|
A Parshall flume, the most recognized and commonly used flume today, is a fixed hydraulic structure developed to measure surface waters and irrigation flow. It is currently used to measure volumetric flow rate in industrial discharges, municipal sewer lines, and influent/effluent flows in wastewater treatment plants. The Parshall flume accelerates flow through a contraction of both the parallel sidewalls and a drop in the floor at the flume throat. Under free-flow conditions the depth of water at specified location upstream of the flume throat can be converted to a rate of flow. Some states specify the use of Parshall flumes, by law, for certain situations (commonly water rights).〔(【引用サイトリンク】title=USBR Water Measurement Manual - Chapter 8 - FLUMES, Section 10. Parshall Flumes )〕 The design of the Parshall flume is standardized under ASTM D1941, ISO 9826:1992, and JIS B7553-1993. The flumes are not patented and the discharge tables are not copyright protected. A total of 22 standard sizes of Parshall flumes have been developed, covering flow ranges from 0.005 cfs (l/s ) to 3,280 cfs (l/s ).〔(【引用サイトリンク】title=Parshall Flumes for Flow Measurement )〕 Submergence transitions for Parshall flumes range from 50% (1”-3” sizes) to 80% (10’-50’ sizes),〔(【引用サイトリンク】title=Flow Characteristics of Parshall Flumes )〕 beyond which point level measurements must be taken at both the primary and secondary points of measurement and a submergence correction must be applied to the flow equations. It is important to note that the secondary point of measurement (Hb) for a Parshall flume is located in the throat, measuring Hb can be difficult as flow in the throat of the flume is turbulent and prone to fluctuations in the water level. 90% is viewed as the upper limit for which corrections for submerged flow are practical.〔(【引用サイトリンク】title=Parshall Flume Submergence )〕 Under laboratory conditions Parshall flumes can be expected to exhibit accuracies to within +/-2%, although field conditions make accuracies better than 5% doubtful. == Development == Beginning in 1915, Dr. Ralph Parshall of the U.S. Soil Conservation Service altered the subcritical Venturi flume include a drop in elevation through the throat of the flume. This created a transition from subcritical flow conditions to supercritical flow conditions through the throat of the flume. Modifications to the Venturi flume that Parshall made include: *Decreasing the angle of convergence of the inlet walls *Lengthening the throat *Decreasing the angle of divergence of the outlet wall *Introducing a drop through the throat of the flume in 1930, the improved flume was named the Parshall Measuring Flume by the Irrigation Committee of the American Society of Civil Engineers (ASCE) in recognition of Parshall's accomplishments. Parshall was additionally honored as a Life Member of the ASCE. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Parshall flume」の詳細全文を読む スポンサード リンク
|