Low-pressure efficient refrigeration method

Abstract

The invention discloses a low-pressure efficient refrigeration method, and relates to the technical field of pressure card refrigeration, and the method is suitable for materials which are sequentially subjected to phase change processes of ordered solid phase (SO), disordered solid phase (SD) and liquid phase (L) along with temperature rise, namely materials with dual phase changes at different temperatures. The method comprises the following steps: firstly, determining the capability of superposing SO-SD phase change and SD-L phase change into a phase change through the processes of boosting and reducing pressure, then determining the solid-liquid phase line temperature, and finally, carrying out boosting and reducing pressure experiments in a certain interval range of the solid-liquid phase line temperature to verify the adiabatic temperature change of the material. Therefore, the low-pressure efficient refrigeration material with 6K adiabatic temperature change under 40MPa and 28K adiabatic temperature change under 100MPa is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of compression card refrigeration, in particular to a low-pressure and high-efficiency refrigeration method. Background Art

[0002] In today's society, with the increasing development of the economy, refrigeration technology is increasingly used in industrial fields such as food, medicine, air conditioning and refrigeration, as well as in daily life. The energy consumption of the refrigeration industry accounts for more than 15% of the total social energy consumption. The most widely used vapor compression refrigeration currently can only achieve an efficiency of 25% using the Carnot cycle, and the gas refrigerant used in vapor compression will destroy the atmospheric ozone layer and cause the greenhouse effect. Innovative and environmentally friendly refrigeration technology is an urgent problem that needs to be solved all over the world. Solid-state refrigeration technology has the advantages of being green, environmentally friendly, stable and reliable, and has received widespread attention in recent years. According to the different external fields (magnetic field, electric field, uniaxial stress, hydrostatic pressure), it can be divided into magnetocaloric effect, electrocaloric effect, elastic caloric effect and pressure caloric effect. With the research boom of solid-state refrigeration technology, many new materials that can achieve refrigeration are constantly emerging. For example, magnetic materials LaFeSi alloys with magnetocaloric effect, elastic card materials Ni-Ti-based and Ni-Ti-Mn-based shape memory alloys with elastic caloric effect, polar electrolyte materials PZT (Pb[Zr 0.95 Ti 0.05 ]O3 has been reported one after another. Magnetic materials are limited by the volume of the magnet. In order to achieve the ideal cooling effect, a larger magnetic field is required, which greatly increases the space cost and difficulty of magnetocaloric cooling. The electrocaloric effect requires higher voltage and current to achieve sufficient cooling effect, which will lead to waste of electric energy and increase in energy cost. Elastic-caloric materials require that the material itself has good elasticity and thermal conductivity. The material is easily damaged and has relatively low energy efficiency. Compared with other thermal effects, the barocaloric effect is a new type of refrigeration material. Relatively speaking, the research time is relatively short and there are fewer related studies. The barocaloric effect is essentially the regulation of the solid-state phase change entropy by external hydrostatic pressure. The hydrostatic pressure acts on all surfaces of the material. Compared with the uniaxial direction used by the elastocaloric effect material, the uniformity of the hydrostatic pressure will greatly reduce the destructive effect on the material itself. The barocaloric effect driven by isostatic pressure is easier to achieve than other external field-driven thermal effects and is the most promising refrigeration material.

[0003] Earlier, pressure-caloric materials used solid-solid phase transitions to achieve refrigeration purposes, and pressure-caloric refrigeration was achieved by regulating the transition from an ordered solid phase to a disordered solid phase. 0.99 gIn 0.01 、Ni 50 Mn 31.5 Ti 18.5Mainly magnetic structure coupling materials and inorganic compounds such as (NH4)2SO4. These types of materials usually need to be carried out under high pressure conditions (>500MPa) to be effective. The adiabatic temperature change effect under pressure loading / unloading is the most direct and effective method for evaluating the performance of pressure-heat materials. Limited by the conditions of proprietary measurement equipment, the evaluation of adiabatic temperature change is extremely inconvenient. Most materials can usually only be estimated by indirect methods using formulas to estimate entropy change. It was subsequently discovered that plastic crystal materials (including TRIS[(NH2)C(CH2OH)3], PG[(CH2)C(CH2OH)3], AMP[(NH2)(CH3)C(CH2OH)2], NPA[(CH3)3C(CH2OH)], NPG[(CH3)2C(CH2OH)2], etc.) can exhibit excellent pressure-heat performance in solid-solid phase transitions, among which NPA can reach 290J·Kg at a pressure of 200 MPa. -1 ·K -1 The isothermal entropy change of 18 K can be calculated by adiabatic temperature change. The pressure-caloric performance of these plastic crystal materials is higher than that of magnetic structure coupling materials and inorganic compounds, making them more promising pressure-caloric refrigeration working fluids. In recent years, the field of pressure-caloric refrigeration has attracted much attention. With the continuous emergence of high-performance pressure-caloric materials, the measurement methods of pressure-caloric effect and pressure-caloric refrigeration methods are also changing.

