An experimental and numerical study on the effect of the wall in a thermocline-type cylindrical enclosure—I Experments

Abstract

In this, the first part of a two-part paper, axisymmetric natural convection flows in a thermocline-type cylindrical enclosure are studied experimentally with a laser Doppler velocimeter. A numerical model was developed using these experimental data and it is presented in the second part of this study. These enclosures find application as storage systems in solar energy power plants. It is shown that the walls of the container can have a strong effect in destroying the thermocline. This effect was studied for an initially established thermocline where the hot fluid (in the top) and the cold fluid (in the bottom) are separated by an adiabatic partition, and the container is well insulated outside. The flowfield that results from this initial condition is symmetric with respect to the partition (except for variations in the fluid and wall properties which were neglibible in our experiments), and it was only necessary to study the development of the initially cold fluid. Both the axial and radial components of the velocity were measured as a function of time and position. Two Rayleigh numbers (based on the temperature difference) were studied: 3.7 × 10 8 and 7.5 × 10 8. The velocities measured ranged between 0.01 cm/sec and 0.45 cm/sec. The error for typical velocities near the wall is ±10 per cent. Very good agreement was found with an available numerical solution.