Multi-Objective Optimization of Heat Transfer Coefficient and Exergy Efficiency in Using Air Bubble Injection as an Active Heat Transfer Enhancement Method

Heat transfer enhancement methods in heat exchangers are subjects of interest for energy engineers. While these methods work for improving the thermal performance of heat exchangers, certain penalties, such as exergy loss due to heat transfer irreversibilities, areunavoidable. This work aims to optimize air bubble injection into the annulus side of a vertical double pipe heat exchanger as an active method of heat transfer enhancement from overall heat transfer coefficient and exergy efficiency perspectives. Multi-objectiveoptimization using genetic algorithm was carried out and the resulting Pareto front revealed that a moderate level of air flow rate (almost 120 NL/h) and high hot flow rate though tube are required to optimally increase heat transfer with the best possible exergy performance.In the optimal state of operation, overall heat transfer coefficient and exergy efficiency were 782.5 W/m2-K and 43.46%, respectively, showing promising increases over their original values without air bubble injection.

Keywords:

Multi-objective optimization , Exergy , Heat transfer enhancement , Double-pipe heat exchanger , Air bubble injection