Self-temperature-adjusting building envelope mathematical model establishing method based on phase change energy storage material
By establishing a mathematical model of a self-regulating building envelope, the shortcomings of existing technologies in the study of the dynamic thermal performance of phase change energy storage materials in building walls have been addressed. This has enabled rapid and low-cost simulation and optimization, and promoted the development of passive energy-saving buildings.
Patent Information
- Application Number
- CN202510768502.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-10
- Publication Date
- 2025-11-14
AI Technical Summary
Existing research has neglected the complex thermal environment and usage conditions of buildings in practical applications, and lacks systematic research on the dynamic thermal performance of phase change energy storage materials in building walls. Traditional experimental methods are time-consuming, costly, and difficult to promote.
A mathematical model of a self-regulating temperature building envelope based on phase change energy storage materials was established. By constructing a three-dimensional physical model, setting assumptions, establishing continuity, momentum, and energy equations, and combining ICEM-CFD software for structured mesh generation, the heat transfer and phase interface changes during the phase change process were simulated.
It enables rapid and low-cost simulation of the self-temperature regulation capability of phase change energy storage materials in real building environments, provides a theoretical basis for designing efficient self-temperature regulation building envelopes, and promotes the development of passive energy-saving buildings.
Smart Images
Figure CN120951412A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of building energy conservation technology, specifically to a method for establishing a mathematical model of a self-regulating building envelope based on phase change energy storage materials. Background Technology
[0002] With the increasing severity of the global energy crisis and environmental problems, building energy conservation has become a hot topic of social concern. The proportion of energy consumption in buildings as a percentage of global total energy consumption is increasing year by year, especially in heating and cooling. To effectively reduce building energy consumption, many new materials and technologies have been introduced into the field of building energy conservation. Among them, phase change energy storage materials, due to their ability to effectively absorb and release large amounts of latent heat during temperature changes, thus achieving a self-regulating temperature effect, are gradually attracting the attention and application of researchers.
[0003] Although numerous studies have explored the properties of phase change energy storage materials (PCEs) and their applications in buildings, most have focused on optimizing the material's performance and testing in laboratory environments. Existing research often overlooks the complex thermal environment and actual usage conditions of buildings, lacking a systematic study of the dynamic thermal performance of PCEs in building walls. Furthermore, traditional experimental research methods are time-consuming, costly, and lack repeatability, hindering widespread application. Therefore, it is necessary to employ mathematical models for simulation analysis, combined with practical conditions, to systematically study the thermal performance and energy-saving effects of PCEs in building walls. Summary of the Invention
[0004] In view of this, the purpose of this invention is to establish a mathematical model of a self-regulating building envelope based on phase change energy storage materials, and to reveal its self-regulating mechanism through theoretical analysis and numerical simulation.
[0005] The method for establishing a mathematical model of a self-regulating temperature building envelope based on phase change energy storage materials according to the present invention includes the following steps:
[0006] Constructing a three-dimensional physical model: A simplified three-dimensional model is established for the melting and solidification process of phase change energy storage materials in building walls to describe the energy exchange, natural convection, and dynamic changes of the phase interface between the solid and liquid phases during the phase change process.
[0007] Assumptions: Neglect shell thickness and contact thermal resistance; assume no heat loss in the heat storage unit and thermal insulation of the external walls; assume the inlet temperature of the heat transfer fluid remains constant; assume both the heat transfer fluid and liquid paraffin are incompressible fluids and satisfy the Boussinesq assumption.
[0008] Establish a continuity equation to describe the mass conservation of the heat transfer fluid;
[0009] A momentum equation is established to describe the flow behavior of fluids around phase change energy storage materials;
[0010] An energy equation was established to simulate the temperature changes experienced by phase change energy storage materials during melting and solidification.
[0011] Determine the initial and boundary conditions:
[0012] For the solidification process, at the initial moment, the temperatures of both the phase change material and the heat exchange fluid are constant. The temperatures of the phase change material and the heat exchange fluid are set to ensure that the temperature gradient causes the phase change material to transfer heat to the heat exchange fluid, thereby initiating the solidification process. In terms of boundary conditions, in the energy storage unit, except for the coupling surface in contact with the heat exchange fluid, all other surfaces are set as adiabatic surfaces to ensure that all heat exchange occurs through the coupling surface in contact with the heat exchange fluid. During the time period s>0, the phase change material and the heat exchange fluid exchange heat through the coupling surface.
