Numerical prediction of mixed convection heat transfer in an enclosure

In this article the transport mechanism of laminar mixed convection in a shear and buoyancy driven cavity flow with locally heated lower wall and moving cooled sidewalls is numerically studied using cubic interpolation profile method. This study focused on the interaction of forced convection with natural convection. The heat is locally introduced into the cavity with the dimensionless value of ԑ=1/5 of the non dimensional length of the bottom wall. Studies were conducted on the effect of mixed convection parameter Gr/Re2 (known as Richardson Number) in the range of 0.1-10. The results were illustrated in the form of streamline and isotherms. Three different regions can be detected as the Richardson number is increased: forced convection, mixed convection and natural convection

Analysis of instability patterns in non-Boussinesq mixed convection using a direct numerical evaluation of disturbance integrals

The Fourier integrals representing linearised disturbances arising from an initially localised source are evaluated numerically for natural and mixed convection flows between two differentially heated plates. The corresponding spatio-temporal instability patterns are obtained for strongly non-Boussinesq high-temperature convection of air and are contrasted to their Boussinesq counterparts. A drastic change in disturbance evolution scenarios is found when a large cross-channel temperature gradient leads to an essentially nonlinear variation of the fluid's transport properties and density. In particular, it is shown that non-Boussinesq natural convection flows are convectively unstable while forced convection flows can be absolutely unstable. These scenarios are opposite to the ones detected in classical Boussinesq convection. It is found that the competition between two physically distinct instability mechanisms which are due to the action of the shear and the buoyancy are responsible for such a drastic change in spatio-temporal characteristics of instabilities. The obtained numerical results confirm and complement semi-analytical conclusions of Suslov 2007 on the absolute/convective instability transition in non-Boussinesq mixed convection. Generic features of the chosen numerical approach are discussed and its advantages and shortcomings are reported

Thermal modeling of phase change solidification in thermal control devices including natural convection effects

Natural convection effects in phase change thermal control devices were studied. A mathematical model was developed to evaluate natural convection effects in a phase change test cell undergoing solidification. Although natural convection effects are minimized in flight spacecraft, all phase change devices are ground tested. The mathematical approach to the problem was to first develop a transient two-dimensional conduction heat transfer model for the solidification of a normal paraffin of finite geometry. Next, a transient two-dimensional model was developed for the solidification of the same paraffin by a combined conduction-natural-convection heat transfer model. Throughout the study, n-hexadecane (n-C16H34) was used as the phase-change material in both the theoretical and the experimental work. The models were based on the transient two-dimensional finite difference solutions of the energy, continuity, and momentum equations

Problems of astrophysical turbulent convection: thermal convection in a layer without boundaries

Thermal convection in fluid layers heated from below are usually realized experimentally as well as treated theoretically with fixed boundaries on which conditions for the temperature and the velocity field are prescribed. The thermal and velocity boundary layers attached to the upper and lower boundaries determine to a large extent the properties of turbulent convection at high Rayleigh numbers. Fixed boundaries are often absent in natural realizations of thermal convection. This paper studies the properties of convection driven by a planar heat source below a cooling source of equal size immersed in an otherwise stably stratified fluid layer are studied in this paper. Unavoidable boundaries do not influence the convection flow since they are separated from the active convection layer by nearly motionless stably stratified regions. The onset of convection occurs in an inner unstably stratified region where the mean temperature gradient is reversed. But the region of a reversed horizontally averaged temperature gradient disappears at higher amplitudes of convection such that the vertical derivative of the mean temperature no longer changes its sig