Heat Transfer under Changing Pressure Conditions during Flame Propagation in a Porous Medium

The gas temperature dynamics is studied using as an example a single cylindrical channel with a diameter of 2 mm—a Raschig ring—placed in a porous medium consisting of such rings. The gas and thermocouple wire temperatures on the channel axis and the temperature distribution in the channel were calculated in two processes: the first is the pressure rise in the closed vessel during flame propagation in the space free of the porous medium, and the second is the cooling of the gas after flame passage through the channel. For both processes, the gas temperature and the equilibrium temperature of the gas and porous medium were measured using a thermocouple with a wire diameter of 15 $$\mu $$ m in a cylindrical pore with a diameter of 2 mm. During gas compression at a constant low rate, the thermocouple can be used to measure the steady-state temperature of the gas. However, when reaching the steady-state value, the larger the wire diameter, the more the thermocouple will lag. During the cooling of the instantaneously heated gas, the thermocouple measurements of the gas temperature were found to be significantly underestimated. This is due to the higher heat capacity of the thermocouple wire compared to the heat capacity of the gas in the pore. During the heating of the thermocouple, the gas cools down due to heat transfer into the pore walls.