Experimental Investigation On The Effect Of Surface Characteristics On The CHF Of Downward-facing Surface

In-Vessel Retention(IVR)strategy is one of the most important severe accidents management strategies,which has been implemented in AP600,AP1000 et al.The key of IVR strategy is the heat flux on the RPV downward facing surface should be lower than the Critical Heat Flux(CHF)at the corresponding location.However,with the increase of reactor power,the effectiveness of IVR strategy may be decrease,which limited to the local Critical Heat Flux(CHF).Therefore,it is necessary to enhance the Reactor Pressure Vessel(RPV)downward facing surface CHF for the success of IVR strategy.In this paper,an electrical heating 316-stainless steel plate section is used to simulate the RPV downward surface situation for pooling boiling and flowing boiling experimental investigation at atmosphere pressure,which aimed to study the method to enhance the CHF of downward facing surface.Pooling boiling experiments are designed to study the influence of surface roughness,surface manufacture technology and Al2O3 nanoparticle deposited on the CHF enhancement.While the flow boiling experiments were designed to study the influence of surface roughness on CHF at different orientation conditions.Moreover,the influence of flow rate and void quality on CHF was studied on the flow boiling experiments.The results show that compared to smooth surface,roughness of the 316-stainless steel plate raise after sand-blasting,which enhance the CHF both on pool boiling and flow boiling experiment.On pool boiling experiment,CHF enhancements range from 13% to 21%,highest CHF 750kW/m2 were get at Ra2.4um surface,which is 21% higher than the smooth surface.On the study of surface manufacture technology on the CHF enhancement,find that sand-blasting gets higher increase than fiber-drawing technology,however,electroplating will decrease the CHF.Al2O3 particle deposited surface gets almost 30% enhancements than the plain surface.Through analysis,theAl2O3 particle deposited enhances the wettability of the surface,which results in the enhancements of CHF.On flow boiling experiment,finds that CHF increase at every orientation conditions,and the CHF is increase with the increase of surface roughness,but the highest increase is only 8.4% at Ra9.3um surface.Moreover,the study finds that the CHF of downward facing surface is increase with the increase of flow rate,decrease with the increase of void quality.