An anisotropic heat transfer analysis method and system suitable for 3D printed walls

Abstract

The application provides a kind of anisotropic heat transfer analysis method and system suitable for 3D printing wall, comprising the following steps: step S1, the structure network model of wall is constructed;Step S2, heat transport equation set is constructed;Step S3, the heat transport equation set is solved by iteration method, the final temperature field of the wall is obtained, the analysis of the anisotropic heat transfer of the wall is realized.The application is different from the solving idea of coordinate transformation, and is not targeted at solving the heat transfer amount in the coordinate direction, but by establishing a structure network model capable of representing the printing direction of the material, the heat transfer process is directly solved in the main heat performance direction of the material, avoiding the problem of inconsistent thermal conductivity in the coordinate direction, and the temperature distribution of the research object under certain environmental conditions and environmental temperature can be obtained.Based on this result, the local temperature condition inside the wall can be analyzed, and whether there is a local thermal defect under the structure can be evaluated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of anisotropic heat transfer of materials, and particularly relates to an anisotropic heat transfer analysis method and system suitable for 3D printed walls. BACKGROUND

[0002] The building industry needs a breakthrough to reduce its adverse effects on the environment and climate change, and the emergence of 3D printed buildings provides a new solution for the sustainable development of the building industry. As the basis for evaluating energy performance, the thermal performance of the external wall greatly affects the energy consumption of the building, so it is very important to study the thermal energy performance of the wall structure developed using innovative 3D printing technology.

[0003] The unique construction process of 3D printed buildings makes them exhibit thermal performance different from traditional buildings, mainly manifested as anisotropic heat transfer characteristics and complex wall geometry. The anisotropic heat transfer characteristics are derived from the uneven geometric distribution of the material caused by the printing process and the different forces in different directions, resulting in heat transfer performance related to the printing direction. At the same time, the macroscopic geometric design of the 3D printed wall may introduce cavity structures, which will form multiple heat transfer forms including conduction, convection and radiation, which increases the difficulty of the overall thermal analysis of the wall.

[0004] Many studies have focused on the anisotropic heat transfer of materials. For anisotropic materials, the dominant thermal coefficient direction can be determined according to the material properties, and the material coordinate system is established accordingly. When studying the anisotropic heat transfer, the heat transfer process can be solved by numerical simulation, and in the solving process, the entire research object has a global coordinate system. Therefore, the main difficulty of anisotropic heat transfer research is that the global coordinate system for simulation and solution has a certain angle with the material coordinate system corresponding to the dominant thermal coefficient, and this angle is the material direction angle. To solve this problem, existing research uses coordinate transformation to obtain the thermal conductivity coefficient in the direction of the global coordinate system being studied, that is, the material direction angle is used to convert the material dominant thermal coefficient matrix into the global thermal conductivity coefficient matrix, so as to establish the heat transfer equation in the global coordinate system for numerical solution.

[0005] However, unlike the anisotropic structures considered in existing research, the construction of 3D printed walls is based on the movement of the printing nozzle, and the printing direction changes in this process, so the material dominant thermal coefficient direction related to the printing direction also changes, that is, the material direction angle may be different at different positions in the same wall structure. According to the existing technical solution, the material direction angle of the 3D printed wall changes with the position, which will calculate the different thermal conductivity coefficients along the direction of the global coordinate system, thereby causing difficulties in numerical solution analysis.

[0006] Therefore, the existing technical solution cannot solve the problem of variable material direction angle, and is not suitable for the new research object of 3D printed walls. SUMMARY

[0007] The present application is to solve the above problems, and proposes an anisotropic heat transfer analysis method and system suitable for 3D printed building walls to adapt to the anisotropic thermal performance and the heat transfer process under the macroscopic complex geometry.

[0008] The present application provides an anisotropic heat transfer analysis method suitable for 3D printed walls, which has the following characteristics, including the following steps:

[0009] Step S1, constructing a structural network model of the wall, the structural network model representing the geometric structure of the wall and the dominant thermal coefficient direction of the material, the dominant thermal coefficient direction corresponding to the printing direction, the height direction and the width direction;

[0010] Step S2, constructing the heat transfer equation set of the structural network model in the dominant thermal coefficient direction;

[0011] Step S3, solving the heat transfer equation set in the structural network model by iteration method to obtain the final temperature field of the wall, and realizing the analysis of the anisotropic heat transfer of the wall.

