The numerical modeling of natural gas cooling in vortex tube
Crude oil consists of a mixture of hydrocarbons as a liquid at reservoir conditions and as a gas-liquid mixture at the wellhead. The gas phase of crude oil is called associated gas. There is a great problem how to transfer it to consumers, because pipelining makes no economic sense on account of low gas production at oil wells. An advanced way to solve this problem is to liquefy gas in vortex tubes and then transport it to the consumers by vehicles. Vortex tubes have no moving parts, so they will have no maintenance service. Research on this application of vortex tubes have been started recently and have not yet led to serial products. The main difficulty is the low accuracy of engineering calculations of vortex tube performance, which are based on the semi-empirical methods and require prototype testing of the product. The best way to solve this problem is modeling the gas cooling processes in the vortex tube by means of computational fluid dynamics. Such methodology is suggested in this paper. The complete formulation of the vortex tube modeling includes the calculation of the flow inside the tube and at the cold and hot outflows, which requires large computational resources. We could reduce the problem to air flow modelling inside the vortex tube only. At the outflows we extended the pipeline to get a reasonable approximation for the output gas pressure being close to atmospheric one. Some simulations have been done for air cooling with vortex tubes which were described previously in other experimental works. Also we have performed and described our own experiment. The local flow characteristics such as velocity field (axial and tangential components), pressure and temperature, which were obtained in calculations, have been the same as for published experimental works. Integral characteristics of the vortex tube - the magnitude of cooling from numerical simulation have differed from experimental data not above than 4-7%.