Abstract
Heat transfer can be enhanced by employing various techniques and methodologies, such as increasing either the heat transfer surface or the heat transfer coefficient between the fluid and the surface, that allow high heat transfer rates in a small volume. Cooling is one of the most important technical challenges facing many diverse industries, including microelectronics, transportation, solid-state lighting, and manufacturing.
There is, therefore, an urgent need for new and innovative coolants with improved performance. The addition of micrometer- or millimeter-sized solid metal or metal oxide particles to the base fluids shows an increment in the thermal conductivity of resultant fluids. But the presence of milli- or microsized particles in a fluid poses a number of problems. They do not form a stable solution and tend to settle down. Apart from the application in the field of heat transfer, nanofluids (nanometer particles in a fluid) can also be synthesized for unique magnetic, electrical, chemical, and biological applications. They also cause erosion and clogging of the heat transfer channels.
The novel concept of “nanofluids” has been proposed as a route to surpassing the performance of heat transfer fluids currently available. A very small amount of nanoparticles, when dispersed uniformly and suspended stably in base fluids, can provide impressive improvements in the thermal properties of base fluids. Nanofluids, which are a colloidal mixture of nanoparticles (1–100 nm) and a base liquid (nanoparticle fluid suspensions), is the term first coined by Choi in 1995 [1] at the Argonne National Laboratory to describe the new class of nanotechnology-based heat transfer fluids that exhibit thermal properties superior to those of their base fluids or conventional particle fluid suspensions.
Several investigations have revealed that the thermal conductivity of the fluid containing nanoparticles could be increased by more than 20% for the case of very low nanoparticles concentrations. Nowadays a fast growth of research activity in this heat transfer area has arisen. In fact, the exponential increase in the number of research articles dedicated to this subject thus far shows a noticeable growth and the importance of heat transfer enhancement technology in general. Just to give some data in table is given the number of papers from 1993 to 2010 (up to April) found in SCOPUS under “Nanofluids” and the other two columns are the papers found under “Nanofluids AND Heat Transfer” and “Nanofluids AND Properties”. Moreover, in SCOPUS under “Nanofluids and Review” about 34 papers were given as that result. This indicates a the high interest in nanofluids activity research and the potential market for nanofluids for heat transfer applications is estimated by the CEA in 2007 to be over 2 billion dollars per year worldwide, with prospect of further growth in the next 5–10 years, as underlined in [2].
The aim of this special issue is to collect basic, application and review articles of the most recent developments and research efforts in this field, with the purpose to provide guidelines for future research directions. The order of the papers is given presenting a possible range of applications, a review on specific heat capacity, and an experimental study to evaluate the effects of particle species, surface charge, concentration, preparation technique, and base fluid on thermal transport capability of nanofluids. A survey on heat transfer in nanofluids is summarized in order to analyze the theories regarding heat transfer mechanisms in nanofluids and to discuss the effects of clustering on thermal conductivity. After some considerations to address whether the heat transfer in nanofluids still satisfies the classical energy equation are theoretically examined by the macroscale manifestation of the microscale physics in nanofluids, an experimental investigation on natural convection heat transfer characteristics in nanofluids in an enclosure and a numerical study on turbulent forced convection flow of nanofluids in a circular tube subjected are presented in the last two papers.
Number of papers on “nanofluids”, “nanofluids and heat transfer”, and “nanofluids and properties” by SCOPUS database.
