Design And Research Of Liquid Flow Standard Device Based On Weighing Method

As an indispensable part of measurement technology,flow measurement is directly related to the development of national economy,society and scientific research technology.This article focuses on the liquid flow standard device based on the weighing method.Taking micro-ml flow calibration of the wide-range syringe pump designed in the project as the starting point,it focuses on how to improve the accuracy and repeatability of the device’s verification.On the basis of completing the overall facility design,the factors affecting the performance of the liquid flow calibration facility were further studied.In order to reduce the impact on the accuracy of the device flow measurement,through the combination of optimization design and simulation of the device,and the simulation results obtained The device has been optimized and improved to reduce the uncertainty of the device and improve the accuracy of the device’s flow measurement.Following contents have been included in the article:(1)The determination of designing index,which is based on the flow verification of wide-range injection pump revised the weighing and regarded it as the fundamental method for the flow standard device in this project while designing the software and hardware of the liquid flow standard facility in a whole,which includes four major components,that is,vacuum degassing unit,stabilizing pressure unit,constant temperature system and weighing system,to design the pipeline of facility with the calculation of hydraulic loss in the pipeline.(2)Through the use of Fluent software for umerical simulation and analysis of the device’s diversion outlet model,three flow parameters are obtained based on th flow of the wide-range injection pump,and 0.05m/s,0.6m/s,and lm/s are applied to the diversion elbow.For the inlet velocity,the velocity distribution of the outlet of the diversion elbow is not uniformly symmetrical through the simulation results.The optimized diversion outlet model reduces the relative error caused by the uneven velocity distribution,and the error value is reduced.8%,and the improved diversion outlet model has a minimum optimization rate of 3%for the flow rate.(3)The simulating research was carried out by simulating the mass transition between the liquid and evaporation phase in the basis of CFD multiphase flow mixing model and user-defined function(UDF).The simulation results show that as the temperature of the liquid increases,the volume distribution of the vapor phase increases,the mixing rate of the gas and the liquid phase increases,and the area with a large evaporation rate is close to the side wall of the weighing vessel.The maximum evaporation rate of the container side wall can reach 0.31m/s.(4)The design of control system for flow rate standard facility and the construction of the hardware platform such as valve control and serial server configuration were completed.The user management,parameter setting,verification monitoring,database management and other system functions which are in basis of Lab View System development platform are developed,achieving the automatic verification process.The mathematical model for flow rate standard facility was established and utilized for evaluating the uncertainly of device with the value of 0.21%(k=2),meeting the designing standard.