A review on nanofluids coupled with extended surfaces for heat transfer enhancement

Recently, due to the increasing demands for effective and efficient devices, the thermal sections of modern machinery deserve considerable attention. Researchers in the field of thermal engineering have since devised strategies of combined passive methods for further heat transfer enhancement. From the available literature, the employment of nanofluids, coupled with extended surfaces is scarce, with limited studies optimizing both techniques. The current investigation summarizes the combined effects of nanofluids coupled with various types of extended surfaces, within numerous applications. Parameters involving the nanofluid type, volume concentration, fin geometry, and flow conditions were examined, whereby their respective effects were investigated on the thermal performances. It was deduced that the effects of surfactants, nanoparticle volume concentration, and Reynolds number significantly contributed to the heat transfer enhancement. The review presents a trend finding that nanoparticle volume concentration would positively contribute to heat transfer enhancement, up to an extent. Surpassing the optimal concentration would lead to lower Brownian motions associated with higher viscosity and density. In terms of extended surfaces, the state-of-the-art review denoted that each fin design possesses a unique attribute that alters the thermal and hydraulic performances. Nevertheless, researchers fabricating novel fin designs should highly prioritize the effects on pressure drop when employing fins. Combining both techniques, the nanofluids and extended surfaces achieved remarkable results. The outstanding results could potentially achieve the standards of active methods, for a fraction of the operational cost. Concluding, the information surrounding the present review may be of aid to researchers developing new approaches utilizing nanofluids and extended surfaces.