Deformation Analysis Of Organic Fluid Scroll Expander Based On Muti-Field Coupling

Scroll expander is the positive-displacement expansion engine used to micro and small-scale organic Rankine cycle(ORC)waste heat recovery system,which combines the advantages of high efficiency,low noise,smooth operation,compact configuration,high reliability,and has the characteristics of small flow and high expansion ratio.This study was expected to provide the theory references for the design problems of a scroll expander used in waste heat recovery system of ORC of vehicle engine,by conducting the fluid-thermal-solid coupling numerical simulation to investigate the deformation characteristics and influence factors of the scroll pair.The main research contents and results are as follows:In accordance with the analysis of the fluid-thermal-solid interaction of the scroll expander in operating status,the fluid-thermal-solid coupling numerical simulation model of the scroll expander was constructed.The numerical model consists of two parts: the fluid mechanics model of internal unsteady flow and conjugate heat transfer,and the structural mechanics model of stress and deformation.The surface pressure and body temperature distributions of the mating scrolls is obtained by solving the 3D finite volume model of flow and heat transfer equations firstly,and then the calculated CFD results are coupled to the finite element model of the scrolls employing one-way coupling method for solving the stress-strain field and acquiring the displacement data of the scrolls.The influences of the flow field distributions of the scroll expander on the pressure and temperature loads of both scrolls were studied,and the effects of different loads on the deformation of the fixed and orbiting scroll were compared.The results show that the temperature along the trajectory of the scroll profiles decrease at first,but then increase,before the temperature finally shows a significant decaying trend rather than a steady decrease from the inside outwards.The distribution characteristics of the deformation under coupling action are similar to that of the thermal deformation,while the deformations induced by pressure loads have only a slight influence on the distribution characteristics of the total deformation and only change the values.The inertial force only increases the deformation of the orbiting scroll tail.The effects of different inlet temperature on the flow field in the working chambers and the deformation characteristics of the scroll members were studied.The results illustrate that the gap flow loss and the pressure difference of the adjacent working chambers increases with increasing the inlet temperature.The pressure of the back pressure chambers and the exhaust resistance decreases with decreasing the inlet temperature.In addition,the pressure and temperature distributions of the exhaust and back pressure chambers on both sides are more uniform as the inlet temperature increases.The deformation distributions of the scroll members under different inlet temperatures are similar.The thermal distortions of the fixed and orbiting scroll plate increase with the increase of the inlet temperature,and the pressure distortions have remained almost unchanged with the increase of the inlet temperature.The flow field distributions in the working chambers and the deformation characteristics of the scroll pair with different inlet pressure were compared.It is found that the increase of the inlet pressure increases the secondary flow losses,the exhaust resistance,the frictions between gas parcels and the temperature in the working chamber through a comparative analysis.Furthermore,raising the inlet pressure improves the heat transfer between the gas and the walls,and makes the temperature distributions of the fixed and orbiting scroll more uneven.The deformation distributions of the fixed and orbiting scroll plate show the similar tendency under different inlet pressure,and the magnitude of deformation has obvious positive correlation with the inlet pressure.A scroll expander of involute of circle with variable radii was proposed,which has the same basic geometric parameters as the expander with conventional scroll profile.Compared to the conventional scroll profile scroll expander,the involute of circle with variable radii scroll expander reduces the frictions of gas parcels and the mechanical energy loss,weakens the secondary flow losses in both sides of the back pressure chamber,and makes the pressure and temperature distributions of the exhaust chambers and the back pressure chambers more uniform.The involute of circle with variable radii scroll expander has the same working ability as the scroll expander with the conventional scroll profile.Furthermore,the involute of circle with variable radii scroll expander has the smaller space of the working chambers,the higher isentropic efficiency and the smaller deformation.