A working fluid suitable for ultra-high temperature heat pump system, preparation method and application thereof

Abstract

The present invention relates to the field of heat exchange materials for heat pumps, and discloses a working fluid suitable for ultra-high temperature heat pump systems, a preparation method thereof, and an application thereof. The working fluid is a binary mixed working fluid composed of 1,2-propylene oxide and n-pentane; in the working fluid, the mass proportion of 1,2-propylene oxide is 56% to 58%, the mass proportion of n-pentane is 42% to 44%, and the sum of the mass proportions of 1,2-propylene oxide and n-pentane is 100%. The working fluid can meet the heating temperature requirements of ultra-high temperature heat pumps above 140°C without further compressing and heating low-parameter steam with a water vapor compressor, and also has the advantages of small temperature glide, high heating capacity per unit mass and energy efficiency ratio, and environmental protection, and can achieve low inlet superheat and low exhaust temperature at the same time within a wide range of compressor isentropic efficiency.

Description

Technical Field

[0001] The present invention relates to the field of heat exchange materials for heat pumps, and in particular to a working fluid suitable for an ultra-high temperature heat pump system, and a preparation method and application thereof. Background Art

[0002] At present, industrial heat demand is mainly met by fossil energy boilers and electric boilers, but both have problems such as high carbon emissions or low energy efficiency. Using heat pump devices to recover a large amount of low-grade waste heat generated in the industrial process and generate high-temperature hot water or steam can not only meet the heat demand, but also reduce the use of electricity and carbon emissions. The working fluid is one of the key parts of the heat pump. During the operation of the heat pump, the working fluid circulates between the heat exchanger and the compressor, and realizes heat exchange by changing its own phase state, thereby realizing heat transfer.

[0003] Ultra-high temperature heat pump refers to a heat pump with a heating temperature higher than 140℃, which is commonly used in industry to recover waste heat and generate high-temperature saturated steam. At present, pentafluoropropane (R245fa) is usually used as a heat pump working fluid to recover industrial waste heat below 80℃ and prepare high-temperature saturated steam or hot water below 130℃. However, when preparing high-temperature saturated steam above 140℃, the R245fa heat pump is limited by a relatively low critical temperature, and there are problems such as small heating capacity and low energy efficiency ratio (COP); when the heating temperature is higher than 150℃, R245fa is not applicable. In order to meet the demand for heat pumps with heating temperatures above 140℃, the commonly used solution is: first use R245fa heat pump to prepare saturated steam below 130℃, and then use a water vapor compressor to further compress and heat the low-parameter steam. However, this method also brings many problems: on the one hand, it is necessary to purchase an additional water vapor compressor, which greatly increases the cost of waste heat recovery and prolongs the cost recovery cycle; on the other hand, the water vapor compressor has technical problems such as low isentropic efficiency and excessively high exhaust temperature. Technical difficulties such as high equipment cost and low energy efficiency have limited the development of existing 140℃ ultra-high temperature heat pump technology. The key to achieving 140℃ ultra-high temperature heat pump is to develop high-temperature environmentally friendly working fluids with higher critical parameters and better thermodynamic properties. Summary of the invention

[0004] In order to solve the above technical problem, that is, conventional heat pump working fluids are difficult to meet the heating demand of ultra-high temperature heat pumps, the present invention provides a working fluid suitable for ultra-high temperature heat pump systems, a preparation method and application thereof. The working fluid can meet the heating temperature demand of ultra-high temperature heat pumps above 140°C without using a water vapor compressor to further compress and heat low-parameter steam, and also has the advantages of small temperature glide, high heating per unit mass and energy efficiency ratio, and environmental protection, and can achieve low inlet superheat and low exhaust temperature within a wide range of compressor isentropic efficiency.

[0005] The specific technical scheme of the present invention is:

[0006] In a first aspect, the present invention provides a working fluid suitable for an ultra-high temperature heat pump system, wherein the working fluid is a binary mixed working fluid composed of 1,2-propylene oxide and n-pentane; in the working fluid, the mass proportion of 1,2-propylene oxide is 56%~58%, the mass proportion of n-pentane is 42%~44%, and the sum of the mass proportions of 1,2-propylene oxide and n-pentane is 100%.