[0004] Tong Peng et al., whose authorization announcement number is CN112940687B, found that more efficient pressure heat refrigeration can be achieved by utilizing solid-liquid phase transition through the transformation process from ordered solid phase to disordered liquid phase. n H 2n+2 In the experiment, an adiabatic temperature change of about 18 K and a heat release rate of 600 J·Kg were obtained at a low pressure of 100 MPa. -1 ·K -1 The solid-liquid phase change refrigeration represented by normal alkanes has a higher pressure-heat performance than the solid-solid phase change refrigeration method represented by plastic crystal materials, making it the most promising pressure-heat refrigeration method.

[0005] Based on the current research on compression materials, based on solid-phase order-disorder phase transition (such as plastic crystal materials) and solid-liquid phase transition (such as even-numbered normal alkanes) as a method of pressure-heat cooling, there are the following problems for the pressure-heat cooling method:

[0006] 1. Existing compression effect materials require high pressure, and efficient and feasible refrigeration technology must require lower applied pressure. Although the solid-solid phase change refrigeration method represented by plastic crystal materials can show excellent pressure-heat performance, the required hydrostatic pressure is very high. Taking NPA as an example, when a very obvious BCE effect can be observed, the required pressure is about 200 MPa.

[0007] 2. Adiabatic temperature change is small under low pressure. Efficient and feasible refrigeration technology must have a large adiabatic temperature change under low pressure. Although the solid-liquid phase change refrigeration method represented by even-numbered normal alkanes responds to very small hydrostatic pressures (<100MPa), the adiabatic temperature change measured by the direct method is very small. Taking n-octadecane as an example, the adiabatic temperature change measured at a pressure of 100MPa is only 18K. Summary of the invention

[0008] In order to solve the problems of the prior art, the purpose of the present invention is to overcome the shortcomings of the existing technology and provide a low-pressure and high-efficiency refrigeration method. By utilizing superimposed phase changes, solid-solid phase changes and solid-liquid phase changes are combined to achieve high-efficiency refrigeration, which can solve the problems mentioned above (1) excessive hydrostatic pressure and (2) low adiabatic temperature change value directly measured under low pressure.

[0009] One of the purposes of the present invention is to provide a low-pressure and high-efficiency refrigeration method, and the specific technical scheme is as follows:

[0010] A low-pressure and high-efficiency refrigeration method is based on the sequential passage of ordered solid phases (S O )-disordered solid phase (S D The material of the phase change process of )-liquid phase (L) is used as the refrigerant, and the refrigeration is carried out by pressure regulation as the driving force.

[0011] Preferably, a temperature within a range of 23K above and below the solid-liquid phase temperature of the refrigerant under a certain pressure is used as the working temperature of the refrigerant.

[0012] Preferably, the initial working pressure of the refrigerant is preferably above 40 MPa, and the unloading pressure serves as the driving force.

[0013] Further preferably, the initial working pressure is preferably 100 MPa to 150 MPa.

[0014] Preferably, the pressure regulation is isostatic pressure regulation.

[0015] Preferably, the refrigerant is an odd-numbered normal alkane material.

[0016] Further preferably, the structural formula of the odd-numbered normal alkane material is C n H 2n+2 (n=17, 19, 21).

[0017] The second object of the present invention is to provide a low-pressure and high-efficiency refrigeration material, and the specific technical solution is as follows:

[0018] A low-pressure and high-efficiency refrigeration material, the refrigeration material has the characteristics of sequentially undergoing ordered solid phases (S O)-disordered solid phase (S D )-liquid phase (L), and under a certain pressure, has the characteristic of superimposed phase change. When the refrigerant is used as a refrigerant and used in a refrigeration process driven by pressure regulation, the refrigerant has an adiabatic temperature change value of less than 30K at the working temperature when pressure is used as the driving force for refrigeration.

[0019] Preferably, the operating temperature is within a range of 23K above and below the solid-liquid phase temperature of the refrigerant under a certain pressure.

