A numerical study of microtube geometry effect on flow boiling and pressure drop using the Volume of Fluid method*

Other than high heat flux pursing, pressure is also crucial for microtube applications since it determines the power and efficiency of the pump. However, only a few studies focus on how tube geometry influences pressure drop. This study conducts a numerical investigation of the geometry effect on microtube flow boiling and pressure drop using the Volume of Fluid (VOF) method. There are three types of geometries used in this study: divergent, normal, and convergent microtubes, with different lengths and hydraulic diameter ratios. It is shown that the total pressure drop in the divergent microtube is the lowest. The heat flux will be decreased as the massive vapor bubbles clog the tube. However, the shorten divergent microtube can even obtain an increase of 35414.3 W/m² in heat flux and reduce of 237.04 Pa in pressure drop compared to the normal one under certain flow conditions while the tube-clogging effect is not dominant. A larger inflow mass flux can delay the vapor bubble formation on the heated wall, which is beneficial to prevent the tube clogging and leads to higher heat flux. On the other hand, higher heat flux can be achieved in the convergent microtube due to the increased velocity inside the tube, but it induces the highest total pressure drop. This study can provide a better fundamental understanding of the microtube geometry effect on flow boiling and relevant physical insight for the future design of microscale heat transfer applications.