Thermoelectric conversion and flow heat exchange coupling calculation method

Abstract

The invention discloses a thermoelectric conversion and flow heat exchange coupling calculation method, which comprises the following steps of: 1, establishing a geometric model of a single thermoelectric power generation sheet, dividing grids, and carrying out thermoelectric conversion steady-state numerical simulation on the basis of COMSOL software; 2, changing the temperatures of the two side surfaces of the thermoelectric power generation sheet and carrying out multi-working-condition calculation to obtain the corresponding relation between the output power and the temperature difference; 3, simplifying a complex thermoelectric power generation sheet into a thin sheet, calculating to obtain the relationship between the equivalent thermal conductivity and the output electric power of the thin sheet and the change of the surface temperature of the two sides, and implanting the thin sheet into FLUENT software through UDF; 4, establishing a geometric model of thermoelectric conversion and flow heat exchange coupling calculation, dividing grids, and completing definition of materials and source items and setting of boundary conditions; 5, coupling calculation of thermoelectric conversion and flow heat exchange is carried out based on FLUENT software; and 6, changing flow parameters and carrying out multi-working-condition calculation to obtain fluid parameters and thermoelectric conversion output power under different working conditions.

Description

Technical Field

[0001] The invention relates to the technical field of thermoelectric conversion and flow heat exchange, and in particular to a thermoelectric conversion and flow heat exchange coupling calculation method. Background Art

[0002] Thermoelectric conversion technology can directly convert thermal energy into electrical energy. It has the advantages of being pollution-free, quiet, and reliable, and is of great value for the utilization of low-grade heat sources. Thermoelectric power generation sheets are the most common thermoelectric conversion devices. Maintaining a stable temperature difference on the two sides of the thermoelectric power generation sheet can continuously output electrical energy. The heat source and cold source on both sides are not limited to the form. The hot side can use solar energy, industrial waste heat, decay heat, etc., and the cold side can be cooled by cooling water. If a hot fluid is used to heat the hot side surface of the thermoelectric power generation sheet and a cold fluid is used to cool the cold side surface, the relevant research needs to include the design of the thermoelectric power generation sheet and the design of the flow heat exchange on both sides. The corresponding numerical simulation is a coupled calculation of thermoelectric conversion and flow heat exchange.

[0003] The three-dimensional numerical simulation of thermoelectric conversion is usually based on the finite element method, while the three-dimensional numerical simulation of flow heat transfer is usually based on the finite volume method. The thermoelectric conversion of the thermoelectric power generation sheet is coupled with the flow heat transfer of the fluid on both sides. If the calculation is based on different platforms, it is not convenient to transfer parameters, which is not conducive to the parameter optimization design of flow heat transfer. After determining the geometry and material of the thermoelectric power generation sheet, its power generation efficiency depends only on the temperature difference between the two sides of the surface, and the output electric power is positively correlated with the temperature difference. If the corresponding relationship between power and temperature difference can be described by a function, the numerical simulation of thermoelectric conversion can be simplified, saving a lot of computing resources, and it is easy to implant the model into other platforms. The three-dimensional numerical simulation of flow heat transfer is relatively complex. The flow channel geometry and fluid parameters are the key factors to be considered in the optimization design. A lot of computing resources are needed to carry out calculations under various working conditions. The simplified thermoelectric conversion model is coupled with the flow heat transfer, and the coupled calculation can be carried out on the same platform. At the same time, the thermal hydraulic parameters and the output electric power can be obtained, which better meets the needs of the optimization design work. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a coupled calculation method for thermoelectric conversion and flow heat exchange. The present invention simplifies a complex thermoelectric power generation sheet into a simple rectangular sheet, simplifies the calculation model of thermoelectric conversion, and implants the model into FLUENT software through the UDF module. The simplified thermoelectric conversion model and flow heat exchange are solved by FLUENT software to realize the coupled solution of thermoelectric conversion of the thermoelectric power generation sheet and convective heat exchange of the fluid on both sides, and obtain the parameters of the fluid and the output electric power.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A thermoelectric conversion and flow heat exchange coupling calculation method is provided, which carries out a thermoelectric conversion numerical simulation of a single thermoelectric power generation sheet, obtains the corresponding relationship between the output power and the surface temperature on both sides of the thermoelectric power generation sheet, describes the corresponding relationship through a function and implants it into FLUENT software, uses the solver of FLUENT software to carry out flow heat exchange calculation and solve the function, realizes the coupled calculation of thermoelectric conversion and flow heat exchange in the same software, and can simultaneously obtain the output electric power, solid temperature field and fluid flow parameters; specifically comprises the following steps:

