JENSEN GERT PRANG (DK)
| WO1997020902A1 | 1997-06-12 | |||
| WO2004083752A1 | 2004-09-30 |
| US5430223A | 1995-07-04 | |||
| US20060065013A1 | 2006-03-30 | |||
| US20060075775A1 | 2006-04-13 | |||
| EP1514915A1 | 2005-03-16 |
CLAIMS
1. A refrigerant for use in a refrigeration system, the refrigerant comprising a mixed gas of at least three different hydrocarbons, including isobutane (C 4 H 10 ), ethene (C 2 H 4 ) and methane (CH 4 ), wherein the mixed gas comprises at least 70% by weight of isobutane (C 4 H 10 ).
2. A refrigerant according to claim 1, wherein one of the hydrocarbons has a boiling point at atmospheric pressure which is higher than or equal to -4O 0 C.
3. A refrigerant according to claim 1 or 2, wherein at least one of the hydrocarbons has a boiling point at atmospheric pressure which is lower than or equal to -100 0 C.
4. A refrigerant according to any of the preceding claims, wherein at least one of the hydrocarbons is in a vapour-liquid region at a temperature within the temperature interval from -45 0 C to 13O 0 C, and at a pressure within the pressure interval from 0.2 bar to 35 bar.
5. A refrigerant according to any of the preceding claims, wherein the mixed gas comprises between 70% and 75% by weight of isobutane (C 4 H 10 ).
6. A refrigerant according to any of the preceding claims, wherein the mixed gas comprises between 1% and 69% by weight of ethene (C 2 H 4 ).
7. A refrigerant according to any of the preceding claims, wherein the mixed gas comprises between 1% and 69% by weight of methane (CH 4 ).
8. A refrigeration system comprising:
- a compressor,
- a condenser,
- a heat exchanger,
- an expansion element, and
- an evaporator, wherein the compressor, the condenser, the heat exchanger, the expansion element and the evaporator are interconnected in a refrigerant path, and wherein the refrigeration system is adapted to have a refrigerant according to any of claims 1-7 filled into the refrigerant path.
9. A refrigeration system according to claim 8, wherein the refrigerant path is at least substantially hermetically closed.
10. A refrigeration system according to claim 8 or 9, wherein the refrigeration system is a freezer.
11. A refrigeration system according to claim 8 or 9, wherein the refrigeration system is a cooling device for a central processing unit (CPU). |
A REFRIGERANT AND A REFRIGERATION SYSTEM
FIELD OF THE INVENTION
The present invention relates to a refrigerant for use in a refrigeration system. More particularly, the present invention relates to a refrigerant which is more environment friendly than prior art refrigerants, and a refrigerant which is capable of providing very low refrigeration temperatures. Furthermore, the present invention relates to a refrigeration system in which a refrigerant according to the invention can be used.
BACKGROUND OF THE INVENTION
Conventional refrigeration systems comprise a refrigeration path in which a refrigerant is allowed to flow. In the refrigerant path a number of components are positioned, normally a compressor, a condenser, an expansion element and an evaporator. The refrigeration path is closed, i.e. the refrigerant circulates in the path. The compressor may be replaced by a rack of parallelly connected compressors. This is usually the case in refrigeration systems with many refrigeration sites, e.g. the kind of refrigeration system which is normally installed in supermarkets.
A refrigeration system as defined above normally functions in the following manner. Gaseous refrigerant enters the compressor where it is compressed. Subsequently the refrigerant enters the condenser where it at least partly condenses, i.e. at least part of the refrigerant is in a liquid state when it leaves the condenser. Next the refrigerant passes an expansion element, e.g. in the form of an expansion valve controlling the flow of refrigerant in the system, where refrigerant is expanded, i.e. the pressure of the refrigerant decreases. Then the refrigerant enters the evaporator where the liquid refrigerant evaporates. Since this is an energy consuming process, heat is drawn from the surroundings, and thereby a refrigerating effect is obtained at the position of the evaporator. Finally, the gaseous refrigerant once again enters the compressor.
In refrigeration systems as the one described above conventional refrigerants, such as R134a, R404A or R507, are used. A disadvantage of such refrigerants is that they can only provide refrigeration within a limited temperature interval. Accordingly, they are normally used in refrigeration systems for use in households or supermarkets, i.e. refrigerators adapted to maintain a refrigeration temperature of approximately 5 0 C or freezers adapted to maintain a refrigeration temperature of approximately -18 0 C.
