Experimental and numerical investigations of heat transfer enhancement in shell and helically microtube heat exchanger using nanofluids

Abstract

Three types of helical microtube coil namely circle, oval and elliptical are introduced and evaluated both experimentally and numerically. Al2O3-water, ZnO-water at three volume fractions (?) of 1.0%, 1.5% and 2% are considered as working fluid as well as the base fluid (water). Different values of pitch are tested with constant pitch/diameter ratio of 1 for all geometries. The numerical simulations are presented the flow structures of helical microtubes in terms of velocity, isotherms, and vorticity contours. Compared to straight coil, the findings show that helical microtube curvature swirls are an important phenomenon to increase heat transfer. In addition, it shows that the heat transfer and friction loss increase as volume fractions of nanofluids and Reynolds number increase. The experiments have also uncovered that the use of helical microtube augment the heat transfer ratio considerably and greatest enhancement ratio was realized by employing circle form with ?= 2% of alumina nanofluid. Over ranges of considered flow, alumina nanofluid was better than ZnO-water nanofluid and the best thermal performance of 3.1 was recorded with using it at ?= 2% at Reynolds number of 1800. Besides, new empirical correlations were proposed and reported based on experimental data.