Energy efficiency evaluation method for filling multi-stage phase change material heat storage

Abstract

The application discloses an energy efficiency evaluation method for a multi-stage phase change material filled heat accumulator, wherein the heat accumulator is filled with multi-stage phase change materials and has a partition wall surface, the sensible heat storage / release amount of the partition wall surface in the whole heat storage / release process is calculated, the calculation parameters of high-thermal-conductivity additive materials used in the heat accumulator are obtained, the sensible heat storage / release amount of the high-thermal-conductivity additive materials is calculated, the calculation parameters of different phase change materials in solid phase states are obtained, the sensible heat storage / release amount of the multi-stage phase change materials in the solid phase states in the whole heat storage / release process is calculated, the calculation parameters of different phase change materials in liquid phase states are obtained, the sensible heat storage / release amount of the multi-stage phase change materials in the liquid phase states is calculated, the total latent heat storage / release amount of the multi-stage phase change materials is calculated, the volume change evaluation factor of the phase change materials in the heat accumulator is obtained, the calculation parameters of heat exchange fluid flow in the heat accumulator are obtained, the pump work consumption caused by fluid heat exchange in the heat accumulator is calculated, and the energy efficiency index of the multi-stage phase change material filled heat accumulator is calculated.

Description

Technical Field

[0001] This invention belongs to the field of phase change thermal energy storage technology, and in particular, it is a method for evaluating the energy efficiency of a thermal energy storage device filled with multi-stage phase change materials. Background Technology

[0002] Energy storage technology is one of the effective ways to address the spatial and temporal distribution differences of energy resources, and it is widely used in renewable energy consumption, distributed cogeneration systems, and transportation. Thermal energy storage technology is a subcategory of energy storage technology, a method of storing and releasing heat. Based on different principles, it is divided into sensible heat storage, latent heat storage, and chemical heat storage. Sensible heat storage utilizes the sensible heat of the material itself to store and release heat, but its heat storage / release capacity is relatively weak. Chemical heat storage completes the process of absorbing and releasing heat through chemical reactions. Although it has extremely high heat storage / release capacity, it has significant drawbacks such as system complexity, poor safety, and low overall efficiency. Latent heat storage systems are filled with phase change materials (PCMs) and store latent heat through a phase change process. Based on different phase change transformation states, it can be divided into solid-solid phase change, solid-liquid phase change, and gas-liquid phase change. Solid-solid phase change has relatively low latent heat and is rarely used as a latent heat storage method; gas-liquid phase change is usually accompanied by large volume change, which places high demands on the pressure and strength of the heat storage device; solid-liquid phase change has a large heat storage density, a wide melting point distribution, and the volume expansion accompanying the phase change is within an acceptable range, and the temperature is almost constant during the phase change process, so it is widely used in medium and low temperature heat storage systems.

[0003] The main bottleneck in the development of phase change thermal energy storage lies in the extremely low thermal conductivity (0.2 W / m²) of the phase change material itself. -1 K -1 -1.0W m -1 K -1 The slow heat storage / release rate is a common problem. A common method to enhance this is to add high thermal conductivity materials to the phase change material (PCM) to create composite PCMs, such as fins, metal foams, expanded graphite, and nanoparticles. While high thermal conductivity materials can effectively enhance the heat storage / release rate of a PCM, they also reduce the amount of PCM used, inevitably decreasing the total heat storage / release capacity. Furthermore, the density of high thermal conductivity materials, such as fins, is several times or even ten times higher than that of PCM, increasing the overall weight of the PCM. Therefore, balancing the trade-off between the heat storage / release rate and the total heat capacity of a PCM is crucial. Currently, these two indicators are usually analyzed and evaluated separately: the completion time of heat storage / release and the corresponding amount of heat stored / released. However, there is a lack of energy efficiency evaluation methods that simultaneously incorporate multiple characteristics such as heat storage / release rate, pump power consumption, total capacity, mass, and volume to guide the analysis and performance comparison of PCMs.

