Flow Characteristics and Optimization of Two-phase Flow Distribution over Plate Surface of Brazed-Plate Heat Exchanger

The homogenous distribution of liquid and vapor over a plate surface is a key factor affecting the performance of brazed-plate heat exchangers in refrigeration and air-conditioning units. The two-phase flow and distribution over the plate surface were investigated with R410A fluid using computational fluid dynamics (CFD) simulation software. The distributions of pressure, velocity, and liquid volumetric fraction were comparatively analyzed. It was observed that the pressure, velocity, and liquid phase were distributed comparatively evenly for the herringbone plate. The velocity and liquid volumetric fraction along the plate centerline were slightly higher than those along the edges. However, for the dimpled plate, the velocities in the proximal zone were significantly higher than those in the distal zone, which is opposite to the distribution of liquid volumetric fraction. New methods called the mean two-phase flow deviation (MTFD) and mean liquid flow deviation (MLFD) at the nominal section were proposed to evaluate the maldistribution of fluid flow over the plate surface. The results indicated that the distribution and sideways flow were better for the herringbone plate than for the dimple plate. The MTFD values were 14.2% and 39.6%, and the MLFD values were 15.6% and 41.3% for the herringbone and dimple plates, respectively. It was determined that the bypass section existed in the flow direction for the round dimple plate, which led to poor sideways flow and earlier separation between the vapor and liquid. The proposed boomerang dimple plate pattern, similar to fish skin, can improve the two-phase flow distribution over the plate surface because it can reduce the size of the bypass section and generate vortices under a concave shape. The new geometry can enhance turbulence and promote the two-phase fluid to move sideways effectively. The MTFD and MLFD values were 7.6% and 8.9%, respectively.