Quenching and rewetting of rock in liquid nitrogen: Characterizing heat transfer and surface effects

Abstract

Cryogenic quenching of cylindrical rock rodlets in liquid nitrogen pool was experimentally investigated. The sample was 25.4 mm in diameter and 60 mm in length. Quenching was performed under saturated condition at the atmospheric pressure. Thermocouple and high speed camera were employed to attain the transient temperature history and the two-phase dynamics during quenching. A numerical simulation scheme was developed to model the heat transfer process during quenching and rewetting. The boiling curves of quenching were established for different rock surfaces based on the temperature and visualization data. The rewetting of cylindrical rock was observed to initiate at the two ends of sample and merged at the upper 2/3 of the sample length. This feature was well captured by our numerical model. It was found that the maximum heat flux during quenching exceeds the stationary boiling limits of liquid nitrogen, the same finding as in the literature. The effect of surface structures on quenching was also explored by experiments and the numerical model demonstrated its applicability for these structured surfaces as well.