[0004] Furthermore, while there is considerable research on thermal storage devices filled with single-stage phase change materials (PCMs), these devices face significant challenges in environmental adaptability due to the limited range of their phase change temperatures. For example, in the thermal storage process, when the heating temperature is below the PCM temperature, the PCM in the storage device fails to undergo a phase change, thus failing to realize the advantages of latent heat storage. Conversely, when the heating temperature is much higher than the PCM temperature, although the phase change process has already been completed, the quality of the stored heat is determined by the PCM temperature, resulting in lower quality. Thermal storage devices filled with multi-stage PCMs utilize PCMs with different phase change temperatures arranged in various configurations to mitigate the shortcomings of single-stage PCMs and improve the adaptability of PCMs to different environments (such as seasons and day / night cycles). Additionally, a well-planned arrangement of multi-stage PCMs can enhance the storage / release rate of the thermal storage device. In summary, a comprehensive evaluation method for multi-stage PCM-filled thermal storage devices is currently lacking, necessitating the development of corresponding evaluation criteria to achieve energy efficiency evaluation and structural optimization design.

[0005] To address the challenges mentioned above, this invention constructs an Energy Efficiency Index (EER) method for evaluating the energy efficiency of multi-stage phase change material (PCM) thermal storage devices. This method considers various characteristics such as heat storage / release rate, heat storage / release capacity, pump power consumption, and the mass / volume of the thermal storage device. It can be applied to experimental or numerical simulation fields to obtain a comprehensive performance evaluation of the thermal storage device under steady-state conditions. Furthermore, it is compatible with PCM thermal storage devices of different structures and enhancement methods, providing theoretical guidance for the performance evaluation, energy efficiency classification, and optimized design of multi-stage PCM thermal storage devices.

[0006] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art in this country. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention proposes an energy efficiency evaluation method for multi-stage phase change material (PCM) thermal storage tanks. This method considers multiple characteristics, including heat storage / release rate, heat storage / release capacity, pump power consumption, and the mass / volume of the thermal storage tank. It defines the heat storage / release density of the multi-stage PCM thermal storage tank per unit time, per unit mass / volume, and per unit pump power, and introduces the volume expansion / contraction factor of the PCM during phase change. Based on experimental or simulation data, the method obtains the energy efficiency evaluation of the multi-stage PCM thermal storage tank under steady-state conditions. This method is compatible with latent heat thermal storage tanks of different structures and enhancement methods, providing theoretical guidance for the performance evaluation, energy efficiency classification, and optimized design of multi-stage PCM thermal storage tanks.

[0008] The objective of this invention is achieved through the following technical solution: a method for evaluating the energy efficiency of a multi-stage phase change material-filled thermal storage device includes:

[0009] Step 1: The thermal storage tank has partition walls and is filled with multi-stage phase change material. The calculation parameters of the partition walls include the mass m of the partition walls used in the thermal storage tank. wall and volume V wall The isobaric specific heat capacity (C) of the partition wall p ) wall The initial and final times τ1 and τ2 of the heat storage / release process, and the average temperature T of the partition wall at the initial and final times of the heat storage / release process. ini，wall and T end，wall ;

[0010] Step 2: Calculate the sensible heat stored / released by the partition wall during the entire heat storage / release process. The heat storage capacity of the partition wall is: The heat released by the partition wall is:

[0011] Third step: Obtain the calculation parameters of the high thermal conductivity additive material used in the thermal storage device. The calculation parameters of the additive material include the mass m of the high thermal conductivity additive material in the thermal storage device. add and volume V add The specific heat capacity at constant pressure (C) of high thermal conductivity additives p ) add The average temperature T of the high thermal conductivity additive at the beginning and end of the heat storage / release process. ini，add and T end，add High thermal conductivity additives include metal fins, metal foam, or expanded graphite, etc.

[0012] Step 4: Calculate the stored / released sensible heat of the high thermal conductivity additive, wherein the stored heat of the high thermal conductivity additive is: The heat release of the high thermal conductivity additive is:

[0013] Step 5: Obtain the calculation parameters of different phase change materials in the solid state. The calculation parameters in the solid state include the mass m of different phase change materials. pcm，i and volume V pcm，s，i The isobaric specific heat capacity (C) of different phase change materials in the solid state p，s ) pcm，i The average temperature T of different phase change materials at the initial and final moments of the heat storage / release process. ini，pcm，i and T end，pcm，i The phase transition temperature of various phase change materials is T. m，i , where i represents the i-th phase change material;

