Experimental study of fluid flow and heat transfer of Al2O3-water nanofluid in helically coiled micro-finned tubes

Inactive methods of enhancing heat transfer in the shell and tube heat exchangers, such as using micro-fins and helically coiled tubes and employing nanofluids as the working fluid, are investigated experimentally. Experiments are carried out to measure the pressure drop and the heat transfer coefficient of the Al2O3-water nanofluid flowing in the shell and helically coiled micro-finned as well as smooth tube heat exchangers. The performed experiments are for the Dean number ranging from 500 to 4000, the fin helix angle between 18 and 25º, and the nanofluid volume fractions of 0, 0.5 1%. The overall heat transfer coefficients of the heat exchangers are calculated using the Wilson plot method. Empirical correlations are proposed for the heat transfer coefficient of nanofluid through the tube-side in terms of the Dean number, the fin helix angle, the fin height and the volume fraction of nanofluid. Based on the experimental results, the microfining of the coiled tube and increasing the microfin helix angle and using nanofluid enhance the heat transfer and increase the pressure drop.