[0007] The present invention finds that when 1,2-propylene oxide and n-pentane are compounded in a specific ratio (wherein the mass proportion of 1,2-propylene oxide is 56% to 58% and the mass proportion of n-pentane is 42% to 44%) and used as a heat pump working fluid, the following effects can be achieved:

[0008] (1) High critical parameters:

[0009] The critical temperature of the heat pump working fluid of the present invention can reach above 200°C, which can be used to recover waste heat sources of not less than 50°C, and can generate saturated water vapor above 140°C without the aid of a water vapor compressor, thus meeting the heating temperature requirement of the ultra-high temperature heat pump above 140°C.

[0010] (2) Small temperature glide:

[0011] Unlike conventional low-temperature heat pumps such as air source water heaters, the product of ultra-high temperature heat pumps is usually water vapor, and the production of water vapor must go through a constant temperature and constant pressure phase change process. If the mixed working fluid is a non-azeotropic working fluid, it means that its slip temperature (slip temperature = dew point temperature - bubble point temperature) is too large, which will cause a large temperature difference between the isobaric condensation process of the mixed working fluid and the evaporation process of water vapor, resulting in unnecessary exergy loss and reduced energy quality. In addition, non-azeotropic working fluids often have component migration during operation, and the circulating concentration of the working fluid is inconsistent with the initial filling concentration, resulting in unstable operation and performance degradation. Therefore, a smaller slip temperature is of great significance for ultra-high temperature heat pumps.

[0012] The temperature glide of the heat pump working fluid of the present invention is less than 0.05°C, which is a near-azeotropic mixed working fluid. Compared with non-azeotropic mixed working fluids, on the one hand, it is not easy to cause component migration, the operation is stable, and the replenishment is convenient; on the other hand, it has a higher temperature match with the constant temperature phase change steam production process, and is more suitable for producing high-temperature steam.

[0013] (3) High compressor friendliness:

[0014] The compressor inlet needs to maintain a certain degree of superheat (compressor inlet superheat = compressor inlet temperature - working fluid evaporation temperature) to ensure that the organic working fluid will not condense into liquid during the compression process, causing irreversible damage to the compressor. If the superheat is too high, on the one hand, a large area in the evaporator is used for heat exchange of superheated gas, and the heat exchange efficiency is low; on the other hand, it may reduce the evaporation temperature and affect the system energy efficiency.

[0015] If the compressor exhaust superheat (compressor exhaust superheat = compressor exhaust temperature - working fluid condensation temperature) is too high, it means that the compressor exhaust temperature is too high, which will bring a variety of potential operating risks: ① The viscosity of the lubricating oil decreases and ages and deteriorates, and even causes the lubrication system to fail; ② The risk of jamming and cylinder damage caused by excessive thermal expansion of the compressor moving parts; ③ Accelerated wear and aging of the compressor.

[0016] The compression process of the heat pump working fluid of the present invention is close to an isentropic process. Even when the isentropic efficiency of the compressor is low, it can simultaneously have the following two characteristics: 1. only a small superheat is required at the compressor inlet to ensure that no liquid hammer occurs during the compression process; and 2. the exhaust gas temperature at the compressor outlet is low.

[0017] (4) Small amount of working fluid used:

[0018] The heat pump working fluid of the present invention has a higher heating capacity per unit mass. Under the condition of equal heating capacity, the required amount of the heat pump working fluid of the present invention is 56% or less of the amount of R245fa.

[0019] (5) High efficiency and energy saving:

[0020] The energy efficiency ratio (COP) of the heat pump working fluid of the present invention is significantly higher than that of R245fa - when the heat power of the heat source remains unchanged, it can save more than 38% of electricity consumption compared with R245fa.

[0021] (6) Strong environmental protection characteristics:

[0022] The ozone depletion potential (ODP) of the heat pump working fluid of the present invention is 0, and the global warming potential (GWP) is less than 4, which is much smaller than the commonly used R245fa, and has good environmental protection.

[0023] Preferably, in the working fluid, the mass proportion of 1,2-propylene oxide is 56%, and the mass proportion of n-pentane is 44%.

[0024] When the mass proportions of 1,2-propylene oxide and n-pentane are set to 56% and 44% respectively, the compressor exhaust superheat can be further reduced, so that the compressor exhaust temperature reaches a lower level, which helps to better slow down the viscosity loss and aging of the lubricating oil as well as the wear and aging of the compressor.

[0025] Preferably, in the working fluid, the mass proportion of 1,2-propylene oxide is 58%, and the mass proportion of n-pentane is 42%.

