Method for calculating the amount of multi-stage latent heat storage

Abstract

The application discloses a kind of multistage latent heat storage's quantity calculation method, first, the multistage latent heat storage required to be evaluated is identified, the multistage latent heat storage required to be evaluated is divided into regions, the boundary condition of the multistage latent heat storage required to be evaluated and the running time are obtained, the evaluation calculation parameter of each phase change material in the divided region is set, the current temperature value of each phase change material of the divided region at time t Is obtained, and the corresponding temperature distribution image is recorded;Solve the heat storage / heat release evaluation physical quantity of each phase change material in the divided region at time t , and the distribution of the heat storage / heat release quantity of each phase change material is obtained according to temperature distribution image;Calculate the total heat storage / heat release quantity of multistage latent heat storage at time t , according to the running time of multistage latent heat storage, the total heat storage / heat release quantity of multistage latent heat storage in the whole running process is calculated.The method realizes the energy quality evaluation of the heat storage, to optimize the performance of heat storage and provide theoretical guidance.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage quality evaluation technology, and in particular to a multi-stage latent heat thermal energy storage device. Methods for quantity distribution. Background Technology

[0002] Latent heat storage devices store / release heat through the phase change process of phase change materials (PCMs). They have advantages such as high energy density, stable energy, small system footprint, simple operation, and system safety, and are widely used in fields such as solar thermal storage, building energy conservation, and industrial waste heat recovery.

[0003] However, the low thermal conductivity of phase change materials (PCMs) significantly limits their application efficiency. Therefore, their heat transfer performance can be enhanced by adding additives with high thermal conductivity or optimizing the reservoir structure. Traditional latent heat reservoirs are filled with single-stage PCMs with a single melting point. When the melting point of the PCM is too high, it cannot melt at lower temperatures, hindering the storage of large amounts of latent heat. While a lower melting point allows for melting and heat storage in cold weather, the energy quality of the latent heat reservoir is low. Compared to latent heat reservoirs filled with single-stage PCMs, multi-stage reservoirs using multi-stage nested concentric heat exchange pipes filled with multiple stages of PCMs with different melting points not only improve heat transfer performance and alleviate the shortcomings of single-melting-point PCMs, enhancing the environmental adaptability of the reservoir, but also exhibit higher energy storage quality under the same environmental conditions.

[0004] Performance evaluation of latent heat storage devices is crucial for promoting the optimization of thermal storage system structures. Currently, storage / release time and the amount of heat stored / released are commonly used as performance evaluation standards for latent heat storage devices. However, these standards only reflect the storage / release rate and the magnitude of the heat stored / released, failing to reflect the energy quality of the stored / released heat. The usable energy of a thermal storage system often better reflects the system's quality; therefore, evaluating the quality of the stored / released heat is more important for thermal storage devices. Under given environmental conditions, in a reversible process, the theoretically maximum useful work that can be done or the minimum useful work that can be consumed can serve as a measure of energy quality. Therefore, for multi-stage latent heat storage devices, through... The method of evaluating the energy quality of thermal storage tanks can better reflect their adaptability to the environment. Therefore, it is crucial to propose an energy quality evaluation method applicable to multi-stage latent heat storage tanks. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a multi-stage latent heat storage device. This method calculates the quantity and evaluates the quality of energy stored in multi-stage latent heat storage tanks. By prioritizing energy quality as the primary optimization objective, it aims to better optimize the performance of the storage tanks, reflect the commercial application value of multi-stage latent heat storage tanks, and provide theoretical guidance for the performance optimization of multi-stage latent heat storage systems.

[0006] To solve the above-mentioned technical problems, the present invention provides a multi-stage latent heat storage device. The method for calculating quantities includes the following steps:

[0007] Step 1: Identify the multi-stage latent heat storage device to be evaluated. If it is an experimental system, only evaluate the multi-stage latent heat storage device module and exclude other experimental system sub-devices. If it is a numerical simulation system, only evaluate the structure with the overall physical model of the system as the external boundary.

[0008] Step 2: Divide the multi-stage latent heat storage tank regions to be evaluated. If it is an experimental system, divide the regions according to the melting points of the different stages of phase change materials added; if it is a numerical simulation system, divide the regions according to the computational grid nodes of the physical model.

