Combined Flow and Temperature Nonuniformity in Compact Cross‐Flow Three‐Fluid Heat Exchangers

ABSTRACT Cryogenic processes often involve the heat interaction of multiple fluids and are highly sensitive to even minor variations in operating conditions. Hence, flow and temperature nonuniformity adversely impact the performance of thermal systems, and their combined occurrence can be especially detrimental. The transient response and thermal effectivity of a cross‐flow three‐fluid heat exchanger are investigated while considering the flow and temperature nonuniformity at the inlet section. Four modes of combined flow and temperature nonuniformity are opted, which replicates the pragmatic situation existing in the working of heat exchangers, and the effectivity of the thermal system is evaluated by its alignment with the uniform flow mode. Flow nonuniformity is implicated in both the inlet section and within the core all along with the effect of fluid back mixing. The “Dankwert's” boundary condition is specifically used to account for the effects of axial dispersion within the fluids. The model incorporates longitudinal heat conduction in partition walls, with the “finite difference method” employed to solve the partial differential equations. To the best of our knowledge, the present study is the first attempt to analyze both the transient response and effectivity of three‐fluid heat exchangers under combined flow and temperature nonuniformity. It is learned that thermal effectivity is degraded by 31.5% and enhanced by 1% under flow nonuniformity mode QPQ and temperature nonuniformity mode 1 respectively. Under the combined mode of both, the effectivity settles down somewhere amid both and is found to be degraded by 8%. The higher NTU comes up with a sharp peak in temperature distribution, which makes the core more prone to cracks.