[0007] Step 1: Use Solidworks software to establish a geometric model of a single thermoelectric generator, including a P-type semiconductor, an N-type semiconductor, a guide plate and a ceramic plate, import the geometric model into COMSOL software, and use structured meshing to perform meshing; define material properties, including Seebeck coefficient, thermal conductivity, electrical conductivity and density; set the surfaces on both sides of the thermoelectric generator as constant temperature boundaries, and the external load is a resistor with a fixed resistance value, and the resistor is connected to the thermoelectric generator to form an electrical circuit; carry out steady-state numerical simulation of thermoelectric conversion, obtain the positive electrode voltage of the thermoelectric generator and the heat flux density on one side of the surface, and obtain the output electric power by calculation;

[0008] Step 2: Change the temperature of the hot side surface or the cold side surface of the thermoelectric power generation sheet, repeat the steady-state numerical simulation of thermoelectric conversion in step 1, and obtain the relationship between the output electric power and the change of the hot side surface temperature and the cold side surface temperature;

[0009] Step 3: Simplify the complex geometry of the thermoelectric power generation sheet into a thin sheet. The thermoelectric conversion problem of the thermoelectric power generation sheet is transformed into a steady-state constant heat conduction problem with an internal heat source. The simplified geometry has a material, the density of the material is calculated by volume weighted average, and the equivalent thermal conductivity of the material is calculated by the surface temperature on both sides of the thermoelectric power generation sheet, the output electric power and the heat flux density on one side of the surface of the thermoelectric power generation sheet; describe the relationship between the equivalent thermal conductivity and output electric power of the simplified geometry and the change of the surface temperature on both sides of the thermoelectric power generation sheet through a function, and implant the relationship into the FLUENT software based on the user-defined function tool (UDF);

[0010] Step 4: Use Solidworks software to establish a geometric model for thermoelectric conversion and flow heat exchange coupling calculation, including a simplified thermoelectric generator, hot-side solid domain and fluid domain, cold-side solid domain and fluid domain; import the established geometric model into FLUENT software, use structured grids to carry out grid division of the solid domain, and use unstructured grids to carry out grid division of the fluid domain; define the thermal conductivity of the material corresponding to the simplified thermoelectric generator and the heat release rate of the internal heat source in the corresponding solid domain through UDF, and the heat release rate of the internal heat source is equivalent to the output electrical power; the outlet surface of the fluid domain is set as a pressure boundary condition, and the inlet surface of the fluid domain is set as a flow boundary condition;

[0011] Step 5: Based on FLUENT software, conduct coupled calculations of thermoelectric conversion and flow heat transfer, including convective heat transfer of hot and cold side fluids, heat conduction of hot and cold side solid domains, and heat conduction of the thermoelectric generator, and obtain the temperature, velocity, and pressure of the fluid domain, the temperature distribution of the solid domain, and the output power of the thermoelectric generator;

[0012] Step 6: Change the inlet flow rate, inlet fluid temperature or outlet pressure of the hot side and cold side fluid domains, repeat the coupling calculation in step 5, and obtain the fluid parameters and thermoelectric conversion output power under different working conditions.

[0013] The equivalent thermal conductivity and output electric power of the simplified thermoelectric generator vary with the hot side surface temperature and the cold side surface temperature, and are calculated using a bilinear interpolation method.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. Numerical simulation of thermoelectric conversion was carried out on a single thermoelectric power generation sheet to obtain the relationship between the output power and the surface temperature change on both sides of the thermoelectric power generation sheet. The complex geometry of the thermoelectric power generation sheet was simplified into a rectangular sheet, and the thermoelectric conversion problem was simplified into a steady-state constant heat conduction problem with an internal heat source. This effectively reduced the computing resources required for numerical simulation of thermoelectric conversion, reduced the complexity of the coupled calculation model, and greatly reduced the number of grids required for calculation.

[0016] 2. The simplified temperature difference power generation model uses a bilinear interpolation method to calculate the heat release rate and equivalent thermal conductivity of the internal heat source. It can be implanted into the FLUENT software through the UDF module, making it easy to realize the coupled calculation of thermoelectric conversion and flow heat exchange in the same software.

[0017] 3. The geometric model of the coupled calculation includes multiple thermoelectric power generation sheets and solid domains and fluid domains of the flow channels on both sides. The calculation resources required are relatively small, the number of thermoelectric power generation sheets and the geometric structure of the flow channels on both sides can be changed, and the scalability is relatively strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the calculation flow of thermoelectric conversion and flow heat exchange coupling of the present invention.

