Numerical investigations of the thermal-hydraulic performance in a rib-grooved heat exchanger tube based on entropy generation analysis

摘要

A numerical simulation has been conducted to examine the turbulent flow characteristics and heat transfer performance in a rib-grooved heat exchanger tube. Ribs and grooves characterized by a discrete and inclined distribution are alternately arranged on the inner wall surface of the test section. The main purpose of this study is to determine thermal-hydraulically superior rib-groove geometry for heat transfer enhancement. Flow structures and local heat transfer characteristics are presented and analyzed at first. Because of the disturbance of ribs and grooves, multiple longitudinal swirl flows are induced, which immensely affect the local heat transfer performance. Then, effects of geometric parameters, including the rib-groove pitch ratio (P*), the number of circumferential ribs and grooves (N), and the rib-groove inclination angle (a) on the heat transfer and flow performance are examined. The results show that the heat transfer ratios (Nu/Nu(0)) are about 1.58 to 2.46, while friction factor ratios (f/f(0)) are about 1.82 to 5.03. Therefore, the performance evaluation criterion (PEC) values vary from 1.19 to 1.68. In addition, entropy generation analysis indicates that the impact of the ribs and grooves is thermodynamically advantageous. The entropy generation number reaches the minimum when P* = 0.35, N = 8 and alpha=45 degrees, under which condition the proposed rib grooved tube would perform the best in practice. (C) 2016 Elsevier Ltd. All rights reserved.