Augmented of turbulent heat transfer in an annular pipe with abrupt expansion

Abstract

This paper presents a study of heat transfer to turbulent air flow in the abrupt axisymmetric expansion of an annular pipe. The experimental investigations were performed in the Reynolds number range from 5000 to 30000, the heat flux varied from 1000 to 4000 W/m 2 , and the expansion ratio was maintained at D/d=1, 1.25, 1.67, and 2. The sudden expansion was created by changing the inner diameter of the entrance pipe to an annular passage. The outer diameter of the inner pipe and the inner diameter of the outer pipe are 2.5 and 10 cm, respectively, where both of the pipes are subjected to uniform heat flux. The distribution of the surface temperature of the test pipe and the local Nusselt number are presented in this investigation. Due to sudden expansion in the cross-section of the annular pipe, a separation flow was created, which enhanced the heat transfer. The reduction of the surface temperature on the outer and inner pipes increased with the increase of the expansion ratio and the Reynolds number, and increased with the decrease of the heat flux to the annular pipe. The peak of the local Nusselt number was between 1.64 and 1.7 of the outer and inner pipes for Reynolds numbers varied from 5000 to 30000, and the increase of the local Nusselt number represented the augmentation of the heat transfer rate in the sudden expansion of the annular pipe. This research also showed a maximum heat transfer enhancement of 63-78% for the outer and inner pipes at an expansion ratio of D/d = 2 at a Re = 30000 and a heat flux of 4000 W/m 2 .

Heat Transfer Improvement in a Double Backward-Facing Expanding Channel Using Different Working Fluids

“…Over the last several years, many studies have focused on using nanofluids with separation flow in BFSs and FFSs, which have been considered by various researchers [18][19][20][21][22][23][24][25][26][27][28][29][30] with similar conclusions. Recently, the modeling of turbulent heat transfer over a microscale BFS was presented by Sadeq et al [31].…”

Efficient Heat Transfer Augmentation in Channels with Semicircle Ribs and Hybrid Al2O3-Cu/Water Nanofluids

“…Nanofluids with fabricated geometries are increasingly employed to improve heat transfer in various applications [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. Dadheech et al [ 6 ] studied natural convection in the attendance of an angled magnetic field and compared the thermal behavior of MoS 2 /C2H 6 O 2 and SiO 2 -MoS 2 /C 2 H 6 O 2 nanofluids.…”