Numerical simulation of turbulent flow forced convection in a twisted elliptical tube

The numerical simulations by turbulent water forced convection in a three-dimensional twisted elliptical tube with constant wall temperature are investigated in this study. Flow resistance and heat transfer characteristics of water in the twisted elliptical tube are studied with the parameters, including Reynolds number and the twist pitch. Effects of the above-mentioned parameters on the performance of the twisted elliptical tubes are analyzed and the overall thermal-hydraulic performance is evaluated. The thermal resistance of the heat exchanger is defined based on the entransy dissipation theory. The results show that in the twisted elliptical tubes, rotational motions are produced in the flowing fluid that improves the synergy between velocity vectors and the gradient of temperature and enhances the heat transfer performance compared with an oval tube. The twist elliptical tubes bring on the pressure drop because of the twisted wall. The results are then compared with the results of the oval tube, the pressure drop of the twisted elliptical tube with d = 96 mm increases 58%-60%. The averaged Nusselt number with d = 96 mm increases 16%-19% compared with the oval tube. In addition, the average Nusselt number and the pressure drop both increase with increasing Reynolds number, while both decrease with the increasing of the twist pitch. The twisted elliptical tube can reduce the entransy dissipation based thermal resistance that provides the great benefit in heat transfer. The twist pitch has an influence on the overall thermal-hydraulic performances. The results show that the twisted elliptical tube with d = 128 mm has the best overall thermal-hydraulic performance.