| Vortex tube,also known as Ranque Hilsch tube,is a kind of equipment to separate high~pressure fluid into high~temperature and low~temperature two low~pressure airflow.Compared with the traditional refrigeration method,vortex tube has the characteristics of simple structure and no moving parts.It can separate high~pressure gas into two streams with different total temperature.It has been widely used in the field of refrigeration,natural gas,mixture separation,aviation and many industrial fields.In this paper,the effect of vortex tube on the efficiency of vortex tube jet absorption refrigeration system is studied by using carbon dioxide as working fluid and fluent numerical simulation.The structure parameters and operation parameters(the analysis of the influence of the cooling and heating effects of the vortex tube,the optimization of the vortex tube structure,provide the optimal vortex tube structure for the vortex tube jet absorption refrigeration system).On this basis,the flow characteristics,velocity,pressure and temperature distribution of carbon dioxide in the tube are analyzed,which lays a foundation for further revealing the energy separation mechanism of vortex tube.The results show that there are three kinds of flow patterns in the vortex tube: the inner and outer swirls with the axial velocity as the zero velocity boundary,the free and forced vortices with the tangential velocity increasing first and then decreasing,and the radial circulation with the radial velocity.On the basis of these three flow patterns,the isothermal distribution of the inlet gas flow similar to the internal and external swirls is formed in the tube.The radial distribution of the inlet gas flow similar to the tangential velocity has violent temperature change at the radial boundary of the internal and external swirls,the free vortex and the forced vortex.The axial distribution and the velocity distribution have strong temperature change near the vortex chamber.With the increase of the axial distance,the gas flow temperature increases Tend to be consistent.The pressure distribution is similar to the temperature distribution.The pressure gradient from the hot end to the cold end provides the power for the movement of low temperature gas and hightemperature gas in the opposite direction.The pressure gradient between the radial axis and the wall promotes the energy exchange of three flow forms.The simulation results show that the vortex tube has the best cooling temperature and heating temperature effect when the number of nozzle channels is 6 and the cooling flow rate is 0.1.When the cooling flow rate of vortex tube changes from 0.1 to 0.9,cop and cooling capacity are 0.57 and 1.08 KW respectively when the cooling flow rate is 0.1,and their peaks are 0.79 and 1.51 KW respectively when the cooling flow rate is 0.6.The cop increment of the new vortex tube absorption refrigeration system is 0.22 and 0.43 KW because of the increase of cooling flow rate.When the expansion ratio of vortex tube changes in the range of 3~4.4,the cop and cooling capacity of the new type of vortex tube absorption refrigeration system are0.74 and 1.49 KW respectively when the expansion ratio is 4.1,and the peak value is 0.83 and 1.69 kW respectively when the expansion ratio is 3.3.The cop increment of the new type of vortex tube absorption refrigeration system is 0.09 and 0.2 KW because of the increase of expansion ratio.When the number of nozzle channels changes in the range of2~6,it has little effect on COP and cooling capacity of the new refrigeration system,cop changes little at about 0.33,and cooling capacity changes little at about 1.24 KW.When the length of the hot end tube of the vortex tube changes from 100 mm to 200 mm,the cop and cooling capacity of the new refrigeration system will be greatly affected.When the length of the hot end tube is 100 mm,the maximum cop and cooling capacity will be 0.75 and 1.43 KW respectively.When the diameter of cold orifice d = 1.5~3.5 mm,it has a great influence on COP and cooling capacity of the new refrigeration system.When the diameter of cold orifice d = 2.5 mm,the maximum COP value is 0.67 and the maximum cooling capacity is 1.28 KW.When the diameter of the hot end pipe r = 4.0~6.0mm changes,it has a great influence on COP and cooling capacity of the new refrigeration system.When the diameter of the hot end pipe r =5.0mm,the maximum COP value is 0.68 and the maximum cooling capacity is 1.28 KW. |
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