AN INVESTIGATION ON THE SUPERIMPOSITION OF THERMAL DEGRADATION EFFECTS DUE TO SIMULTANEOUS FLOW MALDISTRIBUTION ON THE HOT AND COLD SIDES OF A CROSSFLOW HEAT EXCHANGER

This paper reports the work done to investigate the hypothesis that the thermal degradation effect of a crossflow heat exchanger due to simultaneous flow maldistribution on the hot side and cold side fluid streams is a superimposition of the degradation effects due to the individual maldistributed flow acting by itself. The theoretical basis of the combined degradation is developed with a discretized heat exchanger model, where each discrete element is analysed as an individual cross-flow heat exchanger to derive a combined maldistribution thermal degradation factor, Dcombo. A numerical calculation is then performed to verify the model, and comparison is made with other published data, and with experiments. The results from the study shows that Dcombo can be approximated, in cases of maldistribution with low standard deviation and where Cr = Cmin/Cmax -> 0 with constant Cmax fluid stream temperature, as the sum of the thermal degradation factors due to flow maldistribution acting individually in each flow passage. With larger standard deviations on the two fluid streams and with Cr -> 1.0, Dcombo is less than the sum of the individual degradation factors. The findings from this work give useful insights on the interaction of the fluid streams leading to the combined thermal deterioration, and are useful to simplify the design process of crossflow heat exchangers within the established limits.