Influence of boundary effect on supersonic flows and non-equilibrium condensation in a Laval nozzle for natural gas dehydration

The natural gas extraction process is often accompanied by large amounts of water vapor, so natural gas dehydration is the first step in achieving natural gas utilization. Current work focuses on a clean technology that captures water vapor in natural gas through expansion refrigeration. Using water vapor as a medium, a mathematical model for predicting spontaneous condensation caused by non-equilibrium state is established and validated. The influence of boundary effect including surface roughness and wall temperature on supersonic flows and non-equilibrium condensation are studied. The surface roughness affects the energy and momentum exchange between the fluid in the main stream area and near the wall, and thus affects the Wilson point, boundary layer, and non-equilibrium condensation. When the roughness rises by 0.1 mm, the boundary layer thickness increases by 56.7%, and the radial nucleation range decreases by 11.4% from y=±5.27 mm to y=±4.67 mm. The influence of wall temperature on the central area in the nozzle is not significant, but it affects the presence of liquid phase. The radial scope of liquid-phase drops by 3.58% when the wall temperature increases by 100 K.