For some applications a somewhat lower refrigeration temperature is desired. This is, e.g., the case in medical applications, such as storing of certain kinds of vaccines, serum or tissue samples. Such products normally have to be stored at temperatures below -79 0 C. Furthermore, refrigeration temperatures of this order of magnitude are sometimes desired in the food industry, e.g. in order to ensure that none of the stored products obtain a temperature above a critical temperature during transportation, even if the products are shifted from one transporting means to another.
In order to obtain a lower refrigeration temperature, various approaches have been used. One approach is the so-called cascade refrigeration system in which two or more independent refrigeration systems are used. The first refrigeration system cools the refrigerant of the next refrigeration system to an appropriate temperature, etc. By selecting the refrigerants in an appropriate manner, a sufficiently low refrigeration temperature is eventually obtained. This approach has the disadvantage that it is necessary to use two or more compressors, at least one for each step in the cascade, and the system is therefore very energy consuming.
Another approach is the so-called mixed gas refrigeration system in which the refrigerant used in the system is a mixture of various gases with different boiling points. In this approach it is utilised that when one of the gases undergoes a phase transition it either consumes energy from or delivers energy to the surroundings, depending on the kind of phase transition. Thus, when the gas having the highest boiling point evaporates the energy consumption during the evaporation is used for refrigerating the remaining gases, preferably until they start condensing. This may take place in a heat exchanger. In order to obtain a desired result a mixed gas refrigerant comprising two hydrocarbons and a hydrofluoride (HFC) has previously been used. A disadvantage of such mixed gas refrigerants is that the HFC gases are undesired in the environment, and the refrigerants are therefore not optimal from an environmental point of view.
SUMMARY OF THE INVENTION
It is, thus, an object of the invention to provide a refrigerant for providing low refrigeration temperatures, and which is more environment friendly than prior art refrigerants.
It is a further object of the invention to provide a refrigerant which is capable of providing very low refrigeration temperatures without the need for multiple compressors.
It is an even further object of the invention to provide a refrigeration system which is capable of providing very low refrigeration temperatures, and which is more environment friendly than prior art refrigeration systems.
According to a first aspect of the invention the above and other objects are fulfilled by providing a refrigerant for use in a refrigeration system, the refrigerant comprising a mixed gas of at least three different hydrocarbons, including isobutane (C 4 H 10 ), ethene (C 2 H 4 ) and methane (CH 4 ), wherein the mixed gas comprises at least 70% by weight of isobutane (C 4 H 10 ).
The inventors of the present invention have surprisingly found that a mixed gas comprising at least three different hydrocarbons can be used as a refrigerant capable of providing very low refrigeration temperatures in one refrigeration stage, i.e. without the need for cascade refrigeration systems. Thereby only one compressor is necessary, and energy is thereby conserved as compared to the prior art cascade refrigeration systems. Furthermore, since the desired refrigeration is obtained by means of the three or more hydrocarbons, the presence of a hydrofluoride in the mixed gas is not required. Accordingly, the refrigerant according to the invention is more environment friendly than the prior art mixed gas refrigerants.
Thus, the refrigerant according to the first aspect of the invention is capable of providing very low refrigeration temperatures in an environment friendly manner, partly because energy is conserved as compared to the prior art cascade systems, partly because hydrofluorides are avoided in the refrigerant. This is very advantageous.
The mixed gas may comprise further components, such as additional hydrocarbons, e.g. in the form of impurities in one or more of the hydrocarbons, or other kinds of gases or liquids.
The mixed gas comprises a mixture of isobutane (C 4 H 10 ), ethene (C 2 H 4 ) and methane (CH 4 ). The inventors of the present invention have found that this mixed gas is particularly suitable as a refrigerant for providing very low refrigeration temperatures without the need for a cascade refrigeration system. Since isobutane has a relatively high boiling point at atmospheric pressure (approximately -16 0 C), while ethene and methane have relatively low boiling points at atmospheric pressure (approximately -105 0 C for ethene and approximately - 18O 0 C for methane), evaporation of isobutane provides refrigeration for the ethene and the methane present in the mixed gas. Thereby the isobutane 'helps' the ethene and the methane in condensing. Furthermore, the boiling points of ethene and methane are sufficiently different to provide a similar effect for methane when ethene evaporates.
The mixed gas comprises at least 70% by weight of isobutane (C 4 H 10 ), such as between 70% and 85%, such as between 70% and 80%, such as between 70% and 75%. Thus, isobutane forms a major part of the mixed gas. Since isobutane provides refrigeration for the other hydrocarbons as described above, the amount of isobutane present in the mixed gas should be selected in such a manner that it is capable of providing the desired level of refrigeration.
By selecting a relatively large percentage of isobutane a relatively high level of refrigeration of the other hydrocarbons can be obtained, and this is very advantageous for some applications.
