A More Accurate Total Heat Transfer Rate Method of the Single-pipe Heat Exchanger Considering Heat Radiation

摘要

The log mean temperature difference (LMTD) method is conventionally used to calculate the total heat transfer rate of heat exchangers. Because the heat radiation equation contains the 4th order exponential of temperature which is very complicate in calculations, thus LMTD method neglects the influence of heat radiation. From the recent investigation of a metal circular pipe in some practical situations, it is found that even in the situation of the temperature difference between outer pipe surface and surrounding is low to 1°C, the heat radiation effect cannot be ignored in the situations of ambient air with lower convection heat coefficient and oxidized metal pipe with higher surface emissivity. In this investigation, the log mean heat transfer rate (LMHTR) method considering the influence of heat radiation is developed to calculate the total heat transfer rate of single-pipe heat exchanger and much more accurate results can be obtained.