STUDY ON CHARACTERISTICS OF FLUID-FLOW AND HEAT TRANSFER IN THE TORSIONAL FLOW HEAT EXCHANGER WITH DROP-SHAPED TUBE

Adopting enhanced tube is an effective way to enhance the performance of a shell-and-tube heat exchanger. In this paper, a drop-shaped tube with stream-lined cross-section was used to enhance heat transfer of the torsional flow heat exchanger. The characteristics of the fluid-flow and heat transfer in torsional flow heat exchanger with drop-shaped tube were studied numerically, considering three kinds of axis ratios (a/b=1.5, 1.8, 2) of the tube. The reliability of numerical re-sults was verified through experimental results. The results indicate that the wake size of the streamlined drop-shaped tube is smaller than that of the conventional smooth tube, and the drop-shaped tube reduces the flow dead zone in torsional flow heat exchanger. As the axis ratio of a/b increases, the shell side Nusselt num-ber and comprehensive performance increase, due to enhancement of the turbu-lence kinetic energy of the transition section. When the axis ratio is 2, the Nusselt number is increased by 12.44-18.99%, and the comprehensiveness is increased by 13.27-19.2%, compared with the torsional flow heat exchanger with the smooth tube. The quantitative analysis of the velocity indicates that the relative magnitude and proportion of transverse velocity components of fluid are important factors affecting the thermal-hydraulic performance of torsional flow heat exchanger.