Thermophysical property configuration method of hydrated salt thermochemical energy storage material

Abstract

The invention provides a thermophysical property configuration method of a hydrated salt thermochemical energy storage material. The method comprises the following steps: establishing an energy storage process model of the hydrated salt thermochemical energy storage material; in the enthalpy change process of the hydrated salt thermochemical energy storage material, selecting a group of thermophysical parameters of the hydrated salt thermochemical energy storage material, and calculating a global highest temperature and an energy storage progress amount by using an energy storage progress model; traversing and selecting all possible groups of thermophysical parameters of the hydrated salt thermochemical energy storage material in sequence, and calculating the global highest temperature and the energy storage progress quantity in the enthalpy change process of the hydrated salt thermochemical energy storage material corresponding to each group of thermophysical parameters; and determining the optimal thermophysical parameters of the hydrated salt thermochemical energy storage material according to all the global highest temperatures and the energy storage progress quantity. According to the method, not only can the temperature distribution in the cooling process be calculated, but also the energy storage progress quantity of the hydrated salt thermochemical energy storage material in the working process can be directly calculated, and researchers can be helped to visually know the utilization rate of the heat storage material.

Description

Technical Field

[0001] The invention relates to the technical field of energy storage, and in particular to a method for configuring the thermal properties of a hydrated salt thermochemical energy storage material. Background Art

[0002] Electronic devices are becoming more high-frequency, lightweight and highly integrated, and the heat flux density of chip devices is increasing, which poses a challenge to the heat dissipation and cooling system. Common forced air cooling, heat pipe cooling and liquid cooling still cannot meet the needs in some places where high-power devices are used, the environment is closed and quick heat removal is required in a short time. Therefore, the energy storage material cooling method came into being and became a short-time quick heat removal cooling method for high heat flux density devices.

[0003] Cooling systems based on phase change materials can usually cope with situations where the heat flux density is less than 5W / cm2. However, the local heat flux density of today's high-power electronic devices (such as high-performance computing chips, radar components, etc.) has reached more than 30W / cm2, and sometimes even exceeds 100W / cm2, which puts higher requirements on the energy storage density of heat storage materials, and thermochemical heat storage materials can meet this demand. Thermochemical heat storage materials represented by hydrated salts can absorb a large amount of heat by using their solid-liquid phase change and high-temperature thermal decomposition reactions. Their heat storage density is determined by the phase change enthalpy and the thermal decomposition reaction enthalpy. Its advantage is that it has a larger heat storage density, and the chemical reaction heat storage process has small losses. Relevant studies have shown that its heat storage density is generally one order of magnitude higher than that of phase change heat storage materials, reaching 400-870kWh / m3.

[0004] However, since the mechanism of thermal decomposition reaction is more complicated than the phase change process, the simulation of the working condition of hydrated salt thermochemical energy storage materials is limited, which hinders the prediction and design of thermochemical energy storage cooling systems. At present, the existing models of hydrated salt thermochemical energy storage materials focus on describing the reaction kinetics of the thermal decomposition process. Such models are not only complex in form of equations, but also unable to directly calculate the energy storage process of hydrated salt thermochemical energy storage materials during operation, thus making it difficult to provide direct guidance for the design of cooling systems and the selection of physical properties of hydrated salt thermochemical energy storage materials. Summary of the invention

[0005] The embodiment of the present invention provides a method for configuring the thermophysical properties of a hydrated salt thermochemical energy storage material, so as to effectively improve the utilization rate of the hydrated salt thermochemical energy storage material.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme.

[0007] A method for configuring the thermal properties of a hydrated salt thermochemical energy storage material, comprising:

[0008] Establish the energy storage process model of hydrated salt thermochemical energy storage materials;

[0009] During the enthalpy change process of the hydrated salt thermochemical energy storage material, a set of thermophysical property parameters of the hydrated salt thermochemical energy storage material is selected, and the global maximum temperature and energy storage process amount during the enthalpy change process of the hydrated salt thermochemical energy storage material are calculated using the energy storage process model;

[0010] All possible groups of thermophysical parameters of the hydrated salt thermochemical energy storage material are selected in turn, and the global maximum temperature and energy storage process amount in the enthalpy change process of the hydrated salt thermochemical energy storage material corresponding to each group of thermophysical parameters are calculated, and the optimal thermophysical parameters of the hydrated salt thermochemical energy storage material are determined according to all the global maximum temperatures and energy storage process amounts.

[0011] Preferably, the energy storage process model of the hydrated salt thermochemical energy storage material is established, comprising:

[0012] The solid basic heat conduction equation of hydrated salt thermochemical energy storage material is:

[0013]

[0014] Where k is the thermal conductivity of the hydrated salt thermochemical energy storage material, ρ is the density of the hydrated salt thermochemical energy storage material, c is the mass specific heat capacity of the hydrated salt thermochemical energy storage material, is the Laplace operator, t is time, and T is temperature in Celsius;

[0015] The enthalpy value of phase change and thermochemical reaction of hydrated salt thermochemical energy storage material is regarded as internal heat source power Q, and the heat conduction equation of hydrated salt thermochemical energy storage material is established according to the associated variables of internal heat source power Q.