[0020] Preferably, when the refrigerant is at an operating temperature of 315K and the pressure is unloaded at 150MPa, the adiabatic temperature change value is 29K; when the pressure is unloaded at 100MPa, the adiabatic temperature change value is 28K.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention provides a low-pressure and high-efficiency refrigeration method, specifically a high-efficiency refrigeration method using superimposed phase change for refrigeration, which has a high adiabatic temperature change under a relatively low applied pressure. For example, the adiabatic temperature change value at 40MPa can reach 6K; the adiabatic temperature change value at 100MPa can reach 28K, and the adiabatic temperature change value at 150MPa can reach 29K. Compared with the solid-solid phase change method and the solid-liquid phase change method, the superimposed phase change refrigeration effect is significantly higher than the simple solid-solid phase change method and the simple solid-liquid phase change method.

[0023] The method of refrigeration using superimposed phase change proposed by the present invention is a new low-pressure and high-efficiency refrigeration method. This patent provides a new method for finding new refrigeration materials, which will greatly promote the development of pressure-caloric refrigeration technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a heat flow curve of n-heptadecane in Example 1 of the present invention;

[0025] Figure 2 This is a test diagram of adiabatic temperature variation of n-heptadecane at different working temperatures in Example 1 of the present invention, wherein a to e correspond to working temperatures of 289K, 292K, 300K, 305K, and 315K, respectively;

[0026] Figure 3 This is a heat flow curve diagram of n-nonadecane in Example 2 of the present invention;

[0027] Figure 4 This is a heat flow curve of n-heneicosane in Example 3 of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] For ease of understanding, let us first explain the English terms mentioned below:

[0030] S: solid phase; S O : ordered solid phase; S D : disordered solid phase; L: liquid phase;

[0031] Load: loading pressure; unload: unloading pressure.

[0032] First of all, it should be noted that the present invention is directed to the ordered solid phase (S O )-disordered solid phase (S D )-liquid phase (L), that is, a material with double phase transition at different temperatures.

[0033] Example:

[0034] In this example, n-heptadecane (C 17 H 36 ) as an example, the specific implementation process of the low-pressure and high-efficiency refrigeration method is introduced, specifically:

[0035] First, the pressure-controlled phase change test of n-heptadecane was carried out to obtain the heat flow curves under different pressures (such as Figure 1 The upper part of the horizontal axis represents the heat release process during pressurization, and the lower part represents the heat absorption process during depressurization. The specific pressure-phase change table is shown in Table 1. It can be seen that during the pressurization process, at a lower pressure, S O -S D Phase transition and S D The -L phase transition is shown in the form of double peaks in the heat flow curve, and the peak temperatures represent the S O -S D Phase transition and S D -L phase transition temperature, respectively expressed as and At higher pressures (above 60 MPa), the double peaks become single peaks, and S O -S D Phase transition and S D -L phase transition The two phase transitions are superimposed into a superimposed phase transition SL phase transition, and the corresponding phase transition temperature is one, which is expressed as On the contrary, during the decompression process, at higher pressures (above 60 MPa), the single peak represents the superimposed phase transition LS phase transition, and the phase transition temperature is expressed as When the pressure continues to decrease, the single peak becomes a double peak, which is LS D Phase transition and S D -S O phase transition, and the corresponding phase transition temperatures are expressed as and Then, the difference in phase transition temperature between the positive and negative directions of solid-liquid phase transition is

[0036] In other words, the phase transition temperatures of the two phase transitions coincide at the critical pressure, and these two phase transition temperatures (double peaks in the heat flow curve) can be controlled to the same temperature (single peak in the heat flow curve), that is, the superposition of ordered solid phase-disordered solid phase transition and disordered solid phase-liquid phase transition can be achieved.

[0037] Table 1 Heat flow curve data of n-heptadecane

[0038]

[0039] It should be noted that S D -L phase transition and SL phase transition are both solid-liquid phase transitions. D Both phase transition and LS phase transition belong to liquid-solid phase transition, and the corresponding phase transition temperatures are called solid-liquid phase line temperatures.

