Thermal conductivity of suspension containing SiC particles

Abstract

Among various heat transfer enhancement techniques, an innovative way of improving the thermal conductivities of working media is to suspend ultrafine metallic or nonmetallic solid powders in traditional fluids since the thermal conductivities of most solid materials are higher than those of liquids. Theoretical and experimental studies have reported that suspensions containing solid particles have significantly larger thermal conductivities than the base fluids without solid particles [1, 2]. Unfortunately, suspended particles of micrometer, or even nanometer, dimensions may cause some severe problems such as abrasion and clogging in small passages. Furthermore, for all the large particle suspensions, stabilities are very poor since the coarse grained solid particles settle out eventually. Extensive research conducted on nanosized powder preparation and processing technology in recent years may offer a solution to the problem. Nanoparticle suspensions are expected to exhibit excellent properties. The large surface area and enhanced heat capacity of nanocrystalline materials [3–5] could improve the heat transfer capacities of nanoparticle suspensions. Also, Brownian movement of nanoparticles in a suspension increases stability [6]. Furthermore, nanoparticles can act as a lubricating medium because of their small sizes [7]. Adding a small amount of metal or metal oxide nanosized particles to a fluid has increased the thermal conductivity of the suspension over that of the base fluid [8–10]. The enhancement is highly dependent on the surface area of the particles and the thermal conductivity of base fluid. A nanosized metal particle suspension used as a new coolant in a microchannel heat exchanger offered significant benefits [11]. In this study, three types of α-SiC powder were dispersed in water and ethylene glycol (EG), respectively. The properties of SiC powders are summarized in Table I. SiC particles were deagglomerated by intensive ultrasonication after being mixed with base fluid and then the suspensions were homogenized by magnetic force agitation. The pH values of all the aqueous suspensions were adjusted to 10.0 such that the suspensions were stable. The thermal conductivities of the suspensions were measured by the hot-wire method [12] at a temperature of 4 ◦C. The thermal conductivities (λ) of the suspensions with SiC powers dispersed in water and EG as a function of solid particle volume fraction are shown in Fig. 1a and b, respectively. Fig. 2a and b show the ratio of the thermal conductivity enhancement (δλ = λ − λ0)