Liquid Sublayer Dryout Research Articles

A Mechanistic Model for the Prediction of Water-Subcooled-Flow-Boiling Critical Heat Flux at High Liquid Velocity and Subcooling

A new model is presented for the prediction of the critical heat flux (CHF) of subcooled flow boiling based on a liquid-sublayer dryout mechanism, i.e., the dryout of a thin, liquid layer beneath a...

The prediction of the critical heat flux in water-subcooled flow boiling

The prediction of water-subcooled flow boiling critical heat flux (CHF) in peripherally non-uniform heated tubes with or without swirl flow promoters is accomplished using a model based on the liquid sublayer dryout mechanism recently proposed by the authors. Peripheral nonuniform heating and/or twisted-tape inserts are properly and simply accounted for in the model, originally developed for uniform heating and straight flow. Simultaneous occurrence of the two events is also well predicted by the model. Although initially formulated for operating conditions typical of the thermal hydraulic design of fusion reactor high heat flux components, the model is proved to give a satisfactory answer for the prediction of the CHF under more general conditions, provided local thermodynamic conditions of the bulk flow at the CHF are sufficiently far from the saturated state.

Rationalization of existing mechanistic models for the prediction of water subcooled flow boiling critical heat flux

This paper presents an analysis of the critical heat flux (CHF) of subcooled flow boiling based on the liquid sublayer dryout mechanism, i.e. the dryout of a thin liquid layer beneath an intermittent vapour blanket due to the coalescence of small bubbles. Starting from the same basic mechanism adopted in earlier models, a new model is derived for the analysis of the CHF in subcooled flow boiling under conditions of very high mass flux and liquid subcooling, typical of fusion reactors thermal hydraulic design. The model is characterized by the absence of empirical constants always present in earlier models. Predicted CHF values are compared with data of 1888 data points for water, showing a good agreement both in precision and in accuracy.

Theoretical investigation of vapor blanket velocity based on mass, energy, and momentum balance to predict CHF at low quality flow

In this paper a theoretical prediction method of the critical heat flux in flow boiling at low quality is presented based on the liquid sublayer dryout mechanism. The vapor blanket velocity which is the key parameter to predict the DNB type CHF is evaluated by solving mass, energy, and momentum balances simultaneously. The accuracy of the present model is evaluated by comparing model predictions with the experimental data for water. The predictions agree well with the extensive CHF data of water in uniformly heated vertical round tubes.

Prediction of critical heat flux of subcooled flow boiling in round tubes

Based on the liquid sublayer dryout mechanism, a physical model of critical heat flux (CHF) of subcooled flow boiling is presented in a previous paper with a rather tentative correlation of a coefficient k to link the velocity of a vapor blanket with that of two-phase flow. In the present paper, a new correlation of the velocity coefficient k is derived based on CHF data of various kinds of fluids, presenting a generalized method to predict CHF of subcooled flow boiling within the range of subcooling T sat− T L⩾0 K, void fraction α < 0.7, and vapor/liquid density ratio ϱ v/ g9 L ⪢ 0.01. Comparisons of predicted and measured CHF show fairly good accuracy up to high degrees of subcooling.

A physical approach to critical heat flux of subcooled flow boiling in round tubes

This paper presents an analysis of the critical heat flux (CHF) of subcooled flow boiling based on the liquid sublayer dryout mechanism, assuming that it is a similar phenomenon to CHF in pool boiling except for apparent differences between forced and natural convection. Employing the same formula of sublayer thickness as that derived for CHF in pool boiling, a physcial model of CHF is derived with an empirical coefficient relating to the velocity of a vapor blanket sliding on a thin liquid sublayer. Predicted CHF values are compared with experimental data for water, R-12, R-11, nitrogen, helium, and R-113, respectively, suggesting propriety of the present model.

Generalized prediction of critical heat flux of subccoled flow boiling in round tubes.

Based on the liquid sublayer dryout mechanism, a physical model of critical heat flux (CHF) of subcooled flow boiling was presented in a previous paper with a rather tentative correlation of a coefficient to connect the velocity of a vapor blanket with that of two-phase flow. In the present paper, a new correlation of the velocity coefficient is derived based on CHF data of various kinds of fluids, presenting a generalized method of predicting the CHF of subcooled flow boiling within the range of void fraction less than 0.7, and at a vapor/liquid density ratio greater than 0.01. Comparisons of predicted and measured CHF show fairly good accuracy up to very high degrees of subcooling.