A non-catalytic surface for dissociated combustion gases

Abstract

Heat transfer measurements have been made in a detonation tube using hydrogen-oxygen and acetylene-oxygen mixtures. A small diameter wire placed transverse to the tube axis is rapidly heated by the dissociated combustion products behind the advancing detonation front. Because of the high temperature (3000°K–4500°K) in a detonation wave, the combustible gases are appreciably dissociated, usually more than 50 per cent of the total enthalpy being in the form of dissociation energy. The variation of total heat transfer with composition and pressure was found to be close to theoretical expectations. For wires coated with iodine, it was found that the total heat transfer could be reduced by about a factor of 3 in the oxy-hydrogen mixtures, and by a factor of 2 in an equi-molar acetylene-oxygen mixture at low pressure when compared with the uncoated wire experiments. Both these factors could be accounted for by assuming that the energy of dissociation and molecular vibration were not recovered at the cold wall. From separate measurements of the thickness of detonation waves in these same mixtures, it can be seen that for the conditions under which the coated wire substantially reduces the heat transfer, the aerodynamic boundary layer on the wire surface should be “frozen”. Furthermore, theoretical arguments indicate that the effect of iodine evaporation on the net heat transfer should be much smaller than the experimentally observed reduction in heat transfer. Under these conditions, the surface recombination coefficient is estimated to be less than 10 −2.