Impact of Shockwave on Condensation Efficiency of Supersonic Nozzle during Natural Gas Purification

Shock waves in the nozzle during supersonic separation under different conditions can disrupt the flow field’s thermodynamic equilibrium. While it contributes to the recovery of pressure energy, it also leads to the dissipation of mechanical energy. This study aimed to investigate the effects of changes in back pressure on the shock wave position and its subsequent impact on the refrigeration performance of nozzles. A mathematical model for the supersonic gas in a nozzle was established and evaluated via experiments. The results show that when the back pressure is less than 0.2 MPa, no shock wave is generated in the nozzle, and high refrigeration and liquefaction efficiency can be ensured while effective pressure recovery is achieved. When the back pressure (pb) is increased from 0.3 to 0.6 MPa, the refrigeration efficiency of the nozzle decreases, and the shock wave position (x shock) is advanced from 157 to 118 mm. The maximum Mach number (Ma) that can be reached by the fluid in the nozzle is reduced from 1.97 to 1.27. When the back pressure is increased from 0.2 to 0.6 MPa, the minimum temperature is increased by 55.18 K. When the back pressure is greater than 0.3 MPa, the Mach number upstream of the shock wave is reduced from 1.97 to 1.27, the shock wave intensity is weakened, and the thickness of the boundary layer separation caused by the shock wave is also decreased accordingly. Therefore, to ensure refrigeration efficiency, measures should be taken to control the back pressure within a reasonable range.