[0013] For the melting process: At the initial moment, the temperatures of the phase change material and the heat exchange fluid are constant. The temperatures of the phase change material and the heat exchange fluid are set to ensure that the temperature gradient causes the heat exchange fluid to transfer heat to the phase change material, thereby initiating the melting process. In terms of boundary conditions, except for the coupling surface in contact with the heat exchange fluid, all external wall surfaces are set as adiabatic surfaces. During the time period s>0, the phase change material and the heat exchange fluid exchange heat through the coupling surface.
[0014] Furthermore, when constructing the three-dimensional physical model, the symmetry of the energy storage unit in the building wall is utilized, and half of the energy storage unit structure is taken to construct a simplified three-dimensional physical model in a three-dimensional coordinate system. During the solidification process, a physical model without fins is first established, and a structured mesh is generated using ICEM-CFD software to accurately simulate the heat transfer and phase change process inside the material and obtain the evolution of the phase change interface over time. Then, a physical model with fins is established, and a structured mesh is generated in the same way to compare the heat transfer efficiency and energy-saving effect under different structures. A corresponding physical model is established for the melting process and the computational domain mesh is generated. Through numerical simulation of the simplified three-dimensional physical model, the self-temperature regulation capability of the phase change energy storage material during the melting and solidification process in the actual building environment is studied.
[0015] Furthermore, the continuity equation is based on the premise that the mass of the fluid does not change during the flow and heat transfer process, and is constructed using the following formula: in id, i, Z o , j, and α represent the density, velocity vector, specific heat, thermal conductivity, and expansion coefficient of the heat exchange fluid and paraffin, respectively.
[0016] Furthermore, when establishing the momentum equation, a standard laminar flow model is used for calculation of heat transfer fluids. For phase change materials, the momentum equation needs to consider the flow characteristics of the solid-liquid two-phase region and accurately describe the dynamic changes of the solid-liquid interface.
[0017] Furthermore, when establishing the energy equation, the thermal conductivity and latent heat properties of the material need to be considered to handle the absorption and release of energy during the solid-liquid phase transition. At the same time, the energy equation needs to be closely coupled with the continuity equation and the momentum equation to ensure that the interaction between heat transfer and fluid flow can be accurately reflected.
[0018] The beneficial effects of this invention are as follows: By constructing a three-dimensional model that considers energy exchange between solid and liquid phases, natural convection, and dynamic changes at the phase interface, and combining the enthalpy-porous medium method with the Solidification / Melting model, this invention can accurately characterize the heat transfer behavior of phase change energy storage materials during melting and solidification in building envelopes. Utilizing the symmetry of the energy storage units in building walls, modeling only half of the structure significantly reduces computation time and resource consumption. In practical scientific research or engineering applications, key heat transfer laws can be quickly obtained without the need for costly calculations of the complete and complex structure, accelerating technological iteration. The mathematical model constructed in this invention can effectively simulate the self-regulating temperature capability of phase change energy storage materials under different conditions. This provides a theoretical basis for designing more efficient self-regulating temperature building envelopes and promotes the development of passive energy-saving buildings. Attached Figure Description
[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments:
[0020] Figure 1 This is a three-dimensional schematic diagram of an experimental platform for the melting / solidification process in building walls.
[0021] Figure 2 This is a schematic diagram showing the location of the phase change layer. Detailed Implementation
[0022] This invention employs the enthalpy-porous medium method and the Solidification / Melting model to solve the melting / solidification problem of phase change energy storage materials (PCEs) in building walls, aiming to study their self-regulating temperature mechanism and energy-saving effects. The enthalpy-porous medium method treats the phase change enthalpy as a source term in the energy equation. By solving the momentum and energy equations of the solid-liquid two-phase interface of the PCE within a fixed grid region of the building wall, it effectively solves the energy transfer problem at the solid-liquid interface of the PCE. Simultaneously, the mushy region model of the solid-liquid interface of the PCE is treated as a porous medium region, and the different phase proportions are characterized by the liquid phase component, thus handling the discontinuous changes in the physical properties of the solid-liquid two-phase PCE. Furthermore, the Solidification / Melting model effectively simulates complex phase change heat transfer processes, particularly the energy exchange between different phase states and the dynamic changes at the interface.