[0012] In the anisotropic heat transfer analysis method suitable for 3D printed walls provided by the present application, it can also have the following characteristics: wherein, step S1 includes the following substeps:

[0013] Step S1.1, dividing the structure of the wall into a plurality of microelements;

[0014] Step S1.2, establishing the communication channels between the microelements to represent the solving direction;

[0015] Step S1.3, obtaining the microelement geometric data of each microelement and the communication direction of the communication channel.

[0016] In the anisotropic heat transfer analysis method suitable for 3D printed walls provided by the present application, it can also have the following characteristics: wherein, step S1.1 includes:

[0017] Based on the shape profile of the wall, the printing path is obtained, and then the printing direction, the height direction and the width direction of each position of the wall are obtained, and the structure of the wall is divided into a plurality of microelements with certain geometric size by cutting surface parallel to the printing direction, the height direction and the width direction, and other microelements adjacent to each microelement are in the dominant thermal coefficient direction of the microelement,

[0018] Step S1.1 is based on Python programming, and uses PoreSpy open source package to store image information of each microelement, the image information including microelement geometric data, and realizes the construction of microelements in the structural network model.

[0019] In the anisotropic heat transfer analysis method suitable for 3D printed wall provided by the application, the step S1.2 can further have the following characteristics:

[0020] The OpenPNM open source package is used to connect the microelement with the surrounding microelement, build the adjacency matrix and the association matrix between the microelements, form a microelement connection network, and the connected channel is the channel connecting the center points of the microelements, the connected direction of the connected channel is consistent with the dominant thermal coefficient direction, and the connected direction represents the solving direction.

[0021] In the anisotropic heat transfer analysis method suitable for 3D printed wall provided by the application, the step S1.3 can further have the following characteristics:

[0022] By extracting image information, the microelement geometry data of each microelement is obtained, and the microelement geometry data is assigned to the corresponding microelement. By the positional relationship between the microelements, the connected direction of the connected channel is determined, and the connected direction is assigned to the corresponding connected channel.

[0023] In the anisotropic heat transfer analysis method suitable for 3D printed wall provided by the application, the step S2 can further have the following characteristics: according to the energy conservation, the heat transfer equation group between each microelement and the adjacent microelement is established,

[0024] According to the porous medium material of the wall, the microelement includes a material microelement, and the heat transfer equation group includes a heat transfer equation between the material microelements,

[0025] The conductivity between the material microelements is solved by the sum of the series thermal resistance, and the conductivity between the microelements i and j is represented as:

[0026]

[0027] Wherein, R i , R j are the thermal resistances of the material microelements i and j, respectively, λ m,i , λ m,j are the thermal conductivities of the material microelements i and j, respectively, W / (m·K); δ i , δ j are the distances from the material microelements i and j to the contact surface,

[0028] The heat transfer equation established for the material microelement represented by P and the surrounding material microelements is:

[0029]

[0030] Wherein, T is the temperature, K, and the superscript represents the corresponding time; λp,j is the conductivity between the microelement p, j; A P,j is the contact surface area between the microelement p, j; δ P,j is the distance between the microelement p, j; ρ m is the density of the material, kg / m 3 ; c p,m is the specific heat of the material, J / (kg·K); V P is the volume of the microelement p; Δt is the time step, s.

[0031] In the anisotropic heat transfer analysis method for 3D printed wall provided by the application, the microelement can also have the following characteristics: according to the cavity structure of the wall, the microelement also includes a cavity microelement, and the heat transfer equation set also includes a heat transfer equation between the cavity microelement and the material microelement:

[0032]

[0033] The arrangement is:

[0034]

[0035] wherein a T,j = h c,j A j , In the formula, ρ a is the air density, kg / m 3 ; c p,a is the air specific heat, J / (kg·K); λ a is the air thermal conductivity, W / (m·K); V a is the cavity volume, m 3 ; h c,j is the cavity j surface convective heat transfer coefficient, W / (m 2 ·K); A j is the surface area of the cavity j, m 2 ; T x＝j is the surface temperature of the cavity j, K; T int is the average temperature of the cavity, K.

