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

Three types of helical micmtube coil namely circle, oval and elliptical are introduced and evaluated both experimentally and numerically. Al2O3 water, ZnO-water at three volume fractions (phi) 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 micmtube augment the heat transfer ratio considerably and greatest enhancement ratio was realized by employing circle form with phi = 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 phi = 2% at Reynolds number of 1800. Besides, new empirical correlations were proposed and reported based on experimental data.

Automated summary

This study introduces and evaluates three types of helical microtube coils, finding that the curvature swirls of helical microtubes play an important role in increasing heat transfer. Experimental results show that using helical microtubes significantly enhances heat transfer ratio, with the greatest enhancement observed when employing the circular form with phi = 2%.