dp flowmeter 36[1]

8/3/2019 DP FLOWMETER 36[1]

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Presented by

2007-CHEM-36

ABDUR REHMAN

DIFFERNETIAL PRESSURE

FLOWMETERS


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Outline INTRODUCTION WORKING PRINCIPLE

PARTS OF DP FLOWMETERS

TYPES OF DP FLOWMETERS

ADVANTAGES & DISADVANTAGES

CONCLUSION

PrDIFFERNETIAL PRESSURE FLOWMETERSMeasurement

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Introduction:

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The use of differential pressure as an inferred measurement of a liquid's rateof flow is well known. Differential pressure flowmeters are, by far, the mostcommon units in use today. Estimates are that over 50 percent of all liquidflow measurement applications use this type of technology.



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Principle of Operation:

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Differential pressure flow meters incorporate some type of restriction thatgenerates a pressure difference across the sensor and finally gives theflowrate(volumetric).

Bernoullis equation states that pressure drop across the construction is

directly proportional to the square of the flow rate

WORKING PRINCIPLE


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Bernoullis equation states that energy is approximately conserved across

a constriction in a pipe

Static energy (pressure head)

Kinetic energy (velocity head)

Potential energy (elevation head)

Apply Bernoullis equation upstream and downstream of a restriction:

Acceleration of gravity is constant

No elevation change

TYPES OF DP FLOWMETERSMeasurement

WORKING PRINCIPLE


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Parts of Differential Pressure Flowmeters:

A differential pressure flow meter basically consists of two basiccomponents:

Primary elements.

Secondary elements.

PARTS OF DP FLOWMETERSMeasurement


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Primary Element:

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The parts of the meter used to restrict the fluid flow in the pipe line inorder to produce the differential, are known as primary elements i.e.venturi tubes, orifice plates, flow nozzles , pitot tubes etc.

Primary Element



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Secondary Element:

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Secondary element is those which measures the differential pressureproduced by the primary elements and convert them to usable forces orsignals. Various secondary elements are manometers, bellow meters etc.

Secondary elements



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Types of Differential Pressure Flowmeters:

VENTURI METER

ORIFICE METER

PITOT TUBE FLOW NOZZLE

ELBOW METER

DALL TUBES

V-CONE



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Cylindrical section:Cylindrical throat which provides for the low

pressure tap location of the decreased pressure ,in an area where flowvelocity neither increasing nor decreasing.

Divergent section:

Diverging recovery cone in which the velocitydecreases and the decreased velocity head is recovered in term ofpressure head.

TYPES OF DP FLOWMETERS(Veturi meter)Measurement


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Advantages:

It causes low permanent pressure loss.

It is widely used for high flow rates.

It is available in very large pipe sizes.

It has well-known characteristics.

It is more accurate over wide flow ranges than orifice plates or

nozzles. It can be used at low and high beta ratios.

Disadvantages:

Its cost is high.

It is generally not useful below 76.2mm pipe size.

It is more difficult to inspect due to its construction.

It has the limitation of a lower Reynolds number of 150,000.

TYPES OF DP FLOWMETERS(Venturi meter)Measurement


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ORIFICE METER:

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Orifice meter consist of orifice plate, is simply a flat piece of metal with aspecific-sized hole bored in it.

There are four types of orifice plates which are listed below:

Segmental orifice plate

Eccentric orifice plate

Quadrant edge orifice plate

Concentric orifice plate



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ADVANTAGES:

Its cost is low. They can be used in a wide range of pipe sizes (3.175 to

18211.8mm).

They can be used with the differential pressure devices.

They are well known and have predictable characteristics.

They are available in any material.

DISADVANTAGES:

They cause relatively high permanent pressure loss.

They tend to clog, thus reducing use in slurry services.

Their accuracy depends upon care during installation.

They have changing characteristics because of erosion, corrosionand scaling.

TYPES OF DP FLOWMETERS(Orifice meter)Measurement

M


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PITOT TUBE:

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It consists of a tube with an opening at the end. The small hole in the endis positioned such that it faces the flowing fluid. The velocity of the fluid atthe opening of the tube decreases to zero (Stagnation point).

Stagnation Pressure = Static Pressure + Dynamic Pressure


S O O S( i )M


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ADVANTAGES:

These tubes have no process loss. They are economical to install.

Some types can be easily removed from the pipeline.

DISADVANTAGES:

These tubes have poor accuracy.

They are unsuitable for dirty and sticky fluids.

They are sensitive to upstream disturbances.

TYPES OF DP FLOWMETERS(Pitot tube)Measurement

TYPES OF DP FLOWMETERSM t


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FLOW NOZZLE:

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A flow nozzle meter consists of a short nozzle, with a smooth guidedentry and a sharp exit is placed in the pipe to change the flow field andcreate a pressure drop that is used to calculate the flow velocity.

frictional loss in a flow nozzle meter is much less than in an orificemeter, but higher than in a venturi meter.


TYPES OF DP FLOWMETERS(Fl l t )M t


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ADVANTAGES:

Permanent pressure loss is lower than orifice plate.

It is available in numerous materials.

It is useful for fluids containing solids.

It is widely accepted for high temperature and pressure steam flow.

DISADVANTAGES:

Its cost is higher than orifice plate.

It is limited to moderate pipe sizes.

It requires more maintenance.

TYPES OF DP FLOWMETERS(Flow nozzle meter)Measurement

TYPES OF DP FLOWMETERSM t


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ELBOW METERS:

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Elbow meters operate on the principle that when liquid travels in a circularpath, centrifugal force is exerted along the outer edges.

when liquid flows through a pipe elbow, the force on the elbow's interiorsurface is proportional to the density of the liquid times the square of itsvelocity inversely proportional to the elbow's radius.


TYPES OF DP FLOWMETERS(Elb t )Measurement


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ADVANTAGES:

Elbow meters are easy to add in existing installation where elbow

exist.

It cost comparatively low.

It allows no additional pressure loss.

With the elbow taps there are no obstruction in the line.

It has good repeatability.

DISADVANTAGES:

Its accuracy is poor.

Differential pressure developed is relatively small.

TYPES OF DP FLOWMETERS(Elbow meter)Measurement



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DALL TUBES:

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The Dall tube is a shortened version of a Venturi meter, with a lowerpressure drop than an orifice plate. Dall tube produces muchhigher(two times) differential pressure as compare to venturi meter.

Inlet shoulder:

The tube consist of a short, straight inlet section followedby an abrupt decrease in the diameter of the tube.

Converging diverging section:

A converging(flow area decreases) and

diverging section (flow area increases) is attached by a slot or gap.Where the low pressure measures.


TYPES OF DP FLOWMETERS(Dall t be meter)Measurement


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ADVANTAGES:

Very low permanent pressure drop - energy savings.

Easy to install - short overall lengths.

Accurate flow metering of clean gases, liquid and steam.

Negligible wear and erosion therefore require lessmaintenance/inspection

DISADVANTAGES:

Its pressure difference is sensitive to up stream disturbance.

It is not considered for the measuring hot feed water. Not suited for fluids having suspended solids.

TYPES OF DP FLOWMETERS(Dall tube meter)Measurement



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Relative Comparison & Conclusion:

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As the %opening(Primary element) increases the

permanent pressure drop decreases.

At same % opening, the relative pressure drops

Orifice plate > Flow Nozzle > Venturi meter.

More accurate flow measurement is carried out

at the expense of more pressure drop.



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Questions.!!!


Pr


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THANK YOU

Pr

dp flowmeter 36[1]

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