Investigation of the hydraulic and thermal characteristics of a double concentric tubes with an inner twisted spiral tube

The characteristics of heat transfer and fluid flow of twisted spiral tubes with different pitches and depths have been investigated experimentally with respect to a conventional tube (smooth tube) as a particular reference. The effects of the twisted spiral pitch ratios, S/D_hy, depth ratios, H/D_hy, Reynolds number and flow arrangement on the thermal performance of a twisted spiral tube heat exchanger are investigated. Three twisted spiral tubes with different pitches, S, of 3.9, 5.2 and 8.2 mm corresponding to twisted spiral pitch ratios, S/D_hy, of 0.278, 0.372 and 0.586; besides three twisted spiral tubes at different depths, H, of 0.6, 0.95, and 1.15 mm corresponding to twisted spiral height ratio, H/D_hy, of 0.043, 0.068 and 0.082 are experimentally examined in this study. The Reynolds number, Re, ranges in both inner tube side and annular side are 5000-50,000 and 1400-10,400, respectively. The results revealed that the twisted spiral pitch ratios S/D_hy of the 0.278achieved an enhancement of Nu by 38% compare to the smooth tube with a corresponding increase of 33.2% in the f. Also, the twisted spiral depths ratios, H/D_hy, of 0.082 achieved higher Nu by 44.9%, compared to the smooth tube with a corresponding increase of 36.4% in the f. The thermal performance criteria reached 1.93 and 2.03 at S/D_hy of 0.278 and H/D_hy of 0.082, respectively. New correlations to expect Nu_c and f_c were predicted.