Natural convection in a vertical rectangular enclosure with symmetrically localized heating and cooling zones

Numerical and experimental studies of natural convection in a single-phase, closed thermosyphon were carried out, using a vertical, rectangular enclosure model. Two vertical plates, each 100×100 mm2 in dimension, and placed symmetrically play the role of heat transfer surfaces. These symmetrical heat transfer surfaces are separated into three horizontal zones of equal height; the top and bottom thirds of these surfaces are the zones of, respectively, cooling and heating, the intermediate section being an adiabatic zone. Silicon oil is used as the working fluid. Variable parameters are the distance, D, between the two heat transfer surfaces, and temperature difference, ΔT, between the heating and cooling zones. By changing both D and ΔT, three regimes of natural convection flow; steady, quasi-two-dimensional, steady, three-dimensional, and unsteady flows were found in experiment. Converged solutions obtained by numerical simulation agreed well with experimental results with regard to the temperature and velocity of the fluid as visualized by means of thermo-sensitive liquid crystal powders.