[0016] Assuming that in a microelement at a certain position, within a moment dt, the unit mass of the hydrated salt thermochemical energy storage material undergoes an enthalpy change, the temperature of the hydrated salt thermochemical energy storage material changes from t0 to (t0+dt), the mass percentage changes from m0 to (m0+dm), and the energy storage process volume changes from r0 to (r0+dr), then the heat source power Q per unit volume is:

[0017]

[0018] DH stands for enthalpy change

[0019] The enthalpy change of the hydrated salt thermochemical energy storage material during the time dt is:

[0020] dH=Hdr (3)

[0021] H is the total enthalpy change of phase change and decomposition reaction during the whole working process of hydrated salt thermochemical energy storage material;

[0022] The energy storage process r of the reaction at a certain moment is:

[0023]

[0024] In the above formula, m(T) is the weight percentage of the hydrated salt thermochemical energy storage material at time T, m end It is the weight percentage of the hydrated salt thermochemical energy storage material after the entire reaction is completed. The differential of the energy storage process r to the weight m of the hydrated salt thermochemical energy storage material is:

[0025]

[0026] Define the first-order derivative function of the thermal weight loss curve m(T) as DTG(T), and take the differential to get:

[0027] dm=m′(T)dT=DTG(T)dT (6)

[0028] dm is the change in mass percentage during the considered time dt;

[0029] Combining the above equations, we get the heat conduction control equation of the hydrated salt thermochemical energy storage material:

[0030]

[0031] Define the corrected heat capacity C corresponding to the hydrated salt thermochemical energy storage material m (T) is:

[0032]

[0033] The corrected heat capacity C m Substituting (T) into the heat conduction control equation, the heat conduction problem of hydrated salt thermochemical energy storage material becomes a heat conduction problem with variable properties:

[0034]

[0035] The above equations (4)-(9) constitute the energy storage process model of hydrated salt thermochemical energy storage materials.

[0036] Preferably, during the enthalpy change process of the hydrated salt thermochemical energy storage material, a set of thermophysical property parameters of the hydrated salt thermochemical energy storage material is selected, and the global maximum temperature and energy storage process amount during the enthalpy change process of the hydrated salt thermochemical energy storage material are calculated using the energy storage process model, including:

[0037] In the process of enthalpy change of the hydrated salt thermochemical energy storage material, a set of thermophysical parameters is selected according to the hydrated salt thermochemical energy storage material used, and the thermophysical parameters include thermal conductivity k, mass specific heat capacity c, unit mass enthalpy value H and density ρ at the current time t, and the thermophysical parameters are substituted into the energy storage process model one by one, and the corrected heat capacity C is calculated according to formula (8):m (T);

[0038]

[0039] The corrected heat capacity C m Substituting (T) into the heat conduction equation shown in formula (7), we obtain:

[0040]

[0041] Discretize the above equation and write it in explicit difference format. According to the setting The initial condition calculation is:

[0042]

[0043] In the above formula, subscript a represents the chip, subscript b represents the heat storage material container, subscript c represents the hydrated salt thermochemical energy storage material, that is, TCM / EG material, i represents the time iteration step, j represents the spatial node inside the TCM / EG material, P is the chip heating power, k is the heat dissipation coefficient between the system and the environment, and when calculating, the time step is Δt=1s, and the node step is evenly divided into 60;

[0044] In calculating the temperature of the hydrated salt thermochemical energy storage material Finally, the energy storage process of TCM / EG material at any time is calculated using the following formula:

[0045]

[0046] The temperature of the hydrated salt thermochemical energy storage material The energy storage process quantity r is the quantity that changes with time and space position, that is, T(x, y, z, t) and r(x, y, z, t). At the last moment of the enthalpy change process, the mean value r of the energy storage process quantity at each position in the entire calculation domain is calculated in the form of volume weighted average. ave , and calculate the global maximum temperature T max ;

[0047]

[0048] Where, t end Refers to the last moment of the calculated enthalpy change process, x, y, z are the spatial coordinates of the hydrated salt thermochemical energy storage material, and V is the total volume of the hydrated salt thermochemical energy storage material.

