Minimum Heat Flux Point and Liquid-Solid Contact During Rapid Quenching of Thin Wires

Rapid quenching of thin horizontal platinum wires falling at a constant speed was studied experimentally with pure water and ethanol as quenching liquids. The transient boiling curve obtained from the cooling curve had two local minimum-heat-flux points, M1 and M2. Measurement of the liquid-solid contact and observation of the boiling pattern showed that a marked liquid-solid contact began at the first (higher wall superheat) minimum-heat-flux point, M1. The heat transfer results indicated that the M1 point corresponded to the minimum vapor film thickness for stable film boiling. The effects of liquid subcooling and falling velocity on the avarage vapor film thickness and the wall superheat at the M1 point were clarified. The wall superheat at the M2 point was almost constant for each liquid irrespective of liquid subcooling and falling velocity.