[0019] Figure 2 It is a simplified schematic diagram of the geometric structure and model of the temperature difference power generation sheet of the present invention.

[0020] Figure 3 Schematic diagram of geometric modeling for coupling calculation of the present invention. DETAILED DESCRIPTION

[0021] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0022] The present invention provides a thermoelectric conversion and flow heat exchange coupling calculation method, the calculation process is as follows Figure 1 As shown in the figure, the two dotted boxes are the thermoelectric conversion numerical simulation based on COMSOL and the coupling calculation based on FLUENT. The two parts are connected through a simplified thermoelectric conversion model, which specifically includes the following steps:

[0023] Step 1: Use Solidworks software to establish a geometric model of a single thermoelectric generator. The geometric model is as follows: Figure 2 As shown, it includes a P-type semiconductor, an N-type semiconductor, a guide plate and a ceramic plate. The geometric model is imported into COMSOL software, and structured grids are used to perform grid division; material properties are defined. For the materials of P-type semiconductors and N-type semiconductors, the Seebeck coefficient, thermal conductivity, electrical conductivity and density need to be defined; for the material of the guide plate, the thermal conductivity, electrical conductivity and density need to be defined; for the material of the ceramic plate, the thermal conductivity and density need to be defined; the surfaces on both sides of the thermoelectric power generation sheet are set as constant temperature boundaries, and the external load is a resistor with a fixed resistance value. The resistor is connected to the thermoelectric power generation sheet through a circuit module to form an electric circuit; a steady-state numerical simulation of thermoelectric conversion is carried out to obtain the positive electrode voltage of the thermoelectric power generation sheet and the heat flux density on one side of the surface, and the output electric power is obtained by calculation.

[0024] Step 2: Change the temperature of the hot side surface or the cold side surface of the thermoelectric power generation sheet, repeat the steady-state numerical simulation of thermoelectric conversion in step 1, and obtain the relationship between the output electric power and the hot side surface temperature and the cold side surface temperature.

[0025] Step 3: Simplify the complex thermoelectric generator geometry into a thin sheet, as shown below: Figure 2 As shown, the thermoelectric conversion problem of the thermoelectric power generation sheet is transformed into a steady-state constant heat conduction problem with an internal heat source. The simplified geometry has a material, the density of which is calculated by volume weighted average. The equivalent thermal conductivity of the material is calculated by the surface temperature on both sides of the thermoelectric power generation sheet, the output electric power and the heat flux density on one side of the thermoelectric power generation sheet. The calculation formula is as follows:

[0026]

[0027] In the formula, λ e is the equivalent thermal conductivity, Q e is the output electric power, V is the volume of the thermoelectric generator, δ is the thickness of the thermoelectric generator, q1 is the heat flux density on the hot side surface, t1 is the average temperature of the hot side surface, and t2 is the average temperature of the cold side surface.

[0028] The relationship between the equivalent thermal conductivity of the simplified geometry and the output electric power and the surface temperature on both sides of the thermoelectric generator is described by function, and the relationship is implanted into the FLUENT software based on the user-defined function tool (UDF).

[0029] Step 4: Use Solidworks software to establish a geometric model for thermoelectric conversion and flow heat transfer coupling calculation. The geometric model is as follows: Figure 3 As shown, it includes a simplified thermoelectric power generation sheet, a hot-side solid domain and a fluid domain, and a cold-side solid domain and a fluid domain; the established geometric model is imported into the FLUENT software, and a structured grid is used to carry out grid division of the solid domain, and an unstructured grid is used to carry out grid division of the fluid domain; the thermal conductivity of the material corresponding to the simplified thermoelectric power generation sheet and the heat release rate of the internal heat source of the corresponding solid domain are defined by UDF, and the heat release rate of the internal heat source is equivalent to the output electric power; the outlet surface of the fluid domain is set as a pressure boundary condition, and the inlet surface of the fluid domain is set as a flow boundary condition.

[0030] Step 5: Carry out coupled calculations of thermoelectric conversion and flow heat transfer based on FLUENT software, including convective heat transfer of hot and cold side fluids, heat conduction of hot and cold side solid domains, and heat conduction of the thermoelectric generator, and obtain the temperature, velocity, and pressure of the fluid domain, the temperature distribution of the solid domain, and the output power of the thermoelectric generator.