[0049] Preferably, the method of sequentially traversing and selecting all possible groups of thermophysical parameters of the hydrated salt thermochemical energy storage material, calculating the global maximum temperature and energy storage process amount in the enthalpy change process of the hydrated salt thermochemical energy storage material corresponding to each group of thermophysical parameters, and determining the optimal thermophysical parameters of the hydrated salt thermochemical energy storage material according to all the global maximum temperatures and energy storage process amounts includes:

[0050] Determine the global maximum temperature T corresponding to the current group of thermal physical parameters max Whether it meets the cooling system temperature requirements. If not, the global maximum temperature T corresponding to the current group thermal physical property parameters will not be recorded. max and the mean value r of the energy storage process ave ; Select the next set of thermophysical parameters and calculate the T corresponding to the next set of thermophysical parameters max and r ave , determine the global maximum temperature T corresponding to the next set of thermophysical parameters max Whether it meets the temperature requirements of the cooling system, if so, record the corresponding thermal physical parameters and the corresponding r of the next set of thermal physical parameters ave ; Then continue to select the next set of thermophysical parameters and calculate the T corresponding to the next set of thermophysical parameters max and r ave , continue with subsequent judgment and recording operations;

[0051] The above process is repeated until all possible groups of hydrated salt physical parameters are traversed to obtain the global maximum temperature T max Thermophysical parameters and corresponding r of each group of hydrated salt thermochemical energy storage materials that meet the temperature requirements of the cooling system ave , from the recorded thermophysical parameters and the corresponding r ave Find r in ave A set of thermophysical parameters that is closest to 99% is used as the optimal thermophysical parameters of the hydrated salt thermochemical energy storage material.

[0052] It can be seen from the technical solutions provided by the above-mentioned embodiments of the present invention that the embodiments of the present invention propose a thermophysical property configuration strategy based on the energy storage process model. This strategy can help designers of thermochemical heat storage cooling systems find the thermophysical properties of the optimal hydrated salt thermochemical energy storage materials corresponding to a specific cooling system, so as to guide the synthesis of composite heat storage materials.

[0053] Additional aspects and advantages of the present invention will be given in part in the following description, which will become obvious from the following description, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0055] Figure 1 A processing flow chart of a method for configuring the thermal properties of a hydrated salt thermochemical energy storage material provided in an embodiment of the present invention.

[0056] Figure 2 1 is a structural diagram of a chip cooling unit in Example 1 of the present invention, (a) is a cross-sectional diagram with structural components marked, and (b) is an abstract model diagram.

[0057] Figure 3 This is a schematic diagram of the thermogravimetric analysis results of TCM58 / expanded graphite material in Example 2 of the present invention.

[0058] Figure 4 Schematic diagram showing the comparison between the calculation results of the energy storage process model in Example 2 of the present invention and the experimental values.

[0059] Figure 5 This is a schematic diagram showing the effect of the mass ratio of expanded graphite in the TCM58 / expanded graphite material on thermal conductivity and enthalpy in Example 3 of the present invention.

[0060] Figure 6 Schematic diagram of the global maximum temperature and average energy storage process corresponding to each group of thermophysical properties in Example 3 of the present invention. DETAILED DESCRIPTION

[0061] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0062] It will be understood by those skilled in the art that, unless expressly stated, the singular forms "one", "said", and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, the "connection" or "coupling" used herein may include wireless connection or coupling. The term "and / or" used herein includes any unit and all combinations of one or more associated listed items.

[0063] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0064] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings, and each embodiment does not constitute a limitation on the embodiments of the present invention.

[0065] The embodiment of the present invention provides a method for configuring the thermophysical properties of a hydrated salt thermochemical energy storage material, which solves the technical problems that the existing thermochemical heat storage operating condition model cannot directly calculate the energy storage process of the hydrated salt thermochemical energy storage material during operation, and it is difficult to use a simulation method to find the optimal thermophysical properties of the hydrated salt thermochemical energy storage material.

[0066] Enthalpy change is the change in the enthalpy of an object and is a thermodynamic function that describes the state of a system. Enthalpy is the sum of the internal energy of a system plus the product of its volume and the external pressure acting on the system. In a chemical reaction, enthalpy change describes the change in energy during the reaction. If the enthalpy of the reactants is higher than the enthalpy of the products, the excess energy will be released in the form of heat, which is an exothermic reaction; conversely, if the enthalpy of the reactants is lower than the enthalpy of the products, energy needs to be absorbed from the environment, which is an endothermic reaction.

[0067] Example 1

[0068] The processing flow of a method for configuring the thermal properties of a hydrated salt thermochemical energy storage material provided by an embodiment of the present invention is as follows: Figure 1 As shown, the processing steps include the following:

[0069] Step S10, establishing an energy storage process model of the hydrated salt thermochemical energy storage material.

[0070] Step S20, during the enthalpy change process of the above-mentioned hydrated salt thermochemical energy storage material, a set of thermophysical property parameters of the above-mentioned hydrated salt thermochemical energy storage material is selected, and the global maximum temperature and energy storage process amount during the enthalpy change process of the above-mentioned hydrated salt thermochemical energy storage material are calculated using the established energy storage process model.

[0071] Step S30, sequentially traverse and select all possible groups of thermophysical property parameters of the hydrated salt thermochemical energy storage material, calculate the global maximum temperature and energy storage process amount in the enthalpy change process of the hydrated salt thermochemical energy storage material corresponding to each group of thermophysical property parameters, determine the optimal thermophysical property parameters of the hydrated salt thermochemical energy storage material according to all the global maximum temperatures and energy storage process amounts, and form a thermophysical property configuration strategy for the hydrated salt thermochemical energy storage material.

