measuring flow.ppt

7/28/2019 Measuring Flow.ppt

1/31

ACADs (08-006) Covered

Keywords

Flow rate, total flow, differential pressure, percent flow, cotameter,

Bernouli.

Description

Supporting Material

1.1.2.1 5.4.1.7


2/31

Terminal Objective: Given the appropriate equipment and procedures the

I&C Technician will calibrate and maintain flow instrumentation.

Mastery will be demonstrated by successful completion of a Lab

Performance Exercises and written Exam.

Measuring Flow


3/31

Differentiate between Flow Rate and Total Flow

Describe the relationship between differential

pressure and flow Given a percent range of DP sensed by an

orifice plate, calculate the percent flow

Describe the theory of operation of a given flow

measurement device Describe the considerations for

removing/restoring a rotameter from/to service


4/31

Flow Rate vs. Total Flow

Flow Rate is the amount of fluid, either in mass orvolume that passes a point in a given time.Examples: Pounds mass per hour, gallons per

minuteWe measure flow rate using ultrasonics, venturi, orifice

plates, etc.

Total Flow is the flow rate multiplied by anamount of time. It is the accumulated ortotalized flow. Result will be in either mass orvolume.Gas pumps and water meters measure total flow


5/31

Daniel Bernouli

Discovered the square rootrelationship between DP and flow

Bernoulli's Principle states that as the

speed of the fluid increases thepressure in the fluid decreases

Therefore, across a restriction in flow,as the fluid velocity increases,

pressure decreases http://home.earthlink.net/~mmc191

9/venturi.html
http://home.earthlink.net/~mmc1919/venturi.htmlhttp://home.earthlink.net/~mmc1919/venturi.htmlhttp://home.earthlink.net/~mmc1919/venturi.htmlhttp://home.earthlink.net/~mmc1919/venturi.html


6/31

pressureialDifferrent%% Flow

PressuralDifferenti%Flow% 2

-or-


7/31

Flow Instruments

Flow


8/31

Example 1

Pressure drop range: 0-100 in H2O

Flow: 0 to 100 GPM

Currently reading 25 in H2O What is the flow?


9/31

Example 2

Pressure drop range: 0-100 in H2O

Flow: 0 to 1000 GPM

Currently flow is 80 GPM

What is the differential pressure?

What devices may be used for the square rootfunction?


10/31


11/31


12/31

Discovered two centuries ago by Italian scientist

Giovanni

Battista Venturi (1746 - 1822).


13/31

Venturi Tube


14/31

Flow Nozzle


15/31

Elbow

Tap


16/31

Henri de Pitot (1695-1771)


17/31

Annubar


18/31

When flow exists,

there is a constant differential pressure across the float

Rotameter


19/31

Replacing a Rotameter

Isolate the instrument

Drain

Verify correct replacement

part

Install

Verify pressure tight

Un-isolate slowly to

prevent slamming the float

In service leak check


20/31

Flow Instruments: DP Cell


21/31


22/31


23/31

Ultrasonic Flow Measurement Devices

Examples: Controlotron, UFM


24/31

Coriolis

Offer direct mass flow, volume flow, density,

and temperature measurement of liquids,

gases, and slurries

No moving parts

Mass flow rate causes the vibrating tubes to

twist

The twist of the tubes is proportional to mass

flowWatch the Coriolis Flow video-10 min


25/31

Electromagnetic Flow

Measurement

Faradays Law


26/31


27/31

Flowmeter Pressure Loss

Typical

Accuracy

Required upstream pipe

diameters

Relative

cost

Orifice Medium 2 to 4 10 to 30 Low

Venturi tube Low 1 of full scale 5 to 20 Medium

Flow nozzle Medium 1 to 2 10 to 30 Medium

Pitot tube Very low 3 to 5 20 to 30 Low

Elbow meter Very low 5 to 10 30 Low

Positive Displacement High 0.5 of rate None Medium

Turbine High 0.25 of rate 5 to 10 High

Vortex Medium 1 of rate 10 to 20 High

Electromagnetic None 0.5 of rate 5 High

Ultrasonic (Doppler) None 5 of full scale 5 to 30 High

Ultrasonic (Time of Travel) None 1 to 5 5 to 30 High

Mass (Coriolis) Low 0.4 of rate None High


28/31

Other methods of measuring flow

Rotary Vane Positive Displacement-turbine

Nutating Disk or piston

Hot wire method, temperature method

Pelton Wheel Vortex shedding

Calorimetric method

Open Channels

Weirs

Target meter


29/31

Read OE18368 at end of Flow

section in handout.

Discuss: What happened?

Could it happen here? What can we

do to mitigate it?

Discuss control of test leads.


30/31

On toMeasuring Temperature


31/31

measuring flow.ppt

Documents