On the Dominant Factors of the Heat Transfer Phenomena in Industrial Furnaces

The aim of this investigation is to find dominant factors in unsteady heat transfer phenomena during transient heating process in two types of industrial furnace though experiments and numerical simulations. Experiments were carried out using a directly gas-fired batch furnace with a circulating fan whose maximum temperarute was 773 K and heat input was 27 kW, and a indirectly fired furnace with radiant tubes of 1173 K and 26 kW. In the case of the transient heating process of the directly gas-fired furnace, an increase in the circulating rate of the atmosphere promotes uniformity in the atmospheric temperature in the furnace, but causes a drop in the efficiency of the furnace. This is because an increase in the heat transfer rate on the thermal insulating wall surface promotes heat losses through the furnace walls. In the case of the indirectly gas-fired furnace, because the convective heat transfer rate is rather low and the radiative heat transfer plays a major role in the energy transfer in the furnace, the temperature dependencies of the physical properties of the insulating material work as major factord domaining the heat transfer in the furnace. Numerical simulations using a commercial CFD code FLUENT/UNS were also carried out on indirectly gas-fired furnece adopting the dominant factors revealed from the experiments.