A simulation study of the cooling of an isolated metal sphere in aqueous media (quenching)

A quantitative study is carried of a metal cooling process in aqueous and w ater-polymer cooling liquids. In the study, an original spherical hot probe with a heat-insulated stem is used to simulate the cooling conditions of t he operating part of the probe and to correspond to the cooling conditions of an isolated sphere. It has been shown that in this case the process cons ists of distinct consecutive stages, each of which can be studied separatel y in a quantitative way. The cooling process in all stages is described wit h a simple exponential relationship containing two parameters. One of these is the effective temperature of the cooling medium; the other is a time co nstant of the cooling process uniquely related to the heat dissipation coef ficient. In the film boiling stage the effective temperature can be much lo wer than the nominal temperature; moreover, for cooling in cold water it is found to be lower than the absolute temperature, which indicates the domin ant contribution of convection to the heat dissipation. The effective tempe rature of the medium is a monotonously increasing function of the nominal t emperature and rises with rising liquid viscosity. Dependence of the coolin g process time constant on the liquid temperature is influenced by two comp eting processes affecting convection, namely, by variations with temperatur e of the density and viscosity of a liquid. The effect of diminishing densi ty becomes prevalent at temperatures of the liquid above approximate to 80 degreesC. (C) 2001 MAIK "Nauka/Interperiodica".