Thermo-hydraulic performance of nanofluids in enhanced tubes - a review

Abstract

Technological developments are continuously growing to improve the efficiency of thermal systems on the demand of present era. To get rid of the scientists and engineers from traditional heat transfer intensification methods and to miniaturize thermal transport devices, novel and innovative techniques are obligatory. In this whole drive, the effective tube geometries and efficient working fluids perform vital role in the betterment of heat exchange devices. Geometrical argumentations/surface modifications impose on smooth tubes are called as enhanced tubes. These tubes contribute towards high rate of heat transfer by reducing the formation of boundary layer near the wall surfaces of the tube. Also, nanofluids with superior thermo-physical properties compared to conventional fluids also assist the rate of heat exchange in various heat transfer applications. This article begins with the introduction of enhanced tubes and nanofluids and followed by overview of nanofluid synthesis and different tube geometries. An attempt has been made to summarize last decade research contributions in the field of forced convection heat transfer and flow characteristics (HTFC) with employing the combined effect of enhanced tubes and nanofluids. Additional heat transfer enhancement techniques (swirl flow devices, magnetic field, agitation, rotation and pulsation) brace with present ones, are also discreetly deliberated. Proposed correlations by authors are also represented which shows the good agreement with experimental data. Important findings and outcomes from reviewed studies are compiled in discussion section. A number of suggestions and guidelines are highlighted to intensify the heat transfer rate as well as to mitigate the effects of pressure losses in fluid flow pipes.