Quenching Phenomena in Bubble State Boiling and Natural Convection.

Part 1: -Effect due to the conditions of coolants-

Abstract

When a red heated body was quenched into any cooling liquid, the body would cool through three processes, namely film state boiling, bubble state boiling and natural convection.
In our previous papers cooling phenomena by film state boiling due to quenching from high temperature were biscussed. Now in this paper we intend to report the results of investigation for the process of two stages, bubble state boiling and natural convection. The series of experiments were carried out keeping all the initial condition of a test body constant under the various conditions of cooling media.
Arranging the data of the experiments we came to the following conclusions.
(1) In the process of bubble state boiling the values of transfer coefficient are dominated by the initial temperature u₀ and the boiling temperaturet u₂ of coolants, and our experimental data can be generally put into order by using the equation (1) which shows that they are not influenced by the physical properties of coolants.
(2) A transition point appears as soon as cooling phenomena changes from boilling state to that of natural convection. The more the coolant is deairated, the more the transition point appears at hight temperature, and the much the coolant has air and gas, the more the point appears at low temperature.
(3) In the natural convection process, the coefficient α rises up according to the increasing of temperature of cooling liquid and if the temperature is increased over a limit, the coefficient α shows its decreasing. The coefficient α is greatly controled by Gr number as shown in the equation (2) and the smaller the viscosity ν is, the more the coefficient α is developed, in addition, it was confirmed by this experiment that the coefficient α raises itself easily, according to decreasing of the value of surface tension σ. Δu₁=u_R-u₀, Δu₂=u₂-u₀, u_R=surface temperature of test body (°C): Nu=Nusselt Number, Pr=Prandtl Number, Gr=Grashof Number, γ=specific weight of coolant (gr/cm3), R=radius of test body (cylinder) (cm)