Performance of the Cross-Flow Heat Exchanger with Variable Physical Properties : 1st Report, In Case where the Overall Heat Transfer Coefficient Is Variable

Abstract

In case where the overall heat transfer coefficient K varies with positions on the heat exchanger surface or fluid temperature in the cross-flow exchanger, the relations between the number of heat transfer units and the temperature efficiency ε are obtained analytically or numerically, assuming that K = 1+mxⁿ or K = 1+mθⁿ in the nondimensional form referred to the standard value K₀. The effects of parameters m and n are shown quantitatively, arranging the calculated results by the ratio of the efficiency change (ε-ε₀)/ε₀, where ε₀ is the temperature efficiency for K = K₀ and by the single overall coefficient signifying "true mean overall coefficient". Further, it is shown that there is considerable difference among flow arrangements and that conventional methods are not sufficient for large value of m.