Experimental Research On The Surface Features Effects On CHF Of Downward-facing Surfaces

In-vessel retention(IVR)is one of the key severe accident management strategies used at some nuclear power plants.To make the IVR strategy effective,the critical heat flux(CHF)of the downward-facing surface of the reactor pressure vessel(RPV)must be bigger than local heat flux in a severe accident.With the advancing of nuclear power,the effectiveness of the IVR strategy is limited by the critical heat flux of the RPV downward-facing critical heat flux.Surface characteristics affect CHF a lot.To find out how surface characteristics affect CHF is very important for exploring the methods of improving CHF and enlarging the margin of the IVR strategy.Experiments were performed to explore the effects of orientation and surface roughness on CHF of 200 mm×50 mm×0.97 mm 316 stainless steel with deionized water as working medium.The effects of orientation including angles 0°(downward-facing)、10°、18°、26°、34°、42°、54°、62°、70°、78°、82°、90°(vertical)on CHF and heat transfer was studied by flow boiling experiments,while both flow boiling and pool boiling experiments were done for the study of the effect of roughness including 0.498 μm、1.3 μm、2.3 μm、3.2 μm、4.3 μm、6.3 μm、9.3 μm on CHF.The experiments results about orientation revealed that CHF increases with the orientation angles increasing from 0°to 42°,but decreases with the orientation angles increasing from 54°to 82°.The values of CHF at 70° and 90° are a little abnormal higher than the trend.The boiling heat transfer coefficient decreases with the increasing of the orientation angle.The results of the surface roughness experiments revealed that CHF of flow boiling and pool boiling show the same trend along the changing of roughness but the value of flow boling CHF is higher than that of pool boiling at the same roughness.CHF was improved by increasing the roughness of the heating surface before the surface roughness reaches 2.3 μm.After 3.2 μm,the increasing of roughness wouldn’t show any effect on CHF.Under a higher orientation angle,CHF of the same roughness is higher but the trend that CHF change along the changing of roughness is same with the trend when orientation angle is 0°.