Numerical study of the influence of plate characteristics of a thermosiphon on the performance in a permanent laminar regime

The authors study, with the aid of an implicit method of finite difference, natural, laminar, permanent and bidimensional convection, in a fluid situated between two vertical plates consisting of porous material (granular type) saturated with air and crossed by constant density heat flux. In the channel, it admits the hypothesis of the film limit, utilising the Bernoulli equation at the entrance and considers the constant pressure at the exit whereas, in the porous material, it adopts the Brinkman model. The calculations show that for the large values of permeability, the plates behave like walls filled with air and, for small values, like a solid material. If one wants to obtain elevated ventilation outputs, it is preferable to use a rather long thermosiphon, again with solid plates whose thermal conductivity is large; if one desires elevated output temperatures, it is more judicious to use strongly permeable plates, more particularly for large values of modified Grashof number.