[0026] When the mass proportions of 1,2-propylene oxide and n-pentane are set to 58% and 42% respectively, the heating capacity per unit mass of the working fluid can be further improved, which is beneficial to saving more working fluid when the heating capacity is the same.

[0027] Preferably, in the working fluid, the mass proportion of 1,2-propylene oxide is 57%, and the mass proportion of n-pentane is 43%.

[0028] When the mass proportions of 1,2-propylene oxide and n-pentane are set to 57% and 43% respectively, moderate compressor exhaust superheat and unit mass heating capacity can be achieved at the same time.

[0029] Preferably, the critical temperature of the working fluid is higher than 200° C., and the critical pressure is 44-45 bar.

[0030] Furthermore, the critical temperature of the working fluid is 208-209°C.

[0031] Preferably, the temperature glide of the working fluid at 25°C and 0.1 MPa is not higher than 0.05°C.

[0032] Preferably, the bubble point temperature of the working fluid is 35-36°C, and the dew point temperature is 35-36°C.

[0033] Preferably, the working fluid has an ozone depletion potential of 0 and a greenhouse effect potential of less than 4.

[0034] In a second aspect, the present invention provides a method for preparing the working fluid, comprising the following steps: physically mixing 1,2-propylene oxide and n-pentane in a liquid phase to obtain the working fluid.

[0035] In a third aspect, the present invention provides an application of the working fluid in an ultra-high temperature heat pump system, wherein the heating temperature of the ultra-high temperature heat pump system is higher than 140°C.

[0036] Preferably, the compressor inlet superheat of the ultra-high temperature heat pump system is not lower than 5°C and not higher than 10°C, and the compressor exhaust superheat is not higher than 15°C.

[0037] Preferably, in the ultra-high temperature heat pump system, the isentropic efficiency of the compressor is 60% to 80%.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] (1) The critical temperature of the working fluid provided by the present invention is higher than 200°C. Without the aid of a water vapor compressor, saturated water vapor above 140°C can be directly generated, which can meet the heating temperature requirement of an ultra-high temperature heat pump system above 140°C.

[0040] (2) The working fluid provided by the present invention has near-azeotropic characteristics and small temperature glide, which is conducive to achieving higher operating stability, and has a higher temperature matching degree with the constant temperature phase change steam production process, and is more suitable for recovering low-temperature waste heat sources to produce high-temperature steam.

[0041] (3) The compression process of the working fluid provided by the present invention is close to an isentropic process, and can achieve a lower inlet superheat and a lower exhaust temperature within a wider range of compressor isentropic efficiency.

[0042] (4) The working fluid provided by the present invention has a high energy efficiency ratio and heating capacity per unit mass, which is beneficial to reducing electricity consumption and can use less working fluid at the same heating capacity.

[0043] (5) The working fluid provided by the present invention has an ODP of 0 and a GWP of < 4, and has good environmental protection properties. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further clearly and completely described below in conjunction with embodiments.

[0045] A working fluid suitable for an ultra-high temperature heat pump system, the working fluid being a binary mixed working fluid composed of 1,2-propylene oxide and n-pentane; in the working fluid, the mass proportion of 1,2-propylene oxide is 56% to 58%, the mass proportion of n-pentane is 42% to 44%, and the sum of the mass proportions of 1,2-propylene oxide and n-pentane is 100%. The working fluid of the above formula can achieve a higher critical temperature, can achieve heating above 140°C, and has a higher energy efficiency ratio and heating capacity per unit mass; at the same time, the working fluid also has a near-azeotropic characteristic, is suitable for producing high-temperature steam and has high operating stability, and can achieve lower inlet superheat and lower exhaust temperature within a wider range of compressor isentropic efficiency; in addition, the working fluid also has strong environmental protection characteristics.

[0046] As a specific implementation, in the working fluid, the mass proportion of 1,2-propylene oxide is 56%, and the mass proportion of n-pentane is 44%. In this specific implementation, the compressor exhaust superheat can be further reduced.

[0047] As a specific implementation, in the working fluid, the mass proportion of 1,2-propylene oxide is 58%, and the mass proportion of n-pentane is 42%. In this specific implementation, the heating capacity per unit mass of the working fluid can be further increased.

[0048] As a specific implementation, in the working fluid, the mass proportion of 1,2-propylene oxide is 57%, and the mass proportion of n-pentane is 43%. Under this specific implementation, a moderate compressor exhaust superheat and unit mass heating capacity can be obtained.

