V-notch weirs

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...

Because the liquid flow is low also, K-in. v-notched weirs should be used to ensure uniform flow and level across the tray. The bottom of the notches should be 2.5 in. above the tray floor. 

Height of liquid crest over flat weir or measured from weir (straight or circular) or from bottom of notches (v-notch weir), in. 

Cross-sectional flow area in a V-notch weir... 

Equation 8.37 gives the volumetric flow rate Q through a V-notch weir when there is no friction in the system. 

V-notch weirs are particularly useful for measuring flow rates that vary considerably. 

Calculate the volumetric flow rate in m3/s through a V-notch weir when the height of liquid above the weir is 0.15 m given that the notch angle 6 = 20° and the discharge coefficient Cd - 0.62. 

Almost never take a person s word for the water recirculation rate. Check the number of pumps available and the number operational, read the pump plate, use pump curves, read the pump manual, measure using pitot tubes (measures the total pressure and hence indirectly the velocity), orifice plates, V-notch weirs, and distribution deck levels, or calculate based on amperage draw and the discharge pressure, to confirm the volume of water actually circulating in the system. 

Experimental values of Cd vary from 0.58 to 0.68 for water flowing over V-notch weirs with central angles varying from 10 to 90° [29, 30]. 

Lenz, Amo T., Viscosity and Surface Tension Effects on V-Notch Weir Coefficients, Trans. ASME 108 759-802, 1943. 

Example 3.4 A 90-degree V-notch weir has a head H of 0.5 m. What is the flow, Q, through the notch ... 

Triangle weirs—Weirs in which the cross-sectional area of flow where the flow passes through is in the form of a triangle, also called V-notch weirs. 

A suppressed weir is placed upstream of a V-notch weir in an open channel. The height and head over the weir of the upstream weir are 1 m and 0.2 m, respectively. Calculate the length of the suppressed weir if the head over the V-notch weir is 0.5 m ... 

Lenz, A. T. (1943). Viscosity and surface tension effects on V-notch weir coefficients. Trans. AICHE, 108, 759-820. 

Several distributor types are available trough, orifice-rise, and perforated pipe. Examples of these types are shown in Fig. 14-64. The trough distributor provides good distribution under widely varying flow rates of gas and liquid. The liquid may flow through simple V-notch weirs, or it may flow throu tubes that extend from the troughs to near the upper level of the packing. Some deposition of solids can be accommodated. 

Yamall, D.R. (1912). The V-notch weir method of measurement. Trans. ASME 34 1055-1072. Yamall, D.R. (1926). Accuracy of the V-notch weir method of measurement. Trans. ASME 48 939-964. 

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