The measurement of heat-loss rates from a stirred reactor using a thermochemical method

Abstract

Studies of chain-thermal reactions, and in particular of the low-temperature thermal oxidation of hydrocarbons have now progressed sufficiently to demand quantitative knowledge of heat-release rates. Chemical complexity precludes the calculation of heat-release rates from stoichiometries of reaction and enthalpies of formation, so that the only remaining source is that of direct measurement from reactant temperature excesses. Under stirred conditions in a closed reactor, the heat release rate is related very simply to the temperature excesses attained, the relationship involving the heat-transfer coefficient (l) between gas and walls. We have measured l for our stirred reactor by a thermochemical calibration method employing the oxidation of nitric oxide. Typically, l = 23 W K⁻¹ m⁻², and this means that a 1 K temperature excess in our reactor requires the release of 0.69 W. We find that the heat transfer coefficient depends on pressure, density, and transport properties of the reacting gas, but that knowledge of these parameters permits reasonable predictions of l for other gases to be made from that determined by thermochemical calibration.