Study On Fluid-Solid Coupling Heat Transfer Characteristics Of Foam Ceramic Porous Materials

Foam porous materials have the characteristics of high porosity,large specific surface area,and complicated flow paths,which have been widely used in various heat exchange fields to achieve higher heat and mass transfer performance.In this paper,the foam ceramic porous materials are taken as the research object,based on the experimental principle of the single-blow method and the tetrakaidecahedron unit cell foam structure,the experiments and numerical simulations of the flow and heat transfer characteristics were carried out.The influence rules of foam ceramics such as porosity,pore density,sample thickness,superficial velocity and temperature difference on the flow and heat transfer characteristics of ceramics were obtained.Experimental research: based on the principle of single-blow method,a comprehensive experimental platform for gas flow and heat transfer in porous media was designed and established.On the basis of fully debugging and calibrating the experimental system,an experimental study on the pressure drop and heat transfer characteristics of the cylindrical foam ceramic test piece were systematically carried out.The pressure drop experiments were carried out in the lower Reynolds number range(Re: 50-1500),and the corresponding superficial velocities range were from 0.58 m/s to 3.53 m/s;The results of pressure drop experiments show that the pore structure(porosity and pore density PPI)of the foam ceramic and the superficial velocity binding together have determined the pressure drop characteristics.By fitting the experimental data of 270 sets of pressure drop,the pressure drop correlation of the foam ceramic porous material was proposed,and the deviation between the correlation and the experimental value is ± 25%.The experimental study of convective heat transfer was a transient heat transfer research,the medium temperature was in the range of normal temperature(283K-323K),and the initial temperature difference between gas and solid is less than 50 K.An experimental data analysis program for calculating the volumetric heat transfer coefficient of foamed ceramics based on the single-blow method was established,and the sensitivity analysis of the foamed ceramics porosity,pore density,superficial velocity,and sample thickness on the volumetric heat transfer coefficient were conducted;The results indicate that under the same velocity and foam ceramic structure conditions,the increased sample thickness lead to an increase in the area of local thermal equilibrium phenomenon,which in turn reduces the volumetric heat transfer coefficient.By fitting the 270 sets of heat transfer experimental data and introducing thickness parameters,the volumetric heat transfer correlation of the foamed ceramic porous material was established,and the deviation between the correlation and the experimental data is ± 20%.In terms of numerical simulation research: based on the simplified tetrakaidecahedron unit cell structure,a CFD numerical model for fluid-solid coupled heat transfer of foamed ceramics was established;Based on the experimental conditions,the numerical simulation of the flow field and temperature field characteristics of foam ceramics at the pore scale was carried out.The steady-state data simulation results show that the pore structure enhances the internal fluid turbulence,and the local velocity field affects the temperature field,resulting in different degrees of local thermal equilibrium and local thermal non-equilibrium in the foam ceramic.The transient data simulation results show that: the local thermal equilibrium area inside the foam ceramic alternates with time,it starts at the rear end of the foam and gradually decreases to disappear with time,and finally appears at the front end of the foam.Reducing the superficial velocity and increasing the porosity will lead to the occurrence of local thermal equilibrium earlier,and increasing thickness will lead to an increase in the range of local thermal equilibrium.This study enriches the theory of convective heat transfer in porous media,and the research results can provide guidance for the design of foam ceramic materials as medium heat exchange equipment,such as: solar volumetric receiver,compact low temperature heat exchanger,packed bed reactor,etc.