Effects of Nonuniform Passages on Compact Heat Exchanger Performance

Abstract

Neighboring passages in a compact heat exchanger such as a rotary regenerator are never geometrically identical due to manufacturing tolerances. This passage-to-passage nonuniformity can result in a significant penalty on heat transfer performance with only a small compensating effect of reduced pressure drop. Continuous cylindrical passage geometries, operating with laminar flow, are particularly sensitive to these effects. In this paper, a procedure is outlined to establish the effective friction factors and Nusselt numbers for one fluid side of an exchanger having n different cylindrical passage geometries. Two special cases of longitudinal wall temperature variation are considered corresponding to conditions of Cmin/Cmax of zero and unity. The analysis is presented for both fully developed and developing laminar flow.