Low-pressure high-efficiency refrigeration method

Abstract

The application discloses a low-pressure high-efficiency refrigeration method, and relates to the technical field of pressure card refrigeration. O )‑disordered solid phase (S D )‑liquid phase (L) phase transition process, namely, a material with double phase transitions at different temperatures. First, the ability of S O -S D phase transition and S D -L phase transition is determined by superposition into one phase transition through the processes of pressure increasing and pressure decreasing, then the solid-liquid phase line temperature is determined, and finally, the adiabatic temperature change of the material is verified through the experiment of pressure increasing and pressure decreasing in a certain interval range of the solid-liquid phase line temperature. Thus, a low-pressure high-efficiency refrigeration material with 6K adiabatic temperature change at 40MPa and 28K adiabatic temperature change at 100MPa is obtained.

Description

Technical Field

[0001] This invention relates to the field of pressure-cooling technology, specifically a low-pressure, high-efficiency refrigeration method. Background Technology

[0002] In today's society, with the rapid development of the economy, refrigeration technology is increasingly widely used in industrial fields such as food, medicine, and air conditioning, as well as in daily life. The refrigeration industry consumes more than 15% of the total social energy consumption. Currently, the most widely used vapor compression refrigeration, utilizing the Carnot cycle, can only achieve a maximum efficiency of 25%, and the gaseous refrigerant used in vapor compression damages the ozone layer and contributes to the greenhouse effect. Innovative and environmentally friendly refrigeration technologies are urgent problems that the world needs to solve. Solid-state refrigeration technology has the advantages of being green, environmentally friendly, stable, and reliable, and has received widespread attention in recent years. Depending on the external field (magnetic field, electric field, uniaxial stress, hydrostatic pressure), it can be classified into magnetocaloric effect, electrothermal effect, elastothermal effect, and compressive-thermal effect. Along with the research boom in solid-state refrigeration technology, many new materials capable of achieving refrigeration are constantly emerging. For example, there are magnetic materials with magnetocaloric effects such as LaFeSi alloys, elastothermal materials such as Ni-Ti-based and Ni-Ti-Mn-based shape memory alloys, and polar electrolyte materials with electrothermal effects such as PZT(Pb[Zr)). 0.95 Ti 0.05 O3 has been reported successively. Magnetic materials, limited by the volume of the magnet, require a large magnetic field to achieve the ideal cooling effect, greatly increasing the space cost and difficulty of magnetothermal cooling. Electrothermal effects require high voltage and current to achieve sufficient cooling, leading to energy waste and increased energy costs. Elastic-thermal materials require good elasticity and thermal conductivity, making them easily damaged and relatively inefficient. Compared to other thermal effects, the pressure-thermal effect is a novel cooling material, with relatively short research history and limited related studies. The pressure-thermal effect essentially involves the regulation of solid-state phase transition entropy by applied hydrostatic pressure. Hydrostatic pressure acts on all surfaces of the material, and its uniformity, compared to the uniaxial direction used in elasto-thermal materials, significantly reduces its destructive effect on the material. The pressure-thermal effect driven by isostatic pressure is easier to achieve than other externally driven thermal effects and is the most promising cooling material.

[0003] Early pressure-cooling materials utilized solid-solid phase transitions to achieve refrigeration. This was accomplished by controlling the transformation from an ordered solid phase to a disordered solid phase through pressure regulation. Initially, MnCoGe was used as a base for this type of material. 0.99 gIn 0.01 Ni 50 Mn 31.5 Ti 18.5The main materials used are isomagnetic coupling materials and inorganic compounds such as (NH4)2SO4. These materials typically require high pressure (>500 MPa) 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-thermal materials. Due to limitations in specialized measuring equipment, evaluating the adiabatic temperature change is extremely inconvenient; for most materials, the entropy change can usually only be estimated indirectly using formulas. Subsequently, it was found that crystalline 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.) exhibit excellent pressure-thermal performance in solid-solid phase transitions. Among them, NPA can reach 290 J·Kg at a pressure of 200 MPa. -1 ·K -1 The isothermal entropy change can be calculated, and the adiabatic temperature change can be obtained at 18 K. These plastic crystal materials have higher piezothermal properties than magnetically coupled materials and inorganic compounds, making them more promising piezothermal refrigerants. In recent years, the field of piezothermal refrigeration has received much attention. With the continuous emergence of high-performance piezothermal materials, the measurement methods of piezothermal effects and piezothermal refrigeration methods are also being updated and replaced.

