The flow measurement means directly or indirectly measures the amount of liquid flowing per tidsenhert in a pipe or channel. Flowmeters often use different relationships that are based on the energy equation (Bernoulli’s equation) and the continuity equation. Various flowmeter methods are used for flow measurements in pipe flow and channel flow. Flow meters must live up to high standards.
Methods in pipe flow – flowmeters
Within the tube current, no, it is often difficult to measure the flow directly. Here it is easier to build an additional loss in a controlled manner, so you can easily measure the hydrostatic pressure difference which always occurs when the fluid passes through the measuring device. The decrease in the hydrostatic pressure corresponds to the by an increase in the hydrodynamic pressure plus the additional loss, so that the fluid medium speed and therefore the flow can be easily calculated. Often a manometervätska, to simplify the reading of the pressure difference.
Some common methods
- Piezo meter opening
- Pitot tubes
- Pitot piezometer
- Pipe knee
- Orificeplate
- Fluid Nozzle
- Venturi
Methods in channel flow
In the case flow measurements in the channel flow, are a number of different principles are available.
Measuring average speed
In the case of duct flow, the instantaneous rate is usually easily be determined. However, current filed rate varies greatly depending on where in the channel section which measurement takes place. The variations in both laterally and longitudinally. By measuring the various sections can be easily calculated average speed. Average speed can also be calculated by multiplying the measured hastighehen with a suitable coefficient. The flow is then obtained by multiplying the average speed of the cross sectional area.
Some common methods
- Hydrometical wing
- Pitot tubes
- Surface floater
Height difference in assaults and penstock
If it is possible to dam up the river, an assault tank installed. The free flow of assault barricade is a clear correlation between height of water above the threshold and flow. Samba the stock appearance depends entirely and hole in the barricade is constructed, ie the wet cross-sectional area varies with height.
If the sluice gates and other bottenutskov used, one can measure the height difference upstream and downstream damn doors. If the floodgates are completely under water, the wet cross-sectional area constant, so the flow will then be proportional to the square root of the height difference.
Some common methods
- Bottom outlet
- Monk
- Dip Tube
- Assault-tank
Determination section
In a controlling section is the actual water depth the same as the natural water depth. Thus also coincides the geometric case of the hydro-technical case. By measuring the geometric case, calculate the hydraulic radius, and setting an appropriate value of Mannings speech, the flow can be calculated by Manning formula.