[0049] As a specific implementation, the critical temperature of the working fluid is higher than 200°C, the slip temperature at 25°C and 0.1 MPa is not higher than 0.05°C, the critical pressure is 44~45 bar, the bubble point temperature is 35~36°C, and the dew point temperature is 35~36°C.

[0050] As a specific implementation manner, the ozone depletion potential of the working fluid is 0, and the greenhouse effect potential is less than 4.

[0051] A method for preparing the above working fluid comprises the following steps: physically mixing 1,2-propylene oxide and n-pentane in a liquid phase to obtain the working fluid.

[0052] The above working fluid is used in an ultra-high temperature heat pump system, wherein the heating temperature of the ultra-high temperature heat pump system is higher than 140°C.

[0053] As a specific implementation, in the above application, the heat source of the ultra-high temperature heat pump system is normal pressure hot water, and the inlet temperature is not less than 80°C.

[0054] As a specific implementation, in the above application, the evaporation temperature of the working fluid of the ultra-high temperature heat pump system is not higher than 65°C, and the superheat of the compressor inlet is not lower than 5°C.

[0055] As a specific implementation, in the above application, in the ultra-high temperature heat pump system, the isentropic efficiency of the compressor is 60% to 80%.

[0056] As a specific implementation, in the above application, in the ultra-high temperature heat pump system, the compressor exhaust superheat is not higher than 15°C.

[0057] The present invention is described below by specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention, and the attached claims and any equivalents thereof are the protection scope of the present invention.

[0058] Unless otherwise defined, all technical terms and scientific terms used in the present invention have the same meanings as those commonly understood by ordinary technicians in the field to which the present disclosure belongs. Unless otherwise specified, the raw materials and equipment used in the present invention are conventional raw materials and equipment in the field and can be obtained from conventional commercial channels; unless otherwise specified, the methods used in the present invention are conventional methods in the field.

[0059] Example 1: Heat pump fluid formulation and preparation method

[0060] The heat pump working fluid of this embodiment is a binary mixed working fluid, which is composed of 1,2-propylene oxide and n-pentane, and the mass percentages of the two are 56% and 44% respectively.

[0061] The heat pump working fluid of this embodiment is prepared by the following steps: in a liquid state, 1,2-propylene oxide and n-pentane are fully physically mixed in a mass ratio of 56:44 to obtain a heat pump working fluid.

[0062] Example 2: Heat pump fluid formulation and preparation method

[0063] The heat pump working fluid of this embodiment is a binary mixed working fluid, which is composed of 1,2-propylene oxide and n-pentane, and the mass percentages of the two are 57% and 43% respectively.

[0064] The heat pump working fluid of this embodiment is prepared by the following steps: in a liquid state, 1,2-propylene oxide and n-pentane are fully physically mixed in a mass ratio of 57:43 to obtain a heat pump working fluid.

[0065] Example 3: Formula and preparation method of heat pump working fluid

[0066] The heat pump working fluid of this embodiment is a binary mixed working fluid, which is composed of 1,2-propylene oxide and n-pentane, and the mass percentages of the two are 58% and 42% respectively.

[0067] The heat pump working fluid of this embodiment is prepared by the following steps: in a liquid state, 1,2-propylene oxide and n-pentane are fully physically mixed in a mass ratio of 58:42 to obtain a heat pump working fluid.

[0068] Comparative Example 1: Heat Pump Fluid Formula

[0069] The heat pump working fluid of this comparative example is a single-component working fluid, which is completely composed of pentafluoropropane (R245fa).

[0070] Comparative Example 2: Heat Pump Fluid Formula

[0071] The heat pump working fluid of this comparative example is a single-component working fluid, which is completely composed of 1,2-propylene oxide.

[0072] Comparative Example 3: Heat Pump Fluid Formula

[0073] The heat pump working fluid of this comparative example is a single-component working fluid, which is completely composed of n-pentane.

[0074] Comparative Example 4: Formula and preparation method of heat pump working fluid

[0075] The heat pump working fluid of this comparative example is a binary mixed working fluid, which is composed of 1,2-propylene oxide and n-pentane, and the mass percentages of the two are 80% and 20% respectively.

[0076] The heat pump working fluid of this comparative example is prepared by the following steps: in a liquid state, 1,2-propylene oxide and n-pentane are fully physically mixed in a mass ratio of 4:1 to obtain a heat pump working fluid.