[0009] Step 3: Obtain the boundary conditions of the multi-stage latent heat storage tank to be evaluated, as well as the initial operating time t1 and the end time t2 of the multi-stage latent heat storage tank; the boundary conditions include the initial temperature T. ini Heat exchange fluid inlet temperature T in Heat exchange fluid inlet velocity v in Ambient temperature T amb ;

[0010] Step 4: Set the evaluation calculation parameters for each stage of phase change materials in the divided regions. The evaluation calculation parameters include the solidification point T of each stage of phase change materials. sP,i Melting point T lP,i Phase transition point T mP,i Density ρ P,i Volume V P,i Specific heat capacity at constant pressure C pP,i Temperature T P,i Latent heat (L) P,i And the liquefaction rate γ of the phase change material, where i is the i-th stage of the phase change material;

[0011] Step 5: Obtain the current temperature T of each stage of the phase change material in the divided region at time t. P,i The value, and its relationship with the solidification point T of each phase change material. sP,i and melting point T lP,i For comparison, in an experimental system, temperature changes are recorded by a temperature sensing element, and the temperature distribution is imaged by an infrared camera; in a numerical simulation system, temperature changes are monitored by a data monitor, and the temperature distribution is imaged.

[0012] Step Six: Solve for the thermal storage evaluation physical quantities of each stage of phase change material in the divided region at time t. When the multi-stage latent heat storage device is in the thermal storage process, calculate the current thermal storage heat based on the temperature of each stage of phase change material at this moment. QuantityEx P,i as follows:

[0013] When T P,i ≤T sP,i ,

[0014]

[0015] When T P,i ≥T lP,i ,

[0016]

[0017] When T sP,i <T P,i <T lP,i ,

[0018]

[0019] Step 7: Solve for the heat release evaluation physical quantities of each stage of phase change material in the divided region at time t. When the multi-stage latent heat storage tank is in the heat release process, calculate the current heat release based on the temperature of each stage of phase change material at this moment. Quantity E'x P,i as follows:

[0020] When T P,i ≤T sP,i ,

[0021]

[0022] When T P,i ≥T lP,i ,

[0023]

[0024] When T sP,i <T P,i <T lP,i ,

[0025]

[0026] Step 8: Obtain the heat stored / released by each stage of phase change material in the divided region at time t. For the distribution of heat volume, in the case of an experimental system, the temperature distribution recorded by the infrared camera is imaged, and image features are extracted using image processing tools. Steps six and seven are then executed to calculate the current heat storage heat volume. Quantity and current heat release Quantity, to obtain the heat storage / release of phase change materials at various levels. The distribution of quantities; if it is a numerical simulation system, the heat storage / release of each stage of the phase change material is obtained by imaging the temperature distribution recorded by the data monitor. Distribution of quantity;

[0027] Step 9: Calculate the total heat storage / release of the multi-stage latent heat storage tank at time t. The quantity refers to the heat stored / released by the phase change materials at each level within the divided region. Sum of quantities (SumEx) P,i ,

[0028]

[0029] Where n is the number of regions divided;

[0030] Step 10: Calculate the total heat storage / release of the multi-stage latent heat storage tank during the entire operation process. TotalSumEx P,i ,

[0031]

[0032] Where t2-t1 is the operating time of the multi-stage latent heat storage device.

[0033] Furthermore, the multi-stage latent heat storage device in step one has a cubic, cylindrical, triangular prism, or polygonal prism shape, and the other experimental system sub-equipment includes pipes, flow meters, pumps, and test elements.

[0034] Due to the multi-stage latent heat storage device of this invention The calculation method employs the aforementioned technical solution. This method first identifies the multi-stage latent heat storage tanks to be evaluated, divides these tanks into regions, obtains the boundary conditions and operating time of the tanks, sets the evaluation calculation parameters for each stage of phase change materials within the divided regions, obtains the current temperature values ​​of each stage of phase change materials in the divided regions at time t, and records the corresponding temperature distribution image. Then, it solves for the physical quantities of heat storage / release of each stage of phase change materials in the divided regions at time t, and obtains the heat storage / release of each stage of phase change materials based on the temperature distribution image. Distribution of quantities; calculation of the total heat storage / release of the multi-stage latent heat storage tank at time t. Based on the operating time of the multi-stage latent heat storage tank, calculate the total heat storage / release of the multi-stage latent heat storage tank during the entire operation process. This method evaluates the quality of energy stored in multi-stage latent heat storage devices, using energy quality as the primary optimization objective to better optimize device performance, reflect the commercial application value of multi-stage latent heat storage devices, and provide theoretical guidance for the performance optimization of multi-stage latent heat storage systems. Attached Figure Description

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments:

[0036] Figure 1 This invention relates to a multi-stage latent heat storage device. Flowchart of quantity calculation method;

[0037] Figure 2 Schematic diagram of a multi-stage latent heat storage device in cubic, cylindrical, triangular prism, or polygonal prism shape;

[0038] Figure 3 This is a schematic diagram of a cylindrical shell-and-tube type three-stage latent heat storage device.

