TY - JOUR
TI - Augmented of turbulent heat transfer in an annular pipe with abrupt expansion
AU - Togun Hussein
AU - Abdulrazzaq Tuqa
AU - Kazi Salim Newaz
AU - Badarudin Ahmad
JN - Thermal Science
PY - 2016
VL - 20
IS - 5
SP - 1621
EP - 1632
PT - Article
AB - 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/m2, 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 4000W/m2.