Thermal performance enhancement of a double-tube heat exchanger with deep dimpled tubes

Purpose The purpose of this study is to develop a new type of enhanced heat transfer tube (deep dimple tube, DDT) suitable for double-tube heat exchangers. This study explores the influence of its structural parameters on flow and heat transfer characteristics through numerical simulation and verifies its enhanced heat transfer performance. Design/methodology/approach This study adopts the numerical simulation method, taking the smooth tube as a reference, and studies the influence rules of the key structural parameters of the deep dimple tube (dimple depth, radius and pitch) on the convective heat transfer coefficient outside the tube (Nu) and flow resistance (f) within the Reynolds number (Re) range of 5,910–20,100. This study reveals the enhanced heat transfer mechanism of the dimple structure by analyzing the velocity distribution, pressure distribution and temperature field distribution of the flow field. Findings Flow characteristics: Compared with the smooth tube, the velocity of the fluid outside the deep-pit tube decreases inside the pits, and flow reversal occurs on the downstream side, forming a vortex region. The pressure peak is concentrated on the upstream surface of the pits, and the minimum pressure appears in the raised area (the tube wall between the pits), resulting in a significant increase in flow resistance (f/f0 = 1.18–9.73). Heat transfer characteristics: The region of temperature increase is concentrated near the tube wall, and the convective heat transfer capacity is significantly enhanced (Nu/Nu0 = 1.88–4.03); Nu/Nu0 and f/f0 increase with the increase of pit depth and radius and decrease with the increase of pit spacing. Comprehensive performance: Within the studied Re number range, the heat transfer performance evaluation criterion (PEC) is 1.27–1.95, indicating that the comprehensive enhanced heat transfer performance of the deep-pit tube is superior to that of the smooth tube. Originality/value A design of high-efficiency heat transfer enhancement tube based on deep pit structure was proposed; the regulation mechanism of pit geometric parameters on flow and heat transfer was revealed, providing a theoretical basis and reference for structural parameters for the optimized design of double-tube heat exchangers.