Nanotech 2011

Numerical Simulation of the Solidification Process of Nanofluids

Y.M.F. El Hasadi, J.M. Khodadadi
Auburn University, US

Keywords: nanoparticles, nanofluid, solidification, colloidal


Nanofluids are colloidal suspensions which they consist particles in the size range of 100-1 nm. In the recent years nanofluids kept the attention of the scientific community due to their improved thermal physical properties compared to those of the pure liquids. Recently nanofluids were proposed to replace the current phase change materials for thermal energy storage applications as indicated. The solidification process is an essential part of the life cycle of a phase change material, understanding the evolution of the solidification for a nanofluid will be a key element, for evaluating their performance for the propose of energy storage applications. In this paper a numerical simulation of the water with copper nanoparticles will be presented and, for the first time the evolution of the mass transfer of the nanoparticles will be reported. The nanofluid will be tread as a binary mixture which is based on the experimental findings. A rectangular cavity was used as geometry for this study with thermally isolated upper and lower sides. The domain was divided in 10,000 computational cells. The temperature of the left side was maintained at T = 268 K, while the right side was at T = 273 K, the initial temperature was 274 K. The mass fractions that have been used were 1%, 5%, and 10%. The numerical method that has been implemented is based on the one fluid mixture model, and the phase change process was captured by using the enthalpy method. The CFD code Fluent was used to implement the numerical scheme, the numerical results were compared without taking the account the mass transfer effect of the nanoparticles and results were satisfactory with the results available in literature. The development of the liquid interface for the case of water nanolfulid with 10% nanoparticles, as it was expected the interface is planer in the early stages of the solidification, and then develops to a dendritic shape interface due to the supercooling effect, which is consistent with the experimental observations. An increase of the concentration of the particles along the flat interface due to the rejection of the particles from the solid phase as shown in Fig 2 a, however as the solidification proceeds, the nanoparticles tends to move away from the interface due to thermal-solutal convection effects and, also segregates in the space between the dendrites, these two phenomena have been observed experimentally for the both cases of binary mixture and colloidal solidification.

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