[0036] In the anisotropic heat transfer analysis method for 3D printed wall provided by the application, the microelement based on the material surface can be affected by the environment, and the material microelement also includes:

[0037] a material outer surface boundary microelement, a material inner surface boundary microelement, and a material surface microelement in contact with the cavity structure,

[0038] For the material outer surface boundary microelement, the heat transfer equation is:

[0039]

[0040] wherein, h c,e is the convective heat transfer coefficient of the outer surface, W / (m 2 ·K) ; T e is the outdoor air temperature, K; A p,e is the surface area of the boundary microelement p in contact with air, m 2

[0041] For the material inner surface boundary microelement, the heat transfer equation is:

[0042]

[0043] wherein, wherein, h c,i is the convective heat transfer coefficient of the inner surface, W / (m 2 ·K) ; T i is the indoor air temperature, K; A p,i is the surface area of the boundary microelement p in contact with air, m 2

[0044] For the material surface microelement in contact with the cavity structure, the heat transfer equation is:

[0045]

[0046] wherein, h c,int is the convective heat transfer coefficient of the cavity surface, W / (m 2 ·K) ; T int is the average temperature of the cavity, K; φ j is the surface net radiation, W / m 2 .

[0047] In the anisotropic heat transfer analysis method suitable for 3D printed wall provided by the application, the method can further have the following characteristics: wherein, step S3 is realized based on Python programming, and step S3 includes the following sub-steps:

[0048] Step S3.1: Obtain material physical property parameter data, and obtain the thermal conductivity coefficients between microelements in different directions through the stored microelement geometric data and the connected direction;

[0049] Step S3.2: Obtain the environmental temperature of the wall, including the outdoor air temperature T e and the indoor air temperature T i at different times;

[0050] Step S3.3: Obtain the initial temperature field T=T0 of the wall;​​

[0051] Step S3.4, obtain the number of times criterion, time step Δt and error convergence criterion, update the number of times to 0, the error convergence criterion is that the deviation of the temperature values calculated by the previous two iterations is less than a certain value, and the number of times criterion is a value that the number of times needs to reach;

[0052] Step S3.5, iteratively solve the heat transfer equation set in a time step Δt to obtain the temperature value, and the calculation in the time step Δt is completed when the temperature value meets the convergence criterion; and obtain the temperature result;

[0053] Step S3.6, based on the temperature result, update the initial temperature field and the thermal conductivity coefficient to obtain the updated ambient temperature, and increase the number of updates by 1;

[0054] Step S3.7, repeat the process of step S3.5 and step S3.6 in the next time step to obtain the initial temperature field, the thermal conductivity coefficient and the ambient temperature in the next time step;

[0055] Step S3.8, repeat the process of step S3.7 until the number of updates meets the number of times criterion, and the calculation is completed to obtain the final temperature field.

[0056] The application also provides an anisotropic heat transfer analysis system suitable for 3D printed walls, which uses the anisotropic heat transfer analysis method described above and has the following characteristics, comprising:

[0057] A structure network model construction unit constructs a structure network model of the wall, and the structure network model represents the geometric structure of the wall and the dominant thermal conductivity direction of the material, and the dominant thermal conductivity direction corresponds to the printing direction, the height direction and the width direction;

[0058] A heat transfer equation set construction unit constructs a heat transfer equation set of the structure network model in the dominant thermal conductivity direction;

[0059] A final temperature field calculation unit solves the heat transfer equation set in the structure network model by an iterative method to obtain a final temperature field of the wall, and realizes the analysis of the anisotropic heat transfer of the wall.

[0060] Effects of the application

[0061] The application provides an anisotropic heat transfer analysis method and system suitable for 3D printed walls to adapt to the anisotropic thermal performance and the heat transfer process under the macroscopically complex geometric shape. Unlike the solving idea of coordinate transformation, the application does not aim to solve the material transfer process in the coordinate direction, but directly solves the heat transfer process in the dominant thermal performance direction of the material by establishing a structure network model capable of representing the printing direction of the material, thereby avoiding the problem of inconsistent thermal conductivity coefficients in the coordinate direction.

[0062] This invention enables the solution of the heat transfer process in 3D-printed walls, obtaining the temperature distribution of the research object under certain environmental conditions and temperatures. Based on this result, the local temperature situation inside the wall can be analyzed, and the existence of local thermal defects in the structure can be assessed. Attached Figure Description

[0063] Figure 1 This is a flowchart of the anisotropic heat transfer analysis method applicable to 3D printed walls in Embodiment 1 of the present invention;

[0064] Figure 2 This is a schematic diagram of the printing direction and related orthogonal directions of the 3D printed wall in Embodiment 1 of the present invention;

[0065] Figure 3 This is a schematic diagram of the micro-element division according to the printing direction in Embodiment 1 of the present invention;

[0066] Figure 4 This is a schematic diagram of the cross-section of the wall in Embodiment 1 of the present invention;

[0067] Figure 5 This is a schematic diagram of the center point of the micro-element in Embodiment 1 of the present invention;

[0068] Figure 6 This is a schematic diagram of the micro-element connection network of the wall cross-section in Embodiment 1 of the present invention; and

[0069] Figure 7 This is a flowchart of step S3 in Embodiment 1 of the present invention. Detailed Implementation

[0070] To make the technical means, creative features, objectives and effects of this invention easy to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate the anisotropic heat transfer analysis method and system applicable to 3D printed walls.