[0040] Secondly, according to the different phase transition temperatures mentioned above, several temperature values ​​(289K, 292K, 300K, 305K, 315K) were selected as the initial temperature (also called the working temperature) in the range near the solid-liquid phase line temperature T, and the adiabatic temperature change value was characterized under different pressures (0MPa, 20MPa, 40MPa, 60MPa, 80MPa, 100MPa, 150MPa). When pressure was applied, the temperature of n-heptadecane increased to a high temperature point, then exchanged heat with the external environment and returned to the initial temperature. When the pressure was removed, the temperature of n-heptadecane dropped to a low temperature point. The adiabatic temperature change (ΔT ad , referred to as adiabatic temperature change, is the measurement of high temperature point and low temperature point). The measurement results at different temperatures are as follows Figure 2 As shown in Table 2, it can be seen that at a starting temperature of 300K, when the low pressure unloading is 40MPa, the adiabatic temperature change reaches 6K. At a starting temperature of 315K, when the low pressure unloading is 100MPa, the adiabatic temperature change reaches 28K, and when the low pressure unloading is 150MPa, the adiabatic temperature change reaches 29K.

[0041] Table 2 Adiabatic temperature change data of n-heptadecane when loading / unloading pressure (load / unload)

[0042]

[0043] It should be noted that by 19 H 40 ) to conduct pressure-controlled phase change tests and obtain heat flow curves under different pressures (such as Figure 3 The results are similar to those in Example 1. For specific data, see Table 3.

[0044] Table 3 Heat flow curve data of n-nonadecane

[0045]

[0046] It should be noted that by 21 H 44 ) to conduct pressure-controlled phase change tests and obtain heat flow curves under different pressures (such as Figure 4 The results are similar to those in Example 1. For specific data, see Table 4.

[0047] Table 4 Heat flow curve data of n-heneicosane

[0048]

[0049] It can be seen that the structures of odd-numbered normal alkane materials are similar, and the pressure-regulated phase changes are similar. Therefore, it can be inferred that the low-pressure and high-efficiency refrigeration method provided by the present invention can also be used as a low-pressure and high-efficiency refrigeration material. In practical applications, due to the differences in specific materials, the actual working temperature and pressure will be adjusted to a certain extent.

[0050] In summary, it can be seen that materials that have both a large reversible isothermal entropy change and a high pressure sensitivity coefficient can be suitable for the new method of efficient refrigeration we proposed.

[0051] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is limited by the attached embodiments and their equivalents.

Claims

1. A low-pressure and high-efficiency refrigeration method, characterized in that: With the increase of temperature, it undergoes ordered solid phases (S O )-disordered solid phase (S D The material of the phase change process of )-liquid phase (L) is used as the refrigerant, and the refrigeration is carried out by pressure regulation as the driving force.

2. The low-pressure and high-efficiency refrigeration method according to claim 1, characterized in that: A temperature within a range of 23K above and below the solid-liquid phase temperature of the refrigerant under a certain pressure is used as the working temperature of the refrigerant.

3. The low-pressure and high-efficiency refrigeration method according to claim 1, characterized in that: The initial working pressure of the refrigerant is preferably above 40 MPa, and the unloading pressure serves as the driving force.

4. The low-pressure and high-efficiency refrigeration method according to claim 3, characterized in that: The initial working pressure is preferably 100 MPa to 150 MPa.

5. The low-pressure and high-efficiency refrigeration method according to claim 1, characterized in that: The pressure regulation is isostatic pressure regulation.

6. The low-pressure and high-efficiency refrigeration method according to claim 1, characterized in that: The refrigerant is an odd-numbered normal alkane material.

7. The low-pressure and high-efficiency refrigeration method according to claim 6, characterized in that: The structural formula of the odd-numbered normal alkane material is C n H 2n+2 (n=17, 19, 21).

8. A low-pressure and high-efficiency refrigeration material, characterized in that: The refrigeration material has the characteristics of sequentially undergoing ordered solid phases (S O )-disordered solid phase (S D )-liquid phase (L), and under a certain pressure, has the characteristic of superimposed phase change. When the refrigerant is used as a refrigerant in a refrigeration process where pressure regulation is used as a driving force, the adiabatic temperature change value of the refrigerant at the working temperature is within 30K when pressure is used as a driving force for refrigeration.

9. The low-pressure and high-efficiency refrigeration material according to claim 8, characterized in that: The working temperature is the range of 23K above and below the solid-liquid phase temperature of the refrigerant under a certain pressure.

10. The low-pressure and high-efficiency refrigeration material according to claim 8, characterized in that: When the refrigerant is at an operating temperature of 315K and the pressure is unloaded at 150MPa, the adiabatic temperature change value is 29K; when the pressure is unloaded at 100MPa, the adiabatic temperature change value is 28K.

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