Single phase heat transfer and pressure drop analysis of a dimpled enhanced tube

Thermal-hydraulic performance of an enhanced tube was evaluated using experimental and numerical simulation techniques in a pipe-in-pipe heat exchanger. Steady state single phase (liquid-to-liquid) experiments were performed to determine Nusselt number and friction factor. Experiments with water as working fluid were carried out in the Reynolds number range of (500 < Re < 8000), while for water/glycol solution based experiments the Reynolds number range was kept at (150 < Re < 2000). A non-dimensional performance evaluation criterion (PEC) was used to assess the thermal-hydraulic performance of heat transfer enhancement achieved with the enhanced tube. Based on the experimental data, Nusselt number and friction factor estimation correlations were proposed for the enhanced tube. Simulations were carried out to obtain heat transfer and pressure drop characteristics of smooth and enhanced tubes, using commercial CFD software, Fluent. Realizable k-ϵ model was employed to assess the influence of dimples on turbulent flow and velocity field. Simulation results showed that dimples disturb and mix boundary layers and generate secondary flows that improve turbulence level. Comparison between experimental and numerical simulation results showed good agreement as the data fell within ±10% error band.