[0071] <Example 1>

[0072] Figure 1 This is a flowchart of the anisotropic heat transfer analysis method applicable to 3D printed walls in this embodiment, as shown below. Figure 1 As shown, the anisotropic heat transfer analysis method for 3D printed walls in this embodiment includes the following steps:

[0073] Step S1: Construct the structural network model of the wall.

[0074] Figure 2 This is a schematic diagram of the printing direction and related orthogonal directions of the 3D printed wall in Embodiment 1 of the present invention. (See diagram below.) Figure 2As shown, during the printing process of a 3D printed wall, the forward direction of the printing nozzle is the printing direction of the material. In a plane perpendicular to the printing direction, the vertical direction corresponds to the height direction of the material, and the horizontal direction corresponds to the width direction. To match the solution direction of heat transfer with the direction of thermal properties, a structural network model representing the geometry of the wall and the dominant thermal conductivity direction needs to be established. 3D printed walls have different thermal conductivity in different heat transfer directions. The thermal properties of the 3D printed wall are based on the printing direction, and the dominant thermal conductivity direction corresponds to the printing direction, the height direction perpendicular to the printing direction, and the width direction. Considering that the wall structure may have different printing directions at different locations, the established structural network model should match the corresponding dominant thermal conductivity direction at different locations.

[0075] Therefore, step S1 includes the following sub-steps:

[0076] Step S1.1: Divide the wall structure into several micro-elements. Based on the shape and outline of the wall, the printing path can be determined, thereby identifying the printing direction, height direction, and width direction at various locations on the wall. By using cross-sections parallel to the printing direction, height direction, and width direction, the wall structure is divided into several micro-elements with specific geometric dimensions, ensuring that all other micro-elements adjacent to each micro-element are aligned along the dominant thermal coefficient direction of that micro-element.

[0077] Figure 3 This is a schematic diagram of the micro-element division based on the printing direction in this embodiment.

[0078] like Figure 3 As shown, this is a micro-element partitioning scheme for a certain area of ​​a 3D printed wall under the corresponding printing direction. This process is based on Python programming, using the PoreSpy open-source package to extract the micro-element regions from the image of the wall partitioned under the printing direction, and storing the image information of each micro-element. The image information includes the geometric data of the micro-element, thereby realizing the construction of micro-elements in the structural network model.

[0079] Step S1.2 establishes connectivity channels between micro-elements to characterize the solution direction. This step utilizes the OpenPNM open-source package to connect the micro-elements established in Step S1.1 with their surrounding micro-elements, constructing adjacency and affinity matrices between each micro-element, forming a micro-element connectivity network. This network includes micro-elements and connectivity channels, which are equivalent to a 3D-printed wall. A connectivity channel connects the center of one micro-element to the center of another; it's a virtual concept because micro-elements are in direct contact and don't need to be connected through channels. However, quantifying these channels reflects the connection direction between a micro-element and its surrounding micro-elements.

[0080] Figure 5 This is a schematic diagram of the center point of the micro-element in this embodiment. For example...Figure 5 As shown, the central dot represents a cavity microelement, and the surrounding dots represent material microelements. Figure 6 is a schematic diagram of the microelement connection network of the wall cross section in this embodiment. As shown Figure 6 As shown, the cavity microelement is connected to the surrounding material microelements, and the communication channel is the channel connecting the center points of the microelements. One microelement can be connected to multiple microelements, so there can be multiple communication channels starting from the center point of a microelement. Figure 6 The communication channel shown can represent the heat transfer direction between the microelements connected at both ends. This direction matches the dominant thermal coefficient direction, and heat transfer calculation in this direction can make the heat transfer performance represented by the dominant thermal coefficient consistent with the heat transfer solving direction.

[0081] Therefore, since the other microelements adjacent to each microelement are in the dominant thermal coefficient direction of the microelement, the communication direction of the established communication channel is consistent with the dominant thermal coefficient direction of the material, and also corresponds to the solving direction of the wall structure heat transfer.

[0082] Step S1.3, obtain the microelement geometric data of each microelement and the communication direction of the communication channel. The microelement geometric data of each microelement is obtained by extracting image information, and the obtained microelement geometric data is assigned to the corresponding microelement. The communication direction of the communication channel corresponds to the printing direction, the height direction, or the width direction, and the communication direction is assigned to the corresponding communication channel.

