Research On Accuracy Of Twin-screw Flowmeter Under Various Working Condition

Twin-screw flowmeter is one of the positive displacement flowmeter,which derived from cycloidal tri-screw engagement,with features including simple structure,small size,low weight,high turn-down and high accuracy.By compared with other type of positive displacement flowmeter,discovered that twin-screw flowmeter is distinctive with low flow pulsation,high flow stability,requirement for purity of measured fluid and high level accuracy of machining and installation,and lower maximum working pressure.Twin-screw flowmeter was widely applied in all walks of life,and contributed prominently to study of hydraulic elements and systems,experiment,operation,and control of hydraulic systems.This thesis,which based on a type of twin-screw flowmeter and combined theoretical calculation and simulation,calculated the accuracy of this flowmeter under different flowrate and viscosity of measured fluid and effect on accuracy influenced by various condition,and offered theoretical basis and foundation for modification and further research.The main contents of this paper are as follows:(1)Elaborated different types flowmeter and standard to evaluate performance of flowmeter,compared positive displacement flowmeters and screw engagements in different types,explained working theory of twin-screw flowmeter and factors influenced accuracy in detail,made an overview about general research status both in overseas and domestic,summarized main research content and method.(2)Deduced profile equations of screws based on process of cycloid generation,sealing requirements,conjugate theory,and measured data.The profile connection,circle-cycloid-circle,was found.(3)Deduced equation about flowrate and screw rotating speed by calculating flow area of twin-screw flowmeter.Analyzed axial force and viscous friction torque on screw,and deduced pressure drop equation by the relation between power loss and pressure drop of measured fluid.Then calculated theoretical formula of clearance leakage on the basis of pressure drop equation and basic flow in fluid dynamics.Analyzed factors that impact accuracy of twin-screw flowmeter using numerical analysis in MATLAB.(4)Simulated internal flow field of twin-screw flowmeter,which emphasized on variation of pressure and velocity.Then proposed modifications for promot ing measurement range of flowmeter according to results from simulation that operated under various flowrate and viscosity.