Counter-rotation vortex flows and heat transfer mechanisms in a V-spirally-corrugated tube

Abstract

The flow and heat transfer behavior of newly designed V-corrugated tubes with various numbers of starts ( N = 2, 3, 4, and 5), depth ratios ( DR = 0.02–0.14), and pitch ratios ( PR = 1.0–2.0) were studied in the turbulent flow region (5000 ≤ Re ≤ 20,000). The friction factor ( f), friction factor ratio ( f/ f0), Nusselt number ( Nu), Nusselt number ratio ( Nu/ Nu0), and thermal enhancement factor ( TEF) values are reported. The computational results indicate that the conventional spirally-corrugated tube create swirl flows while V-corrugated tubes generate a counter-rotating vortex flow that impinges upon the lower zone of the tubes and enhances fluid transfer between tube core and near-wall regions. The results also show that the f, Nu, f/ f0, Nu/ Nu0 monotonically increase with decreasing PR, increasing DR and N, while the TEF is dependent on a tradeoff between f/ f0 and Nu/ Nu0. Over the studied range, the f/ f0, Nu/ Nu0, and TEF were in the ranges of 1.36–43.82, 1.00–5.35, and 0.80–2.11, respectively. The maximum TEF, 2.11, was achieved with a V-corrugated tube with an N of 4, DR of 0.06, and PR of 2.0 at Re = 5000.