[0004] Tong Peng et al., authorized by publication number CN112940687B, discovered that through the transformation process from an ordered solid phase to a disordered liquid phase, more efficient pressure-thermal refrigeration can be achieved using solid-liquid phase transitions, in even-numbered n-alkanes with n=16 and 18. n H 2n+2 In the middle, an adiabatic temperature change of about 18 K and 600 J·Kg can be obtained under a low pressure of 100 MPa. -1 ·K -1 The enormous isothermal entropy change value. Solid-liquid phase change refrigeration, represented by n-alkanes, has superior piezothermal performance compared to solid-solid phase change refrigeration methods represented by plastic crystal materials, making it the most promising piezothermal refrigeration method currently available.

[0005] Based on current research on pressure-sensitive materials, the use of solid-state ordered-disorder phase transitions (e.g., plastic crystal materials) and solid-liquid phase transitions (e.g., even-numbered n-alkanes) as piezothermal refrigeration methods has the following problems:

[0006] 1. Existing pressure-sensitive materials require high pressures, while efficient and feasible refrigeration technologies necessarily require lower applied pressures. Solid-solid phase change refrigeration methods, represented by plastic crystal materials, exhibit excellent pressure-thermal properties, but require very high hydrostatic pressures. For example, with NPA, a pressure of approximately 200 MPa is required to observe a significant BCE effect.

[0007] 2. Small adiabatic temperature change at low pressure: Efficient and feasible refrigeration technologies must have a large adiabatic temperature change at low pressure. Although solid-liquid phase change refrigeration methods, represented by even-numbered n-alkanes, have a response to very small hydrostatic pressures (<100MPa), the adiabatic temperature change measured by direct methods is very small. For example, the adiabatic temperature change of n-octadecane measured at 100MPa pressure is only 18 K. Summary of the Invention

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

[0009] One of the objectives of this invention is to provide a low-pressure, high-efficiency refrigeration method, the specific technical solution of which is as follows:

[0010] A low-pressure, high-efficiency refrigeration method utilizes a system that, as temperature increases, sequentially undergoes an ordered solid phase (S... O )-Disordered solid phase (S D The material in the phase change process of the liquid phase (L) is used as the refrigerant, and refrigeration is achieved by pressure regulation as the driving force.

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

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

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

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

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

[0016] More preferably, the general structural formula of the odd-numbered n-alkane material is C0 n H 2n+2 (n = 17, 19, 21).

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

[0018] A low-pressure, high-efficiency refrigeration material, wherein the refrigeration material undergoes sequential orderly solid-phase (S) changes with increasing temperature. O)-Disordered solid phase (S D The phase change process of the liquid phase (L) and the superimposed phase change characteristics under certain pressure, when the refrigeration material is used as the refrigerant in the refrigeration process driven by pressure regulation, the adiabatic temperature change value of the refrigerant is within 30K at the working temperature when the 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, the refrigerant has an adiabatic temperature change of 29K when unloading at a pressure of 150MPa at an operating temperature of 315K and an adiabatic temperature change of 28K when unloading at a pressure of 100MPa.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention provides a low-pressure, high-efficiency refrigeration method, specifically a highly efficient refrigeration method utilizing superimposed phase change. This method exhibits high adiabatic temperature change at relatively low applied pressure. For example, the adiabatic temperature change value reaches 6K at 40MPa; 28K at 100MPa; and 29K at 150MPa. Compared to solid-solid and solid-liquid phase change methods, the superimposed phase change refrigeration effect is significantly higher than that of simple solid-solid and simple solid-liquid phase change methods.

[0023] The method for refrigeration using superimposed phase change proposed in this invention is a novel low-pressure, high-efficiency refrigeration method. This patent provides a new approach for finding novel refrigeration materials and will greatly promote the development of compressive refrigeration technology. Attached Figure Description

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

[0025] Figure 2 The diagram shows the adiabatic temperature change test of n-heptadecane in Example 1 of this invention at different operating temperatures, where a to e correspond to operating temperatures of 289K, 292K, 300K, 305K, and 315K, respectively.

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

[0027] Figure 4 This is a heat flow curve of n-docosane in Example 3 of this invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] To facilitate understanding, the English terms mentioned below will be explained first:

[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, it should be noted that this invention addresses the sequential process of an ordered solid phase (S) as the temperature increases. O )-Disordered solid phase (S D Materials that undergo a phase transition process from liquid to liquid phase (L), i.e., materials that undergo a dual phase transition at different temperatures.

