Analysis of Heat Transfer and Flow Characteristics of a Helically Coiled Tube with Twisted Elliptical in a Low Reynolds Number Flow

Abstract

In this paper, the heat transfer and flow characteristics of a helically coiled tube with twisted elliptical in a low Reynolds number (Re = 500–3000) flow were investigated numerically. The working fluid flowed in a laminar regime. Numerical results were compared with empirical correlations in the existing literature, demonstrating the accuracy of the analysis in this study. Firstly, we investigated the effects of geometric parameters and Reynolds number on the heat transfer and flow characteristics. The results showed that lower twist pitch length and semi-major axis length could induce sufficient fluid mixing and a larger temperature gradient near the tube wall, enhancing the heat exchange and producing larger friction resistance. Overall, the heat transfer performances were improved by about 1.04–1.21 times and 1.02–1.23 times for different semi-major axis lengths and different twist pitch lengths, respectively, compared to the smooth helical coil. Secondly, by changing the working fluid, it was found that the Nu when oil was chosen as the working fluid was all 6–6.8 times higher than that of water. Moreover, the effect of using Al2O3 nanofluids with a concentration of 0.10 wt.%, 0.25 wt.% and 0.50 wt.% was discussed. It can be seen that the heat transfer capacity of nanofluids increased by approximately 2–18% compared to the reference model with water as the working fluid, and the nanofluid solution with higher concentration has better heat transfer performance. Finally, Nu and f correlations are given to predict the heat transfer and pressure drop in practical applications.

Fluid Flow in Helically Coiled Pipes

“…As was outlined by Wang et al [51], the overall temperature of the twisted pipe is higher than that of the smooth pipe for a comparable cross-sectional perimeter. These authors derived by means of multiple linear regression analysis correlations for the Nusselt number and the friction factor as functions of the Reynolds number, which obey the expressions…”

“…However, their centers change with different position of corrugation on the cross-sectional plane. In a more recent work, Wang et al [51] studied by means of numerical simulations the flow and heat transfer characteristics of a twisted helical pipe of elliptical cross-section for 500 ≤ Re ≤ 3000. The physical details of their twisted helical pipe are provided in Figure 20.…”

“…In comparison to experimental research, numerical papers on helically coiled flow appear to be much more numerous. Most of this work has been oriented to study the prediction of laminar flow and heat transfer [40][41][42][43][44], turbulent flow [17,45,46], entropy generation [47], pulsating flow [48] and flow characteristics [49][50][51]. Investigations on multiphase flow in helical pipes are by far much more scarce (see, for instance, Colombo et al [52] and references therein).…”