Lattice Boltzmann study of pool boiling heat transfer enhancement on structured surfaces

Abstract

Pool boiling heat transfer enhancement on structured surfaces with columns is investigated by a thermal two-phase lattice Boltzmann model. The effects of geometrical parameters, including column height (H), width (W) and gap spacing (D), are discussed in detail. The size of columns is comparable to the diameter of a typical detached bubble (db). It is found that the heat transfer performance mainly depends on two factors: the heated surface area A and local convective flow field. When W and D are properly chosen as about W=D≈4db, increasing H enhances the heat transfer solely due to the increase of the surface area. When W and D are small, it is observed that the top of the columns and the channels are mostly covered by a layer of vapor, respectively, which weaken the convection. Under the circumstances, although surface area A increases, heat transfer enhancement is not so significant. For the surface tension effect, the enhancement of the structured surface decreases with the increase of capillary number compared to that of the plain surface. The mechanism is that at larger capillary number, the convection close to the channel may be partially blocked, which hinders the heat transfer. An optimal enhancement could be achieved when A is as large as possible and meanwhile the convection is not hindered by the bubbles behaviors. The finding here may shed some light on mechanism of heat transfer enhancement on structured surfaces with columns.