[0014] Step 6: Calculate the sensible heat stored / released in the solid state of the multi-stage phase change material during the entire heat storage / release process. The sensible heat stored / released is: The heat absorbed during thermal storage is The heat released during exothermic reactions is n represents the total category of phase change materials used in the thermal storage device;

[0015] Step 7: Obtain the calculation parameters of different phase change materials in the liquid phase state. The calculation parameters in the liquid phase state include the isobaric specific heat capacity (C) of different phase change materials in the liquid phase state. p，l ) pcm，i and volume V pcm，l，i ;

[0016] Step 8: Calculate the stored / released sensible heat in the liquid phase state of the multi-stage phase change material, wherein the stored / released sensible heat is: The heat absorbed during thermal storage is The heat released during exothermic reactions is

[0017] Step 9: Obtain the latent heat (L) absorbed / released during the phase transition of different phase change materials. pcm，i， Calculate the total latent heat storage / release of the multi-stage phase change material, wherein the total latent heat storage / release is:

[0018] Step 10: Calculate the time required for the entire heat storage / release process to complete: Δt = τ2 - τ1;

[0019] Step 11: Calculate the total mass or volume of the entire thermal storage tank, where the total mass is: The total volume of the heat storage device is: Due to the volume expansion of PCM after phase change to liquid, the filling volume of phase change material in the design of thermal storage tanks is based on liquid PCM.

[0020] Step 12: Calculate the volume change evaluation factor of the PCM in the entire thermal storage tank. When in thermal storage state, the corresponding volume expansion of the PCM is given by the volume change evaluation factor. When in an exothermic state, corresponding to the volume shrinkage of the PCM, the volume change evaluation factor is:

[0021] Step 13: Obtain the calculated parameters of the heat exchange fluid flow in the heat storage tank. These parameters include the volumetric flow rate q of the heat exchange fluid in different pipes. v，j and pressure drop ΔP j , j is the j-th heat exchange fluid pipe in the heat storage tank;

[0022] Step 14: Obtain the pump power consumption caused by fluid heat exchange in the heat storage tank, wherein the pump power consumption is: k is the total number of heat exchange fluid pipes in the heat storage tank;

[0023] Step 15: Calculate the energy efficiency index of the multi-stage phase change material thermal storage device, including the heat storage / release density and volume change evaluation factors per unit time, unit mass, and unit pump work: And evaluation factors for heat storage / release density and volume change per unit time, unit volume, and unit pump work: α and β are weighting factors, reflecting the weight of thermal storage density and volume change evaluation in this energy efficiency index. They can be selected according to different actual needs, and the sum of the two is 1; η represents the coefficient for converting low-quality thermal energy into high-quality electrical energy.

[0024] In the energy efficiency evaluation method for the multi-stage phase change material thermal energy storage device, the coefficient η for converting low-quality thermal energy into high-quality electrical energy is calculated based on the source of electrical energy.

[0025] Compared with existing technologies, this invention has the following advantages: This invention simultaneously considers multiple characteristics such as heat storage / release rate, heat storage / release capacity, pump power consumption, heat storage tank mass / volume, and PCM volume expansion and contraction. It can be applied to experimental or numerical simulation fields to obtain a comprehensive performance evaluation of the heat storage tank under steady-state conditions. It is also compatible with phase change heat storage tanks with different structures and different enhancement methods, providing theoretical guidance for the performance evaluation, energy efficiency classification, and optimization design of multi-stage phase change material heat storage tanks. The higher the energy efficiency index value, the better the comprehensive heat storage / release performance of the multi-stage phase change material heat storage tank. The energy efficiency evaluation method per unit volume or mass can be selected according to different target scenarios. Attached Figure Description

[0026] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0027] In the attached diagram:

[0028] Figure 1 This is a schematic diagram of a multi-stage phase change material thermal storage device according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of a high thermal conductivity additive material according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram illustrating different fin arrangements according to an embodiment of the present invention;

[0031] Figure 4This is an energy efficiency evaluation diagram showing different fin arrangements according to an embodiment of the present invention.