[0083] For a 3D printed wall, the printing direction can be intuitively determined, so in the microelement connection network, the communication direction of the communication channel belongs to Figure 2 As shown in ①, ②, and ③, the corresponding direction can also be intuitively determined. Specifically, this process finds the communication channel belonging to the ① direction, marks it as the ① direction, finds the communication channel belonging to the ② direction, marks it as the ② direction, and finds the communication channel belonging to the ③ direction, marks it as the ③ direction. The method of "finding" can be found by numbering. Each microelement in the microelement connection network has its own number, and each communication channel also has its own number. The corresponding number of the communication channel is assigned to the corresponding communication direction.

[0084] Through steps S1.1, S1.2, and S1.3, a structure network model representing the geometric structure of the wall and the dominant thermal coefficient direction of the material is established. The transfer direction of one microelement to the next microelement is only related to the connectivity between the microelements, and is independent of the coordinate direction. This method of representing the structure and transfer relationship of the research object is the basis for further solving the heat transfer process.

[0085] Step S2, constructing heat transfer equation set of structure network model. The typical structure of 3D printed wall body includes porous medium material and cavity structure, and the microelement includes material microelement and cavity microelement. Before analyzing and solving the heat transfer process of 3D printed wall body, the heat transfer equation between material microelement and cavity microelement needs to be established. Therefore, the heat transfer equation set between each microelement and adjacent microelement is established according to energy conservation.

[0086] The heat transfer equation set includes the heat transfer equation between material microelements and the heat transfer equation between cavity microelements and material microelements. Because the microelement on the surface of the material will be affected by the environment, the microelement inside the material and the microelement on the surface of the material need to be distinguished. For the wall body with cavity, the outer surface is in contact with the external environment, the inner surface is in contact with the indoor environment, and the cavity surface is in contact with the air in the cavity. Therefore, the material microelement includes: material outer surface boundary microelement, material inner surface boundary microelement, material surface microelement in contact with cavity structure and material internal microelement.

[0087] The conductivity between material microelements is solved by series thermal resistance, and the conductivity between microelements i and j is represented as:

[0088]

[0089] Wherein, R i , R j are the thermal resistance of material microelements i and j, respectively, λ m,i , λ m,j are the thermal conductivity of material microelements i and j, respectively, W / (m·K); δ i , δ j are the distances from material microelements i and j to the contact surface, respectively, and δ i , δ j have been stored in the microelement geometry data of the microelement.

[0090] The heat transfer equation established for the material internal microelement represented by P point and the surrounding material microelement is:

[0091]

[0092] Wherein, T is temperature, K, and the superscript represents the corresponding time; λ p,j is the conductivity between microelements p and j; A P,j is the contact surface area between microelements p and j; δ P,j is the distance between material microelements p and j; ρ m is the density of the material, kg / m 3 ; c p,m is the specific heat of the material, J / (kg·K); VP is the volume of the volume p; At is the time step, s.

[0093] For a material outer surface boundary volume element, the heat transfer equation is:

[0094]

[0095] where, h c,e is the convective heat transfer coefficient for the outer surface, W / (m 2 · K); T e is the outdoor air temperature, K; A p,e is the surface area of the boundary volume p in contact with air, m 2 .

[0096] For a material inner surface boundary volume element, the heat transfer equation is:

[0097]

[0098] where, where, h c,i is the convective heat transfer coefficient for the inner surface, W / (m 2 · K); T i is the indoor air temperature, K; A p,i is the surface area of the boundary volume p in contact with air, m 2 .

[0099] For a material surface volume element in contact with a cavity structure, the heat transfer equation is:

[0100]

[0101] where, h c,int is the convective heat transfer coefficient for the cavity surface, W / (m 2 · K); T int is the average temperature of the cavity, K; φ j is the net radiative flux at the surface, W / m 2 .

[0102] Heat transfer equation between a cavity volume element and a material volume element:

[0103]

[0104] which reduces to:

[0105]

[0106] where, a T,j = h c,j A j , where ρ is the air density, kg / m3; c is the air specific heat, J / (kg·K); λ is the air thermal conductivity, W / (m·K); V is the cavity volume, m3; h is the cavity j surface convection heat transfer coefficient, W / (m2·K); A is the surface area of cavity j, m2; T is the surface temperature of cavity j, K; T is the cavity average temperature, K. a 3 p,a a a 3 c,j 2 j 2 x＝j int

[0107] Step S3, solve the heat transfer equation group established in step S2 in the structural network model established in step S1, each microelement has a heat transfer equation, and the heat transfer equations of all microelements together constitute a matrix form of heat transfer equation group, which is solved by an iterative method, so as to obtain the final temperature field in the wall structure and realize the analysis of anisotropic heat transfer of the wall.

