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Physical and Materials Chemistry division
CSIR-National Chemical Laboratory, Pune, India
E-mail:pa.joy@ncl.res.in, Tel.: 02025902579
Decanoic acid and oleic acid coated magnetite nanoparticles are synthesized by simple coprecipitation method. The effect of the surfactant on thermal conductivity of the magnetic nanofluid was studied by dispersing the nanoparticles in toluene. The results show that the enhancement in thermal conductivity is higher for decanoic acid coated fluid. However, in the presence of a magnetic field, oleic acid coated fluid shows higher enhancement than the decanoic acid coated fluid.
Keywords: Magnetic fluids, thermal conductivity, surfactant effect, magnetite, Brownian motion
Nanofluids are the potential and innovative coolants for diverse industrial applications including microelectronics, transportation, optical devices and manufacturing [1]. The present day research is focusing on the enhancement of the thermal conductivity by changing the various factors such as particle size, particle volume concentration, particulate material, temperature, viscosity, surfactants, carrier fluids etc.
Out of these, surfactant plays an important role in the nanofluid stability. Oleic acid is a widely studied surfactant for the magnetite nanoparticle. The long aliphatic chain present on the nanoparticles surface provides stability to the particles in fluid and particles are well separated from each other. Increase in thermal conductivity with particle volume percentage has been studied for many materials. Thermal conductivity of the suspension having small clusters shows larger enhancement than the individual particles in fluid [2].
Due to the high stability of the nanoparticles, the inter particle interaction can be suppressed.
The objective this work is to study the effect of surfactant length on the enhancement in thermal conductivity of nanofluids. In order to study this effect, we have prepared two sample magnetite nanofluids of nanoparticles with different surfactants on its surface such as oleic acid and decanoic acid.
Magnetite nanofluids were prepared by coprecipitation of iron(II) and iron(III) chloride salts with ammonium hydroxide base at 80 °C in the presence of the surfactants. The reaction product was washed with acetone-hexane mixture and dried at room temperature. The dried powders were redispersed in toluene and the fluid samples were used for thermal conductivity studies.
The surfactant coated nanoparticles were characterized by XRD, IR, TGA, HRTEM and SQUID-
VSM. Thermal conductivity studies were done using a home-made cell based on the Transient Hot wire method (THW).
The thermal conductivity measurement of the decanoic acid coated sample shows slightly higher enhancement than the oleic acid coated sample at 2 volume percentage. This is attributed to the increase in the interparticle interaction in decanoic acid coated sample which makes easy transfer of heat between the particles.
Fig. 1: Thermal conductivity enhancement of decanoic acid and oleic acid coated magnetic nanofluids as a function of magnetic field
In the presence of magnetic field oleic acid coated sample shows relatively larger enhancement at high fields due to the slow response to the magnetic field.
R. Lenin is thankful to UGC for financial support.
[1] J. A. Eastman, S. U. S Choi, S. Li, W. Yu, and L. J.
Thompson, “Anomalously increased effective thermal conductivities of ethylene glycol based nanofluids containing copper nanoparticles”, Applied Physics
Letters , 78, 6, (2001), 718-720.
[2] T. K. Hong, H. S. Yang and S. U. S. Choi, “Study of the enhanced thermal conductivity of Fe nanofluids”,
Journal of applied Physics , 97, 064311, (2005), 1-4.