[0023] To investigate the self-regulating temperature mechanism and energy-saving effect of phase change energy storage materials in building walls, this invention employs a simplified three-dimensional model of the melting and solidification processes of the energy storage unit. Due to the symmetry of the energy storage unit within the building wall, to reduce computation time and resource consumption, only half of the structure is considered in the three-dimensional coordinate system to establish a physical model. This simplified model effectively describes the energy exchange between the solid and liquid phases, natural convection, and dynamic changes at the phase interface during the phase change process. During solidification, a physical model without fins is first established and then meshed using ICEM-CFD software. This method accurately simulates the heat transfer and phase change processes within the material and obtains the evolution of the phase change interface over time. To further explore the influence of fins on the phase change process, a physical model with fins is also established and meshed using the same structure to compare the heat transfer efficiency and energy-saving effect under different structures. For the melting process of the energy storage unit, a corresponding physical model is established, and the computational domain is meshed. Numerical simulations of simplified models can effectively study the heat transfer behavior of phase change energy storage materials in actual building environments, especially the self-regulating temperature capability of the materials during melting and solidification.
[0024] To investigate the self-regulating temperature mechanism and energy-saving effect of phase change energy storage materials in building walls, this invention makes a series of assumptions about the three-dimensional model of the melting and solidification processes to ensure the effectiveness and convenience of numerical calculations, and to maintain consistency with the heat storage unit in the experiment. The specific assumptions are as follows:
[0025] 1) Ignoring shell thickness and contact thermal resistance: In practical applications, shell thickness and contact thermal resistance may affect heat transfer, but in order to simplify the calculation, this invention assumes that these factors are ignored, so as to focus on the heat transfer characteristics of the phase change energy storage material itself.
[0026] 2) No heat loss in the thermal storage unit, with insulated external walls: It is assumed that the thermal storage unit has no heat loss during the entire phase change process, and the external walls are insulated. This assumption simplifies the calculation and allows the focus to be placed on the heat transfer process inside the phase change material, avoiding the influence of the external environment on the results.
[0027] 3) The inlet temperature of the heat transfer fluid remains constant: To simplify the model and ensure the stability of the calculation, it is assumed that the inlet temperature of the heat transfer fluid remains constant. This helps to clarify the influence of the heat transfer fluid on the system when studying the melting and solidification process of phase change materials.
[0028] 4) Both the heat transfer fluid and liquid paraffin are incompressible fluids, satisfying the Boussinesq assumption: In actual phase change heat transfer processes, density changes in the fluid may affect buoyancy and flow characteristics. This invention assumes that both the heat transfer fluid and liquid paraffin are incompressible fluids and satisfy the Boussinesq assumption, i.e., density changes are considered only in the buoyancy term, while other physical properties remain constant. This assumption simplifies the solution of the fluid dynamics equations and improves computational efficiency.
[0029] In order to study the self-temperature regulation mechanism and energy-saving effect of phase change energy storage materials in building walls, this invention mainly constructs a three-dimensional model of the melting / solidification process in the following detailed steps.
[0030] For heat transfer fluids, a continuity equation must first be established to describe the mass conservation of the fluid. This equation ensures that the mass of the fluid remains constant during flow and heat transfer. This step is fundamental to the entire model, ensuring that the fluid can be correctly simulated during heat transfer. It is assumed that the density, velocity vector, specific heat, thermal conductivity, and expansion coefficient of the heat transfer fluid and paraffin are determined by... Let id, i, Zo, j, and α represent the values. Then the calculation formula is:
[0031]
[0032] Next, a momentum equation is established to describe the flow behavior of the fluid around the phase change energy storage material. For the heat transfer fluid, since the Rayleigh number is less than 10... 9 Therefore, a standard laminar flow model was used for calculations. This model is applicable to natural convection and ensures accurate simulation of fluid flow at low speeds.