[0031] Step 6: Change the inlet flow rate, inlet fluid temperature or outlet pressure of the hot side and cold side fluid domains, repeat the coupling calculation in step 5, and obtain the fluid parameters and thermoelectric conversion output power under different working conditions.

[0032] As a preferred embodiment of the present invention, the equivalent thermal conductivity and output electric power of the simplified temperature difference power generation sheet vary with the hot side surface temperature and the cold side surface temperature, and are specifically calculated using a bilinear interpolation method.

[0033] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, as long as they are within the essential spirit of the present invention, changes and modifications to the above-mentioned embodiments should be deemed to be within the scope of the claims of the present invention.

Claims

1. A thermoelectric conversion and flow heat exchange coupling calculation method, characterized in that: Carry out numerical simulation of thermoelectric conversion of a single thermoelectric power generation sheet, obtain the corresponding relationship between the output power and the surface temperature on both sides of the thermoelectric power generation sheet, describe the corresponding relationship through a function and implant it into the FLUENT software, use the solver of the FLUENT software to carry out flow heat transfer calculation and solve the function, realize the coupled calculation of thermoelectric conversion and flow heat transfer in the same software, and can simultaneously obtain the output electric power, solid temperature field and fluid flow parameters; The specific steps include: Step 1: Use Solidworks software to establish a geometric model of a single thermoelectric power generation sheet, including a P-type semiconductor, an N-type semiconductor, a guide plate and a ceramic plate, import the geometric model into COMSOL software, and use structured meshing to perform meshing; define material properties, including Seebeck coefficient, thermal conductivity, electrical conductivity and density; set the surfaces on both sides of the thermoelectric power generation sheet as constant temperature boundaries, and the external load is a resistor with a fixed resistance value, and connect the resistor to the thermoelectric power generation sheet to form an electrical circuit; carry out steady-state numerical simulation of thermoelectric conversion, obtain the positive electrode voltage of the thermoelectric power generation sheet and the heat flux density on one side of the surface, and obtain the output electric power by calculation; Step 2: Change the temperature of the hot side surface or the cold side surface of the thermoelectric power generation sheet, repeat the steady-state numerical simulation of thermoelectric conversion in step 1, and obtain the relationship between the output electric power and the change of the hot side surface temperature and the cold side surface temperature; Step 3: Simplify the complex geometry of the thermoelectric power generation sheet into a rectangular sheet. The thermoelectric conversion problem of the thermoelectric power generation sheet is transformed into a steady-state constant heat conduction problem with an internal heat source. The simplified geometry has a material whose density is calculated by volume weighted average. The equivalent thermal conductivity of the material is calculated by the surface temperature on both sides of the thermoelectric power generation sheet, the output electric power and the heat flux density on one side of the thermoelectric power generation sheet. The relationship between the equivalent thermal conductivity and the output electric power of the simplified geometry and the surface temperature on both sides of the thermoelectric power generation sheet is described by a function, and the relationship is implanted into the FLUENT software based on the user-defined function tool UDF. Step 4: Use Solidworks software to establish a geometric model for thermoelectric conversion and flow heat exchange coupling calculation, including a simplified thermoelectric generator, hot-side solid domain and fluid domain, cold-side solid domain and fluid domain; import the established geometric model into FLUENT software, use structured grids to carry out grid division of the solid domain, and use unstructured grids to carry out grid division of the fluid domain; define the thermal conductivity of the material corresponding to the simplified thermoelectric generator and the heat release rate of the internal heat source in the corresponding solid domain through UDF, and the heat release rate of the internal heat source is equivalent to the output electrical power; the outlet surface of the fluid domain is set as a pressure boundary condition, and the inlet surface of the fluid domain is set as a flow boundary condition; Step 5: Based on FLUENT software, conduct coupled calculations of thermoelectric conversion and flow heat transfer, including convective heat transfer of hot and cold side fluids, heat conduction of hot and cold side solid domains, and heat conduction of the thermoelectric generator, and obtain the temperature, velocity, and pressure of the fluid domain, the temperature distribution of the solid domain, and the output power of the thermoelectric generator; Step 6: Change the inlet flow rate, inlet fluid temperature or outlet pressure of the hot side and cold side fluid domains, repeat the coupling calculation in step 5, and obtain the fluid parameters and thermoelectric conversion output power under different working conditions.

2. A thermoelectric conversion and flow heat exchange coupling calculation method according to claim 1, characterized in that: The equivalent thermal conductivity and output electric power of the simplified thermoelectric generator vary with the hot side surface temperature and the cold side surface temperature, and are calculated using a bilinear interpolation method.

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