) is provided which enables regulation of the quantity of said liquid coolant or oil recovered via this recovery path (10).
Cooling cycle according to Claim 1 characterized in that it is provided with a coolant discharge temperature sensor (12) which detects the temperature of the coolant discharged from said compressor, and a control means which controls said regulator valve in accordance with the coolant discharge temperature detected by said coolant discharge temperature sensor.
Cooling cycle according to Claim 1 characterized in that it is provided with a control means which controls said regulator valve where it is expected that the discharge temperature will rise with a high cycle load due to the outside temperature, pressure within the cycle, room temperature or the like.
Cooling cycle according to Claim 1 characterized in that said internal heat exchanger (7) and said regulator valve (11) are built into said accumulator (6) .
Cooling cycle according to Claim 1 in which said cooling cycle is a supercritical vapour compression cooling cycle which uses carbon dioxide as the coolant.