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A mathematic model considering the effect of Brownian motion for subcooled nucleate pool boiling of dilute nanofluids
Author: Li Ke | Print | Close | Text Size: A A A | 2016-10-28

A new mathematic model was presented to investigate the nucleate pool boiling of nanofluids. The model considered the heat exchange due to Brownian motion of nanoparticles. A new closure correlation is also included in the model to count the active site density and the bubble departure diameter, which were calculated based on the experimental data of a nucleate pool boiling. The new model combines with two-fluid boiling model was used to simulate the nucleate pool boiling process. The simulation focused on the heat transfer due to Brownian motion of nanoparticle. The purpose is to improve surface heat exchange which was induced by the random motion of nanoparticles during the boiling process. The results give a reasonable agreement with the experimental data of nanofluids nucleation boiling with lower heat flux (lower than 100 kW/m2) and Nusselt number of 200. The simulation result indicates that the predicted accuracy for a nucleate boiling process of nanofluids can be improved by taking into account both the Brownian motion of nanoparticles and the nucleate site density due to the surface morphology modification.

A classic two-fluid model incorporated with a new heat flux partitioning model and closure correlations for the active site density was presented for dilute nanofluids. The model is considered the heat transfer due to Brownian motion for nucleate boiling of pure liquids. Emphasis was put on the effects of the new heat flux partitioning model and its' validation. The model was validated using the latest experimental data available in the literature. The simulation results are in good agreement with experimental data and the model has a good accuracy for nucleate pool boiling of dilute nanofluids under lower heat fluxes. In addition, the model for alternative systems involving different nanofluids can be implemented. The main conclusions are as follows.

1. Nucleate heat transfer in low excess temperature has been simulated and compared with similar empirical results, which has a good agreement with experimental results. The Brownian motion of nanoparticles during boiling process plays an important

role in affecting the boiling heat transfer performance of nanofluids. The model can predict the rates of heat transfer during the pool boiling phenomenon of heat transfer due to Brownian motion with good accuracy.

2. Convection heat transfer can be neglected with the enhancement of total heat flux because it is more important in high wall heat fluxes.

3. The partitioning model combined with two-fluid two-phase model gives an accurate prediction for a subcooled nucleate pool boiling of nanofluids.

4. The surface wettability could not be fully responsible for the heat transfer performance of nanofluids and other factors such as morphology modification still need to be taken into account. Obviously, more studies on the correlation model of bubble departure diameter in different nanofluids flow regime are needed for further improvement.

The results have been published on INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER  Volume: 84  Pages: 46-53.

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