One of the hydrocarbons may have a boiling point at atmospheric pressure which is higher than or equal to -4O 0 C, such as higher than or equal to -25 0 C, such as higher than or equal to -16 0 C.
Alternatively or additionally, at least one of the hydrocarbons may have a boiling point at atmospheric pressure which is lower than or equal to -100 0 C, such as lower than or equal to -12O 0 C, such as lower than or equal to -15O 0 C. One of the hydrocarbons may have a boiling point within the temperature interval from -12O 0 C to -100 0 C, while another of the hydrocarbons has a boiling point which is lower than or equal to -15O 0 C. In this case the hydrocarbon with the higher boiling point may, when evaporating, be used for refrigerating the one with the lower boiling point.
In an advantageous embodiment of the invention, one of the hydrocarbons has a boiling point at atmospheric pressure which is higher than or equal to -4O 0 C, and two of the hydrocarbons have boiling points at atmospheric pressure which are lower than or equal to - 100 0 C, i.e. one of the hydrocarbons has a relatively high boiling point and two of the hydrocarbons have a relatively low boiling point. Thereby the hydrocarbon with the high boiling point, when evaporating, provides refrigeration for the other two hydrocarbons as described above.
Alternatively or additionally, at least one of the hydrocarbons may be in a vapour-liquid region at a temperature within the temperature interval from -45 0 C to 13O 0 C, and at a pressure within the pressure interval from 0.2 bar to 35 bar. This has the advantage that at least one of the hydrocarbons is in a vapour-liquid region under normal operating conditions. Thereby this hydrocarbon is capable of providing refrigeration for other hydrocarbons in the manner described above.
The mixed gas may comprise between 1% and 69% by weight of ethene (C 2 H 4 ), such as between 1% and 50%, such as between 5% and 40%, such as between 15% and 30%, such as between 20% and 25%.
Alternatively or additionally, the mixed gas may comprise between 1% and 69% by weight of methane (CH 4 ), such as between 1% and 50%, such as between 2% and 30%, such as between 3% and 20%, such as between 5% and 10%.
According to a preferred embodiment the mixed gas comprises approximately 71% by weight of isobutane, approximately 24% by weight of ethene and approximately 5% by weight of methane. Using such a mixed gas it is possible to reach refrigeration temperatures which are below -79 0 C, such as below -85 0 C, and even lower. As mentioned above, these low refrigeration temperatures are reached without the need for a cascade refrigeration system and without adding a hydrofluoride to the refrigerant.
According to a second aspect of the invention the above and other objects are fulfilled by providing a refrigeration system comprising:
- a compressor,
- a condenser,
- a heat exchanger,
- an expansion element, and
- an evaporator,
wherein the compressor, the condenser, the heat exchanger, the expansion element and the evaporator are interconnected in a refrigerant path, and wherein the refrigeration system is adapted to have a refrigerant according to the first aspect filled into the refrigerant path.
It should be noted that a skilled person would readily recognise that any feature described in combination with the first aspect of the invention could equally be combined with the second aspect of the invention, and vice versa.
The second aspect of the invention provides a refrigeration system which is adapted to apply the refrigerant according to the first aspect of the invention. Accordingly, the refrigeration system according to the second aspect of the invention is adapted to provide low refrigeration temperatures at low energy consumption and without imposing special requirements on the components of the refrigeration system in terms of durability, strength, etc.
The functions of the compressor, the condenser, the expansion element and the evaporator have been described above. The refrigeration system further comprises a heat exchanger. The heat exchanger preferably functions in the following manner. The heat exchanger is
passed by refrigerant running in opposite directions, and heat is thereby exchanged between refrigerant running in one direction and refrigerant running in the opposite direction. This will be described in further detail below with reference to Fig. 1.
The refrigerant path forms a closed circuit as described previously. Preferably, the refrigerant path is at least substantially hermetically closed.
The refrigeration system may be a freezer. According to this embodiment the evaporator provides refrigeration to a refrigerated volume in which products of a desired kind may be stored. Since the provided refrigeration temperature is very low as described above, the storage temperature inside the refrigerated volume will be correspondingly low. Thus, the products are stored at a very low temperature. This is, e.g., suitable for storing medical products, such as certain kinds of vaccines, serum or tissue samples. At the same time the freezer functions in a manner which is very similar to the function of an ordinary household freezer, and it is thereby very easy and simple to install and drive.
