Boiling Crisis in the Horizontal Channel : 1st Report, Critical Heat Flux for Square Channel with Separately Heated Top or Bottom

抄録

Visual study was made of the flow and boiling pattern near critical heat flux in the horizontal square ducts, and the critical heat flux was measured at the top or the bottom of the duct heated separately by high pressure steam.Two types of dryout were observed. For large quality region, the flow pattern is annular and the dryout occurs due to extinction of the annular liquid film. In this case, the difference between the top and the bottom is not remarkable. The other type of dryout occurs due to the defect of liquid at the top of the duct by phase separation. This phase separation is more liable to occur when the flow velocity is smaller and the duct height is larger. In this case, the critical heat flux at the top is significantly small as compared with that at the bottom.