HEAT TRANSFER ENHANCEMENT IN THE SHELL SIDE OF THE SELF-SUPPORT IN RECTANGULAR CONVERGING-DIVERGING TUBE BUNDLE HEAT EXCHANGERS WITH DIFFERENT INSERTS

Three-dimensional numerical investigation of turbulent heat transfer and fluid flow characteristics of the new class of heat exchangers - the self-support of rectangular converging diverging (SS-RCD) tube bundle heat exchangers - with different inserts was performed. The values of the Reynolds number varied from 27,900 to 41,900. The baseline configuration (without an insert) was compared with three enhanced configurations (with inserts): a regularly spaced twisted-tape elements (RSTT) case, a twisted tape (TT) case, and a baffle plate (BP) case. The inserts led to the variation of velocity distribution and uniformity of temperature. Compared with the baseline case, the air-side heat transfer coefficient of the three enhanced cases was improved by 31.07-33.08%, 28.32-33.13%, and 38.01-46.74%, with an associated pressure drop penalty increase of 69.32-77.42%, 54.35-65.74, and 68.49-87.16%, respectively. The overall performance was conducted by the j/f(1/3) factor. It is found that the BP case had the best overall performance, followed by the TT and RSTT cases, the baseline case had the worst one. The results indicated that the key point of enhancing heat transfer of the shell side is to improve the heat transfer performance of the converging diverging tube. The numerical results were analyzed from the view point of the field synergy principle. It was found that the reduction in the average intersection angle between the velocity vector and the temperature gradient was one of the essential factors that influence the heat transfer performance.