Abstract
This paper presents corrections for existing hydrodynamic instability-based critical heat flux (CHF) models in pool boiling by taking into account the effect of the viscosity, geometry and size of the liquid–vapor interface. Based on the existing literature, the Kelvin–Helmholtz (KH) theory, used by the most commonly adopted CHF models, can lead to noticeable errors when predicting the instability conditions. The errors are mainly due to the inaccuracy of the inviscid flow assumptions and the oversimplification of the interface geometry. In addition, the literature suggests the most unstable condition predicted by the viscous correction for viscous potential flow (VCVPF) theory for the cylindrical interfaces best match the observed air column breakup conditions in water. In this paper, the most unstable instability conditions predicted by the VCVPF theory are used to correct the existing CHF models. The comparison between the existing and corrected CHF models suggests that the corrected models always predict a higher CHF value. In addition, the corrected Zuber model predicts similar CHF value to the Lienhard and Dhir model. The comparison with experimental data suggests that the correction to the Zuber model can increase its prediction accuracy in most cases, but not necessary for the Lienhard and Dhir model. When compared to experimental CHF data for boiling cryogens at different pressures, the corrected CHF models are consistently more accurate than the original CHF models.
Highlights
Boiling has many important practical applications due to its effectiveness in dissipating excessive thermal load by taking advantages of the liquid-vapour phase change processes and the associated large latent heat
The calculated Critical Heat Flux (CHF) values from the existing models and the corrected models will be compared to the experimental data collected from different pool boiling conditions
It shows the viscosity contributes to stabilize the interface by reducing the instability growth rate. These results indicate that, when compared to the existing CHF models which based on the PIPF critical condition (i.e. Eq(2)), the viscosity and size-corrected CHF models based on the critical instability condition will predict a lower CHF value since the CHF value is proportional to the velocity, while the corrected CHF based on the most unstable condition will predict a higher CHF value
Summary
Boiling has many important practical applications due to its effectiveness in dissipating excessive thermal load by taking advantages of the liquid-vapour phase change processes and the associated large latent heat. [1,2,3] The negligence of the effects of viscosity, the inaccurate geometry, and the lack of size parameter in the PIPF analysis could introduce noticeable error in predicting the instability condition. All the existing CHF models based on the PIPF-KH theory need to be corrected to capture the physics more accurately. The comparison between the results of existing CHF models, the corrected models and the experimental data will be presented in Section 4 to show the difference
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