Thermo-hydraulic performance evaluation of heat transfer tubes with different configuration forms

Abstract

Fluid mixing induced by changes in tube direction is an effective method to enhance the heat transfer performance of heat transfer tubes. This study proposes three types of configuration forms for heat transfer tubes that improve their thermo-hydraulic performance, named cases 1, 2, and 3. Case 1 is distributed on the same plane and has the following configuration form: horizontal to vertical upward to horizontal to vertical downward to horizontal. Cases 2 and 3 transform the front and rear tubes into two parallel planes through the middle horizontal tube, with a 180° difference at the outlet direction. The thermo-hydraulic performance of heat transfer tubes with different configuration forms is evaluated by quantitative comparison of the Nusselt number (Nu), friction coefficient (f), and performance evaluation criterion (PEC), within a Reynolds number range of 5000–40 000. The distribution results of velocity, streamline, turbulent kinetic energy, skin friction coefficient, and so on are analyzed to reveal the underlying mechanisms of difference in the thermo-hydraulic performance of heat transfer tubes with different configurations. The results show that the thermo-hydraulic performance of heat transfer tubes with different configurations is better than that of a straight tube due to induced fluid mixing within the tube. In addition, case 1 rather than cases 2 and 3 has a more significant influence on the thermo-hydraulic performance of heat transfer tubes, especially at high Reynolds numbers, and the maximum PEC of case 1 exceeds cases 2 and 3 by 6% and 8.5%, respectively. Furthermore, the decrease in connection length of case 1 improves the heat transfer performance, which is more pronounced at high Reynolds numbers. These research findings serve as a valuable reference for designing heat transfer tube configurations to enhance heat transfer efficiency.