[0039] Figure 4 A schematic diagram of a grid model for a cylindrical shell-and-tube type three-stage latent heat storage device;

[0040] Figure 5 For the liquefaction rate, temperature, heat capacity, and other parameters of the thermal storage process in a cylindrical shell-and-tube three-stage latent heat storage device. A schematic diagram of the quantity distribution. Detailed Implementation

[0041] Implementation, for example Figure 1 As shown, the multi-stage latent heat storage device of the present invention The method for calculating quantities includes the following steps:

[0042] Step 1: Identify the multi-stage latent heat storage device to be evaluated. If it is an experimental system, only evaluate the multi-stage latent heat storage device module and exclude other experimental system sub-devices. If it is a numerical simulation system, only evaluate the structure with the overall physical model of the system as the external boundary.

[0043] Step 2: Divide the multi-stage latent heat storage tank regions to be evaluated. If it is an experimental system, divide the regions according to the melting points of the different stages of phase change materials added. That is, the phase change material with the first melting point is the first region, the phase change material with the second melting point is the second region, the phase change material with the third melting point is the third region, and so on, with the phase change material with the nth melting point being the nth region. If it is a numerical simulation system, divide the regions according to the computational grid nodes of the physical model. That is, if there are n computational grids, then it is divided into n different regions.

[0044] While ensuring convenient experimental operation, high accuracy of numerical simulation calculation, and short calculation time, the number of regions should be kept as large as possible.

[0045] Step 3: Obtain the boundary conditions of the multi-stage latent heat storage tank to be evaluated, as well as the initial operating time t1 and the end time t2 of the multi-stage latent heat storage tank; the boundary conditions include the initial temperature T. iniHeat exchange fluid inlet temperature T in Heat exchange fluid inlet velocity v in Ambient temperature T amb ;

[0046] Step 4: Set the evaluation calculation parameters for each stage of phase change materials in the divided regions. The evaluation calculation parameters include the solidification point T of each stage of phase change materials. sP,i Melting point T lP,i Phase transition point T mP,i Density ρ P,i Volume V P,i Specific heat capacity at constant pressure C pP,i Temperature T P,i Latent heat (L) P,i And the liquefaction rate γ of the phase change material, where i is the i-th stage of the phase change material;

[0047] Step 5: Obtain the current temperature T of each stage of the phase change material in the divided region at time t. P,i The value, and its relationship with the solidification point T of each phase change material. sP,i and melting point T lP,i For comparison, in an experimental system, temperature changes are recorded by a temperature sensing element, and the temperature distribution is imaged by an infrared camera; in a numerical simulation system, temperature changes are monitored by a data monitor, and the temperature distribution is imaged.

[0048] It is important to note that when recording temperature in experiments and numerical simulations, it is necessary to keep the time intervals as short as possible in order to obtain more data and ensure the accuracy of the results.

[0049] Step Six: Solve for the thermal storage evaluation physical quantities of each stage of phase change material in the divided region at time t. When the multi-stage latent heat storage device is in the thermal storage process, i.e., the melting process of each stage of phase change material, calculate the current thermal storage heat based on the temperature of each stage of phase change material at this moment. QuantityEx P,i as follows:

[0050] When T P,i ≤T sP,i ,

[0051]

[0052] When T P,i ≥T lP,i ,

[0053]

[0054] When T sP,i <T P,i <T lP,i ,

[0055]

[0056] Step 7: Solve for the exothermic evaluation physical quantities of each stage of phase change material in the divided region at time t. When the multi-stage latent heat storage tank is in the exothermic process, i.e., the solidification process of each stage of phase change material, calculate the current exothermic heat based on the temperature of each stage of phase change material at this moment. Quantity E'x P,i as follows:

