Analysis of Profile and Unsteady Flow Performance of Variable Base Circle Radius Scroll Expander

To study the complex internal flow field variation and output characteristics of a variable base radius scroll expander,this paper uses dynamic mesh techniques and computational fluid dynamics(CFD)methods to perform transient numerical simulations of a variable base radius scroll expander.Analysis of the flow field in the working cavity of a variable base radius scroll expander at different spindle angles and the effect of different profiles,speeds and pressures on the output characteristics of the scroll expander.The results of the study show that due to the periodic blocking of the inlet by the orbiting scroll,the fluid hits the internal walls of the expander at different flow rates,with excessive mechanical losses,resulting in an uneven distribution of the internal flow field.At the same temperature,pressure and scroll plate diameter,the variable base radius scroll expander increases the output torque by 0.046 N·m,the output power by 9.634 W and the isentropic efficiency by 3.8%compared to the fixed base circle scroll expander.As the speed is inversely proportional to the output torque,the isentropic efficiency of the expander tends to increase and then decrease as the speed increases.The density of the fluid is directly proportional to the pressure over a range of pressures.As the pressure increases from 0.6 to 0.9 Mpa,the average mass flow rate and isentropic efficiency increase by 0.02357 kg/s,and 6.61%,respectively.

On the mechanical aspect of additive manufactured polyether-ether-ketone scaffold for repair of large bone defects

Polyether-ether-ketone(PEEK)is widely used in producing prosthesis and have gained great attention for repair of large bone defect in recent years with the development of additive manufacturing.This is due to its excellent biocompatibility,good heat and chemical stability and similar mechanical properties which mimics natural bone.In this study,three replicates of rectilinear scaffolds were designed for compression,tension,three-point bending and torsion test with unit cell size of 0.8 mm,a pore size of 0.4 mm,strut thickness of 0.4 mm and nominal porosity of 50%.Stress-strain graphs were developed from experimental and finite element analysis models.Experimental Young’s modulus and yield strength of the scaffolds were measured from the slop of the stress-strain graph to be 395 and 19.50 MPa respectively for compression,427 and 6.96 MPa respectively for tension,257 and 25.30 MPa respectively for three-point bending and 231 and 12.83 MPa respectively for torsion test.The finite element model was found to be in good agreement with the experimental results.Ductile fracture of the struct subjected to tensile strain was the main failure mode of the PEEK scaffold,which stems from the low crystallinity of additive manufacturing PEEK.The mechanical properties of porous PEEK are close to those of cancellous bone and thus are expected to be used in additive manufacturing PEEK bone implants in the future,but the lower yield strength poses a design challenge.