24-07-2012, 03:17 PM
Nanofluids for Improved Efficiency in Cooling Systems
Nanofluids-for-Improved-Efficiency-in-Cooling-Systems.pdf (Size: 319.11 KB / Downloads: 63)
Abstract
The present scenario of high thermal loading coupled with high flux levels demands
exploration of new heat transfer augmentation mechanisms. In this context, ‘Nanofluids’ may
emerge as alternative heat transfer fluids. The term ‘Nanofluids’ is used to indicate a special
class of heat transfer fluids that contain stabilized nanoparticles (≤50 nm) of metallic/non
metallic substances uniformly and stably suspended in an engineering fluid. This paper deals with
the property characterization, performance and potential applications of nanofluids .
Keywords Nano size, Properties, Potential benefits, Applications
INTRODUCTION
Heat transfer technology stands at the cross roads of miniaturization on one hand and
astronomical increase in heat flux on the other. The usual enhancement techniques for heat
transfer can hardly meet the challenge of ever increasing demand of heat removal in processes
involving electronic chips, laser applications or similar high energy devices. The factors which
limit the usual techniques are many folded. One major limitation is the poor thermal
characteristics of usual heat transfer fluids. Metals in solid form have orders-of-magnitude higher
thermal conductivities than those of fluids. This inherent inadequacy of these fluids makes the
heat removal mechanism less effective even with the best utilization of their flow properties. For
example, the thermal conductivity of copper at room temperature is about 700 times greater than
that of water and about 3000 times greater than that of engine oil,
THERMO PHYSICAL PROPERTIES OF NANOFLUIDS
There have been models to evaluate the thermal conductivities of fluids suspended with
nano/micro sized particles. With the Hamilton and Crosser model applied to copper
nanoparticles in water, the effective thermal conductivity of the copper/water system was
estimated[1]. The effects of particle volume fraction and shape on the thermal conductivity ratio
for a copper-water system
POTENTIAL BENEFITS OF NANOFLUIDS AS A COOLANT
There is now great industrial interest in nanofluids. Some of the specific potential
benefits of nanofluids are described below.
Improved Heat Transfer and Stability: Because heat transfer takes place at the surface of the
particle, it is desirable to use a particle with a large surface area. Nanoparticles provide
extremely high surface areas for heat transfer and therefore have great potential for use in heat
transfer. The much larger relative surface areas of nanophase powders, when compared with
those of conventional micrometer-sized powders, should markedly improve the heat transfer
capabilities and stability of the suspensions.