[0108] Figure 7 is the flow chart of step S3 in this embodiment, and this process is realized based on Python programming. As shown in Figure 7 , step S3 includes the following sub-steps:

[0109] Step S3.1: Obtain material physical property parameter data, and solve the thermal conductivity coefficients in different directions between microelements through the microelement geometric data and connection direction stored in the structural network model. Step S2 constructs the heat transfer equation between microelements in the dominant thermal coefficient direction of the material, and the thermal conductivity coefficient is calculated based on the thermal conductivity coefficient of the material. The thermal conductivity coefficient is equivalent to the coefficient of the heat transfer equation.

[0110] Step S3.2, obtain the environmental temperature of the wall, i.e. the outdoor air temperature T e and the indoor air temperature T i at different times, which is equivalent to the environmental working condition of the research object. The environmental temperature is the outdoor air temperature T e and the indoor air temperature T i used in the heat transfer equations of the material outer surface boundary microelement and the material inner surface boundary microelement, and the environmental temperature is given at each solving time step in the entire solving process.

[0111] ​​​​​​​​​​​​Step S3.3, obtaining the initial temperature field T=T0 of the wall, assigning the initial temperature field to the wall, the initial temperature field being the initial temperature value of each microelement. The initial temperature field corresponds to the temperature at time "k" in the heat transfer equation, and the superscript of the temperature T in the heat transfer equation is k, so as to solve the temperature at time "k+1", and the superscript of the temperature T in the heat transfer equation is k+1.

[0112] Step S3.4, obtaining the time step Δt, the number of times criterion and the error convergence criterion of the numerical analysis process, setting the number of updates to 0, and setting the error convergence criterion satisfied by the calculated temperature value to be that the deviation of the temperature values calculated by the previous two iterations is less than a certain value, and the number of times criterion being a value that the number of updates needs to reach.

[0113] Step S3.5, iteratively solving the heat transfer equation set in a time step Δt to obtain the temperature value, and when the temperature value satisfies the convergence criterion, the calculation in the time step Δt is completed; obtaining the temperature result.

[0114] Step S3.6, based on the temperature result, updating the initial temperature field and the thermal conductivity coefficient, obtaining the updated ambient temperature, and increasing the number of updates by 1.

[0115] Step S3.7, repeating the process of step S3.5 and step S3.6 in the next time step to obtain the updated initial temperature field, thermal conductivity coefficient and ambient temperature.

[0116] Step S3.8, repeating the process of step S3.7 until the number of updates satisfies the number of times criterion, and the calculation is completed, and obtaining the final temperature field based on the updated initial temperature field.

[0117] <Embodiment 2>

[0118] The embodiment provides an anisotropic heat transfer analysis system suitable for a 3D printed wall, which uses the anisotropic heat transfer analysis method suitable for a 3D printed wall described above, and the system comprises:

[0119] A structure network model construction unit constructs a structure network model of the wall, and the structure network model represents the geometric structure of the wall and the dominant thermal conductivity direction of the material, and the dominant thermal conductivity direction corresponds to the printing direction, the height direction and the width direction.

[0120] A heat transfer equation set construction unit constructs a heat transfer equation set of the structure network model in the dominant thermal conductivity direction.

[0121] A final temperature field calculation unit solves the heat transfer equation set in the structure network model by using an iterative method to obtain a final temperature field of the wall, and realizes the analysis of the anisotropic heat transfer of the wall.

[0122] It should be understood that the parts of the anisotropic heat transfer analysis system for 3D printed wall described in embodiment 2 can correspond to the steps of the anisotropic heat transfer analysis method for 3D printed wall described in embodiment 1. Therefore, the operations, features and advantages described above for the steps of the anisotropic heat transfer analysis method for 3D printed wall also apply to the parts of the anisotropic heat transfer analysis system for 3D printed wall. For the sake of brevity, certain operations, features and advantages are not repeated here.

[0123] Effects of the embodiments

[0124] The present application proposes an anisotropic heat transfer analysis method and system for 3D printed wall to adapt to the anisotropic thermal performance and heat transfer process under the macroscopic complex geometry. Unlike the solution approach of coordinate transformation, the solution of heat transfer process is not targeted at the material transfer process in the coordinate direction, but by establishing a structure network model that can represent the printing direction of the material, the heat transfer process is directly solved in the direction of the dominant thermal coefficient of the material, avoiding the problem of inconsistent thermal conductivity in the coordinate direction.

