【摘要】 排水取气,由于简单易行,在工作中得到了较为广泛的应用。本文通过理论分析和计算,推导出液面等速下降容器的曲线方程,介绍如何应用液面等速下降容器使变水头非稳定流变为变水头稳定流排水取气的工作原理,并通过试验装置加以验证,为排水取气的应用寻找了一条新的途径。更多还原

【Abstract】 Objective.When using the method of water-drainage-air-suction to calibrate meters,the volume of air sucked into container changes all the time because of the continuous water head-falling in either a cylindrical or a cylindroconical container.Evidently,both the speed of head-falling and water flowrate are the function of time.In order to get the steady flow,i.e.,liquid drained off with a constant speed head-falling and constant flow-rate,a new concept with a view to reforming the container shape is suggested based on hydraulics analysis and experiments.A quartic parabolic equation for designing container shape is derived aswhere r——radius of container at the head H calculated from outlet;μ----coefficient of flow;A——cross-sectional area of outletu——speed of head-falling.The curved surface of a container shaped according to this equation ensures the constant speed of head-falling but the air sucked into container or water flowrate,still changes with time.So,an interconnected vessel consisting of a paraboloidal container and a cylindrical container is designed and set up,shown as in Fig3.Thus,air is sucked in through an equal cross-sectional area and the volume of air being sucked keeps constant.With a constant speed of head-falling and constant air volume sucked,a steady flow can be obtained in watcr-drainage-air-suction.Correctness of this concent has been proved by tests.Using the simple device designed,an absolute volume is obtained in thermo-electric anemometer calibration with ease,stability and reliability. Fig.1 Water head in different container with relation to head-falling speed1-cylindrical 2-cylindroconicah 3-perfect,with constant speed of head-falling.Fig.2 A perfect container,its cross-sectional area is changing with water head.Fig.3 New concept of steady flow in water-drainage-air-suction process 1-air 2-cylindrical container 3-paraboloidal container.Fig.4 Practical device for constant speed head-falling and constant air volume suckedFig.5 Testing deviceFig.6 Correction curve of No.098 thermo-electric anemometerTab.1 Calibrated values of head-falling speedTab.2 Corrected values of QDF-2 thermo-electric anemometer更多还原