Investigation On Forced Convection And Coupled Heat Transfer With High Temperature Radiation In Cellular Porous Material

The cellular porous materials are characterized by a three-dimensional network of solid matrix and interconnected pore channels. Their small pores and large specific area play an important role from the thermal point of view, leading higher heat transfer rates. The mechanism and feature of coupled heat transfer in the cellular porous material at high temperature are significant to the development of the technologies for solar thermal conversion and heat transfer enhancement. In this dissertation, the mechanism of coupled radiative and convective heat transfer, numerical computational method and transport properties of forced flow in the cellular porous material are investigated with a macroscopic approach.For the numerical analysis of the coupled radiative and convective heat transfer in the cellular porous material, three methods are employed to solve the radiation from the solid phase, including Monte Carlo method(MCM), the P1 approximation and the Rosseland approximation. The program modules are developed in Fluent software. The analysis of coupled heat transfer can be conducted with this approach, considering the effect of thermal radiation along with the local thermal non-equilibrium(LTNE) heat transfer between the two phases. The computational method is validated with three aspects, including the simulation of thermal radiation, LTNE heat transfer simulation and comparison with experiment. The precision of P1 approximation and the Rosseland approximation are tested, compared with the MCM simulation. It shows that more reliable resluts can be otbained using the P1 approximation.Temperature measurement is a key to the research of heat transfer in the cellular porous material. A numerical transient heat transfer model for thermocouple is established for the high-temperature measurement inside the cellular porous material. The thermal response of thermocouple and the information represented by the thermocouple temperature are discussed. The resluts show that the temperature of thermocouple can not be representative of the fliud and solid temperatures. A radiative transfer model is built for the infrared temperature measurement. The effect of semitransparent property on the infrared measurement is illustrated, taking the semitransparent medium layer as an analytical case.A test rig is designed and built for the investigation of forced convection in the cellular porous material within a tube. Three porous materials, Cu, Ni and Si C are tested. Twelve empirical correlations for the pressure drop prediction are compared with the experimental data, while seven correlations for the volumetric heat transfer coefficient are compared. New correlations are proposed based on the experimental data within a error of ±40%. The experiment of heat transfer at high temperature is performed with Si C porous material. The fluid and solid temperatures are obtained with the correction of thermocouple temperature. A simulation is performed based on the experiment. The deviation between the numerical and experimental data is less than 25.2%.The coupled heat transfer in cellular porous material within a tube is numerically studied under the boundaries of constant wall temperature and constant wall flux, respectively. The effects of pore structure parameters and emissivity of tube wall are discussed. Then, the volumetric absorption characteristics of porous receiver exposed to the highly concentrated solar radiation are investigated with MCM simulation. Thermal performance analysis of solar receiver is carried out considering the nonuniform characteristics of the incident concentrated solar radiation. Three approaches to model the concentrated solar radiation on the front surface of absorber are compared. It is found that the approach considers the solar radiation on the front surface as thermal boundary condition has a lagre deviation up to 25.8%. Finally, the heat transfer performance of solar receiver with double-layer porous absorber is predicted with gradual design of the pore structure parameters and different thicknesses of each layer.Through the investigations, the numerical method and program modules for the coupled radiative and convective heat transfer in the cellular porous material are validated. The temperature measurement in the high-temperature experiment of porous material is well understood. The experimental data and correlations are obtained, as well as the heat transfer characteristics of cellular porous material within a tube and under the solar condition. The achievements presented in this dissertation will provide significant reference for the thermal design, evaluation and optimization of the high-temperature thermal system with cellular porous material.