Alternatively, the refrigeration system may be a cooling device for a central processing unit (CPU). A CPU positioned in a computer device will often need cooling. Such cooling may be provided by means of a refrigeration system according to the second aspect of the invention. In this case the evaporator should be positioned in the proximity, preferably in thermal contact with a heat generating part of the CPU.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in further detail with reference to the accompanying drawings in which
Fig. 1 is a schematic drawing of a refrigeration system according to an embodiment of the invention, and
Fig. 2 is a phase diagram illustrating the cycle of the refrigerant present in the refrigeration system of Fig. 1.
DETAILED DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic drawing of a refrigeration system 10 with a compressor 11, a first condenser 12, a filter drier 13, a second condenser 14, a heat exchanger 15, an expansion element 16, an evaporator 17, and an accumulator 18 connected in such a manner that a
closed circuit is formed. Inside the closed circuit a refrigerant according to the first aspect of the invention is allowed to flow. The function of the refrigeration system 10 will now be described with reference to the situation where a refrigerant comprising a mixed gas of isobutane (C 4 H 10 ), ethene (C 2 H 4 ) and methane (CH 4 ) is used.
Gaseous refrigerant enters the compressor 11 where it is compressed. The compressed refrigerant then enters the first condenser 12 in which the refrigerant at least partly condenses. Subsequently the refrigerant enters the filter drier 13, where moisture present in the system is absorbed and impurities present in the system are collected. Then the refrigerant enters the second condenser 14 where the refrigerant undergoes further condensation.
Upon leaving the second condenser 14 the refrigerant enters the heat exchanger 15 where heat is exchanged with refrigerant flowing in the opposite direction in a separate tube. This will be described further below. From the heat exchanger 15 the refrigerant passes the expansion element 16 where the pressure of the refrigerant decreases, and the expanded refrigerant continues into the evaporator 17 where the refrigerant evaporates, thereby providing refrigeration, e.g. to a refrigerated volume. The evaporated refrigerant then enters the heat exchanger 15. Next, the refrigerant enters the accumulator 18. The accumulator functions as a 'refrigerant buffer' in the sense that it is capable of compensating for variations in the mass flow of the refrigerant as a consequence of variations in refrigeration load. Finally, the refrigerant once again enters the compressor 11.
In the heat exchanger 15 the following takes place. In the refrigerant entering the heat exchanger 15 from the second condenser 14 the isobutane is undergoing a phase transition from a liquid phase to a gaseous phase, i.e. the isobutane of the refrigerant consumes energy from the surroundings, thereby providing refrigeration for the ethene and the methane of the refrigerant. At a certain point, the ethene will reach its boiling point, and it will thereby start to undergo a phase transition from a gaseous to a liquid phase, i.e. it will start to condensate. As the refrigerant undergoes further refrigeration, the methane will similarly start condensing. The refrigerant flowing in the opposite direction, i.e. the refrigerant entering the heat exchanger 15 from the evaporator 17 typically has a lower temperature than the refrigerant flowing in the direction from the second condenser 14 towards the expansion element 16. Since heat is exchanged between the two flows of refrigerant, this has the consequence that the refrigerant flowing from the evaporator 17 towards the accumulator 18 'helps' in cooling the ethene and the methane flowing in the opposite direction. Thus, the cooler refrigerant 'helps' the warmer refrigerant in reaching the condensations points of the ethene and the methane.
Fig. 2 is a phase diagram illustrating the cycle of the refrigerant present in the refrigeration system 10 of Fig. 1. Reference numerals 1-5 indicate specific points in the refrigeration system. These points are also marked, using corresponding reference numerals, in Fig. 1. From point 1 to point 2 the refrigerant passes the heat exchanger 15 in the direction from the second condenser 14 towards the expansion element 16. It is clear from Fig. 2 that this has the consequence that the temperature of the refrigerant decreases and the energy (enthalpy) decreases. When the refrigerant has completely entered the liquid phase, the curve defining the boundary between liquid phase and two phase is followed until point 2 is reached.
From point 2 to point 3 the refrigerant passes the expansion element 16. It is clear from Fig. 2 that this has the consequence that the temperature decreases (due to the pressure decreasing), while the energy is maintained at a constant level. Furthermore, the two phase region is once again entered.
From point 3 to point 4 the refrigerant passes the evaporator 17, i.e. the refrigerant undergoes evaporation. It is clear from Fig. 2 that this has the consequence that the temperature is maintained at a constant level, due to the phase transition taking place. The energy is increased, i.e. energy is consumed from the surrounding, and thereby refrigeration is provided.
From point 4 to point 5 the refrigerant passes the heat exchanger 15 in the direction from the evaporator 17 towards the accumulator 18. It is clear from Fig. 2 that this has the consequence that temperature as well as the energy is increased.
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