| With the depletion of traditional energy and the aggravation of environmental pollution,countries all over the world have to focus on the use of existing energy while vigorously developing new energy and clean energy.Among them,the recovery and utilization of residual heat and pressure energy is an effective measure to improve energy efficiency and reduce energy costs.As a volumetric rotary machine,twin screw expander can be used to recover residual pressure and heat energy in fluid and convert it into mechanical energy.The twin-screw expander was originally developed to recover residual pressure and heat energy by reversal operation of the twin-screw compressor.Its design method mainly comes from the basic design theory of the screw compressor.Although they have some similarities,the expander modified by compressor can not fully adapt to the thermal performance of working medium,which greatly affects the operating efficiency and reliability of screw expander in high temperature and high pressure medium.Therefore,exploring the design theory of twin screw expander and studying its transient characteristics is an important research topic for researchers.In this paper,the performance of a 4/6-tooth twin-screw air expander is predicted by using the method of full-flow 3D computational fluid dynamics(CFD)and thermodynamics.The fluid domain model of twin-screw expander is constructed by SCORG software,and the high-quality dynamic mesh generation is carried out.The unstructured mesh generation of the inlet and outlet fluid domain is carried out by Pumplinx software.The unsteady calculation of the fluid domain model of twin-screw expander is carried out by Pumplinx software.The effects of unsteady working conditions and import structure on the performance and suction pressure fluctuation of the twin-screw expander are studied.The main work of this paper is as follows:(1)The research background and significance of the subject are discussed.The research status of screw expander at home and abroad is summarized in detail.The main research contents and research methods are determined.(2)The design method of twin-screw expander rotor profile and the calculation methods of various geometric characteristics are discussed in depth,including the calculation methods of tooth curve equation,conjugate curve equation of tooth curve,meshing line equation,calculation method of tooth area,area utilization coefficient,tooth volume,torsion angle coefficient and content area ratio.On this basis,the calculation method of the performance parameters,the structure and working principle of the twin screw expander are analyzed and studied.(3)A three-dimensional flow field model of twin screw expander is established by combining computational fluid dynamics with thermodynamics.SCORG and Pumplinx software are used to mesh the screw basin and the inlet and outlet basins respectively.A set of radial grid layers and the number of grid in the screw basin are determined by grid independence analysis.The unsteady flow field distribution and leakage of screw expander were studied by Pumplinx software.The periodic variation of flow rate,torque,axial force and radial force was analyzed.(4)The effects of different rotational speeds,inlet pressure and inlet angle on the internal flow field characteristics of twin screw expander were studied.The periodic variation law of radial force and axial force under various parameters is revealed.In this paper,CFD numerical simulation method is innovatively used to discuss the effect of adjusting speed on the performance parameters of screw expander,such as flow rate,power and efficiency,under the condition of unstable inlet flow.(5)Based on the results of unsteady numerical simulation for the first time,the causes of pressure fluctuation at the inlet of twin-screw expander and the variation law of pressure fluctuation are deeply studied.The influence laws of inlet pressure,rotating speed and inlet angle on suction pressure fluctuation are summarized,which provides a theoretical support for the structural optimization design at the inlet of twin-screw expander. |
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