Experimental Investigation on Three-Fluid Compact Heat Exchanger Under Uniform and Non-Uniform Flow

Enhancing heat transfer through high surface area density is a key goal in cryogenics, and multi-fluid compact heat exchangers are among the most promising solutions. This study investigates a three-fluid plate-fin heat exchanger operating in parallel flow using water at three temperature levels: hot (70 °C), intermediate (40 °C), and cold (28 °C). Both uniform and non-uniform flow conditions are examined, with non-uniformity introduced through a specially designed tri-entry header. Tri-entry inlet header splits the main stream flow into three streams at different flow rates, which are controlled by ball valves. The induced controlled variation in flow of each streams generates different flow non-uniformity condition at the entrance of the core. This induces controlled non-uniformity in the inlet conditions, helping to study its effect on heat exchanger performance under realistic, non-ideal scenarios. The study first evaluates performance under uniform flow, then explores the effects of flow non-uniformity, temperature non-uniformity, and external heat loss. Four flow configurations are analyzed by varying the central hot fluid’s flow rate, which exchanges heat with both neighboring streams. The counter-current–co-current configuration yields the highest cooling efficiency under uniform flow, while a co-current configuration improves it by 1.5% under non-uniform flow with inverse parabolic profile. Under a combined flow non-uniformity pattern resembling the straight parabolic profile and a temperature non-uniformity mode resembling the left-sided parabolic profile, the heating efficiency of the intermediate stream drops by 5.2%.