[0033] Example:

[0034] This embodiment uses n-heptadecane (C 17 H 36 Taking (e.g.) as an example, the specific implementation process of the low-pressure, high-efficiency refrigeration method is introduced as follows:

[0035] First, pressure-controlled phase transition tests were performed on n-heptadecane to obtain heat flow curves at different pressures (e.g., Figure 1 As shown in Table 1, the upper part of the horizontal axis represents the pressurization and heat release process, and the lower part represents the depressurization and heat absorption process. The specific pressure-phase change table shows that during the pressurization process, at lower pressures, S... O -S D Phase transition and S D The -L phase transition is represented by a bimodal pattern in the heat flow curve, with the peak temperatures representing the SL and SL phase transitions, respectively. O -S D Phase transition and S D The phase transition temperatures of the -L phase transition are expressed as follows: and At higher pressures (above 60 MPa), the bimodal distribution becomes a single peak, S O -S D Phase transition and S D -L phase transition: Two phase transitions are superimposed into one superimposed phase transition (SL phase transition), and the corresponding phase transition temperature is one, denoted as: Conversely, during the depressurization process, at higher pressures (above 60 MPa), a single peak represents the superimposed phase transition (LS phase transition), and the phase transition temperature is expressed as... As 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 follows: and Therefore, the difference in phase transition temperature between the two directions of the solid-liquid phase transition is:

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

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

[0038]

[0039] It should be noted that S D Both -L phase transition and SL phase transition are solid-liquid phase transitions, LS 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, based on the different phase transition temperatures mentioned above, several temperature values ​​(289K, 292K, 300K, 305K, 315K) were selected as initial temperatures (also known as operating temperatures) within the range close to the solid-liquid phase line temperature T. The adiabatic temperature change was characterized under different pressures (0MPa, 20MPa, 40MPa, 60MPa, 80MPa, 100MPa, 150MPa). When pressure was applied, the temperature of n-heptadecane rose to a high temperature point, then exchanged heat with the external environment, returning to the initial temperature. When the pressure was released, the temperature of n-heptadecane dropped to a low temperature point. The adiabatic temperature change (ΔT) of n-heptadecane was measured directly. ad Absolutely referred to as adiabatic temperature variation, it involves measuring the temperature at both high and low points. The measurement results at different temperatures are as follows: Figure 2 As shown in Table 2, it can be seen that at an initial temperature of 300K, the adiabatic temperature change reaches 6K when unloading at a low pressure of 40MPa. At an initial temperature of 315K, the adiabatic temperature change reaches 28K when unloading at a low pressure of 100MPa, and 29K when unloading at a low pressure of 150MPa.

[0041] Table 2. Adiabatic temperature change data for n-heptadecane under load / unload pressures.

[0042]

[0043] It should be noted that, through the analysis of n-nonadecane (C 19 H 40 Pressure-controlled phase transition tests were conducted to obtain heat flow curves under different pressures (e.g., Figure 3 As shown in Table 3, the results are similar to those of Example 1.

[0044] Table 3. Heat flow curve data for n-Nicotinane

[0045]

[0046] It should be noted that, through the analysis of n-docosane (C... 21 H 44 Pressure-controlled phase transition tests were conducted to obtain heat flow curves under different pressures (e.g., Figure 4 As shown in Table 4, the results are similar to those of Example 1. For detailed data, please refer to Table 4.

[0047] Table 4. Heat flow curve data for n-docosahexane

[0048]

[0049] It can be seen that the structures of odd-numbered n-alkane materials are similar, and the pressure-controlled phase transitions are similar. Therefore, it can be inferred that the low-pressure high-efficiency refrigeration method provided by this invention can also be used as a low-pressure high-efficiency refrigeration material. In practical applications, the actual working temperature and pressure will be adjusted to some extent due to the different materials.

[0050] In summary, it can be seen that materials with both large reversible isothermal entropy changes and high pressure sensitivity coefficients are suitable for our proposed new method of efficient refrigeration.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended embodiments and their equivalents.

Claims

1. A low-pressure, high-efficiency refrigeration method, characterized in that, With increasing temperature, it sequentially undergoes an ordered solid phase ( - Disordered solid phase ( The phase change process of the liquid phase (L) is carried out, and under certain pressure, the material with superimposed phase change characteristics is used as the refrigerant, and the refrigeration is carried out by pressure regulation as the driving force. The initial working pressure of the refrigerant is 100MPa~150MPa, and the unloading pressure is used as the driving force. The adiabatic temperature change of the refrigerant is within 30K when it is cooled by pressure at the operating temperature. The refrigerant is an odd-numbered n-alkane material, and the general structural formula of the odd-numbered n-alkane material is C0. n H 2n+2 n=17, 19, 21; The operating temperature of the refrigerant is defined as a temperature within a 23K range above and below the solid-liquid phase temperature of the refrigerant under a certain pressure.

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

3. The low-pressure, high-efficiency refrigeration method according to claim 1, characterized in that, The refrigerant has an adiabatic temperature change of 29K when unloading at a pressure of 150MPa at an operating temperature of 315K and 28K when unloading at a pressure of 100MPa.

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