[0077] Comparative Example 5: Formula and preparation method of heat pump working fluid

[0078] The heat pump working fluid of this comparative example is a binary mixed working fluid, which is composed of 1,2-propylene oxide and n-pentane, and the mass percentages of the two are 20% and 80% respectively.

[0079] The heat pump working fluid of this comparative example is prepared by the following steps: in a liquid state, 1,2-propylene oxide and n-pentane are fully physically mixed in a mass ratio of 1:4 to obtain a heat pump working fluid.

[0080] Test Example 1: Physical properties of binary mixed fluids and single component fluids

[0081] The physical properties of the heat pump working fluids of Comparative Examples 1 to 3 and Examples 1 to 3 are shown in Table 1 and Table 2, respectively.

[0082] Table 1 Physical properties of single component working fluid

[0083]

[0084] Table 2 Physical properties of single component working fluid

[0085]

[0086] According to the data recorded in Table 1 and Table 2, the following conclusions can be drawn:

[0087] (1) The ODP of the heat pump working fluids in Examples 1 to 3 is 0, and the GWP is less than 4 (significantly lower than the traditional R245fa), indicating that they have strong environmental protection characteristics.

[0088] (2) The critical temperatures of the heat pump working fluids in Examples 1 to 3 are all over 200°C, and thus can meet heating demands above 140°C.

[0089] (3) The slip temperature of the heat pump working fluids in Examples 1 to 3 is no higher than 0.05°C, and thus they are near-azeotropic working fluids, suitable for producing ultra-high temperature steam above 140°C, and have high operating stability and are not prone to component migration during the circulation process.

[0090] Test Example 2: Application Performance of Working Fluid in Heat Pump

[0091] In order to further illustrate the significant advantages of the heat pump working fluid provided by the present invention in the scenario of recovering industrial waste heat and generating ultra-high temperature steam, the working fluids of Examples 1 to 3 and Comparative Examples 1 to 5 are respectively applied to heat pumps, and according to the common industrial waste heat conditions, uniform operating conditions are set for each embodiment and comparative example, as follows:

[0092] (1) The heat source is hot water at normal pressure, with an inlet temperature of 80°C and an outlet temperature of 70°C;

[0093] (2) The maximum evaporation temperature of the working fluid is 65°C, and the compressor inlet superheat (compressor inlet superheat = compressor inlet temperature - working fluid evaporation temperature) is at least 5°C to ensure that no liquid hammer occurs during the compression process;

[0094] (3) Ignore the pressure loss in the heat exchanger;

[0095] (4) The condensing temperature is 145°C, and the subcooling degree (subcooling degree = condenser outlet temperature - condensing temperature) is 5°C, which can meet the heating demand of 140°C.

[0096] Considering that the isentropic efficiency of the current high-temperature heat pump compressor is generally 60% to 80%, it is adopted as the isentropic efficiency range of the compressor. Taking two extreme values ​​of isentropic efficiency, the heat pump performance parameters of each embodiment and comparative example are obtained as shown in Table 3 and Table 4 respectively.

[0097] Table 3 Heat pump performance parameters when compressor isentropic efficiency = 60%

[0098]

[0099] Table 4 Heat pump performance parameters when compressor isentropic efficiency = 80%

[0100]

[0101] According to the data recorded in Table 3 and Table 4, the following conclusions can be drawn:

[0102] (1) When the heat pump working fluids of Examples 1 to 3 are used, the evaporation pressure and condensation pressure of the heat pump are much lower than those of Comparative Example 1 (i.e., the R245fa working fluid commonly used in industrial high-temperature heat pumps), and the pressure resistance requirements for the heat exchanger material are lower, and it is less likely to leak.

[0103] (2) When the heat pump working fluids of Examples 1 to 3 are used, the heating capacity per unit mass of the heat pump is increased by at least 78% compared with that of Comparative Example 1 (R245fa), which means that more working fluid can be saved when the heating capacity is the same.

[0104] (3) When the heat pump working fluids of Examples 1 to 3 are used, the COP (energy efficiency ratio) of the heat pump can reach 2.65 or above when the compressor isentropic efficiency = 60%, and can reach 3.21 or above when the compressor isentropic efficiency = 80%, both of which are higher than that of Comparative Example 1 (R245fa) - when the compressor isentropic efficiency is low (= 60%), the same heating capacity can save at least 38.8% of the electricity consumption; when the compressor isentropic efficiency is high (= 80%), at least 39.4% of the electricity consumption can be saved.

