Heat transfer in reacting systems Effect of chemical kinetics on the thermal conductivity of gases

Abstract

The effect of chemical kinetics on the conduction of heat through a reacting gas at rest between a pair of infinite parallel plates has been analysed by solving the non-linear equations of change with the aid of an electronic-analog computer. A technique for solving the so-called “stiff” differential equations is presented. For illustrative purposes the analysis has been applied to the case of purely homogeneous gas-phase reversible reactions with two quite different kinetic mechanisms being considered: (1) isomerization with uni-molecular forward and reverse steps: A ⇄ B and (2) a more complicated reaction with bimolecular forward and reverse steps: 2AB ⇄ A 2 + B 2. Complete temperature equilibration of the gas with the solid walls was assumed. The temperature differences between the plates were not restricted to small values and thus the variation in reaction rate with position could not be neglected. The analysis leads to a dimensionless parameter consisting of a ratio of an effective diffusion time to an effective reaction time, the effective thermal conductivity of the gas increasing with an increase in this parameter. Values of the ratio of the effective reacting thermal conductivity to the reacting thermal conductivity at equilibrium are presented as a function of this parameter.