[0072] The above step S10 specifically includes: the derivation and establishment process of the energy storage process model is as follows:

[0073] Start with the basic heat conduction equation for solids given in heat transfer theory.

[0074]

[0075] Where k is the thermal conductivity of the hydrated salt thermochemical energy storage material [W / (m·K)], and ρ is the density of the hydrated salt thermochemical energy storage material [kg / m 3 ], c is the mass specific heat capacity of the hydrated salt thermochemical energy storage material [J / (kg·℃)], is the Laplace operator, t is time [s], and T is temperature in Celsius [℃].

[0076] The enthalpy of phase change and thermochemical reaction of hydrated salt thermochemical energy storage material is regarded as the internal heat source power Q, and the heat conduction equation of hydrated salt thermochemical energy storage material is established according to the associated variables of the internal heat source power Q.

[0077] Assume that in a microelement at a certain position, within a moment dt, the unit mass of the hydrated salt thermochemical energy storage material undergoes an enthalpy change dH due to phase change or decomposition reaction, the temperature of the hydrated salt thermochemical energy storage material changes from t0 to (t0+dt), the mass percentage changes from m0 to (m0+dm), and the energy storage process volume changes from r0 to (r0+dr). Then the heat source power Q per unit volume is expanded as:

[0078]

[0079] DH stands for enthalpy change

[0080] In chemical reaction kinetics, it is generally believed that the enthalpy change heat effect is uniform as the reaction progresses. Then the enthalpy change that occurs during the time dt is:

[0081] dH=Hdr (3)

[0082] H is the total enthalpy change of phase change and decomposition reaction during the entire working process of the hydrated salt thermochemical energy storage material.

[0083] The hydrated salt thermochemical energy storage material undergoes a dehydration and weight loss process during phase change and decomposition reactions, and the amount of dehydration is proportional to the weight lost. The energy storage process r of the reaction at a certain moment is:

[0084]

[0085] In the above formula, m(T) is the weight percentage of the hydrated salt thermochemical energy storage material at time T, m end It is the weight percentage of the hydrated salt thermochemical energy storage material after the entire reaction is completed. The differential of r to the weight m of the hydrated salt thermochemical energy storage material is:

[0086]

[0087] The thermogravimetric curve (TG curve) gives the relationship between mass percentage and temperature. The thermogravimetric analysis test and thermophysical property test of the hydrated salt thermochemical energy storage material used are carried out to obtain the thermogravimetric curve m(T) and DTG(T) curve and basic thermophysical properties. The first-order derivative function of the thermogravimetric curve m(T) is defined as DTG(T), and the differential is obtained:

[0088] dm=m′(T)dT=DTG(T)dT (6)

[0089] dm is the change in mass percentage during the considered time dt.

[0090] Combining the above equations, we get the heat conduction control equation of the hydrated salt thermochemical energy storage material:

[0091]

[0092] In order to make the above formula simple, the modified heat capacity C corresponding to the hydrated salt thermochemical energy storage material is defined as m (T):

[0093]

[0094] The corrected heat capacity C m Substituting (T) into the heat conduction control equation, the heat conduction problem of hydrated salt thermochemical energy storage material becomes a heat conduction problem with variable properties:

[0095]

[0096] The above equations (4)-(9) constitute the energy storage process model of hydrated salt thermochemical energy storage materials.

[0097] The above step S20 specifically includes:

[0098] Since the energy storage process model of the above-mentioned hydrated salt thermochemical energy storage material can directly calculate the energy storage process amount r during the solution process, a thermophysical property configuration strategy can be further proposed based on this energy storage process model. When regulating the matrix composite properties of hydrated salt thermochemical energy storage materials, the question of whether high thermal conductivity or high enthalpy is better is usually encountered. In order to guide the selection of thermophysical properties of hydrated salt thermochemical energy storage materials in a cooling system, the following strategy is proposed to select the best thermophysical property to ensure that the enthalpy of the hydrated salt thermochemical energy storage material is fully utilized during use and the thermal conductivity is increased as much as possible.

[0099] The process of thermophysical property configuration strategy of hydrated salt thermochemical energy storage materials includes the following steps:

[0100] (1) During the enthalpy change of the hydrated salt thermochemical energy storage material due to phase change or decomposition reaction, the position, temperature and energy of the hydrated salt thermochemical energy storage material will change. A set of thermophysical property parameters is selected according to the hydrated salt thermochemical energy storage material used. The thermophysical property parameters include thermal conductivity k, mass specific heat capacity c, unit mass enthalpy value H and density ρ at the current time t. There can be many groups of thermophysical property parameters, and the thermophysical property parameters of each group are selected in turn.

