I have observed in literature that four ways of modeling nanofluids are there viz. 1). single phase field model, 2). mixture model ,3). eulerian-lagrangian model (Discrete Particle Model: DPM) , and 4) discrete element method (DEM).
Of these the most accurate is the DPM and fastest is the single phase based model. Now How to model CNT based nanofluids, where in nanoparticles have cylindrical shape taking into account its shape as well as it has been reported to have an effect on its thermal properties?
Hi Bharat, when using a 2-phase modelling approach, some CFDs (like Ansys CFX) allow you to specify the particle shape-factor, length and diameter. However, I'm not so sure that the CFDs account for heat transfer of nano-sized particles. I performed a CFD study of a CNT-water nanofluid using the single-phase approach (based on experimental measurements of thermal conductivity, viscosity, specific heat and density) with CFX 13. When trying a 2-phase approach, results were inaccurate because the particles were too small for the heat transfer to be significant.
Single phase model has gross approximations which cannnot account for all the effects of nanofluids. THere are in my knowledge 3-5 studies regarding camparison of single phase model, mixture model, and eulerian-lagrangian model. They have successfully validated experimental data with their eulerian-lagrangian model which they found to be most accurate.
Kindly refer...
10.1016/j.applthermaleng.2009.06.019
I'm not sure about Fluent, I used CFX for my work. In CFX, for a 2-phase study, you also have to specify either the average mass of a nanoparticle and the total quantity of nanoparticles for a given volume fraction, both hard to measure directly. Aditionally you have to specify the thermal conductivity of the nanoparticles used. For carbon nanotubes, the thermal conductivity in the literature varies from 1500 to 3000 W/(mK), a very large interval, especially if you take into account the effect of nano-layer formation around the nanoparticles and its contribution to the overall heat transfer of nanofluids. Additionally for a 2-phase model, you cannot use the thermal conductivity of the base fluid alone. When manufacturing nanofluids, it is typical to use dispersants to avoid particle agglomeration/sedimentation, these have their own thermal conductivity. The paper you refer to doesn't mention such considerations.
Obviously it would be better and more accurate to have a 2-phase model, but you have to have more info of parameters like the ones mentioned, which are difficult (if not impossible) to measure directly and which may not be accounted for by present versions of comeercial CFDs.
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