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EXPERIMENT 8: FLOW MEASURING DEVICES
Transcript of EXPERIMENT 8: FLOW MEASURING DEVICES
The apparatus is designed such a way that to measure flow rate using different type of flow measuring devices such as venturi meter, orifice and rotameter.
-Water enters venturi meter along the pipe until a certain distance.
-Then, it passes through the orifice plate meter.
-The flow continues till meets right-angled bend and flows into rotameter.
-The position of plummet in the rotameter is the measure of the flow rate.
1) To determine the flow rate using
Venturi meter, Orifice meter and
2) To compare these measuring devices to
3) To determine the head loss in venturi
meter, orifice, rotameter, diffuser and
Flow measuring devices, hydraulic bench and stop watch
Working Principle of Rotameter
1) The apparatus is connected to hydraulic bench and also pipe connections.
2) The valve is opened until the reading of the rotameter reaches 10mm.
3) After constant flow has been achieved, manometer readings are recorded and necessary calculations are tabulated.
4) The flow rate from the hydraulic bench is measured
5) Steps 2,3 and 4 are repeated for different sets of reading
MASS FLOW RATE
INLET KINETIC HEAD
To calculate mass flow rate of venturi meter
To calculate mass flow rate of orifice meter plate
- For Rotameter , refer from the rotameter calibration curve
-Hydraulic bench, ṁ = Volumetric flow rate x Water Density, where Water Density = 1000kg/m³
To calculate inlet kinetic head loss
Analysis of Result
-Flow measuring devices show a good accuracy when compared to hydraulic bench
-Comparing head loss:
Venturi meter < Orifice < Rotameter
-Comparing mass flow rate:
Orifice < Venturi < Rotameter
- no moving parts
- low head loss
- occupies space
- more expensive
- low cost
- easy to install
- high head loss
- prone to inaccuracies
-direct visual indication on a linear scale
-requires no power or fuel
- must always be vertically
- poor resolution (plummet
Working principle of Venturi Meter
Working Principle of Orifice
-the tube has a diverging cross sectional area
-pressure difference is created at top and bottom of plummet
-the plummet is pushed upwards by drag force
-the plummet is pushed downwards by gravity force
-pressure difference is created (at different cross-sectional area)
- Inlet CS-area > Throat CS-area
-Velocity at throat > Velocity at inlet
- Pressure at throat < Pressure at inlet
-thin plate with hole
-when fluid passes through, pressure builds up
-Pressure decreases as velocity increases when fluid forced through hole
-flow rate determined from pressure difference
To calculate actual flow rate, Q for Venturi meter
To calculate actual flow rate,Q for orifice meter
- Rotameter has high frictional force against the wall as well as the float
- Venturi meter has smallest head loss due to the gradual change in diamater of the structure
- Sudden change in diameter of orifice plate makes streamline difficult to change directions suddenly
-Venturi meter, orifice and rotameter shows good accuracy, hence they are used at their best.
-Venturi meter offers the best accuracy with least head loss
-Orifice is the easiest to install and takes almost no space
-Rotameter can be used for wide range of fluids including corrosive ones