Numerical Investigation of Mixed Convective Heat Transfer of a Twisted Square Tube

Abstract

Study of the heat transfer performance of twisted tubes have been limited to forced convective conditions (inertia-dominated flow) without studying the effect of different isothermal wall temperature (buoyancy force). Therefore, this work investigated the flow and heat transfer behavior of a twisted square tube of a varying pitch length at different mixed convective regimes. The model continuity, momentum, and energy equations were solved using the finite volume technique. The numerical model setup was validated using experimental results and a satisfactory result was achieved. The result shows that the twisted square tube performs better than the smooth tube subjected to the same conditions. The heat transfer rate and drag coefficient increase with decreasing twist pitch length. In addition, the result shows that increment of buoyancy force, while inertia force is kept constant leads to a high reduction of drag as compared to increasing inertia force, while buoyancy force is kept constant. Overall, a 15% increase (at Ri=1) is obtained in the drag coefficient and a 13% increase (at Ri=0.5) is obtained in the heat transfer rate in the 100 mm twist pitch length as compared to the 600 mm twist pitch length.