Development of Heat Transfer Fluids for Energy Applications
D. Singh, S. Cingarapu, E. Timofeeva, W. Yu, and J. L. Routbort
Argonne National Laboratory, Argonne, Illinois, USA
Keywords: heat transfer, fluids, nanoparticles, silicon carbide, thermal conductivity
Introduction
Nanofluids or liquids in which nanoscale particles are uniformly dispersed, have
the potential for enhanced thermal performance. The interest in nanofluids as potential
heat transfer fluids has been because of promising results on the enhanced thermal
conductivity for a nanofluid containing copper in pump oil1. Majority of the studies
have been conducted for the water base fluid, one of the nature’s best heat transfer
fluids due to a favorable combination of high thermal conductivity and low viscosity.
Addition of nanoparticles to water system increases the viscosity of the fluid that
translates to increased pumping power. It was shown in several studies2 that the base
fluids with the higher viscosity and lower thermal conductivity benefits most from the
addition of nanoparticles.
In this paper, we report the properties of SiC nanofluids prepared in a widely used
heat transfer fluid for cooling in transportation and power electronics: ethylene glycol
(EG) and water (H2O) mixture with a 50/50 volume ratio. Results of thermal
conductivity have been rationalized based on the existing theories of heat transfer in
fluids. Overall efficiency of nanofluids and its implications for engineering cooling
applications will be discussed.
Results and Discussion
Thermal conductivity and mechanical effects of nanofluids in water and ethylene
glycol/water mixtures were investigated. Particles of SiC with varying sizes (16-90 nm)
have been investigated. Mean sizes of nanoarticles were determined from small-angle
x-ray scattering (SAXS) and dynamic light scattering techniques. Effects of viscosity of
the nanofluids with temperature and particle loadings were established. Thermal
conductivity of the fluid was measured as a function of the particle sizes and base fluid
at a nominal nanoparticle loading of 4 vol.% (Fig. 1). Enhancements in thermal
conductivities for the nanofluids with varying nanoparticle loadings were maintained at
elevated temperatures.
Heat transfer measurements as a function of fluid velocity, as shown in Figure 2,
indicated a dependence on the particle size. Larger (90 nm) particle size of SiC
demonstrated ~15% enhancement over the base fluid at the sample fluid velocity. At
smaller particles sizes, the enhancement was minimal. Thermal conductivity and heat
transfer enhancements as a function of particles sizes is rationalized based on the
interfacial resistance between the particle and the fluid.
Criteria to evaluate the efficiencies of the nanofluids in both the laminar and
turbulent flow conditions were applied to establish the performance of the nanofluid for
an application.
Figure 1. Thermal conductivity enhancements for water and water/ethylene glycol
mixtures as a function of SiC nanoparticle size at a constant loading of 4 vol.%
30000
50/50 EG/H O
2
2
Heat transfer coefficient (W/m K)
16-nm SiC in 50/50 EG/H O
2
25000
28-nm SiC in 50/50 EG/H O
2
66-nm SiC in 50/50 EG/H O
2
90-nm SiC in 50/50 EG/H O
2
20000
15000
10000
(a) Particle size effect
5000
2.5
3.0
3.5
4.0
4.5
Velocity (m/s)
5.0
5.5
Figure 2. Heat transfer coefficient of SiC/EG-water nanofluids with fluid velocity at
different nanoparticle sizes
Conclusions
For the system investigated, use of larger particles provides better heat transfer
properties in both laminar and turbulent flow regimes. The efficiency of nanofluids
improves with increasing temperature due to viscosity decreases. The suspensions in
EG/H2O show higher efficiencies as heat transfer fluids than the similar H2O-based
nanofluids due to the demonstrated base fluid effect. The suspensions with the higher
concentration of nanoparticles (within the linear property increase region) show higher
heat transfer efficiency than the less concentrated ones.
References
[1] J. A. Eastman, U. S. Choi, S. Li, L. J. Thompson and S. Lee, 1996 Fall meeting of the Materials
Research Society (MRS), Boston, MA (United States), 2-6 Dec 1996 ; PBD: Nov (1996).
[2] H. Q. Xie, J. C. Wang, T. G. Xi, Y. Liu and F. Ai, Journal of Materials Science Letters 21 (19), 14691471 (2002).