Heat Transfer during Condensation of Liquid Vapor on Horizontal Circular Tube in Hydrophobic Granular Layer

Analytical modeling of heat transfer during condensation onto a horizontal round tube placed in a hydrophobic granular layer has been performed. According to generalized experimental results of the authors, the area under study was divided into three regimes of the condensate film flow: Re \(< 5\), \(5 < {\rm Re} < 10\), and Re \(> 10\). For the first two regimes, in the absence of effect of capillary forces, theoretical solutions were found based on the representation of a near-wall pore channel in the form of a flat annular slot with hydrophobic side surfaces; the solutions are in good agreement with the experimental data. At Re \(> 10\), a self-similar regime of the hydrodynamics of the condensate film settles, independent of the Re number, with a constant mean film thickness over the tube perimeter and the condensate part not involved in the heat transfer in the tube draining into the pore space of the layer. In all analyzed cases, there is heat transfer deterioration by two to three times on a horizontal tube in a hydrophobic layer in comparison with a smooth hydrophilic tube, because of the peculiarities of the hydrodynamics of the condensate flow in the wall pore channels. For all modes, formulas were obtained for calculation of the Nusselt numbers of heat transfer in dependence on the Re number.