[0032] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0033] The following will refer to the appendix. Figures 1 to 4 Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0034] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0035] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0036] To better understand, such as Figures 1 to 4 As shown, the energy efficiency evaluation method for a multi-stage phase change material thermal storage device includes the following steps:

[0037] Step 1: Obtain the calculated parameters of the partition walls used in the multi-stage phase change material thermal storage tank. These calculated parameters include the mass m of the partition walls used in the thermal storage tank. wall (kg) and volume V wall (m 3 ), the isobaric specific heat capacity (C) of the partition wall p ) wall (J kg -1 K -1 ), the initial and final times τ1(s) and τ2(s) of the heat storage / release process, and the average temperature T of the partition wall corresponding to the initial and final times of the heat storage / release process. ini，wall (K) and T end，wall(K). The heat storage device may include partition walls of different structures to separate multi-stage phase change materials and heat exchange fluids, such as... Figure 1 As shown.

[0038] Step 2: Calculate the sensible heat stored / released by the partition wall during the entire heat storage / release process. The heat storage capacity of the partition wall is: The heat released by the partition wall is:

[0039] Step 3: Obtain the calculated parameters of the high thermal conductivity additives used in the multi-stage phase change material thermal storage tank. These calculated parameters include the mass m of the high thermal conductivity additives in the thermal storage tank. add (kg) and volume V add( m 3 ), the isobaric specific heat capacity (C) of high thermal conductivity additives p ) add (J kg -1 K -1 The average temperature T of the high thermal conductivity additive at the beginning and end of the heat storage / release process. ini，add (K) and T end，add (K). Preferably, the high thermal conductivity additive can be selected from any heat transfer enhancement method, such as adding fins, metal foam, etc. (e.g.) Figure 2 (As shown).

[0040] Step 4: Calculate the stored / released sensible heat of the high thermal conductivity additive, wherein the stored heat is: The heat released is:

[0041] Step 5: Obtain the calculation parameters of different phase change materials in the solid state. The calculation parameters in the solid state include the mass m of different phase change materials. pcm，i (kg) and volume V pcm，s，i (m 3 ), the isobaric specific heat capacity (C) of different phase change materials in their solid state p，s ) pcm，i (J kg -1 K -1 The average temperature T of different phase change materials at the initial and final moments of the heat storage / release process. ini，pcm，i (K) and T end，pcm，i (K), the phase transition temperature of various phase change materials is T m，i (K); where i represents the i-th phase change material.

[0042] Step 6: Calculate the sensible heat stored / released in the solid state of the multi-stage phase change material during the entire heat storage / release process. The sensible heat stored / released is: Furthermore, the heat absorbed during thermal storage is The heat released during exothermic reactions is The n represents the total category of phase change materials used in the thermal storage device.

[0043] Step 7: Obtain the calculation parameters of different phase change materials in the liquid phase state. The calculation parameters in the liquid phase state include the isobaric specific heat capacity (C) of different phase change materials in the liquid phase state. p，l ) pcm，i (J kg -1 K -1 ) and volume V pcm，l，i (m 3 ).

[0044] Step 8: Calculate the explicit heat storage / release in the liquid phase state of the multi-stage phase change material, wherein the heat storage / release is: Furthermore, the heat absorbed during thermal storage is The heat released during exothermic reactions is

[0045] Step 9: Obtain the latent heat (L) absorbed / released during the phase transition of different phase change materials. pcm，i (J kg -1 ), calculate the total latent heat of the multi-stage phase change material, wherein the latent heat of the material is:

[0046] Step 10: Calculate the time required for the entire heat storage / release process to complete, where the time is: Δt = τ2 - τ1.

[0047] Step 11: Calculate the total mass or volume of the entire thermal storage tank, where the total mass is: The total volume of the heat storage device is: Due to the volume expansion of PCM after phase change to liquid, the filling volume of phase change material in the design of thermal storage tanks is based on liquid PCM.

[0048] Step 12: Calculate the volume change evaluation factor of the PCM in the entire thermal storage tank. When in thermal storage state, the corresponding volume expansion of the PCM is given by the volume change evaluation factor. When in an exothermic state, corresponding to the volume shrinkage of the PCM, the volume change evaluation factor is:

[0049] Step 13: Obtain the calculated parameters of the heat exchange fluid flow in the heat storage tank. These parameters include the volumetric flow rate q of the heat exchange fluid in different pipes. v，j (m 3 s -1 and pressure drop ΔP j (Pa), where j is the j-th heat exchange fluid pipe in the heat storage tank.

