The Axial-thrust Research And Simulation Of Turbo-expander

Turbo-expander is a machine which can get refrigeration and recover energy through adiabatic isentropic expansion flow of the gas. It is the key component of low temperature environmental simulation, air separation, natural gas liquefaction, hydrogen and helium liquefaction and other devices, and also is the heart device to ensure stable operation of the whole equipment. With the highly development of economy, which makes turbo-expander also toward large-scale, high-speed direction to develop. In this case, some problems such traverse of impellers on axial movement can easily arise. While that problem is caused by inaccurate calculation in axial-thrust on the rotor of design phase. So, through study the axial-thrust of turbo-expander can improve the accuracy of axial-thrust, stability of the shaft and the reliability of the whole equipment, which have a great theoretical significance and high practical significance for the design of turbo-expander and extend machine’s life.A turbo-expander is chosen as an example, axial-thrust on its rotor system is studied, and computational fluid dynamics (FLUENT) is applied for numerical simulation of the axial-thrust.By analyzing the force, the mechanical model and the three-dimensional model of the impeller clearance and labyrinth seal were established. The axial thrust acting on the impeller was simulated by using the low Reynolds number k-ε turbulence model and the SIMPLEC algorithm of the FLUENT software, with considering the impact of leakage, compressible and viscosity of the gas. The change of the axial thrust and leakage at different gap of labyrinth seal which cased by mechanical wear was predicted, and the results show that with the size increases, the axial thrust of the impeller clearance decreases gradually and leakage of impeller side gap is increase rapidly. At the same time the correlation of the grid is researched, and the result of numerical simulation has nothing to do with the grid density, and comparing the simulation results with the results calculated by the empirical method. The origin which makes the different result is found.In order to solve the stress distribution on impellers, the velocity distribution on axial direction and the size of the gap leakage,the axial-thrust of turbo-expander change with the different seal chamber of the impellers side gap was studied,meanwhile, the axial-thrust of different seal chamber were compared. The axial force change with straight seal was studied, and comparing the different sealing, the change of impellers clearance side leakage and the axial-thrust. In the end the reason which make the leakage and axial-thrust different are analysis, and point a way to improve the efficiency of the turbo-expander.