Thermal Performance Reduction in Air-Cooled Heat Exchangers Due to Nonuniform Flow and Temperature Distributions

Abstract

The effect of nonuniform (or maldistributed) inlet airflow and temperature on the thermal performance of cross-flow air-cooled heat exchangers, with both fluids unmixed, and taking into consideration differences in performance characteristics of individual tube rows, is addressed in this article. The latter may be due to different fin pitches or other geometric variations or row effects due to changes in air turbulence. Downstream tube rows in such a multirow tube bundle experience higher performance reductions than the tube row at the air inlet. A nonuniform air velocity distribution to a tube row leaves the row with a distorted temperature profile. This temperature nonuniformity increases as the air passes through subsequent tube rows, and causes the downstream rows to be progressively less effective. The present analysis is used to evaluate the performance of the individual tube rows and ultimately the entire bundle. Velocity distributions which have been measured on air-cooled heat exchanger models ar...