Compound heat transfer enhancement of helical channel with corrugated wall structure

Newly, the use of corrugated structures in heat exchange devices has become a useful technique due to the combined merits of extended surfaces and turbulators. However, employing of this technique in curved channels is very scarce. To this aim, as a new passive compound technique, the periodical corrugated structure is proposed to enhance the overall hydrothermal performance of a helical channel with square cross-section. Firstly, calculated results for the smooth model are compared with existing empirical correlations in the literature to explore the reliability and accuracy of the current analysis. Secondly, the corrugated structure on each side (upper, lower, inner, and outer) as well as opposite sides (upper-lower and inner-outer) of the helical channel is tested individually. It is found that corrugating the side walls of the helical channel prevents the development of thermal boundary layers through the flow direction and changes continuously the location and strength of generated secondary flows and velocity contours, leading to more uniform temperature. Thirdly, three different levels of corrugation-amplitude (A = 0.8, 1.6, and 2.4 mm) and coil-diameter (D = 50, 100, and 150 mm) are considered. At the studied range of Reynolds number (100 <= Re <= 500), the best enhanced model is the case of upper-lower at A = 2.4 mm and D = 100 mm, and the maximum performance index of 1.46 is recorded for water flow through this model at Re = 400. (C) 2019 Elsevier Ltd. All rights reserved.