{"id":2357,"date":"2020-04-02T08:01:55","date_gmt":"2020-04-02T08:01:55","guid":{"rendered":"https:\/\/seismicconsolidation.com\/?p=2357"},"modified":"2020-04-02T08:01:55","modified_gmt":"2020-04-02T08:01:55","slug":"to-study-flow-characteristics-through-parshall-flume","status":"publish","type":"post","link":"https:\/\/seismicconsolidation.com\/to-study-flow-characteristics-through-parshall-flume\/","title":{"rendered":"To study flow characteristics through Parshall flume"},"content":{"rendered":"

<\/a>To study flow characteristics through Parshall flume<\/h1>\n

<\/a>Objectives:<\/h2>\n
    \n
  1. To draw water surface profiles of flow through Parshall flume<\/li>\n
  2. To determine coefficient of discharge of Parshall flume<\/li>\n<\/ol>\n

    <\/a>Apparatus:<\/h2>\n
      \n
    1. S6 tilting flume<\/li>\n
    2. Point gauge<\/li>\n
    3. Parshall flume<\/li>\n<\/ol>\n

      <\/a>Related theory:<\/h2>\n

      <\/a>Parshall flume:<\/h3>\n

      The\u00a0Parshall flume<\/strong>\u00a0is an open channel flow metering device that was developed to measure the flow of sub critical waters and irrigation flows.<\/p>\n

      The Parshall flume is a fixed\u00a0hydraulic structure. It is used to measure\u00a0volumetric flow rate\u00a0in 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.<\/p>\n

      Under laboratory conditions Parshall flumes can be expected to exhibit accuracies to within +\/-2%, although field conditions make accuracies better than 5% doubtful.<\/p>\n

      \"\"<\/p>\n

      Figure: Parshall flume<\/p>\n

      <\/a>Difference between Venturi flume and Parshall flume:<\/h3>\n

      Beginning in 1915, Dr. Ralph Parshall of the U.S. Soil Conservation Service altered the subcritical\u00a0Venturi flume\u00a0to 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.<\/p>\n

      Modifications to the Venturi flume that Parshall made include:<\/p>\n

        \n
      1. Decreasing the angle of convergence of the inlet walls<\/li>\n
      2. Lengthening the throat<\/li>\n
      3. Decreasing the angle of divergence of the outlet wall<\/li>\n
      4. Introducing a drop through the throat of the flume<\/li>\n<\/ol>\n

        \"\"<\/p>\n

        Parshall Flume\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Venturi Flume<\/p>\n

        <\/a>Function of different parts:<\/h3>\n

        The Parshall Flume acts essentially as a constriction, a downward step, and then an expansion: the upstream section is uniformly converging and flat, the throat is a short parallel section that slopes downward, and the downstream section is uniformly diverging and slopes upward to an ending elevation that is less than the upstream starting elevation. The width of the throat determines the flume size; 22 standardized sizes have been developed, ranging from 1 in. to 50\u00a0ft. (0.005 ft3<\/sup>\/s to 3,280 ft3<\/sup>\/s).<\/p>\n

        <\/a>Free and submerged flow conditions:<\/h3>\n

        There are two conditions of flow that can occur in a Parshall Flume: free flow and submerged flow.<\/p>\n

        When free flow conditions exist, the user only needs to collect one head measurement (Ha<\/sub>, the primary point of measurement) to determine the discharge. For submerged flow a secondary head measurement (Hb<\/sub>) is required to determine the flume is submerged and the degree of submergence.<\/p>\n

        The primary point of measurement (Ha<\/sub>) is located in the inlet of the flume, two-thirds of the length of the converging section from the flume crest. The secondary point of measurement (Hb<\/sub>) is located in the throat of the flume.<\/p>\n

        A hydraulic jump occurs downstream of the flume for free flow conditions. As the flume becomes submerged, the hydraulic jump diminishes and ultimately disappears as the downstream conditions increasingly restrict the flow out of the flume.<\/p>\n

        The free-flow discharge can be summarized as<\/p>\n

        \"\"<\/p>\n

        Where,<\/p>\n

        Q<\/em>\u00a0is flow rate<\/p>\n

        H<\/em>a<\/sub><\/em>\u00a0is the head at the primary point of measurement<\/p>\n

        <\/a>Construction<\/h3>\n

        A wide variety of materials are used to make Parshall flumes, including<\/p>\n

          \n
        1. Fiberglass (wastewater applications due to its corrosion resistance)<\/li>\n
        2. Stainless steel (applications involving high temperatures \/ corrosive flow streams)<\/li>\n
        3. Galvanized steel (water rights \/ irrigation)<\/li>\n
        4. Concrete (large Parshall throat widths 144″ [3.66 m] and above)<\/li>\n
        5. Aluminum (portable applications)<\/li>\n
        6. Wood (temporary flow measurement)<\/li>\n
        7. Plastic (PVC or polycarbonate \/ Lexan) (teaching\/laboratory investigation)<\/li>\n<\/ol>\n

          <\/a>Installation<\/h3>\n

          Dr. Parshall’s initial focus was for the use of his namesake flume to measure flows in irrigation channels and other surface waters.<\/p>\n

          Over time, however, the Parshall flume has proven to be applicable to a wide variety of open channel flows including:<\/p>\n