A parametric study on heat transfer and pressure drop characteristics of circular tube with alternating flattened flow path

Abstract

Abstract A parametric study is carried out on circular tube with alternating flattened flow path. This analysis is performed numerically with experimental validation on the reference model, which has mid-levels of the design factors. Three design factors, namely straight pitch (a), transient length (b), and minimum axis (c) at five different levels are investigated for 500\xa0≤\xa0Re\xa0≤\xa01500. The main purpose is to enhance the thermal performance of circular tube by producing multi-normal vortices. The results show that new vortices are formed as a result of both increasing Reynolds number and decreasing design factors. Among the studied factors, the minimum axis has the highest effects, followed by the transient length and the straight pitch. Compared to the smooth tube, changing a, b, and c would increase the Nusselt number and frcition factor by 1.34–3.21 and 2.78–4.91, 1.23–4.45 and 2.75–7.5, and 1.04–5.06 and 1.39–16.74, respectively. Almost all enhanced models show an improved thermal performance factor, especially at high Reynolds numbers. The best thermal performance factor is around 2.27 for the model with a\xa0=\xa010, b\xa0=\xa05, c\xa0=\xa05.5\xa0mm. Finally, three correlations are developed for predicting the hydrothermal parameters of such tubes with average errors within 5%.