[0057] When T P,i ≤T sP,i ,

[0058]

[0059] When T P,i ≥T lP,i ,

[0060]

[0061] When T sP,i <T P,i <T lP,i ,

[0062]

[0063] Among them, the physical quantities used for evaluation can be not only stored / released heat. The quantity can also be the melting / solidification rate, heat storage / release, heat storage / release efficiency, or heat storage / release of phase change materials at each level in the divided region. Efficiency, etc.;

[0064] Step 8: Obtain the heat stored / released by each stage of phase change material in the divided region at time t. For the distribution of heat volume, in the case of an experimental system, the temperature distribution recorded by the infrared camera is imaged, and image features are extracted using image processing tools. Steps six and seven are then executed to calculate the current heat storage heat volume. Quantity and current heat release Quantity, to obtain the heat storage / release of phase change materials at various levels. The distribution of quantities; if it is a numerical simulation system, the heat storage / release of each stage of the phase change material is obtained by imaging the temperature distribution recorded by the data monitor. Distribution of quantity;

[0065] Among them, the phase change materials at each level in the divided regions can achieve a distribution of physical quantities that is not only the stored / released heat. The quantity can also be the melting / solidification rate or heat storage / release rate of phase change materials at various levels;

[0066] Step 9: Calculate the total heat storage / release of the multi-stage latent heat storage tank at time t. The quantity refers to the heat stored / released by the phase change materials at each level within the divided region. Sum of quantities (SumEx) P,i ,

[0067]

[0068] Where n is the number of regions divided;

[0069] Step 10: Calculate the total heat storage / release of the multi-stage latent heat storage tank during the entire operation process. TotalSumEx P,i ,

[0070]

[0071] Where t2-t1 is the operating time of the multi-stage latent heat storage device.

[0072] Preferred, such as Figure 2 As shown, the multi-stage latent heat storage device in step one has the following shape and structure: cubic 1, cylindrical 2, triangular prism 3, or polygonal prism 4. Its concentric nested multi-stage heat exchange pipes are filled with multiple stages of phase change materials 5 with different melting points. The other experimental system sub-equipment includes pipes, flow meters, pumps, and test elements.

[0073] This method can determine the transient heat storage / release of a multi-stage latent heat storage tank. Quantity, and The distribution of quantity, based on heat storage / release Quantity and The distribution of energy can better guide the optimized design of the thermal storage device's structure and operation, thereby leading to a high-performance multi-stage latent heat storage device capable of storing high-quality heat.

[0074] This method is applicable to multi-stage latent heat storage tanks with different structures, arrangements, types of phase change materials, and levels of phase change materials, enabling the evaluation and optimization of the heat quality of multi-stage latent heat storage tanks.

[0075] To further understand this invention, examples of this method are as follows:

[0076] like Figure 3 As shown, the total number of meshes n in the numerical simulation of a cylindrical shell-and-tube three-stage latent heat storage device is 55939. At the initial temperature T... ini The temperature is 298.15 K, and the inlet temperature of the heat exchange fluid is T. in The temperature is 338.15 K and the inlet velocity of the heat exchange fluid is 0.25 m / s. 1 Ambient temperature T amb Calculate the thermal properties of this three-stage latent heat storage device during the heat storage process at a temperature of 298.15 K. Quantity distribution. Its grid model is as follows: Figure 4 As shown, highly thermally conductive Al2O3 nanoparticles with a volume concentration of 1% were added to the phase change material RT35(T mP,1 =315.15K), RT42(T mP,2 =323.15K), RT50(T mP,3 =333.15K) and heat transfer fluids, used to enhance heat transfer capacity. For example... Figure 3 As shown, RT35, RT42, and RT50, with added nanoparticles, are filled into the three heat exchange pipes 61, 62, and 63 of the three-stage latent heat storage device, respectively.

[0077] The relevant structural parameters are shown in Table 1:

[0078] Table 1 Structural Parameters

[0079]

[0080] The relevant physical properties are shown in Table 2:

[0081] Table 2 Physical Properties

[0082]

[0083] Based on the structural and physical property parameters in the above specific embodiments, the filling volume of different mixed phase change materials can be obtained. By performing step-by-step calculations according to this method, the following can be obtained: Figure 5 The liquefaction rate, temperature, heat capacity, and other parameters of the three-stage latent heat storage process are shown in the diagram. Distribution of quantities. Due to the symmetry of the model structure, the left region shows the distribution of liquefaction rate and heat, while the right region shows the distribution of temperature and... The distribution of quantities; furthermore, light-colored areas represent large values, and dark-colored areas represent small values. This allows for an effective assessment of the energy quality of the thermal storage device, providing theoretical support and guidance for subsequent optimization design, so as to achieve optimal thermal storage performance in practical engineering applications.

