Abstract
The present volume is the third special issue on heat transfer in nanofluids and we hope that it will be a series that periodically enables researchers to highlight their new findings related to nanofluids. The growth of research activity in this heat transfer area is still significant, as shown in Figure 1. This figure demonstrates the large interest in heat transfer enhancement technology, in general, and the actual interest in nanofluids, in particular. In this figure some recent data on the number of papers from 1993 to 2013 found in SCOPUS under “Nanofluids,” “Nanofluids AND Heat Transfer,” and “Nanofluids AND Properties” are reported. In SCOPUS under “Nanofluids and Review” about 134 papers were found. This data confirms the intense interest and activity in research and engineering applications for nanofluids. The aim of this special issue is to present some basic, applied, and review articles on the recent developments and research efforts in this field, with the purpose of providing guidelines for future research in this area.
The number of papers published related to nanofluids, heat transfer in nanofluids, and nanofluids properties.
In the present issue, many papers report studies on natural convection. A numerical investigation on natural convection in a heated cavity to evaluate the effect of nanofluids on heat transfer from discrete heat sources is presented by R. Ben-Mansour and M. A. Habib. The results show that the presence of nanoparticles affects the structure of the fluid flow and causes an increase in the heat transfer rate. M. Alipanah et al. report a numerical study on the effect of nanoparticles on natural convection in enclosures. Results are obtained for three different nanofluids (Cu, TiO2, and Al2O3 in pure water as base fluid). The results illustrate that suspended nanoparticles substantially increase the heat transfer rate at any given Rayleigh number and aspect ratio. The heat and flow characteristics of temperature-sensitive ferrofluid in a square cavity with and without the magnetic intensity are studied numerically by M.-Y. Lee and J.-H. Seo. It is found that natural convection and heat transfer characteristics of the ferrofluids within the cavity depend on both magnetic intensity and magnetic volume fractions of magnetite. Moreover, the mean Nusselt numbers and mean velocity of the ferrofluid in a square cavity are shown to increase with the rise of the magnetic intensities. C. V. Popa et al. propose a theoretical model for laminar external natural convection on a vertical wall. In their study, the vertical wall is considered to be at a uniform wall temperature or at a uniform heat flux and two different nanofluids are considered (Cu/water and CuO/water). The results show that natural convection heat transfer increases with the volume fraction for a fixed Grashof number regardless of the nanofluid; even though the heat transfer enhancement is more pronounced for Cu/water as compared to CuO/water nanofluid. An experimental investigation to evaluate thermal conductivity of nanofluids is presented by M. Mojahed et al. together with a measurement protocol. The tested nanofluid is composed of single walled carbon nanotubes dispersed in water. The effect of liquid temperature on thermal conductivity is also investigated. Obtained results confirm the potential of nanofluids in enhancing thermal conductivity and show that the thermal conductivity temperature dependence is nonlinear. M. H. M. Yasin et al. present a numerical study on steady mixed convection boundary layer flow over a vertical surface embedded in a thermally stratified porous medium saturated by a nanofluid. Results are reported for three nanoparticles (Cu, Al2O3, and TiO2) in a water-based fluid. The skin friction coefficient and the velocity and temperature profiles are presented and discussed. As expected, the addition of nanoparticles shows an improvement in the heat transfer rate from the surface and the type of nanofluid is found to have a definitive effect on the heat transfer enhancement. An analysis based on the second law of thermodynamics applied to a water-Al2O3 nanofluid is given by V. Bianco et al. for a circular section of the tube subject to a constant wall temperature. The results show that there is a substantial variation in the entropy generation. It is shown that, for a given Reynolds number, there is an increase in the entropy generation whereas for an assigned mass flow rate or velocity entropy generation decreases.