Weirs triangular-notch

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. 

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... 

For weirs with triangular notches, notches not fully covered by liquid (2,67) ... 

Pa-s (1 to 150 cP) and surface tension over the range of 0.03 to 0.07 N/m (30 to 70 dyn/cm). His equation predicts about an 8 percent increase in flow for a liquid of 0.1-Pa-s (100-cP) viscosity compared with water at 0.001 Pa s (1 cP) and about a 1 percent increase for a liquid with one-half of the surface tension of water. For fluids of moderate viscosity, Ranga Raju and Asawa [Proc. Am. Soc. Civ. Eng., J. Hydraul. Div., 103 (HY 10), 1227-1231 (1977)] find that the effect of viscosity and surface tension on the discharge flow rate for rectangular and triangular-notch ((j) = 45°) weirs can be neglected when... 

Weir distributors are prone to out-of-levelness more than any other distributor because the flow rate through a triangular notch is proportional to the liquid head raised to the power of 2.5 (flow rate through an orifice is only proportional to the liquid head raised to the 0.5 power). With weir distributors, an out-of-levelness of 1 or 2 in is sufficient to cause severe maldistribution (237, 436). One case was reported (436) in which a distributor in a 40-ft tower was installed to a level tolerance of Vie in to avoid this problem. Adjustable leveling screws are often provided and should always be specified with this distributor to enable an in situ level adjustment. The problem is most severe at low liquid rates and tumed-down conditions. 

Figure 6.7 Unique outlet weir designs, (a) Adjustable (b) swept back (c) rectangular notch (cl) Intermittent triangular notch (e) continuous triangular notch. (Parts a, and c toe from Henry Z. Kister, excerpted by special permission from Chemical Engineering, September 8,1980 copyright by McGraw-Hill, Inc., New York, NY 10020.)...

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...

Two triangular weirs are put in series in an open channel. The upstream weir has a notch of 60° while the downstream weir has a notch of 90°. If the head over the 90-degree notched weir is 0.5 m, what is the head over the 60-degree notched weir ... 

At low liquid loads, a liquid crest of Vi to V2 in may be difficult to achieve unless notched weirs (Fig. 6.7c to e) are used. Notches can be triangular or rectangular. The only notched weirs which are effective... 

Greve, F.W. (1932). Flow of water through circular, parabolic and triangular vertical notch-weirs. 

In many instances in process engineering and in agriculture, liquids are flowing in open channels rather than closed conduits. To measure the flow rates, weir devices are often used. A weir is a dam over which the liquid flows. The two main types of weirs are the rectangular weir and the triangular weir shown in Fig. 3.2-5. The liquid flows over the weir and the height /iq (weir head) in m is measured above the flat base or the notch as shown. This head should be measured at a distance of about 3/iq m upstream of the weir by a level or float gage. 

The flow over V-notched (triangular) weirs and rectangular weirs can be taken from the nomographs shown in Fig. 4.67. 

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