Definition Of Flow

Flow Measurement Introduced by : Ammar Wahid Khbab Hussain

Supervised by : Dr. Zaid Abu Ghnam

Date : 3 / 3 / 2015IntroductionThe measurement of fluid flow is important in applications ranging from measurements of blood-flow rates in a human artery to the measurement of the flow of liquid oxygen in a rocket.Many research projects and industrial processes depend on a measurement of fluid flow to furnish important data for analysis.For many industrial operations the accuracy of a fluid-flow measurement is directly related to profit (i.e. gasoline station or water meter at home ) It is easy to see how a small error in flow measurement on a large natural gas or oil pipeline could make a difference of thousands of dollars over a period of time.What is flowmeter ?

Aflow meteris a device used to measure the flow rate or quantity of agasor liquid in a pipe. Flow measurement applications are very diverse; consider these examples: water flow through an open channel, hydraulic valve leakage, fuel measurement through a fuel injector, or respiratory flow through a peak expiratory flow meter.Selecting a Flow Meter

There are no universal flow meters which are suitable for all applications. Selecting the proper technology for your application requires writing a flow specification which covers the use of the meter. There are usuallytrade-offs with each meter type, so knowing the critical specifications will be important.

Things you must know :

What Gas or Liquid will be measured . Minimum and maximum flow rates. What are the accuracy requirements . The fluid temperature and viscosity. Fluid compatibility with the materials of construction. The maximum pressure at the location. What pressure drop is allowable . Will the meter be mounted in a hazardous location . Is the fluid flow continuous or intermittent . What type of output signal or readout do you need . Is the fluid clean . What is the minimum and maximum process temperature . what is the size of the pipe .

Units of flowFlow rate is expressed in both volume and mass units of varying sizes. Some commonly used terms are1 gallon per minute (gpm)= 231 cubic inches per minute (in3/min) = 63.09 cubic centimeters per second (cm3/s)

1 liter = 0.26417 gallon = 1000 cubic centimeters

1 cubic foot per minute (cfm, or ft3/min) = 0.028317 cubic meter per minute (m3/min) = 471.95 cubic centimeters per second (cm3/s)Flow Devices RotameterThe rotameter is a very commonly used flow-measurement device. The flow enters the bottom of the tapered vertical tube and causes the bob or float to move upward. The bob will rise to a point in the tube such that the drag forces are just balanced by the weight and buoyancy forces. The position of the bob in the tube is then taken as an indication of the flow rate. The device is sometimes called an area meter because the elevation of the bob is dependent on the annular area between it and the tapered glass tube.

Application :Volume flow measurement of liquids and gasesComponents : Vertical conical measuring tube . Mobile float .Balance of forces :Weight = Drag + Buoyancy

W and B = constant D = variable

The position of the float is a flow indicator .

Flow Devices Ultrasonic FlowmeterThe Doppler effect is the basis for operation of the ultrasonic flowmeter . A signal of known ultrasonic frequency is transmitted through the liquid. Solids, bubbles, or any discontinuity in the liquid will reflect the signal back to the receiving element. Because of the velocity of the liquid, there will be a frequency shift at the receiver which is proportional to velocity. Accuracies of about 5 percent of full scale may be achieved with the device. Most devices require that the liquid contain at least 25 parts per million (ppm) of particles or bubbles having diameters of 30 m or more. The price is quite high.

Flow Devices Electromagnetic Flowmeter The principle of operation for themagnetic flowmeteris based on the Faradays Law of Electromagnetic Induction.

An electrical current (I) is applied to a coil package inside theflowmeter.As a result, a magnetic field (B) is created across the metering pipe.

When aconductiveliquidflows through the magnetic field, a smallvoltage(u) is induced. This voltage is proportional to the velocity of the flow and is accurately measured by twostainless steelelectrodes mounted opposite each other inside the metering pipe. The two electrodes are connected to an advanced electronic input circuitry which processes the signal and in turn feeds it to the a microprocessor inside the electronics module. The microprocessor then calculates the volumetric flow and controls the various outputs on the terminal board.

Flow Devices Turbine FlowmeterTurbine flowmeters use the mechanicalenergyof the fluid to rotate a pinwheel (rotor) in the flow stream. Blades on the rotor are angled to transform energy from the flow stream into rotational energy. The rotor shaftspinson bearings. When the fluid moves faster, the rotor spins proportionally faster.Shaft rotation can be sensed mechanically or by detecting the movement of the blades. Blade movement is often detected magnetically, with each blade or embedded piece of metal generating a pulse. Turbine flowmeter sensors are typically located external to the flowing stream to avoid material of construction constraints that would result if wetted sensors were used. When the fluid moves faster,morepulses are generated. The transmitter processes the pulse signal to determine the flow of the fluid. Transmitters and sensing systems are available to sense flow in both the forward and reverse flow directions.