[0101] (2) Substitute the thermophysical parameters into the energy storage process model one by one for finite element calculation and solution, and obtain the temperature T corresponding to the current thermophysical property and the change of the energy storage process quantity r with the position at the last moment in the solution time range, and then calculate the global maximum temperature T max and the global average energy storage process r ave , the calculation formulas are as follows:

[0102]

[0103] Where, t end Refers to the last moment of calculation, x, y, z are the spatial coordinates of the hydrated salt thermochemical energy storage material, and V is the total volume of the hydrated salt thermochemical energy storage material. The above-mentioned last moment refers to the last time node of the time range set during finite element solution. For example, in Example 3, the time range of solution is set to 0-3000s, then the last moment is the node at 3000s. The time range of solution is set according to the time period that the researcher wants to investigate.

[0104] Since the temperature of each position of the heat storage material is different during operation, the energy storage process r of each position of the material is also different. That is, r changes with time and also changes with position. Formula (4) defines the energy storage process r of a certain position, from which r of each position can be calculated. However, when considering the thermal property configuration strategy, the average degree of different positions needs to be used as a reference, so the global average energy storage process r is proposed ave The meaning of formula (11) is: at the last moment, the mean value r of the energy storage process at each position in the entire calculation domain is calculated in the form of volume weighted average ave .

[0105] Equations (2)-(6) are derived based on a microelement at a certain position within a moment dt. The purpose of this is to expand the heat source term of equation (1) in differential form, so that in equation (7) Merge similar terms. Because it is described based on a certain position, the equation does not show the properties of the variables T and r distributed with the spatial position, but these derivations are also valid when extended to other positions, so in fact there is such a property. Equations (7)-(9) are the derivation results and the control equations of the model. They actually contain spatial coordinates and Laplace operator terms. The full expansion of For the simplicity of the equation, we used The way of writing.

[0106] By using the control equations (7)-(9), the initial conditions and boundary conditions are set, and the solution can be obtained after discretization (the solution process is introduced in Example 2 of this article and will not be described in detail here). The temperature T and energy storage process r obtained by the solution are quantities that change with time and spatial position, namely T(x, y, z, t) and r(x, y, z, t). Equation (10) is to calculate the maximum value of the solved T(x, y, z, t) to find t end The maximum value of T in the calculation domain at the moment; Formula (11) is the volume weighted average calculation of the solved r(x, y, z, t). In short, T max and r ave The solution results of equations (7)-(9) are used for secondary calculation to extract the representative information of the maximum and average values ​​in the solution results for use in the next step.

[0107] The above step S30 specifically includes: (3) determining the global maximum temperature T corresponding to the current group thermal physical property parameters max Does it meet the cooling system temperature requirements? If not, go back to step (2) to select the next set of thermophysical parameters, and then calculate the T corresponding to the next set of thermophysical parameters. max and r ave . Determine the global maximum temperature T corresponding to the next set of thermophysical parameters maxWhether it meets the temperature requirements of the cooling system, if so, record the corresponding thermal physical parameters and the corresponding r of the next set of thermal physical parameters ave Then, return to step (2) to continue calculating the T corresponding to the next set of thermophysical parameters. max and r ave , and continue with subsequent judgment and recording operations.

[0108] Repeat steps (2) and (3) until all possible groups of hydrated salt physical parameters are traversed and the global maximum temperature T is obtained. max Thermophysical parameters and corresponding r of each group of hydrated salt thermochemical energy storage materials that meet the temperature requirements of the cooling system ave , from the recorded thermophysical parameters and the corresponding r ave Find r in ave The set of thermophysical parameters closest to 99% is the thermophysical parameters of the best hydrated salt thermochemical energy storage material in this cooling system. This step ensures that the thermal conductivity of the hydrated salt thermochemical energy storage material used can meet the temperature control requirements, and also keeps the heat storage capacity of the hydrated salt thermochemical energy storage material from being completely exhausted during the entire use process, and is in an effective temperature control working state.

[0109] The entire optimization strategy focuses on the global maximum temperature T corresponding to each set of thermal properties. max , and the global average energy storage process r ave During the screening, we first ensured that the thermal conductivity of the hydrated salt thermochemical energy storage material was able to conduct the heat from the heat source in a timely manner to meet the required temperature of the cooling system, and then on this basis, we looked for situations where the heat storage capacity was maximized and fully utilized.

[0110] After obtaining the optimal thermophysical parameters of the hydrated salt thermochemical energy storage material, the material manufacturer can change the compound ratio accordingly, and adjust the physical properties of the product to be as close as possible to the optimal thermophysical parameters of the present invention, so that the heat storage material product can meet the optimal heat storage effect of a specific usage scenario. The present invention can also be used to calculate the optimal thermophysical parameters for different usage scenarios to develop hydrated salt heat storage materials suitable for different scenarios (such as heat storage, solar heat storage system, electronic device heat absorption, etc.).

