Heat Transfer by Combined Forced Convection and Thermal Radiation in a Heated Tube

An analysis is made to study the heat exchange by combined forced convection and thermal radiation in a tube when there is a specified heat flux imposed at the tube wall. The gas flowing in the tube is assumed transparent to radiation, so that the radiation which is included takes place between the elements of the internal tube surface and between this tube surface and the environment at each end of the tube. The inside surface of the tube is a black emitter and the outside is assumed perfectly insulated. The heat-transfer coefficient for convection alone from the tube wall to the gas is assumed constant. The energy equation governing the heat exchange is solved by two methods which provide results that are in good agreement with each other. Numerical examples of the wall and gas-temperature variations along the tube show the influence of the system parameters such as inlet gas temperature, tube length, and convective heat-transfer coefficient. A simple method is outlined, which can be used under some conditions to obtain an approximate wall-temperature distribution.