[0033]
[0034] For phase change materials, due to the phase changes they undergo during melting and solidification, the momentum equation needs to consider the flow characteristics of the solid-liquid two-phase region and accurately describe the dynamic changes at the solid-liquid interface. The fuzzy region constant is given by X. MU This indicates that the reference temperature is determined by S.RE It is shown that the enthalpy value at the reference temperature is represented by g RE It is shown. The total enthalpy is represented by G, and the liquid fraction of the phase change material is represented by ε. Then there is the calculation formula:
[0035]
[0036] The energy equation is the core equation for describing heat transfer and is used to simulate the temperature changes experienced by the phase change energy storage material during the melting and solidification processes. This equation needs to consider the thermal conductivity and latent heat characteristics of the material and reasonably handle the absorption and release of energy during the solid-liquid phase change process. At the same time, the energy equation also needs to be tightly coupled with the continuity equation and the momentum equation to ensure that the mutual influence between heat transfer and fluid flow can be accurately reflected.
[0037]
[0038] G = g + εM
[0039]
[0040] In the simulation of the phase change material, the liquid fraction ε is an important parameter used to describe the proportion of the solid and liquid phases of the material during the melting and solidification processes. Through the liquid fraction, the phase state distribution of the material at different time points can be dynamically reflected. This step represents the liquid fraction through field variables, thereby simplifying the explicit solution of the solid-liquid interface and accurately simulating the evolution process of the phase interface over time. The introduction of this parameter makes the simulation of the phase change process more intuitive and accurate.
[0041]
[0042] Figure 1 Shows a three-dimensional schematic diagram of the experimental platform for the melting / solidification process in a building wall. When studying the three-dimensional model of the melting / solidification process of the phase change energy storage material in a building wall, in order to reveal its self-regulating temperature mechanism and energy-saving effect, the present invention first makes a detailed setting of the initial conditions and boundary conditions for the solidification process. The following are the initial conditions and boundary conditions of this model during the solidification process. At the initial moment (s = 0), the temperatures of the phase change material and the heat exchange fluid are both constant, where the temperature of the phase change material is set to S PC = S0 = 361K, and the temperature of the heat exchange fluid is set to S AI = S1 = 356K. Since S1 < S0, this setting ensures that at the beginning moment, the temperature gradient causes the phase change material to start transferring heat to the heat exchange fluid, thereby initiating the solidification process. Figure 2 Gives a schematic diagram of the layout position of the phase change layer during the experiment of the present invention.
[0043] Regarding boundary conditions, for adiabatic surfaces, in the energy storage unit, all surfaces except the coupling surface in contact with the heat exchange fluid are set as adiabatic surfaces. This means that these surfaces will not transfer heat, thus ensuring that all heat exchange occurs only through the coupling surface in contact with the heat exchange fluid. This setting simulates the situation where the energy storage unit is isolated from the outside world in practical applications, making the calculation model closer to reality.
[0044]
[0045] The coupling surface of the energy storage unit is the only surface that exchanges heat with the heat exchange fluid. During the time interval s>0, the phase change material inside the energy storage unit exchanges heat with the external heat exchange fluid through this coupling surface. This setting ensures that the phase change material transfers heat to the heat exchange fluid through the coupling surface during solidification, thereby gradually reducing its temperature and undergoing a phase change. Accurate simulation of this process is crucial for studying the self-regulating temperature mechanism and energy-saving effect of phase change materials in building walls.
[0046]
[0047] The initial and boundary conditions during the melting process are described in detail below. At the initial moment (s = 0), the temperatures of both the phase change material and the heat exchange fluid are constant, with the temperature of the phase change material set to S. PC =S3=301K, while the temperature of the heat exchange fluid is set to S AI =S4=359K. Since S4 is higher than S3, this setting ensures that at the beginning, the temperature gradient causes the heat exchange fluid to transfer heat to the phase change material, thereby initiating the melting process.
[0048] In the energy storage unit, all external walls, except for the coupling surfaces in contact with the heat exchange fluid, are designed as adiabatic surfaces. This means that these surfaces will not transfer heat, ensuring that all heat exchange occurs only through the coupling surfaces in contact with the heat exchange fluid. This design simulates the situation where the energy storage unit is isolated from the outside world in real-world applications, making the computational model more realistic.
[0049]
[0050] The coupling surface of the energy storage unit is the only surface that exchanges heat with the phase change material (PCM). During the time interval t>0, the PCM inside the energy storage unit exchanges heat with the heat exchange fluid inside the U-shaped tube wall through this coupling surface. This configuration ensures that the PCM absorbs heat from the heat exchange fluid through the coupling surface during the melting process, thereby gradually increasing its temperature and undergoing a phase change. Accurate simulation of this process is crucial for studying the self-regulating temperature mechanism and energy-saving effect of PCM in building walls.