Claims

1. A multi-stage latent heat storage device The method for calculating quantities is characterized by This method includes the following steps: Step 1: Identify the multi-stage latent heat storage device to be evaluated. If it is an experimental system, only evaluate the multi-stage latent heat storage device module and exclude other experimental system sub-devices. If it is a numerical simulation system, only evaluate the structure with the overall physical model of the system as the external boundary. Step 2: Divide the multi-stage latent heat storage tank regions to be evaluated. If it is an experimental system, divide the regions according to the melting points of the different stages of phase change materials added; if it is a numerical simulation system, divide the regions according to the computational grid nodes of the physical model. Step 3: Obtain the boundary conditions of the multi-stage latent heat storage tank to be evaluated, as well as the initial operating time t1 and the end time t2 of the multi-stage latent heat storage tank; the boundary conditions include the initial temperature T. ini Heat exchange fluid inlet temperature T in Heat exchange fluid inlet velocity v in Ambient temperature T amb ; Step 4: Set the evaluation calculation parameters for each stage of phase change materials in the divided regions. The evaluation calculation parameters include the solidification point T of each stage of phase change materials. sP,i Melting point T lP,i Phase transition point T mP,i Density ρ P,i Volume V P,i Specific heat capacity at constant pressure C pP,i Temperature T P,i Latent heat (L) P,i And the liquefaction rate γ of the phase change material, where i is the i-th stage of the phase change material; Step 5: Obtain the current temperature T of each stage of the phase change material in the divided region at time t. P,i The value, and its relationship with the solidification point T of each phase change material. sP,i and melting point T lP,i For comparison, in an experimental system, temperature changes are recorded by a temperature sensing element, and the temperature distribution is imaged by an infrared camera; in a numerical simulation system, temperature changes are monitored by a data monitor, and the temperature distribution is imaged. Step Six: Solve for the thermal storage evaluation physical quantities of each stage of phase change material in the divided region at time t. When the multi-stage latent heat storage device is in the thermal storage process, calculate the current thermal storage heat based on the temperature of each stage of phase change material at this moment. Quantity Ex P,i as follows: When T P,i ≤T sP,i , When T P,i ≥T lP,i , When T sP,i <T P,i <T lP,i , Step 7: Solve for the heat release evaluation physical quantities of each stage of phase change material in the divided region at time t. When the multi-stage latent heat storage tank is in the heat release process, calculate the current heat release based on the temperature of each stage of phase change material at this moment. Quantity E'x P,i as follows: When T P,i ≤T sP,i , When T P,i ≥T lP,i , When T sP,i <T P,i <T lP,i , Step 8: Obtain the heat stored / released by each stage of phase change material in the divided region at time t. For the distribution of heat volume, in the case of an experimental system, the temperature distribution recorded by the infrared camera is imaged, and image features are extracted using image processing tools. Steps six and seven are then executed to calculate the current heat storage heat volume. Quantity and current heat release Quantity, to obtain the heat storage / release of phase change materials at various levels. The distribution of quantities; if it is a numerical simulation system, the heat storage / release of each stage of the phase change material is obtained by imaging the temperature distribution recorded by the data monitor. Distribution of quantity; Step 9: Calculate the total heat storage / release of the multi-stage latent heat storage tank at time t. The quantity refers to the heat stored / released by the phase change materials at each level within the divided region. Sum of quantities (SumEx) P,i , Where n is the number of regions divided; Step 10: Calculate the total heat storage / release of the multi-stage latent heat storage tank during the entire operation process. TotalSumEx P,i , Where t2-t1 is the operating time of the multi-stage latent heat storage device.

2. The multi-stage latent heat storage device according to claim 1 The method for calculating quantities is characterized by: The multi-stage latent heat storage device in step one has a cubic, cylindrical, triangular prism, or polygonal prism shape. The other experimental system sub-equipment includes pipes, flow meters, pumps, and test elements.

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