[0050] Step 14: Obtain the pump power consumption caused by fluid heat exchange in the thermal storage, wherein the total pump power consumption is: k represents the total number of heat exchange fluid pipes in the thermal storage tank.

[0051] Step 15: Calculate the energy efficiency index of the multi-stage phase change material thermal storage device, including the heat storage / release density and volume change evaluation factors per unit time, unit mass, and unit pump work: And evaluation factors for heat storage / release density and volume change per unit time, unit volume, and unit pump work: α and β are weighting factors, reflecting the weight of thermal storage density and volume change evaluation in this energy efficiency index. They can be selected according to different actual needs, and the sum of the two is 1. η represents the coefficient for converting low-quality thermal energy into high-quality electrical energy, which can be calculated according to the source of electrical energy.

[0052] The higher the value of the energy efficiency index, the better the overall heat storage / heat release performance of the multi-stage phase change material (PCM) thermal storage device. The energy efficiency evaluation method per unit volume or mass can be selected according to different target scenarios. In this invention, the proposed energy efficiency evaluation method for multi-stage PCM thermal storage devices is applicable to different structures, different arrangements, different stages of PCM, and different types of PCM, achieving a unified evaluation and comparison of thermal storage device performance.

[0053] To further understand the present invention, a specific calculation example of the present invention is as follows. Figure 1 This is a schematic diagram of a three-stage phase change material thermal storage device according to a specific embodiment of the present invention. Taking the enhanced heat transfer method of adding fins as an example, this embodiment compares the energy efficiency indicators of the three-stage phase change material thermal storage device with different numbers of fins added. Figure 3 The diagram shows cross-sectional views of the thermal storage device corresponding to different numbers of fins. In this embodiment, only the energy efficiency evaluation under the thermal storage state is taken as an example; the evaluation process under the exothermic state is similar.

[0054] Paraffin waxes with melting points of 315.15 K (PCM1), 323.15 K (PCM2), and 333.15 K (PCM3) were selected as phase change materials and filled into the respective... Figure 1 Positions 1, 2, and 3 are specified. Copper is chosen as the material for the separating wall and fins. The inlet temperature of the heat exchange fluid is set at 343.15 K for heat storage in the accumulator, with the complete melting of all PCMs within the accumulator marking the end of heat storage.

[0055] The relevant structural parameters are as follows: the axial length of the heat storage device is 1m, the radii of the 1 to 3 layers of phase change material in the radial direction are 0.031m, 0.051m and 0.071m respectively, the radii of the heat exchange fluid on the inner and outer sides are 0.01m and 0.08m respectively, and the thickness of the fins and partition walls is 0.001m.

[0056] The relevant physical properties are: the density of PCM1 is 760 kg / m³. -3 Specific heat capacity 2000 J kg -1 K -1 The latent heat of phase transition is 165 kJ / kg. -1 The density of PCM2 is 760 kg m³. -3 Specific heat capacity 2000 J kg -1 K -1 The latent heat of phase transition is 160 kJ / kg. -1 The density of PCM3 is 770 kg m³. -3 Specific heat capacity 2000 J kg -1 K -1 The latent heat of phase transition is 160 kJ / kg. -1 The density and specific heat capacity of copper are 8978 kg m³. -3 and 381J kg -1 K -1 .

[0057] By combining structural and physical property parameters, the filling volume and mass of different PCMs, partition walls, and fins can be obtained. The initial and final state parameters of the three-stage phase change material thermal storage device in this embodiment were obtained through numerical simulation, as shown in Table 1. Note that the final moment of the thermal storage device is defined as the moment when the phase change material is completely melted or solidified.

[0058] Table 1. State parameter table of a specific embodiment of the present invention.

[0059]

[0060]

[0061] Based on the structural, operational, and state parameters in the above specific embodiments, the energy efficiency evaluation method for multi-stage phase change material thermal storage devices proposed according to the present invention is used for step-by-step calculation. Figure 4 The energy efficiency indicators of this embodiment are shown, demonstrating that the energy efficiency evaluation method can effectively help in the comprehensive evaluation of the storage / heat release performance of multi-stage phase change material thermal accumulators, energy efficiency classification, and performance comparison, thereby providing theoretical support and guidance for their subsequent optimization design.

