Numerical Study Of Flow And Condensation Process In Supersonic Flow Field

In the process of storage and transport for natural gas,water vapour in natural gas could transform into liquid water through spontaneous condensation,the presence of water has bad influences for the equipment of storage and transport.So in the process of storage and transportation for natural gas,It's very important to avoid the spontaneous condensation of vapour.There are many ways to extract water in natural gas,including heating and drying methods,all of it need complex and expensive device.However,supersonic separation device is very simple and stable,it make full use of the natural condensing zone,turn saturated vapour into oversaturated,after that,the water vapour begin to transform into little water droplet.The liquid phase would be separated by centrifugal force after condensation.This paper focused on a two-component mixed gases of nitrogen and water vapour,using one dimensional numerical calculation and three dimensional numerical simulation to describe the spontaneous condensation in the Laval nozzle,got the cloud picture of the important parameters in the process of coagulation.We also explored the impact of pressure,temperature and condensation degree of inlet in the process of condensation.Under the condition of Pin=60 kPa,Pout=18 kPa,Tin=287 K and yin=0.01,the magnitude of nucleation rate near the throat of Laval nozzle reached about 10²⁵;Droplet density increase to 2.6×10²² suddenly in very small scope near the nozzle throat,then it decreases slowly after reaches the peak,and finally stabilize on the level of 10²²;The maximum number of Mach number in the nozzle can reach 1.9,about 89.2%of water vapour would transform into liquid water at outlet of the nozzle,it illustrated that the supersonic nozzle can meet the demand of industry.We studied the effect of inlet parameters on the condensation efficiency inside the nozzle and got the following results.Those parameters would change obviously when changing the pressure of inlet,with the increase of pressure.Pressure and temperature along the axis of nozzle increased with increasing pressure of inlet.It has the same effect with nucleation rate and droplet number along the axis of nozzle;Mach number near the throat has decreased,but did not change significantly in the nozzle exit;Because of the influence of the nucleation rate,the condensation efficiency of water vapour improved.The temperature,nucleation rate and the number of droplets along the axis of nozzle changed obviously when we enhanced the temperature of inlet,but the Mach number and pressure of the flow almost unchanged.Water vapour condensation efficiency decreases when the temperature of inlet increased due to the decreased nucleation rate.And content of vapour has remarkable effect on those parameters inside the nozzle.With the increase of water content,nucleation rate and droplet number increases obviously,but condensation efficiency would reduce because vapour release out a lot of energy when coagulating which could convert into heat.