Numerical analysis on the transient measurement of gas temperature in porous material using thermocouples at high temperatures

Heat transfer in porous materials is significantly important in various engineering fields. The temperature distributions are essential. for comprehensive understanding of the process. The current study aims to investigate the uncertainties associated with the gas temperature measurement in porous material using thermocouples at high temperatures by means of two hierarchical models. The transient coupled radiative and convective heat transfer within porous material is firstly simulated using the local thermal non-equilibrium model with Monte Carlo method. The flow is transient, incompressible and laminar. The porous material is considered as a homogeneous, absorbing, emitting and isotropic scattering medium. Based on the velocity and temperature fields, a numerical heat transfer model for thermocouple junction is developed with the lumped energy balance. Monte Carlo method is also adopted for the radiation simulation between the junction and porous material. The transient temperature response of thermocouple is computed and compared with the local gas temperature. The effects of wall temperature and the emissivity and diameter of thermocouple junction are analyzed. The results show that thermal inertia of thermocouple and thermal radiation have a significant effect on the gas temperature measurement inside porous material. The measurement error varies obviously during the transient measurement process. The junction diameter has a higher influence on the measurement error than junction emissivity. In addition, compared with low emissivity, the error is larger for high junction emissivity when the steady state is reached. (C) 2015 Elsevier Ltd. All rights reserved.