[0105] (4) The compressor inlet needs to maintain a certain degree of superheat to ensure that the organic working fluid will not condense into liquid during the compression process, causing irreversible damage to the compressor. If the superheat is too high, on the one hand, it means that a large area in the evaporator is used for heat exchange of superheated gas, and the heat exchange efficiency is low; on the other hand, it may reduce the evaporation temperature and affect the energy efficiency of the system, such as Comparative Example 3 (n-pentane) and Comparative Example 5 (20% 1,2-propylene oxide + 80% n-pentane) when the compressor isentropic efficiency = 80%. In engineering applications, a compressor inlet superheat of about 5°C is usually adopted. Within a wider range of compressor isentropic efficiency (60%~80%), when the heat pump working fluids of Examples 1 to 3 are used, it can be guaranteed that when the compressor inlet superheat is only 5°C, no liquid hammer occurs during the compression process, which is equivalent to Comparative Example 1 (R245fa).

[0106] (5) If the compressor exhaust superheat (compressor exhaust superheat = compressor exhaust temperature - condensing temperature) is too high, it means that the compressor exhaust temperature is too high, which will bring a variety of potential operating risks: ① The viscosity of the lubricating oil decreases and ages, and even causes the lubrication system to fail; ② The risk of jamming and cylinder damage caused by excessive thermal expansion of the compressor moving parts; ③ Accelerated wear and aging of the compressor. When the heat pump working fluids of Examples 1 to 3 are used, the compressor exhaust superheat is less than 15°C, which is close to Comparative Example 1 (R245fa), and the above potential operating risks can be avoided.

[0107] (6) When the heat pump working fluids of Examples 1 to 3 are used, the two compressor temperature indicators of "the compressor inlet superheat does not exceed 5°C to meet the requirement of no liquid hammer during compression" and "the compressor exhaust superheat does not exceed 15°C" can be achieved simultaneously within a relatively wide compressor isentropic efficiency range (60% to 80%), and the compressor has strong compressor adaptability. However, 1,2-propylene oxide single substance (Comparative Example 2), n-pentane single substance (Comparative Example 3), or other ratios of 1,2-propylene oxide and n-pentane binary mixture working fluids (Comparative Examples 4 and 5) cannot simultaneously meet these compressor temperature indicators within the isentropic efficiency range.

[0108] (7) In Examples 1 to 3: the use of the heat pump working fluid of Example 3 (58% 1,2-propylene oxide + 42% n-pentane) can achieve a higher heating capacity per unit mass; the use of the heat pump working fluid of Example 1 (56% 1,2-propylene oxide + 44% n-pentane) can achieve a lower compressor exhaust superheat.

[0109] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. Use of a composition as a working fluid in an ultra-high temperature heat pump system, characterized in that: The composition is a binary mixed working fluid consisting of 1,2-propylene oxide and n-pentane; in the composition, the mass proportion of 1,2-propylene oxide is 56% to 58%, the mass proportion of n-pentane is 42% to 44%, and the sum of the mass proportions of 1,2-propylene oxide and n-pentane is 100%.

2. The use according to claim 1, characterized in that: In the working fluid, the mass proportion of 1,2-propylene oxide is 56%, and the mass proportion of n-pentane is 44%.

3. The use according to claim 1, characterized in that: In the working fluid, the mass proportion of 1,2-propylene oxide is 58%, and the mass proportion of n-pentane is 42%.

4. The use according to claim 1, characterized in that: In the working fluid, the mass proportion of 1,2-propylene oxide is 57%, and the mass proportion of n-pentane is 43%.

5. The use according to any one of claims 1 to 4, characterized in that: The critical temperature of the working fluid is higher than 200° C., and the critical pressure is 44-45 bar.

6. The use according to any one of claims 1 to 4, characterized in that: The temperature glide of the working fluid at 25°C and 0.1 MPa is no higher than 0.05°C.

7. The use according to any one of claims 1 to 4, characterized in that: The ozone depletion potential of the working fluid is 0, and the greenhouse effect potential is less than 4.

8. The use according to claim 1, characterized in that: The method for preparing the working fluid of the ultra-high temperature heat pump system comprises the following steps: physically mixing 1,2-propylene oxide and n-pentane in a liquid phase to obtain the working fluid.

9. The use according to claim 1, characterized in that: The heating temperature of the ultra-high temperature heat pump system is higher than 140°C.

10. The use according to claim 1, characterized in that: In the ultra-high temperature heat pump system, the isentropic efficiency of the compressor is 60% to 80%.

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