Gaganpreet Chadha; Sunita Srivastava
Abstract
A theoretical model for the specific heat of nanofluids containing oxide-based nanoparticles of different sizes and at different temperatures has been presented. The model proposed by Xuan and Roetzel has been modified by incorporating the effect of semi-solid interfacial layer, which is formed due to ...
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A theoretical model for the specific heat of nanofluids containing oxide-based nanoparticles of different sizes and at different temperatures has been presented. The model proposed by Xuan and Roetzel has been modified by incorporating the effect of semi-solid interfacial layer, which is formed due to adsorption of base fluid molecules on the surface of nanoparticles. The contribution of this layer has been taken into account by assuming that the heat capacity, as well as the density of interfacial layer, lies between the corresponding values for the nanoparticle and the fluid and as such these have been estimated by taking the arithmetic and the geometric means of the relevant quantities. It is observed that the specific heat capacity of the nanofluid decreases with increase in particle volume fraction and that the presence of interfacial layer enhances the value even though its thickness has been taken to be only 1-2 nm as estimated by Xue et al. using molecular dynamics simulation. The effects of interfacial layer thickness, nanoparticle size, volume fraction, and specific heat ratio of particle to fluid have been discussed. The obtained results are in good agreement with some recent available experimental data.
Venu H. Mankad; Sanjeev K. Gupta;Prafulla K. Jha
Abstract
The size dependent vibrational and thermodynamical properties of Zinc Oxide Nanowire (ZnO NWs) along with its bulk counterparts has been studied using the first principles calculations within density functional theory. The thermodynamical parameters such as specific heat at constant volume, entropy, ...
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The size dependent vibrational and thermodynamical properties of Zinc Oxide Nanowire (ZnO NWs) along with its bulk counterparts has been studied using the first principles calculations within density functional theory. The thermodynamical parameters such as specific heat at constant volume, entropy, internal energy and Helmholtz energy as function of temperature for the different size of nanowires are obtained and compared with the bulk ZnO in wurtzite phase. We address the effects of structural confinement on the phonon dispersion, vibrational density of states and qualitatively on the sound velocities and thermal conductance. The phonon dispersion curves for considered ZnO nanowires and its bulk counterpart indicates dynamical stability. The band gap increases from bulk to nanowire and an inverse size dependency in the case of nanowires arising due to quantum confinement. The analysis of bands character in context of growth characteristics and thermodynamical properties are also discussed. Our findings will give some reference to the insight understanding of the electronic, vibrational and thermodynamical properties of size orientation dependent ZnO nanowire.