Please enable JavaScript.
Coggle requires JavaScript to display documents.
FLOW MEASUREMENT AND MEASUREMENT OF LIQUID LEVEL - Coggle Diagram
FLOW MEASUREMENT AND MEASUREMENT OF LIQUID LEVEL
Introduction
Flow measurement
A technique used in any process requiring the transport of a material from one point to another.
Knowledge of the direction and velocity of flow. (Reynolds
Number, Bernoulli’s equation)
Types of flow: Laminar flow & Turbulent flow.
If Re < 2000 = laminar flow.
If Re > 4000 = turbulent flow.
If 2000<= Re <= 4000 = Critical zone between laminar & turbulent.
Bernoulli Equation
The conservation of
energy principle appropriate for flowing fluids.
Application
transportation of slurries material (cement)
compressed natural gas in pipelines
water and gas supply systems to domestic consumers
Elements that needs to consider during flow measurement:
a. Clean or dirty.
b. Wet or dry.
c. Hazardous/corrosive or safe.
d. laminar or turbulent.
e. Pressure (vacuum ~ high pressure)
f. Temperature.
g. Flow rate.
Flow measuring devices categories.
Primary devices (quantity meter)
Measure the amount of fluid in terms of mass or volume that
flows past a given point in a definite period of time.
The time required to collect a particular amount of fluid is determined accurately and the average flow rate can be evaluated.
Advantages: Simple, economic and extremely accurate.
Volumetric method.
The fluid flowing in the flowmeter, which being calibrated is diverted into a tank known as volume
When tank is completely filled, this known volume is compared with the integrated volumetric quantity
Gravimetric method.
The fluid flowing in the flowmeter, which being calibrated is diverted into a vessel.
The weight of the liquid collected is compared with the gravimetric quantity
Positive-displacement meters
Applied to a flow measuring device so that designed metered fluid is repeatedly filled and emptied from a space of known volume.
The liquid flows through a meter and moves the measuring element that seals the measuring chamber into a series of measuring compartments each holding a definite volume.
Widely used in low flow rate metering applications where high accuracy and repeatability under steady flow conditions are required.
Advantages: Easy to install/maintained and have moderate cost.
Secondary devices (rate meter)
This type of measurement instrument, they not measure the flow directly but instead measure another physical quantity which related to flow.
Flow rate meters
a. Variable head meters.
b. Variable area meters.
c. Variable head and variable area meters.
d. Constant head device.
Velocity meters
a. Variable head meter.
b. Target flow meter.
d. Turbine/propeller type meter.
e. Ultrasonic flow meter.
f. Hot wire/ hot film anemometer.
g. Laser Doppler Anemometer.
Pitot Tube
Commonly used variable head velocity measuring device.
Better know as the air-speed indicator used in aircrafts.
Advantages:
a. Simple n low cost.
b. No pressure loss in the flow system.
c. Easily inserted to a small hole.
d. Useful in checking the mean velocities.
Drawbacks:
a. Not suitable for measuring low velocities < 5 m/s
b. Sensitive to misalignment. 20° -> 2% error.
c. Not suitable for highly fluctuating velocities.
MEASUREMENT OF LIQUID LEVEL
To measure the quantity of liquid held in a container or vessel.
Direct method.
Method which the actual liquid level is directly indicated by a
simple mechanical type of device.
Dip-stick Method
Determining the liquid level by dipping a graduated rod in a
liquid.
Sight Glass Method
Determining the liquid level by a graduated glass tube mounted on the side of the liquid containing vessel for providing a visual indication of the liquid level.
Hook Gauge Method
Determining the liquid level in a large tank for accurate
measure of a very small changes.A small change in a large tank
would mean large volumetric changes.
Float Gauge Method
Determining the liquid level that always follow the varying
liquid level. The float usually used are hollow metal spheres,cylindrical ceramic float or disc shaped floats of synthetic
material.
Indirect method.
