Abstract
In this study, the nanostructures and thermophysical properties (thermal conductivity, viscosity, and specific heat) of one new type of nanostructured heat transfer fluid, water/polyalphaolefin nanoemulsion fluid, are investigated. The water/polyalphaolefin nanoemulsion fluids are thermodynamically stable containing dispersed water nanodroplets formed by self-assembly. It has been found that the nanostructure inside nanoemulsion fluids may affect their thermophysical properties, especially the phase change heat transfer characteristics. The small-angle neutron scattering technique has been used to help identify the nanostructure inside the water/polyalphaolefin nanoemulsion fluids. By using the 3-region Guinier–Porod model, the fitting curve shows that there is a nonlinear variation of the nanodroplets’ size and shape with water’s concentration, which also coincides with the trend of its viscosity and specific heat. On the other hand, the thermal conductivity increases linearly with higher volume fraction of water which, however, appears to be insensitive to the nanostructure change. While the water nanodroplets inside can increase the thermal conductivity of the nanoemulsion fluid by 16%, its effective specific heat can be boosted up to 90% when the water nanodroplets undergo liquid–solid phase change.
Highlights
Advanced thermal management is a complex and challenging problem widely faced in industrial and military applications.[1,2,3,4,5,6,7,8,9,10,11,12] Conventional coolants, lubricants, and other heat transfer fluids used in today’s thermal management systems typically have relatively poor heat transfer properties
Based on the shape of the scattering curves, they can be classified into three ranges: the 1.8%–4.5% volume fraction ones with a smooth and gradually increasing scattering intensity for low-q range; the 5.3%–7.8% volume fraction ones with a sharper increase of q for the high-q range and a flatter intensity curve for low-q; and for even higher concentrations like 8.6% and 10.3% volume fractions ones tested here, the ‘‘hump’’ for high q is even more obvious and the intensity for low q increases more sharply which gives very obvious three sections of scattering curves
The thermal conductivity increase is rather moderate in these fluids, for example, a 16% increase for 8.6% volume fraction sample, which agrees well with the classical colloidal theory
Summary
Advanced thermal management is a complex and challenging problem widely faced in industrial and military applications.[1,2,3,4,5,6,7,8,9,10,11,12] Conventional coolants, lubricants, and other heat transfer fluids used in today’s thermal management systems typically have relatively poor heat transfer properties. Utilizing the phase change process to increase the heat transfer properties of conventional fluids is another promising direction.[13,14,15,16] Recently, the author has proposed a new ‘‘nanoemulsion heat transfer fluid’’ system in which one liquid of lower boiling point is dispersed into another immiscible liquid and formed self-assembled nanodroplets which help improving the fluid thermal properties especially. Advances in Mechanical Engineering its phase change characteristics.[7,12,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32] The nanoemulsion heat transfer fluids belong to the family of selfassembled colloid system and are thermodynamically stable
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