Numerical simulation of structured surface roughness effects on flow boiling characteristics in microchannel

Abstract

Effects of structured roughness shape and size on flow boiling heat transfer in microchannels are numerically investigated with the Volume of Fluid (VOF) method and the Lee model. Rh is proposed to characterize the area-averaged height of 3D roughness. First, roughness shapes of triangular pyramid, cube, and hemisphere are compared by assessing the Nusselt (Nu) and Poiseuille (fRe) numbers. Then, the base edge length a and height h of the triangular pyramid roughness elements are varied to examine their effects on flow boiling. The results indicate that microchannels with triangular pyramid roughness exhibit the best heat transfer performance among the three shapes. Furthermore, increasing either a or h of the triangular pyramid roughness elements can enhance the thermal-performance of the rough microchannels. Additionally, Nu increases by 1.64 % when a is raised by 25 %, while increasing h by 25 % results in a 4.45 % increase in Nu. Similar scenario occurs for fRe. This indicates that h rather than a has greater effects on the microchannel flow boiling. However, the effect of Rh on Nu and fRe exhibits complexity due to the shape dependence.