Experimental Study On Critical Heat Flux Of High Speed Jet Impingement Boiling On Nano-structure Surface

On some industrial production occasions, such as steel industry, nuclearpower process and electronic equipment production and control process, Jetimpingement cooling is widely used as a highly effective cooling method toenhance boiling heat transfer. The jetting liquid with a certain speed canpass through the vapor bubble that caused by evaporation on the heatedsurface to acquire a solid-liquid contact. The Critical Heat Flow density(CHF) can be delayed greatly. So the surface temperature can be controlledeven if the surface heat flux reaching a high value. Comparing to commonpool boiling, the heat flux of Jet impingement cooling can increased bymaybe an order of magnitude, and it is a highly effective steady state heattransfer method.The process of boiling on heated surface can be divided into forced convection nuclear boiling, transition boiling and film boiling. it will reachCHF in the late stage of nuclear boiling, if heat flow density continue toincrease, the wall temperature will take a bigger step, for example, thewall temperature will be surged to1000℃on some nuclear reactor coolingcondition, and it is very dangerous. As a matter of fact, the industrial heattransfer process is commonly designed in nuclear boiling area. Water as acommon fluid, is widely used as cooling medium in the flow boilingprocess.A systematically steady experimental research about the CHF ofsaturated and sub-cooled water cylindrical jet impingement cooling on threekinds of surfaces with different contact angles at the mode B (The conditionof jet flow’s cross section area is equal to or bigger than the heat transfersurface area) was carried out. The speed of jet is from5to40m/s, the jetdiameter is3mm, sub-cooled temperature of water is from0to50℃.Different contact angles are prepared by adhering nano-structure hydrophilicor hydrophobic layer to ordinary copper surface through sol-gel process.The contact angles of hydrophilic and hydrophobic surface is5°and105°, common copper surface is60°. A series of experimental equations forindicating the high speed saturated water and sub-cooling water jet criticalheat flow density on three kinds of surfaces with different contact angles are established through the study based on both experience and theory.The Laboratory’s previous related research data on different surface arereviewed and summarized to obtain a half-theory and half-experienceequation that consider influence of contact angle, these equations get abroader application scope in predicting Critical Heat flux of jet impingementboiling on heated surface, and match very satisfactorily with theexperimental data.