Sizing of heat exchangers with non-uniform coefficients

A technique is presented to include the effects of a non-uniform, overall heat transfer coefficient in double-pipe heat exchanger analysis using the effectiveness (or efficiency) method. The local overall coefficient is permitted to vary with the local temperature difference between the two fluids according to (T?t)ⁿ, where the exponent “n” assumes individual values for various physical situations. A procedure is provided to estimate the appropriate value of “n” for a particular problem. The development provides a correction factor to the ordinary results of the effectiveness method for uniform overall coefficients.