Correlations Of Subcooled Flow Boiling Heat Transfer Coefficient In Tubes

Subcooled flow boiling heat transfer has been widely used in the fields of nuclear energy,thermal power plant and electronic equipment cooling.Because of its excellent heat transfer capacity,it has great application potential in the cooling channel of HHF divertor component in Tokamak.Firstly,based on 1915 groups of subcooled boiling experimental data from 14 published literatures,16 subcooled boiling heat transfer correlations are evaluated.The evaluation results show that the prediction deviation of Baburajan correlation is the smallest,and the mean absolute deviation(MAD)is 28.6%.Secondly,the factors influencing the subcooled flow boiling heat transfer characteristics are studied,and the influence of the Boiling number(Bo)calculated by the gas density on the subcooled flow boiling heat transfer characteristics is analyzed.A new subcooled flow boiling heat transfer correlation is obtained by fitting the Boiling number and the related dimensionless number.The MAD of the correlation is 19.3%,and the prediction deviation of 70.4%data points is within±20%,which improves the calculations accuracy of subcooled flow boiling heat transfer.By using the high heat flux comprehensive experimental platform,The experimental study of subcooled flow boiling in a horizontal rectangular tube with single side heating on the upper wall was carried out under the experimental conditions of system pressure of 1,1.5,2 MPa,inlet temperature of 20,40,60? and flow velocity of 1,2,3,4,5m/s.371 experimental points of subcooled flow boiling heat transfer were obtained.The experimental data of Reynolds number in the range of 77000-420000 and the experimental data of subcooled boiling in the upper wall heated horizontal tube were expanded.Finally,the relationship between Nusselt number(Nu)and Grashov number(Gr)is analyzed by using the experimental data in the literature and the experimental data obtained in this paper,and the influence of buoyancy on the subcooled flow boiling heat transfer performance in the tube is discussed.The results show that the influence of buoyancy on the heat transfer characteristics is related to the direction of water flow and the way of heating.In the vertical tube,the buoyancy force increases the disturbance of bubbles to the subcooled fluid,thus enhancing the heat transfer;for the horizontal rectangular tube,when the bottom is heated,the buoyancy force helps the bubbles to separate from the heated wall,and the bubbles increase the disturbance of the fluid,thus enhancing the heat transfer;when the upper wall is heated,the upward buoyancy force hinders the diffusion of bubbles to the mainstream liquid,which makes the heat transfer worse.According to the classification of different tube types and heating methods in the new experimental database,the correlations of subcooled flow boiling heat transfer of water in tubes modified by Gr were obtained under the conditions of vertical tube,bottom wall heating horizontal tube and upper wall heating horizontal tube.The MADs of modified heat transfer correlations are 13.6%,12.9%and 12.1%,respectively;and the deviation within±20%experimental data accounted for 87.8%,89.0%and 90.3%of the total experimental data,respectively,which further improved the prediction ability and applicability of water subcooled flow boiling heat transfer in the tube,and provided a useful reference for the application of water subcooled boiling heat transfer in the cooling channel of water-cooled divertor...