Enhanced heat transfer performance for multi-tube heat exchangers with various tube arrangements

Numerical evaluations were conducted on multi-tube heat exchangers with transverse corrugated tubes and helically corrugated tubes. The complex flow features (coupled by multiple secondary flow, spiral flow and turbulent pulsation) and enhanced heat transfer mechanism were analyzed by coupling the global flow contours and entropy generation distributions. The average performances were measured using two evaluation methods. The results showed that the produced spiral flows have little effect on thermal efficiency, but can inhibit the increment of flow resistance significantly. The two evaluation methods for the four cases presented the same results, that the multi-tube heat exchanger with staggered tube arrangement of helically corrugated tube show the best overall performance than the other cases. The thermal efficiency can improve 2.46~1.61 and the pumping power increases 5.86~5.25 compared with the multi-tube heat exchanger with smooth tubes, under the Reynolds number 7, 200~36, 000. In order to ensure the energy benefit is positive the Reynolds number should be maintained above 25, 200 to keep performance evaluation criterion above 1.0 and Bejan number could above 0.85, simultaneously. In addition, the identical tube arrangement of helically corrugated tube is the optimum case, according to the two-objective optimization with heat flux and pumping power.