Book Description

Transient cool-down process of a fluid from an initial high temperature to a target temperature in a closed container is investigated numerically. The fluid has a quadratic density-temperature relationship, and the maximum density occurring at Tm. Cooling is accomplished by abruptly lowing the sidewall temperature, and the mean temperature passes through Tm in the course of cool-down. A finite-volume method is employed to acquire numerical solutions to the full, time-dependent two-dimensional Navier-Stokes equations. In order to simulate the realistic situations under micro gravity, the Rayleigh number, Ra, encompasses the range 10 to the 5th less than or equal to Ra less than or equal to 10 to the 8th. The effects of the density inversion on the cool-down are illuminated. Based on the structures of the sidewall boundary layer, three characteristic flow regimes are identified at early time the qualitative early-time behavior is determined by the density inversion factor. Evolutions of the global fields of flow and temperature of each flow regime are described. The analysis of time-dependent heat transfer characteristics reveals that the cool-down process is divided into several definite transient phases. The relevant time scales for the overall cool-down process are estimated. The specific effects of the Rayleigh number, density inversion factor, and the aspect ratio of the container on each evolutionary stage are elaborated.