A direct contact heat exchanger using particle-suspended gas as a heat transfer medium is analyzed with an extended emphasis on the radiation, i.e., considering the radiation by both gas and particles. Nongray model for gas-particle two phase media is newly proposed. While the Runge-Kutta method is used for a numerical analysis of the momentum and energy equations, the finite volume method is utilized to solve the radiative transfer equation.
This thesis consists of two parts. one is the analysis where the gray assumption is used and the other is focused on the nongray effect. First, the study assuming gray shows a notable effect by the gas radiation in addition to the particle radiation, especially when changing the chamber length as well as the gas and particle mass flow rate. When the gas and particle mass flow rate is raised, the gas temperature in the particle heater still increases as the gas absorption coefficient increases, which is different from the results for the small scale heat exchanger. However, the scattering effects by particles were found to be insignificant. Also, it is found that the one dimensional approximation is just valid for the optically thick condition.
Secondly, It is evaluate that the nongray effect of water vapor in air preheater of gas-particle direct-contact heat exchanger. Only the gas is treated as nongray, while the particles are assumed gray. The absorption coefficient in gray model was calculated from the mean beam length. Present study shows that the gary model overestimates the radiation effect, compared with the nongray model.
