Weirs rectangular

Fully contracted rectangular weir—Rectangular weir where the flow in the channel being measnred contracts as it passes through the rectangular opening. 

Suppressed rectangular weir—Rectangular weir where the contraction is absent, that is, the contraction is suppressed. 

Fig. 10. Stream flow over (a) a broad-crested, rectangular weir (b) a cross-current view of the rectangular and CipoUetti weirs (c) a trape2oidal-notch or CipoUetti weir (d) a sharp-crested, triangular, or V-notch weir (e) a cross-current view of the V-notch and hyperboHc-notch weirs and ( a...

Measurement by Liquid Level. The flow rate of Hquids flowing in open channels is often measured by the use of weirs (see Liquid-LEVEL measurement). The most common type is the rectangular weir shown in Figure 22e. The flow rate across such a weir varies approximately with the quantity. Other shapes of weirs are also employed. Standard civil engineering handbooks describe the precautions necessary for constmcting and interpreting data from weirs. 

Liquid flow in an open channel may be metered by means of a weir, which consists of a dam over which, or through a notch in which, the liquid flows. The terms rectangular weir, triangular weir, etc., generally refer to the shape of the notch in a notched weir. AU weirs considered here have flat upstream faces that are perpendicular to the bed aud walls of the channel. 

For the flow of high-viscosity liquids over rectangular weirs, see Slocum, Can. ]. Chem. Eng., 42, 196-200 (1964). His correlation is based on data for liquids with viscosities in the range of 2.5 to 500 Pa s (25 to 5000 cP), in which range the discharge decreases markedly for a given head as viscosity is increased. 

Permanent head loss approximately 3-4% Ah. Rectangular Weir... 

Equations 8.27 and 8.28 give the volumetric flow rate Q through a rectangular weir when there is no friction in the system. 

In addition to rectangular weirs, V-notch or triangular weirs are commonly used with a cross-sectional flow area as shown in Figure 8.9. In... 

Flow measurement in open unpressurised channels is a requirement generally associated with waste water systems and sewers. The use of a weir or notch to measure the flow of a liquid presenting a free surface is described in Volume 1, Section 6.3.8. The flow through a rectangular notch (Fig. 6.7a) is given by (Volume 1, equation 6.42) ... 

Bubble-Cap Trays (Fig. 14-27a) These are flat perforated plates with risers (chimneylike pipes) around the holes, and caps in the form of inverted cups over the risers. The caps are usually (but not always) equipped with slots through which some of the gas comes out, and may be round or rectangular. Liquid and froth are trapped on the tray to a depth at least equal to the riser or weir height, giving the bubble-cap tray a unique ability to operate at very low gas and liquid rates. 

Weir with end contractions. When the length B of the crest of a rectangular weir is less than the width of the channel, there will be a lateral contraction of the nappe so that its width is less than B. It is believed that end contractions are a source of error, and so this type of weir is not considered so accurate as the preceding. Its chief virtue is that the approach channel need not be of uniform cross section or have smooth sides. 

When the width B of a rectangular weir is less than that of the channel, Francis concluded that the effect of each side contraction is to reduce the width of the nappe by 0.1H. The usual contracted weir will have a contraction at each side, but occasionally a weir is placed against one side wall, so that the contraction on one side is suppressed. If n = the number of contractions, which may be 2, 1, or 0, the Francis formula based on Eq. (10.74) is... 

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