3D numerical study and comparison of thermal-flow performance of various annular finned-tube designs

With the increase of heat transfer problems in marine vehicles and submerged power stations in oceans, the search for an efficient finned-tube heat exchanger has become particularly important. The purpose of the present investigation is to analyze and compare the thermal exchange and flow characteristics between five different fin designs, namely: a concentric circular finned-tube (CCFT), an eccentric circular finned-tube (ECFT), a perforated circular finned-tube (PCFT), a serrated circular finned-tube (SCFT), and a star-shaped finned-tube (S-SFT). The fin design and spacing impact on the thermal-flow performance of a heat exchanger was computed at Reynolds numbers varying from 4,300 to 15,000. From the numerical results, and when the fin spacing has been changed from 2 to 7 mm, an enhancement in the Colburn factor and a reduction in the friction factor and fin performances were observed for all cases under study. Three criteria were checked to select the most efficient fin design: the performance evaluation criterion P_EC, the global performance criterion G_PC, and the mass global performance criterion$M_{G_{PC}}$. Whatever the value of Reynolds number, the conventional CCFT provided the lowest performance evaluation criterion P_EC, while the SCFT gave the highest amount of P_EC. The most significant value of G_PC was reached with the ECFT; however, G_PC remained almost the same for CCFT, PCFT, SCFT, and S-SFT. In terms of the mass global performance criterion, the S-SFT provides the highest $M_{Gpc}$as compared with the full fins of CCFT (41–73% higher) and ECFT (29–54% higher). Thus, the heat exchanger with S-SFT is recommended to be used in the cooling of offshore energy systems.