Optimization of Fin and Tube Heat Exchanger: Effect of Recirculation

This paper explores the use of stream recirculation to enhance the thermo-economic performance of a fin-and-tube heat exchanger. The study introduces a recirculation factor (RF) to represent the portion of the tube-side stream allocated for recirculation. The optimization framework focuses on two main objectives—maximizing effectiveness and minimizing annual cost—using nine design parameters related to RF and heat exchanger geometry. To assess the benefits of recirculation, the optimization is also applied to a conventional, non-recirculating setup. Four scenarios with varying tube-side mass flow rates are analyzed in detail. The thermo-economic results are consistently better in the recirculation case compared to the conventional setup across all studied cases. Effectiveness increases by 1.28–8.33%, and annual cost decreases by 0.81–9.60% when recirculation is employed. The optimum results indicate that achieving better effectiveness requires a higher RF. Additionally, in the recirculation case, the heat exchanger needs a smaller heat transfer surface area but larger fin pitch, tube diameter, and no-flow length compared to the conventional setup for the same value of effectiveness.