FILM-BOILING HEAT-TRANSFER WITH A CATALYTIC DECOMPOSITION REACTION

Film-boiling heat transfer of saturated methanol with decomposition reaction is investigated experimentally using a cylindrical heater with a catalytic surface. Platinum black powder which is bound to the cylinder shows sufficient activity to catalyze the reaction. The heat transfer coefficient markedly increases with slight increase of the wall superheat, becoming about 50% higher than Bromley's prediction for the case of no reaction. Such high heat transfer is considered to be due to the endothermic action and the evolution of hydrogen, the thermal conductivity of which is about five times that of methanol vapor. However, once the wall superheat exceeds about 510 K, the heat transfer coefficient decreases and approaches that for the case of no reaction. This may be due to the sintering of the catalyst in the present study. The heat transfer coefficient predicted by taking account of the absorbed heat and change of the properties of the vapor phase due to the evolution of decomposed gases is in good agreement with the high coefficient measured experimentally.