[0111] Embodiment 2:

[0112] TCM58 / Expanded Graphite Material Temperature and Energy Storage Process Simulation in Chip Cooling Unit

[0113] The TCM58 / expanded graphite material (hereinafter referred to as TCM / EG) used is a commercial composite hydrated salt thermochemical heat storage material that can be directly purchased and applied to the chip cooling system. After thermal property testing, its basic thermal properties are listed in Table 1. The structural diagram of the chip cooling unit is shown in the attached figure. Figure 2As shown, the model parameters related to it are listed in Table 1.

[0114] Table 1 Model parameters used in Example 1

[0115]

[0116]

[0117] Use a thermogravimetric analyzer to perform thermogravimetric analysis on TCM / EG materials. The test results are as follows Figure 3 As shown. The weight loss temperature range of TCM / EG material is mainly concentrated in 45-150℃. After 150℃, the total weight loss is 34.84%, and the crystal water of hydrated salt molecules is completely decomposed. Figure 3 The weight loss curve in is recorded as m(T), and its derivative function curve is recorded as DTG(T). The curve data is recorded in a piecewise straight line (interval is 1°C), and the stable value of the weight loss curve at high temperature is recorded as m end .

[0118] According to formula (8), the corrected heat capacity C is calculated m (T), record C in a segmented straight line (interval of 1°C) m (T) changes with T.

[0119]

[0120] The above corrected heat capacity C m Substituting (T) into the heat conduction equation shown in formula (7), we obtain:

[0121]

[0122] according to Figure 2 (b) The model abstraction discretizes the above equation and writes it in explicit difference format. According to the setting to find the numerical solution.

[0123]

[0124] In the above formula, subscript a represents the chip, subscript b represents the heat storage material container, subscript c represents the hydrated salt thermochemical energy storage material, that is, TCM / EG material, i represents the time iteration step, j represents the spatial node inside the TCM / EG material, P is the chip heating power [W], and k is the heat dissipation coefficient between the system and the environment [W / K]. When calculating, the time step is Δt=1s, and the node step is evenly divided into 60.

[0125] The initial conditions used are:

[0126]

[0127] Figure 4 Schematic diagram of the comparison between the calculation results and experimental values ​​of the energy storage process model in Example 2 of the present invention. After numerical solution, the chip temperature of interest and the temperature at the center of TCM / EG are plotted as follows: Figure 4 As shown in the upper part. It can be seen that the temperature rise process of TCM / EG experienced two "platforms", which occurred at about 55°C and 110°C respectively; this shows that the energy storage process model can basically reflect the phase change and thermal decomposition reaction of the thermal storage material. In addition, whenever TCM / EG enters the state of phase change or decomposition reaction, the chip temperature curve will become flat, which conforms to the basic laws of heat transfer, indicating that the model can preliminarily reflect the basic process of the use of thermal storage materials.

[0128] After the temperature has been calculated, the energy storage process of TCM / EG material at any time is calculated using the following formula:

[0129]

[0130] For example, at 3500s, the center temperature of the TCM / EG material is 110.7°C. According to the above formula, the energy storage process at the center of the TCM / EG material is 71.6%, indicating that its heat storage capacity has not been completely exhausted.

[0131] In order to verify the accuracy of the energy storage process model proposed in this invention, we built a chip cooling unit for actual measurement and calculated the percentage error between the experimental value and the simulation value at each moment to measure the accuracy of the model. Figure 4 As shown in the lower part, the model is prone to large errors when the temperature rises in the initial stage, when the phase change ends, and during the thermal decomposition stage. For the temperature prediction after long-term operation, the average error of the energy storage process model is 4.87%, which is acceptable for engineering application scenarios, and also shows that the calculation results of this model are accurate and have engineering application value.

[0132] Example 3: Optimal thermophysical configuration of TCM58 / expanded graphite material in chip cooling unit

[0133] Example 2 calculates the temperature change process and energy storage process of the TCM / EG material in the chip cooling unit, but at the last moment r = 71.6%, the heat storage capacity of the thermochemical heat storage material is not fully utilized. Therefore, the thermal properties of the TCM / EG material can also be optimized to guide the material preparation party to develop the most suitable TCM / EG material for this cooling system.

[0134] Changing the mass ratio of expanded graphite in TCM / EG can significantly affect the thermal properties of the material, especially thermal conductivity and enthalpy. Figure 5Schematic diagram of the effect of the mass ratio of expanded graphite in the TCM58 / expanded graphite material on thermal conductivity and enthalpy in Example 3 of the present invention. Figure 5 As shown, for this reason, we searched for the best mass ratio of expanded graphite through this embodiment.