[0125] The present application can solve the heat transfer process of 3D printed wall and obtain the temperature distribution of the research object under certain environmental conditions and environmental temperature. Based on this result, the local temperature condition inside the wall can be analyzed to evaluate whether there is a local thermal defect under this structure.

[0126] Further, the key point of the present application is to match the heat transfer structure network corresponding to the printing path of the 3D printed wall structure, by establishing this structure network reflecting the dominant thermal performance direction of the material, the matching of the heat transfer performance direction and the heat transfer solving direction is realized. The main innovation is to match the material dominant thermal coefficient direction and the solving direction.

[0127] Further, the present application establishes the dominant thermal performance direction of the wall structure at different positions, which is the key to solving. The wall structure is divided into micro elements, and the dominant thermal performance direction of each micro element is identified, the connectivity relationship of each micro element in the corresponding direction is established, and then the wall structure network that can represent the printing direction of the material is constructed.

[0128] Further, the present application uses the lumped method to simplify the natural convection and radiation heat transfer process in the cavity, which simplifies the complexity of calculation while considering multiple heat transfer forms.

[0129] Further, the technical scheme proposed by the present application can take the anisotropic heat transfer of solid phase material, the convection and radiation heat transfer in the cavity structure into the solving analysis process, and provides an innovative solution for the anisotropic heat transfer solving of 3D printed building wall under complex geometry.

[0130] Further, the application can evaluate the overall heat conduction coefficient of the wall structure by calculation to analyze whether it meets the thermal performance required by the building specification.

[0131] Further, the application establishes a heat transfer model based on the main direction of thermal conductivity of the material by characterizing the main direction of thermal conductivity of the material, and solves the heat transfer process through python programming, which is simple and efficient.

[0132] Those skilled in the art should understand that the application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the application, and various changes and improvements can be made without departing from the spirit and scope of the application, and these changes and improvements all fall within the scope of the claimed application. The scope of protection of the application is defined by the appended claims and their equivalents.

Claims

1. A method for analyzing anisotropic heat transfer in 3D printed walls, characterized in that, Includes the following steps: Step S1: Construct a structural network model of the wall. The structural network model represents the geometric structure of the wall and the dominant thermal coefficient direction of the material. The dominant thermal coefficient direction corresponds to the printing direction, the height direction, and the width direction. Step S2: Construct the heat transfer equations of the structural network model in the direction of the dominant thermal coefficient; Step S3: In the structural network model, the heat transfer equations are solved iteratively to obtain the final temperature field of the wall, thereby realizing the analysis of anisotropic heat transfer in the wall. Step S1 includes the following sub-steps: Step S1.1: Divide the structure of the wall into several micro-elements; Step S1.2: Establish the connection channels between the infinitesimal elements to characterize the solution direction; Step S1.3: Obtain the geometric data of each of the micro-elements and the connection direction of the connecting channels. Step S1.1 includes: Based on the shape and contour of the wall, a printing path is obtained, and then the printing direction, height direction, and width direction of each position of the wall are obtained. By using tangents parallel to the printing direction, the height direction, and the width direction, the structure of the wall is divided into several micro-elements with geometric dimensions. Other micro-elements adjacent to each micro-element are all located in the direction of the dominant thermal coefficient of the micro-element. Step S1.1 is based on Python programming, using the PoreSpy open-source package to store the image information of each micro-element. The image information includes the geometric data of the micro-element, thereby realizing the construction of the micro-element in the structural network model. Step S1.2 includes: Using the OpenPNM open-source package, the micro-element is connected to the surrounding micro-elements to construct the adjacency matrix and correlation matrix between each micro-element, forming a micro-element connection network. The connecting channel is the channel connecting the center point of the micro-element, and the connecting direction of the connecting channel is consistent with the direction of the dominant thermal coefficient. The connecting direction represents the solution direction.

2. The anisotropic heat transfer analysis method for 3D printed walls according to claim 1, characterized in that: in, Step S1.3 includes: By extracting the image information, the geometric data of each micro-element is obtained, and the geometric data of the micro-element is assigned to the corresponding micro-element. Based on the positional relationship between the micro-elements, the connection direction of the connecting channel is determined, and the connection direction is assigned to the corresponding connecting channel.