[0051]
[0052] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations; any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the protection scope of the present invention.
Claims
1. A method for establishing a mathematical model of a self-regulating temperature building envelope based on phase change energy storage materials, characterized in that, Includes the following steps: Constructing a three-dimensional physical model: A simplified three-dimensional model is established for the melting and solidification process of phase change energy storage materials in building walls to describe the energy exchange, natural convection, and dynamic changes of the phase interface between the solid and liquid phases during the phase change process. Assumptions: Neglect shell thickness and contact thermal resistance; assume no heat loss in the thermal storage unit and that the external walls are insulated; Assume that the inlet temperature of the heat transfer fluid remains constant; assume that both the heat transfer fluid and the liquid paraffin are incompressible fluids and satisfy the Boussinesq assumption. Establish a continuity equation to describe the mass conservation of the heat transfer fluid; A momentum equation is established to describe the flow behavior of fluids around phase change energy storage materials; An energy equation was established to simulate the temperature changes experienced by phase change energy storage materials during melting and solidification. Determine the initial and boundary conditions: For the solidification process, at the initial moment, the temperatures of both the phase change material and the heat exchange fluid are constant. The temperatures of the phase change material and the heat exchange fluid are set to ensure that the temperature gradient causes the phase change material to transfer heat to the heat exchange fluid, thereby initiating the solidification process. In terms of boundary conditions, in the energy storage unit, except for the coupling surface in contact with the heat exchange fluid, all other surfaces are set as adiabatic surfaces to ensure that all heat exchange occurs through the coupling surface in contact with the heat exchange fluid. During the time period s>0, the phase change material and the heat exchange fluid exchange heat through the coupling surface. For the melting process: At the initial moment, the temperatures of the phase change material and the heat exchange fluid are constant. The temperatures of the phase change material and the heat exchange fluid are set to ensure that the temperature gradient causes the heat exchange fluid to transfer heat to the phase change material, thereby initiating the melting process. In terms of boundary conditions, except for the coupling surface in contact with the heat exchange fluid, all external wall surfaces are set as adiabatic surfaces. During the time period s>0, the phase change material and the heat exchange fluid exchange heat through the coupling surface.
2. The mathematical model establishment method according to claim 1, characterized in that: When constructing the three-dimensional physical model, the symmetry of the energy storage unit in the building wall is utilized. Half of the energy storage unit structure is taken and a simplified three-dimensional physical model is constructed in the three-dimensional coordinate system. During the solidification process, a physical model without fins is first established and structured mesh is generated using ICEM-CFD software to accurately simulate the heat transfer and phase change process inside the material and obtain the evolution of the phase change interface over time. Then, a physical model with fins is established and structured mesh is generated in the same way to compare the heat transfer efficiency and energy saving effect under different structures. A corresponding physical model is established for the melting process and the computational domain mesh is generated. Through numerical simulation of the simplified three-dimensional physical model, the self-temperature regulation capability of the phase change energy storage material during the melting and solidification process in the actual building environment is studied.
3. The mathematical model establishment method according to claim 1, characterized in that: The continuity equation is based on the premise that the mass of the fluid does not change during the flow and heat transfer process, and is constructed using the following formula: Where θd, θ, id, i, Zo, j, and α are the density, velocity vector, specific heat, thermal conductivity, and expansion coefficient of the heat exchange fluid and paraffin, respectively.
4. The mathematical model establishment method according to claim 1, characterized in that: When establishing the momentum equation, a standard laminar flow model is used for calculations of heat transfer fluids. For phase change materials, the momentum equation needs to consider the flow characteristics of the solid-liquid two-phase region and accurately describe the dynamic changes of the solid-liquid interface.
5. The mathematical model establishment method according to claim 1, characterized in that: When establishing the energy equation, the thermal conductivity and latent heat properties of the material need to be considered, and the absorption and release of energy during the solid-liquid phase transition process need to be handled. At the same time, the energy equation needs to be closely coupled with the continuity equation and the momentum equation to ensure that the interaction between heat transfer and fluid flow can be accurately reflected.