Numerical Simulation Research On Ram-compression Process Of Spiral Compression Expansion Refrigerator

With the rapid development of modern science and technology,natural gas liquefaction technology,aerospace technology and superconducting technology,the demand for cryogenic refrigeration technology is increasingly urgent.In recent years,due to the advantages of clean,safe,small size and easy transportation of liquefied natural gas,the proportion of China's liquefied natural gas in the energy structure has increased rapidly,and the role of low-temperature refrigeration technology in the process of liquefied natural gas production is becoming more and more important.Spiral compression expansion refrigerator is a new type of refrigerator.It has the advantages of high refrigeration efficiency,small volume,high single-stage pressure ratio,continuous compression process and simple working process.It can replace other refrigerators in natural gas liquefaction process.It can not only accelerate the production speed and liquefaction efficiency of LNG,but also greatly simplify the production process of LNG.The research on the ram-compression process of spiral compression expansion refrigerators provides theoretical basis for the development and utilization of spiral compression expansion refrigerators,plays an important role in promoting the application of this new type of refrigerators in LNG liquefaction process,and has great significance for the development of LNG industry.Firstly,the ram-compression technology used in the compression section of the spiral compression expansion refrigerator is systematically expounded.Combined with the Brayton refrigeration cycle process,a refrigeration cycle of a spiral compression expansion refrigerator is proposed.The performance of this refrigeration cycle and the traditional refrigeration cycle is compared and analyzed.Secondly,The physical and mathematical model of three-dimensional spiral blade with varied pitch are established.The three-dimensional spiral distribution regulation of velocity caused the ram-compression effect and the corresponding pressure and other flow-field parameters are studied in specific spiral surface.The theoretical calculation model of different flow-field parameters in spiral space are researched on the condition of varied diameter and varied pitch.Theoretical model of the three-dimensional ram-compression is researched when the pitch of the spiral surface changes under specific speed conditions.The best variable pitch spiral surface physical model when the ram-effect is generated,and the distribution law of compression parameters of variable pitch spiral curved surface under different parameters was studied by curve fitting methods.Finally,the optimal model of the ram-compression of the spiral compression expansion refrigerator is used to the physical model of numerical simulation.Changing the rotational speed of the spiral impeller,the numerical theoretical calculation of the optimal model is carried out under certain working conditions for researching the optimal model spiral impeller compression performance parameters with the rotation speed.And study the effect of back pressure on the performance of the spiral impeller stamping compression process by changing the back pressure of the spiral impeller.The research shows that the refrigeration cycle of the spiral compression expansion refrigerator saves 13.4%of the compression work compared with the Brayton refrigeration cycle under the same cooling capacity.The refrigeration cycle of the spiral compression expansion refrigerator is closer to the isothermal compression process than the Brayton cycle,and the refrigeration coefficient is more large,energy efficiency ratio is higher and more energy efficient.Through numerical simulation,it is found that the closer to the outer edge of the spiral blade,the more the shock wave,the more obvious the ramjet effect.The existence of the shock wave causes the flow field velocity of the airflow to increase along the flow direction,and the flow field dynamic pressure increases along the flow direction.The variable-pitch spiral impeller model with a shaft diameter of 120 mm and a helical acceleration of-6.5 mm/s~2 is the best physical model for ram-compression.The flow loss is the smallest,the dynamic pressure is the fastest,the ram-compression effect is obvious,and the flow field distribution is stable.When the mass flow rate is constant,the change of the static pressure and the outlet dynamic pressure of the variable pitch spiral channel with the rotation speed accords with the Exponential function.When the rotation speed and flow rate are constant,the inlet static pressure and the outlet dynamic pressure change with the shaft diameter respectively according to the Parabola and ExpDec1 function,and the pressure in the spiral channel changes with the spiral acceleration follows the exponential function distribution law.Under the condition that the inlet mass flow rate is constant,the dynamic pressure of the optimal model of the impeller decreases with the increase of the rotational speed by the Exponential function.When the rotational speed is 15000 r/min,the inlet flow condition is easier to meet the requirements,and the ram-effect is most obvious.With the increase of the outlet pressure of the best model,the more difficult the ram-compression flow condition is,the ram-effect is not obvious.