3. The anisotropic heat transfer analysis method for 3D printed walls according to claim 2, characterized in that: in, Step S2 includes: establishing a set of heat transfer equations between each infinitesimal element and its adjacent infinitesimal elements based on the law of energy conservation. Based on the porous medium material of the wall, the micro-element comprises material micro-elements, and the heat transfer equation set comprises heat transfer equations between the material micro-elements. The conductivity between the material elements is solved by the sum of series thermal resistances. , The conductivity between them is expressed as: ， in, , They are material micro-elements , thermal resistance, , They are material micro-elements , thermal conductivity, ; , They are material micro-elements , Distance to the contact surface, The heat transfer equation established for the material element represented by point P and the surrounding material elements is as follows: ， in, , , , For temperature, The superscript indicates the corresponding time. It is a micro-element , The conductivity between them; It is a micro-element , The contact area between them; For material micro-elements , The distance between them; It is the density of the material. ; It is the specific heat of the material. ; It is a micro-element Volume; It is the time step. .

4. The anisotropic heat transfer analysis method for 3D printed walls according to claim 3, characterized in that: in, Based on the cavity structure of the wall, the micro-element further includes a cavity micro-element, and the heat transfer equation set further includes heat transfer equations between the cavity micro-element and the material micro-element: ， Summarized as follows: ， in, , , In the formula, air density, ; For the specific heat of air, ; The thermal conductivity of air, ; The volume of the cavity. ; Cavity Surface convective heat transfer coefficient, ; Cavity Surface area, ; Cavity Surface temperature, ; The average temperature of the cavity. .

5. The anisotropic heat transfer analysis method for 3D printed walls according to claim 4, characterized in that: in, Micro-elements based on the material surface are affected by the environment, and the material micro-elements also include: Material outer surface boundary micro-element, material inner surface boundary micro-element, and material surface micro-element in contact with the cavity structure. For the boundary element of the outer surface of the material, the heat transfer equation is: ， in, , It is the convective heat transfer coefficient of the outer surface. ; It is the outdoor air temperature. ; Boundary infinitesimal element Surface area in contact with air , For the boundary micro-element of the inner surface of the material, the heat transfer equation is: ， in, ,in, The convective heat transfer coefficient of the inner surface ; Indoor air temperature ; Boundary infinitesimal element Surface area in contact with air , For a micro-element of the material surface in contact with the cavity structure, the heat transfer equation is: ， in, , The convective heat transfer coefficient of the cavity surface ; The average temperature of the cavity. ; This is the net surface radiation. .

6. The anisotropic heat transfer analysis method for 3D printed walls according to claim 5, Its features are: Step S3 is implemented using Python programming and includes the following sub-steps: Step S3.1: Obtain material property parameter data, and obtain the thermal conductivity coefficients between the micro-elements in different directions by using the stored micro-element geometric data and connection direction; Step S3.2: Obtain the ambient temperature of the wall, including the outdoor air temperature at different times. and indoor air temperature ; Step S3.3: Obtain the initial temperature field T=T0 of the wall; Step S3.4: Obtain the number criterion, time step Δt, and error convergence criterion. Set the update number to 0. The error convergence criterion is the value that the deviation of the temperature values ​​calculated in two consecutive iterations is less than a certain value. The number criterion is the value that the update number needs to reach. Step S3.5: Iteratively solve the heat transfer equations within one time step Δt to obtain the temperature value. When the temperature value satisfies the convergence criterion, the calculation within the time step Δt ends; the temperature result is obtained. Step S3.6: Based on the temperature results, update the initial temperature field and thermal conductivity coefficient to obtain the updated ambient temperature, and increment the update count by 1; Step S3.7: Repeat steps S3.5 and S3.6 in the next time step to obtain the initial temperature field, thermal conductivity coefficient and ambient temperature for the next time step; Step S3.8: Repeat step S3.7 until the number of updates meets the number criterion, the calculation is completed, and the final temperature field is obtained.

7. An anisotropic heat transfer analysis system suitable for 3D printed walls, using the anisotropic heat transfer analysis method for 3D printed walls according to any one of claims 1-6, characterized in that, include: The structural network model construction unit constructs a structural network model of the wall. The structural network model represents the geometric structure of the wall and the dominant thermal coefficient direction of the material. The dominant thermal coefficient direction corresponds to the printing direction, the height direction, and the width direction. The heat transport equations construction unit constructs the heat transport equations of the structure network model in the direction of the dominant thermal coefficient; The final temperature field calculation unit solves the heat transfer equations in the structural network model using an iterative method to obtain the final temperature field of the wall, thereby realizing the analysis of the anisotropic heat transfer of the wall.

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