Computational prediction of surface-tension flow mechanism of molten filler in a V-shaped groove geometry in the brazing process of a heat exchanger

Abstract

When the temperature rises during the brazing process, only the brazing material melts because of its low melting point. Several analytical approaches have been used to describe filler flow in channels and the progression of erosion grooves. However, only a few studies have examined filler-flow behavior in microgrooves during brazing. In this study, a computational model was constructed to examine the flow in microgrooves on an extruded material’s surface. The capillary flow of the aluminum brazing material was numerically analyzed to investigate the physical properties and surface behavior. Specifically, the surface-tension flow behavior was analyzed by simulating various cross-sectional shapes of the channel grooves and various contact angles of the filler. The effects of various parameters, such as viscosity and boundary conditions, on the filler flow were also analyzed. When the cross-sectional area of the channel groove increases, the filler-flow velocity increases, and the rate of unsteady fluctuation increases with the increasing filler tip velocity. The driving force of the filler flow in the channel groove is considered to be (1) the surface tension, which is based on the filler free-surface curvature, or (2) the dynamic change in the shape of the meniscus, which can be unsteady and induced by Rayleigh–Taylor instability. As the cross-sectional area of the channel groove increases, the capillary force based on the dynamic change in meniscus shape dominates the unsteady change in filler tip velocity, rather than the surface tension based on the filler free-surface curvature formed in the groove.