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 using pure water and ethanol as the quenching liquids. The transient boiling curve obtained from the cooling curve had two local minimum heat-flux (MHF) points. Measurements of liquid-solid contact and observations of boiling patterns showed that a marked liquid-solid contact began at the first (higher wall superheat) MHF 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 average vapor film thickness and the wall superheat at the M1 point were explained. The wall superheat at the second MHF point M2 was almost constant for each liquid regardless of the liquid subcooling and the falling velocity.