环形管内沸腾传热与临界热流密度研究/Research of Flow Boiling Heat Transfer and Critical Heat Flux
The annular channels have profound background in nuclear industry, therefore more and more attention is paid on the heat transfer character and the prediction of the critical heat flux. In present study, the single-phase forced convection and flow boiling heat transfer in an annular tube is experimentally investigated with outer tube wall heating condition. The ID of the outer tube is 23mm and the OD of the inner tube is 18.9mm. The test results show that the enhancement of heat transfer of single-phase flow in annular tube is not remarkable which is less than that in circular tube under the same condition, whereas the saturated boiling heat transfer is enhanced because of the small channel geometry. The correlations to calculate the single-phase heat transfer and boiling heat transfer are obtained. Furthermore, the prediction of critical heat flux is numerical studied as well. Since the flow regime at both subcooled boiling CHF and annular flow CHF in the annular tube has no distinction with that in circular tube, the well-established mechanistic models about critical heat flux commonly used in the circular tube flow can be modified and employed in the annular tube flow. According to the special characteristics of the flow velocity field and the fluid temperature field, a hydrodynamic diameter and a heat diameter are re-defined. With the re-defined diameter, the subcooled boiling CHF model is modified based on the liquid sublayer dryout model, and the annular flow CHF model is also modified based on liquid film dryout model. The two modified models is employed to calculate CHF with water vertical flowing in a concentric annular tube and with all types of heat conditions which includes inner tube heating, outer tube heating, bilaterally tube heating. Good agreement is obtained between the numerical predictions and experimental data with the following parameter ranges: for subcooled boiling CHF, p=1.27~18.6MPa, G>500kg/(m2s), xc=-0.5~0; for annular flow CHF, p=0.57~15.01MPa, G=198~3790kg/(m2s), xc=0.07~0.86.