Simultaneous Retrieval of Total Hemispherical Emissivity and Specific Heat From Transient Multimode Heat Transfer Experiments

Transient cooling experiments of a heated vertical aluminum plate with an embedded heater, in quiescent air, were conducted for the simultaneous estimation of total hemispherical emissivity and specific heat of the plate material. During cooling, the heat loss from the hot plate by natural convection and radiation was taken into account. During the experiments, plate temperatures were recorded at several locations using a data acquisition system. A numerically computed transient response of the plate is then compared with the experimentally known transient response to estimate the residual, the minimization of which using Levenberg–Marquardt’s iterative procedure retrieves the parameters pertinent to the problem. The experiments were conducted for three different surface emissivities of the plate obtained by using suitable surface treatment. A consistency test for the present approach was also done by conducting transient heating experiments using the retrieved values of parameters and a comparison of simulated and calculated natural convection heat transfer coefficients as a function of temperature. The experiments have been performed over a temperature range of $320–430K$ and a Rayleigh number range of $2×106–2×107$⁠. The emissivity values are in good agreement with previous reported results.