Numerical Simulation Of Critical Heat Flux On Cruved Surface

Critical Heat Flux(CHF)is the local heat flux where occurs the heat transfer deterioration.The first wall,divertor in fusion reactor and fuel rod buddle,lower head in fission reactor were facing a fairly high heat flux on the transient operation or accident condition.Under the circumstances,it may reach critical heat flux and possibly lead to serious accidents.Thus,the study on CHF of the key component is of great significance for the design and safe operation of the reactor.Computational Fluid Dynamic(CFD)method was first introduced to analyze the phenomena of critical heat flux of the divertor cooling tube with swirl tape in this paper.At the same time,the CFD results was compared with the experimental results.On a high-pressure condition,there was little difference between the experimental results and the CFD results under different experimental flow rates.Moreover,CHF calculations with different inlet subcoolings(144K,108K,72K,48K and 36K)were performed,results shows that the inlet subcooling didn't affect CHF results linearly.Meanwhile,it also can be found,under a lower inlet subcooling condition,the CHF occurred position located at the inlet of heated section mainly result from the single-side heated and swirling flow structure.Focus on CHF of single-side heating curved flow channel,which is the simplified object of external reactor cooling channel,the sensitivity of multiphase models as well as the CHF of both semi-spherical and ellipsoidal flow channel were studied.Based on this CFD study,it can be conclude that the choice of the height of first near heated wall mesh grid,bubble diameter and nucleate density affected the CHF results much and the turbulence dissipation force has the greatest influence on the CHF results among the non-drag forces.Under the same heat distribution and CFD model,results of CHF distribution with angle for both spherical and ellipsoidal lower head cooling channel showed that the different lower head shapes didn't affect the CHF value much and it only changes the shape of the CHF distribution.Combined with the CFD results in this paper,it can be concluded that CHF value is mainly concerned with two factors.First is the local heat flux should reach to an extent,then is the local vapor should concentrate to a certain degree.Meanwhile,the degree of vapor concentration is affected by both the integrated upstream heating power and the local force conditions which is varied with the local inclination.Under the effect of above two factors,the rules of CHF changing with angle result to be complex for curved cooling channel.In summary,CFD method is able to give a preliminary prediction on CHF of a complex geometry structure.Especially,on high pressure condition,the CFD results have a good agreement with experimental results.However,on low pressure condition,auxiliary models such as bubble diameter and nucleate site density are not really applicable,which leads to the large difference between the CFD results and the experiment's.Nevertheless,the CHF changes rule still helps for related experiments and designers.The sub model's optimizing is in process now,it can be believed that the numerical difference can be further reduced based on the new models.