Enhancement of Gas Enthalpy-Radiation Conversion by Utilizing Multilayer Open-Cellular Porous Materials

Multilayer porous gas enthalpy-radiation converter consisting of two porous plates divided by free space is proposed to enhance the performance of single layer porous converter. The energy equations of the gas and the solid phases are employed by using separate energy equations model, and the convective heat transfer between the two phases based on an empirical volumetric heat transfer coefficient proposed by Kamiuto and San San Yee is estimated. The P₁ approximation method is employed to evaluate the radiation of transfer equation. Results show that high porosity and PPI (pores per inch) are effective to raise the gas enthalpy-radiation conversion. The upstream porous layer should be lower in porosity and PPI than the downstream porous layer. To increase the temperature drop across the porous gas enthalpy-radiation converter, the inlet gas temperature should be high and the upstream radiation temperature should be low. To obtain maximum temperature drop across the multilayer porous converter, both layers should be made of pure absorbing porous materials. In case the upstream radiation temperature exceeds an inlet gas temperature, however, use of pure scattering porous plate on the upstream side and pure absorbing porous plate on the downstream side will obtain the maximum temperature drop across the converter. The validity of the predicted numerical model also has been confirmed by the experimental data.