Heat transfer enhancement of nanofuids
Yimin Xuan *, Qiang Li
School of Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, People's Republic of China
Received 5 February 1999; accepted 1 September 1999
Abstract
This paper presents a procedure for preparing a nanofuid which is a suspension consisting of nanophase powders and a base
liquid. By means of the procedure, some sample nanofuids are prepared. Their TEM photographs are given to illustrate the stability
and evenness of suspension. The theoretical study of the thermal conductivity of nanofuids is introduced. The hot-wire apparatus is used to measure the thermal conductivity of nanofuids with suspended copper nanophase powders. Some factors such as the volume fraction, dimensions, shapes and properties of the nanoparticles are discussed. A theoretical model is proposed to describe heat transfer performance of the nanofuid fowing in a tube, with accounting for dispersion of solid particles.
Keywords: Nanofuid; Enhanced heat transfer; The hot-wire apparatus; Dispersion
1. Introduction
Low thermal conductivity of process fuid hinders high compactness and eectiveness of heat exchangers, although a variety of techniques is applied to enhance heat transfer. Improvement of the thermal properties of energy transmission fuids may become a trick of augmenting heat transfer. An innovative way of improving the thermal conductivities of fuids is to suspend small solid particles in the ¯uids. Various types of powders such as metallic, non-metallic and polymeric particles can be added into ¯uids to form slurries. The thermal conductivities of ¯uids with suspended particles are expected to be higher than that of common ¯uids. An industrial applicationest was carried out by Liu et al. (1988) and Ahuja (1975), in which the eect of particle volumetric loading, size, and fow rate on the slurry pressure drop and heat transfer behavior was investigated. In conventional cases, the suspended particles are of lm or even mm dimensions. Such large particles may cause some severe problems such as abrasion and clogging. Therefore, ¯uids with suspended large particles have little practical application in heat transfer enhancement.