Experimental investigation of the heat transfer for non-circular tubes in a turbulent air cross flow

Abstract

ABSTRACT The purpose of this experimental study is to measure the drag and heat transfer coefficients of the non-circular tubes including square, elliptic, and cam-shape tubes in a turbulent air cross flow. Studies have been made at 0° to 180° angles of attack () and Reynolds numbers (Re) based on the equivalent diameter of a circular tube within the range of 1.4 × 104 < Reeq < 7.5 × 104. The equivalent diameter Deq = 46 mm was chosen for the tubes. The results show that the minimum and maximum drag coefficients (Cd) belong to the cam-shape and square tubes at 0°, respectively. The (Cd) of the cam-shape and square tubes are 60% less and 25% more than the equivalent circular tube, respectively. Also, the ratio of the average Nusselt number () to the drag coefficient, /Cd, was used to compare non-circular tubes and with their equivalent circular ones. The results show that the maximum value belongs to the cam tube and the minimum occurs for the square tube at α = 0°. The /Cd ratio of the cam tube is 128% more than the equivalent circular tube, while the square tube yields a /Cd ratio that is13% less than its circular equivalent.