Numerical study of natural convection in the interior of a thermosiphon consisting of two vertical plane walls. Limits of approximation of the film limit

The authors study, with the aid of two numerical methods, the entry and exit conditions on the characteristics of a thermosiphon consisting of vertical plane walls, crossed by heat fluxes with equal and uniform densities. The first act calls, for the approximations of the film limit in the channel, the Bernoulli equation at its entry and the constant pressure at the exit. The second utilises the SIMPLER calculation code. According to the conditions of the calculation, the speed variations of the output, the average temperature in the exit section and the Nusselt average number on a wall, can differ rather a lot. Meanwhile for a channel of sufficiently large height and much elevated Grashof number, the two methods confirm the existence of zones of discharge and internal heat transfer characterised by constant longitudinal gradients.