Research On The CFD Simulation Of Narrow Double-side Heating Vertical Channel

The annular tubes once-through-steam-generator is one of the main equipments of the integral pressurized water reactor.The improvement of the thermal-hydraulic analysis is important to the designation of reactors.The flow and heat transfer of the second loop fluid is a problem of the analysis of the OTSG for its complexity.The secondary side undercooled feedwater of the OTSG is heated by the high temperature coolant on both sides of the annulus,and is transformed to superheated steam in the end of the channel,and then flows out from the inside of single-pipe section.The process evolved into a variety of flow patterns.The narrow channel has the advantages of compact structure,low heat exchange temperature difference,etc.However,due to its special geometric conditions,the flow and heat exchange conditions are more complicated,which leads to more difficult calculation of heat transfer in narrow channel.In this paper,ANSYS FLUENT 17.0 is chosen to simulate the slender circular tube,doublesided heating narrow vertical rectangular channel,and double-sided heating vertical narrow annulus flow field and heat transfer analysis of the working fluid gradually heated from the inlet subcooled state to the superheated steam in the end.The key parameters trend and the important factors which affect the heat transfer were analyzed.At the same time,the verage heat transfer coefficient in the double-sided heating vertical narrow annulus where the dryout boiling occurred was fitted by experimental correlation.The flow in the narrow vertical annulus of a annular tubes OTSG show different flow pattern,bubbly flow,annulus flow,plug flow,post dry-out steam flow.Taking a both side heatingnarrow vertical annulus as the research object withANSYS FLUENT 17.0.By analyzing the flow pattern caused by heating from the wall surface,the heat transfer coefficient is calculated by the formula from the simulation experiment.As to the requirements for validation and verification of CFD calculation,this paper takes the geometric parameters and the heat transfer conditions of tube which was uniformly heated experimental device published by Becker in 1983 as object,and compares the experimental data with the simulation data to select the calculation model.The results shows that the EulerEuler two-fluid model with the enhanced wall boiling function is the best method.The standard k-ε turbulence model was selected to get the best wall temperature simulation results.Finally,the simulation of the dryout boiling in the vertical narrow channels with different geometry was taken to fit the average heat transfer coefficient of the whole pipe section of the double-sided heating vertical narrow annulus with the help of Jens-Lottes formula.