Experimental study of periodic heat transfer coefficient in the entrance zone of an exhaust pipe

The application of new standards of pollutant gas emission restrictions has forced the motor-car industry to improve their level of knowledge on heat transfers occurring between intermittent gas flows and exhaust system pipes. In this paper we present a study that we carried out in order to estimate the heat transfer coefficient in exhaust pipes. We developed an experimental device which re-creates engine working conditions. This experiment set up has been designed in order to check all assumptions of the theoretical model. Measurements are carried out with heat flux sensor, gas temperature probes and pressure sensor in the entrance zone of a cylindrical exhaust pipe. First results show that the heat transfer coefficient estimated in the case of an intermittent gas flow is higher than the one measured on a continuous flow with identical inlet conditions: same mass flow and inlet temperature. Measurements show that, for a given flow rate, the intensification of the heat transfer due to the flow intermittency corresponds to the eigen frequency of the exhaust pipe.