V-notch gives more accurate results for low discharge coefficientcompared to rectangularnotch. This is due to the space for the water to flow through the notch . For rectangular notch, the space of water it is constant for every depth.
Why does the V notch give more accurate flow measurement than any other weirs and orifices when the flow is slightly fluctuating?
In this case, the notch is “V” in shape. Depth of water above the bottom of the V is called head (H). The V-notch design causes small changes in discharge hence causing a large change in depth and thus allowing more accurate measurement than with a rectangular notch.
Why is a V notch more efficient than a rectangular notch?
The basic principle is that discharge is directly related to the water depth above the bottom of the V- notch, this distance is called head. The V-notch design causes small changes in discharge to have a large change in depth allowing more accurate head measurement than with a rectangular notch.
What is the unique feature of the V notch so that it is preferred over other notches to measure the head over the notch?
V notch weirs really are just that – a thin plate weir with a ‘V’ notch cut into it . The weir is placed to obstruct open channel flow and allow water to flow over the notch. This enables us to accurately measure the flow, by measuring the head upstream of the V notch.
Why V notch is preferable over rectangular weir as a flow measuring device?
It is used to meter flow of water in the channel, by measuring the head of water over the v notch crest. The v notch weir is especially good for measuring a low flow rate , because the flow area decreases rapidly as the head over the v notch gets small.
What is the minimum distance is case of V notch?
The bottom of the “V” should be at least 1.5 ft. (45 cm) above the bottom of the upstream channel.
Why do we need weird ventilation?
A free nappe, which is ventilated to maintain atmospheric pressure below , does not come into contact with the underside of the weir. A depressed nappe is partially ventilated, which creates negative pressure beneath the nappe. ... Clinging nappes have no air beneath, and the stream flows along the face of the weir.
What are the advantages of V-notch?
What are the advantages of vee notch? Answer. Well a V-score gives better exact outcomes when contrasted with rectangular indent . A traingular indent gives more precise outcomes for low releases than a rectangular score.
Why do we use triangular notch?
The triangular-notch, thin-plate weir is a convenient, inexpensive, and relatively precise flow-measuring instrument. It is frequently used to measure the flow of water in laboratories and in small, natural streams.
What is calibration of V-notch?
As water approaches the notch, its surface becomes curved . Therefore, the head over the notch is to be measured at the upstream of the notch where the effect of curvature is minimum. Also, it should be close to the notch so that the loss of energy between head measuring section and notch is neglegible.
How do you calculate V-notch?
- Head H < 1.25 ft (38 cm).
- Width B > 3 ft (91 cm).
- Height P > 1.5 ft (46 cm).
- Ratio b/H ≥ 2.0.
- Head/width ratio H/B ≤ 0.2.
What are the applications of notches?
The applications of notch include tanks, reservoirs, or any water storage devices that have a passage for water escape . Similarly, a weir is a notch on a large scale used to measure flows of rivers and canals. Apart from measuring, notch and weir are also used to regulate the discharge of small and large channels.
What is Francis formula?
The Francis (1883) equation is convenient for weirs operating under favorable prescribed conditions. The Francis equation is: Q = 3.33h 1 3 / 2 (L-0.2h 1 ) (7-4)
What is the purpose of V-notch and rectangular weir?
To conserve delivery head and reduce head loss , the rectangular and wide V-notch weirs rated by Kindsvater methods should be selected. These weirs provide the capability to use shorter heights from the approach channel invert to the crest.
Where are V-notch weirs used?
Rectangular weirs and triangular or v-notch weirs are often used in water supply, wastewater and sewage systems . They consist of a sharp edged plate with a rectangular, triangular or v-notch profile for the water flow.
Why We Use weir in the channels?
Weirs allow water to be routed through a structure of known dimensions , permitting flow rates to be measured as a function of depth of flow through the structure. Thus, one of the simplest and most accurate methods of measuring water flow in open channels is by the use of weirs.