[0135] pass Figure 5 According to the change law in the graphite mass, a total of 31 groups of material thermal properties are obtained in the range of 20%-50% (interval 1%). Subsequently, the thermal property parameters of these 31 groups of materials are sequentially substituted into the energy storage process model for calculation (other parameters remain constant), and the calculation process is as described in Example 2, and the simulation time is 0-3000s. The global maximum temperature T is calculated for each group of results. max , and the global average energy storage process r ave , the calculation formulas are as follows:

[0136]

[0137] Next, determine whether the global maximum temperature Tmax meets the cooling system temperature requirement. In this example, the cooling system temperature requirement is set to be lower than 160°C. If it does not meet the requirement, calculate the next set of thermal properties Tmax. max and r ave If it meets the requirements, record this set of thermophysical properties and the corresponding r ave , and then calculate the next set of thermophysical properties T max and r ave . Figure 6 is the T corresponding to each group of thermal properties in Example 3 of the present invention max and r ave Schematic diagram, such as Figure 6 As shown, when r ave When it is less than 100%, it means that the heat storage capacity is not fully utilized. ave When it reaches 100%, it means that the heat storage capacity is not enough to meet the needs of this cooling system. Therefore, it is more appropriate to select a storage process of 99%, which can ensure that the TCM / EG heat storage capacity is just fully utilized.

[0138] From the recorded thermophysical properties and the corresponding r ave Find r in ave The set of thermophysical properties closest to 99%, so the optimal TCM / EG thermophysical property parameters for this cooling system are 35% of the mass of expanded graphite. Specifically, the thermal conductivity is 12.6W / (m··K), the phase change enthalpy is 185J / g, and the thermal decomposition reaction enthalpy is 454J / g.

[0139] In this case, in order to find the optimal EG content of TCM / EG, it is necessary to make full use of the enthalpy of TCM / EG materials during the working process so as to complete the reaction at the last second. This strategy not only maintains the temperature control capability of the entire process, but also pursues the highest possible thermal conductivity.

[0140] In summary, the embodiment of the present invention provides an energy storage process model for hydrated salt thermochemical energy storage materials. This energy storage process model can not only calculate the temperature distribution during the cooling process, but also directly calculate the energy storage process of the hydrated salt thermochemical energy storage material during the working process, which can help researchers intuitively understand the utilization rate of the heat storage material. The present invention can make full use of the enthalpy value of the hydrated salt heat storage material during use and improve the thermal conductivity as much as possible, and find the balance point between the heat storage capacity and thermal conductivity of the material.

[0141] The energy storage process model of the present invention is easy to use. Compared with the existing model that introduces the reaction kinetics equation, the present invention does not need to perform complex reaction kinetics tests on the hydrated salt thermochemical energy storage material, but only uses the thermal weight loss curve to calculate the corrected heat capacity, which simplifies the simulation calculation process for researchers. The energy storage process model of the present invention can reveal the consumption process of the heat storage capacity of the hydrated salt heat storage material during the working process. The physical property configuration strategy based on this energy storage process model can guide the optimization of the thermal management system using the heat storage material.

[0142] The prediction accuracy of the energy storage process model of the present invention is good. The average deviation between the calculated value and the experimental value of the energy storage process model for temperature is 4.87% (Example 2), which meets the requirements of industrial design.

[0143] Those skilled in the art can understand that the accompanying drawings are only schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required to implement the present invention.

[0144] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The device and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0145] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for configuring the thermal properties of a hydrated salt thermochemical energy storage material, characterized in that: include: Establish the energy storage process model of hydrated salt thermochemical energy storage materials; During the enthalpy change process of the hydrated salt thermochemical energy storage material, a set of thermophysical property parameters of the hydrated salt thermochemical energy storage material is selected, and the global maximum temperature and energy storage process amount during the enthalpy change process of the hydrated salt thermochemical energy storage material are calculated using the energy storage process model; All possible groups of thermophysical parameters of the hydrated salt thermochemical energy storage material are selected in turn, and the global maximum temperature and energy storage process amount in the enthalpy change process of the hydrated salt thermochemical energy storage material corresponding to each group of thermophysical parameters are calculated, and the optimal thermophysical parameters of the hydrated salt thermochemical energy storage material are determined according to all the global maximum temperatures and energy storage process amounts.

