CONVECTIVE COOL-DOWN OF A CONTAINED FLUID THROUGH ITS MAXIMUM DENSITYTEMPERATURE

A numerical study is made of transient natural convective cool-down pr ocess of a fluid in a cylindrical container. The density-temperature r elationship of the fluid is given by a quadratic function, with the ma ximum density rho(m) occurring at T-m. Cooling is accomplished by abru ptly lowering the sidewall temperature, and the mean temperature passe s through T-m in the course of cool-down. Numerical solutions are acqu ired to the fun, time-dependent Navier Stokes equations. The flow is g overned by a properly defined Rayleigh number Rn, the density inversio n factor gamma, the aspect ratio A, and the Prandtl number, Pr. Evolut ions of the flow and temperature fields are analyzed. Based on the str uctures of the sidewall boundary layer al early times, three character istic flow regimes are identified. The qualitative early-time behavior is determined by gamma. The intermediate-stage features for large gam ma disclose the flow restructuring. When A or Ra is large, boundary la yer waves are monitored for moderate Values of gamma. The analysis of time dependent heat transfer characteristics suggests that the coal-do wn process is divided into several transient phases. The relevant time scales for the overall cool-down process are estimated. The specific effects of Ra, gamma and A on each evolutionary stage are elaborated. (C) 1997 Elsevier Science Ltd.