[0062] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for evaluating the energy efficiency of a thermal storage device filled with multi-stage phase change material, characterized in that, It includes the following steps, Step 1: The thermal storage tank has partition walls and is filled with multi-stage phase change material. The calculation parameters of the partition walls include the mass of the partition walls used in the thermal storage tank. and volume The specific heat capacity at constant pressure of the partition wall The initial and final moments of the heat storage / release process and The average temperature of the partition wall at the initial and final moments of the heat storage / release process. and ; Step 2: Calculate the sensible heat stored / released by the partition wall during the entire heat storage / release process. The heat storage capacity of the partition wall is: The heat release of the partition wall is: ; Third step: Obtain the calculation parameters of the high thermal conductivity additive material used in the thermal storage device. The calculation parameters of the additive material include the mass of the high thermal conductivity additive material in the thermal storage device. and volume The specific heat capacity at constant pressure of high thermal conductivity additives The average temperature of the high thermal conductivity additive at the beginning and end of the heat storage / release process. and The high thermal conductivity additives are metal fins, metal foam, or expanded graphite; Step 4: Calculate the stored / released sensible heat of the high thermal conductivity additive, wherein the stored heat of the high thermal conductivity additive is: The heat release of the high thermal conductivity additive is: ; Step 5: Obtain the calculation parameters of different phase change materials in the solid state. The calculation parameters in the solid state include the mass of different phase change materials. and volume Specific heat capacity at constant pressure in the solid state of different phase change materials The average temperature of different phase change materials at the initial and final moments of the heat storage / release process. and The phase transition temperature of various phase change materials is , where i represents the i-th phase change material; Step 6: Calculate the sensible heat stored / released in the solid state of the multi-stage phase change material during the entire heat storage / release process. The sensible heat stored / released is: The heat absorbed during thermal storage is The heat released during exothermic reactions is ; n represents the total category of phase change materials used in the thermal storage device; Step 7: Obtain the calculation parameters of different phase change materials in the liquid phase state, including the isobaric specific heat capacity of different phase change materials in the liquid phase state. and volume ; Step 8: Calculate the stored / released sensible heat in the liquid phase state of the multi-stage phase change material, wherein the stored / released sensible heat is: The heat absorbed during thermal storage is The heat released during exothermic reactions is ; Step 9: Obtain the latent heat absorbed / released during the phase transition process of different phase change materials. Calculate the total latent heat storage / release of the multi-stage phase change material, wherein the total latent heat storage / release is: ; Step 10: Calculate the time required for the entire heat storage / release process to complete: ; Step 11: Calculate the total mass or volume of the entire thermal storage tank, where the total mass is: ; The total volume of the heat storage device is: The volume expansion phenomenon of phase change material after phase change to liquid; the filling volume of phase change material in the design of heat storage tank is based on liquid phase change material. Step 12: Calculate the volume change evaluation factor of the phase change material in the entire thermal storage tank. When in thermal storage state, the corresponding volume expansion of the phase change material is determined by this volume change evaluation factor. When in an exothermic state, the corresponding phase change material experiences volume shrinkage, and the volume change evaluation factor is: ; Step 13: Obtain the calculated parameters of the heat exchange fluid flow in the heat storage tank. These parameters include the volumetric flow rate of the heat exchange fluid in different pipes. and pressure drop , j is the j-th heat exchange fluid pipe in the heat storage tank; Step 14: Obtain the pump power consumption caused by fluid heat exchange in the heat storage tank, wherein the pump power consumption is: k is the total number of heat exchange fluid pipes in the heat storage tank; Step 15: Calculate the energy efficiency index of the multi-stage phase change material thermal storage device, including the heat storage / release density and volume change evaluation factors per unit time, unit mass, and unit pump work: ; And evaluation factors for heat storage / release density and volume change per unit time, unit volume, and unit pump work: ; α and β are weighting factors, reflecting the weight of thermal storage density and volume change evaluation in energy efficiency indicators, and the sum of the two is 1; It represents the coefficient by which low-quality thermal energy is converted into high-quality electrical energy.

2. The energy efficiency evaluation method for a multi-stage phase change material thermal storage device according to claim 1, wherein, The coefficient by which low-quality heat energy is converted into high-quality electrical energy The conversion is based on the source of the electricity.

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