Enhancing Pool Boiling Heat Transfer by Structured Surfaces– A Lattice Boltzmann Study

Abstract

The structured surface-enhanced pool boiling process and associated heat transfer enhancement characteristics are numerically investigated by using the pseudopotential multiphase flow lattice Boltzmann (LB) model coupled finite difference method (FDM). In the current study, the effects of different microstructure geometries(square structures, triangular serrated structures, triangular-raised structures) and varying spacing in triangular-raised structures (d = 0, 22, 44, 66, 88, 110 l.u. (lattice units)) on boiling heat transfer (BHT) characteristics and bubble dynamics behavior are studied in detail. The results showed that microstructure can accelerate bubble nucleation. Among the three microstructures, the heat transfer performance of triangular-raised structures was significantly better than that of square and triangular serrated structures in the nucleate boiling (Ja number is 0.124-0.145). The oscillation and deformation of bubbles led to the lateral migration of bubbles, the continuous nucleation of small bubbles. The phenomenon of re-wetting of heating surface occurred in the process of bubble migration, necking, deformation and detachment was found, which enhances heat transfer in nucleate boiling. At the same time, the growth, oscillation and detachment of bubbles also perturb the liquid and enhance the natural convection around the bubbles.Therefore the main BHT mechanism of nucleate boiling on the three kinds of structured surface is the combined action of transient heat conduction and micro-convection. The variation of the spacing between microstructures showed an important effect on the BHT performance of the heating surface and the generation of activated nucleation sites in the nucleate boiling. Triangular-raised structures can enhance transient heat conduction and micro-convection, with the strongest enhancement effect at d = 66 l.u when the Ja number is 0.124.