Research On Subcooled Flow Boiling Under High Heat Flux And Its Application

Subcooled flow boiling is characterized by the presence of thermodynamic nonequilibrium between the liquid and vapor phases.In subcooled boiling,the temperature of the liquid is below the saturation temperature and bubbles formed at the surface may condense in the liquid.The subcooled flow boiling heat transfer characteristics of water have been widely applied in many fields such as national defense,aerospace and space technology.For most of the narrow channel heat exchanger,the cooling medium in working condition is in the state of subcooling.The subcooled boiling heat transfer caused by the high flow flux plays a very important role in the the whole heat exchanger equipment.A better understanding of subcooled flow boiling would allow for development of better methods for predicting the flow characteristics in subcooled boiling heat transfer applications.In this paper,a series of investigations on the subcooled flow boiling heat transfer are conducted.The main work and achievements are as follow:(1)The characteristic points of water subcooled flow boiling in the tube are discussed,including onset of nucleate boiling,onset of significant void and critical heat flux.The experimental databases of the characteristic points of subcooled flow boiling are established.The calculation models and empirical correlations of the onset of nucleate boiling,onset of significant void and critical heat flux are reviewed.And the influence of flow parameters and dimensionless parameters on the characteristic points is analyzed.Analysis and comparisons using database experimental data show that the Sato–Matsumura model for onset of nucleate boiling performs best and the Dix correlation for onset of significant void has the most accurate prediction and the Hall–Mudawar model for critical heat flux has the highest accuracy.In addition,the effects of mass flow rate,pressure,subcooling,sectional scale and dimensionless parameters on the characteristic points are analyzed.(2)In this paper,26 subcooled flow boiling heat transfer models are reviewed in detail,and the experimental database of subcooled flow boiling heat transfer in the tube is established.By using the experimental points in the database,the error between the predicted values and the experimental values of 26 subcooled flow boiling models is analyzed.The Baburajan model performs best with the mean absolute deviation of 21.8%.It is found that the subcooled flow boiling heat transfer coefficient increases with the flow velocity or mass flow rate,pressure and excess temperature,and under different experimental conditions,the models accuracy is also different.This paper carries out the study on the mechanism of subcooled boiling flow,according to the experimental data in the database,through the analysis of a number of dimensionless numbers,and proposes a new subcooled boiling flow heat transfer coefficient based on least–square method.It has a meam absolute deviation of 11.5% and a meam relative deviation of 0.97%.(3)The subcooled flow boiling heat transfer of water in a tube is numercal simulated.A reasonable physical model is established,and the calculation method of RPI model in the FLUENT software is applied.The numercal simulation of subcooled flow boiling heat transfer in a tube reveals the flow and heat transfer characteristic of subcooled flow boiling,which provide references for further research and application in subcooled flow boiling heat transfer of water.(4)The subcooled flow boiling of the water cooling design of divertor is studied.The numerical simulation method of divertor cooling system is proposed,and the temperature distribution of solid material and the flow field and temperature field in the cooling pipe are analyzed,and the influence factors of the divertor water cooling system are researched.The optimization design of the cooling pipe shape of the water cooling system of divertor is proposed,which provides a useful reference for the improvement of the application of the divertor.