2. The method according to claim 1, characterized in that The energy storage process model of establishing the hydrated salt thermochemical energy storage material comprises: The solid basic heat conduction equation of hydrated salt thermochemical energy storage material is: Where k is the thermal conductivity of the hydrated salt thermochemical energy storage material, ρ is the density of the hydrated salt thermochemical energy storage material, c is the mass specific heat capacity of the hydrated salt thermochemical energy storage material, is the Laplace operator, t is time, and T is temperature in Celsius; The enthalpy value of phase change and thermochemical reaction of hydrated salt thermochemical energy storage material is regarded as internal heat source power Q, and the heat conduction equation of hydrated salt thermochemical energy storage material is established according to the associated variables of internal heat source power Q. Assuming that in a microelement at a certain position, within a moment dt, the unit mass of the hydrated salt thermochemical energy storage material undergoes an enthalpy change, the temperature of the hydrated salt thermochemical energy storage material changes from t0 to (t0+dt), the mass percentage changes from m0 to (m0+dm), and the energy storage process volume changes from r0 to (r0+dr), then the heat source power Q per unit volume is: DH stands for enthalpy change The enthalpy change of the hydrated salt thermochemical energy storage material during the time dt is: dH=Hdr (3) H is the total enthalpy change of phase change and decomposition reaction during the whole working process of hydrated salt thermochemical energy storage material; The energy storage process r of the reaction at a certain moment is: In the above formula, m(T) is the weight percentage of the hydrated salt thermochemical energy storage material at time T, m end It is the weight percentage of the hydrated salt thermochemical energy storage material after the entire reaction is completed. The differential of the energy storage process r to the weight m of the hydrated salt thermochemical energy storage material is: Define the first-order derivative function of the thermal weight loss curve m(T) as DTG(T), and take the differential to get: dm=m′(T)dT=DTG(T)dT (6) dm is the change in mass percentage during the considered time dt; Combining the above equations, we get the heat conduction control equation of the hydrated salt thermochemical energy storage material: Define the corrected heat capacity C corresponding to the hydrated salt thermochemical energy storage material m (T) is: The corrected heat capacity C m Substituting (T) into the heat conduction control equation, the heat conduction problem of hydrated salt thermochemical energy storage material becomes a heat conduction problem with variable properties: The above equations (4)-(9) constitute the energy storage process model of hydrated salt thermochemical energy storage materials.

3. The method according to claim 2, characterized in that In the process of enthalpy change of the hydrated salt thermochemical energy storage material, a set of thermophysical property parameters of the hydrated salt thermochemical energy storage material is selected, and the global maximum temperature and energy storage process amount in the enthalpy change process of the hydrated salt thermochemical energy storage material are calculated using the energy storage process model, including: In the process of enthalpy change of the hydrated salt thermochemical energy storage material, a set of thermophysical parameters is selected according to the hydrated salt thermochemical energy storage material used, and the thermophysical parameters include thermal conductivity k, mass specific heat capacity c, unit mass enthalpy value H and density ρ at the current time t, and the thermophysical parameters are substituted into the energy storage process model one by one, and the corrected heat capacity C is calculated according to formula (8): m (T); The corrected heat capacity C m Substituting (T) into the heat conduction equation shown in equation (7), we obtain: Discretize the above equation and write it in explicit difference format. According to the setting The initial condition calculation is: In the above formula, subscript a represents the chip, subscript b represents the heat storage material container, subscript c represents the hydrated salt thermochemical energy storage material, that is, TCM / EG material, i represents the time iteration step, j represents the spatial node inside the TCM / EG material, P is the chip heating power, k is the heat dissipation coefficient between the system and the environment, and when calculating, the time step is Δt=1s, and the node step is evenly divided into 60; In calculating the temperature of the hydrated salt thermochemical energy storage material Finally, the energy storage process of TCM / EG material at any time is calculated using the following formula: The temperature of the hydrated salt thermochemical energy storage material The energy storage process quantity r is the quantity that changes with time and space position, that is, T(x, y, z, t) and r(x, y, z, t). At the last moment of the enthalpy change process, the mean value r of the energy storage process quantity at each position in the entire calculation domain is calculated in the form of volume weighted average. ave , and calculate the global maximum temperature T max ; In the formula, t end Refers to the last moment of the calculated enthalpy change process, x, y, z are the spatial coordinates of the hydrated salt thermochemical energy storage material, and V is the total volume of the hydrated salt thermochemical energy storage material.

4. The method according to claim 3, characterized in that The method of sequentially traversing and selecting all possible groups of thermophysical parameters of the hydrated salt thermochemical energy storage material, calculating the global maximum temperature and energy storage process amount in the enthalpy change process of the hydrated salt thermochemical energy storage material corresponding to each group of thermophysical parameters, and determining the optimal thermophysical parameters of the hydrated salt thermochemical energy storage material according to all the global maximum temperatures and energy storage process amounts, includes: Determine the global maximum temperature T corresponding to the current group of thermal physical parameters max Whether it meets the cooling system temperature requirements. If not, the global maximum temperature T corresponding to the current group thermal physical property parameters will not be recorded. max and the mean value r of the energy storage process ave ; Select the next set of thermophysical parameters and calculate the T corresponding to the next set of thermophysical parameters max and r ave , determine the global maximum temperature T corresponding to the next set of thermophysical parameters max Whether it meets the temperature requirements of the cooling system, if so, record the corresponding thermal physical parameters and the corresponding r of the next set of thermal physical parameters ave ; Then continue to select the next set of thermophysical parameters and calculate the T corresponding to the next set of thermophysical parameters max and r ave , continue with subsequent judgment and recording operations; The above process is repeated until all possible groups of hydrated salt physical parameters are traversed to obtain the global maximum temperature T max Thermophysical parameters and corresponding r of each group of hydrated salt thermochemical energy storage materials that meet the temperature requirements of the cooling system ave , from the recorded thermophysical parameters and the corresponding r ave Find r in ave A set of thermophysical parameters that is closest to 99% is used as the optimal thermophysical parameters of the hydrated salt thermochemical energy storage material.

Images