Flow Part2

7/31/2019 Flow Part2

1/24

FLOW MEASUREMENT

Positive Displacement Meter

Nutatin Disc

Oval gear type

Helix type.


2/24

Positive Displacement Flowmeter

Measures the volume of fluid passing

through the flowmeter

This achieved by repeatedly filling a bucketwith fluid before dumping the contents

downstream.

Number of times that the bucket is filled and

emptied is indicative of the flow through the

flow meter


3/24


4/24

Nutating Disc

also known as disk meter, is used extensively

for residential water service.

The moving assembly, which separates thefluid into increments consists of an assembly

of a radially slotted disk with an integral ball

bearing and an axial pin.


5/24

Nutating Disc


6/24

Nutating Disc

Metering chamber divided into four volumes,

two above the disk on the inlet side and two

e ow e s on e ou e s e. Pressure drop from inlet to outlet causes the

disk to wobble or nutate,

For each cycle to display a volume equal to

the volume of the metering chamber minus

the volume of the disk assembly.


7/24

Nutating Disc

The end of the axial pin, which moves in a

circular motion, drives a cam that is connected

o a gear ra n an e o a z ng reg s er. Inaccuracy : 1 to 2%.

Temperature range : 150 to 120C.

Max working pressure : 10 kg/cm2.


8/24

Oval Gear Type

A special variety of the rotating tube flow

meter is the oval geared metering elements.

These oval-geared meters are generally usedon very low viscous liquid, which is difficult

to measure using other flow meters.

A precise volume of liquid is captured by the

gap formed between housing and the gear


9/24

Oval Gear Type


10/24

Oval Gear Type

In position A, uniform forces are applied equallyon the top and bottom of oval gear B, so that theear does not rotate.

Rotor A has entrapped a known volume of liquidbetween the rotor and the meter body, and there isa balanced force on the bottom of the gear.

However, there is a force on the bottom of gear A,causing it to rotate clockwise (CW). This causesgear B to rotate in a counter clock wise (CCW)

direction to position B.


11/24

Oval Gear Type

In position B, fluid enters the space between

gear B and the meter body, as the fluid that was

en rappe e ween gear an e o ysimultaneously leave the area of entrapment.

The higher upstream pressure oppose the lower

downstream pressure at the ends of gear A andgear B, which makes gear A and gear B

continue to rotate in CW and CCW directions

respectively, to position C.


12/24

Oval Gear Type

In position C, a known amount of fluid has been

entrapped between gear B and the meter body.

This operation is then repeated, with eachrevolution of the gears representing the passage

of four times the amount of fluid that fills the

space between the gear and the meter body. Therefore, the fluid flow is directly proportional

to the rotational velocity of the gears.


13/24

Oval Gear Type

If slippage between the oval-gears and the housingis small, and the flow rate and viscosity are high,these flow meters can rovide hi h accuracies.

(0.1%). These flow meters are available in the sizes

suitable for 6 mm to 400 mm diameters pipelines.

Their materials of construction include brass,carbon steel, and 316 stainless steel.

Operating pressures are available up to 100

kg/cm2 and temperatures up to 300C.


14/24

Helix Type Flow Meters

Utilizes two uniquely nested, radically pitched

helical rotors as the measuring elements.

Close machining tolerances ensure minimumslippage and thus high accuracy.


15/24

Rotameter

In this meter, a weighted float or plummet

contained in an upright tapered tube, is lifted to

e pos on o equ r um e ween edownward force of the plummet and the upward

force of the fluid in addition to the buoyancy

effect of the fluid flowing past the float throughthe annular orifice.

The flow rate can be read by observing the

position of the float.


16/24

Rotameter


17/24

Rotameter - Theory

Consists of a tapered metering tube and a floatwhich is free to move up and down within the

.

The metering tube is mounted vertically with the

small end at the bottom.

The fluid to be measured enters at the bottom ofthe tube, passes upward around the float, and

out at the top.


18/24

Rotameter - Theory

When there is no flow through the meter, the

float rests at the bottom of the metering tube

w ere e max mum ame er o e oa sapproximately the same as the bore of the tube.

When fluid enters the metering tube, the

buoyant effect of the fluid lightens the float, butit has a greater density than the liquid and the

buoyant effect is not sufficient to raise it.


19/24

Rotameter - Theory

There is a small annular opening between the float andthe tube.

The pressure drop across the float increases and raises the

the upward hydraulic forces acting on it are balanced byits weight less buoyant force.

The metering float is floating in the fluid stream.

The float moves up and down in the tube in proportion tothe fluid flow rate and the annular area between the floatand the tube.

It reaches a stable position in the tube when the forces are

in equilibrium.


20/24

Rotameter - Theory

With upward movement of the float towards thelarger end of the tapered tube, the annularopening between the tube and the float

increases. As the area increases, the pressure differential

across the float decreases.

The float assumes a position, in dynamicequilibrium, when the pressure differentialacross the float plus the buoyancy effect

balances the weight of the float.


21/24

Rotameter - Theory

Any further increase in flow rate causes the float torise higher in the tube ; a decrease in flow causesthe float to dro at a lower osition.

Every float position corresponds to one particularflow rate and no other for a fluid of a given densityand viscosity.

It is merely necessary to provide a reading orcalibration scale on the tube and flow rate can bedetermined by direct observation of the position of

the float in the metering tube.


22/24

Rotameter - Theory

According to Bernoullis Theorem


23/24

Rotameter - Theory


24/24

Rotameter - Theory

Flow Part2

Documents