Comparison of heat transfer and pressure drop in horizontal and vertical helically coiled heat exchanger with CuO/water based nano fluids

In this paper, a comparison of heat transfer and pressure drop characteristics of CuO/water nanofluids in a helically coiled heat exchanger held in horizontal and vertical positions is presented. Experiments were conducted in the turbulent flow regimes using water and CuO/water nanofluids of 0.1% and 0.2% volume concentrations. The experimental results show that there is no much difference between horizontal and vertical arrangements in the enhancement of convective heat transfer coefficient and friction factors of nanofluids compared to water. Irrespective of the positions of the helically coiled heat exchanger, the enhancement in internal Nusselt numbers is high for higher concentration nanofluids at turbulent flow. Also the experimental friction factors obtained are high for higher concentration nanofluids at low flow rates. Based on the experimental data, correlations are proposed for Nusselt number and friction factor. (C) 2012 Elsevier Inc. All rights reserved.