Fluid Engineering

8/13/2019 Fluid Engineering

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Fluid MechanicsSCB 233 4Pressure Measurement

GROUP MEMBERS:

FARHAN ARIF BIN AIYUB 54270212159

MUHAMMAD SAFWAN BIN AHMAD ZAKI 54270212313

MUHAMMAD ADDHAM BIN MOHD AINI 54270212011


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OVERVIEW

Introduction

What is Pressure?

Why measure Pressure?

Measuring Devices-Ultra Low Pressure Sensors

-Low Pressure Sensors

-Medium Pressure Sensors

-High Pressure Sensors

-Calibrating

-Elastic Deformation Sensors


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WHAT IS PRESSURE?

Pressure is a normal force exerted by a

fluid over a surface area

Absolute, Gage, Vacuum Pressure Static & Dynamic Pressure

Pa, Bar, atm, Psi


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WHY MEASURE PRESSURE?

Pressure negates the properties of a fluid:

-State, flow, forces

Quality and Safety of Operation:-Tire, compressors, etc

Pressure measurements is used in various

general, industry and research applications


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INDUSTRY APPLICATION

-Drilling Technology utilize pressure sensors

for real time downhole data transfer

-Weather forecasting-Medicine

-Aviation

-Pressure Vessels


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Sphygmomanometer Fluid Manometer


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>Ultra LowPressure Sensors


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Also known as Ultra High Vacuum (UHV)

Pressures below 100 nPa (10~9 torr)

Extreme conditions so require extensive measures to

ensure accuracy. Its include:-High Speed Pumps. No one single pump is capable of

operating from standard pressure to UHV so need several.

-SealsNeed special metal seals to prevent trace leakage.

-Extremely Clean.-Minimal Surface area

-Outgassing. Construction materials absorb other

chemicals.


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Uses for UHV generally revolve around research:

-X ray photoelectron spectroscopy (XPS)

~Analyze the composition, chemical and electrical state within

a material.

-Auger electron spectroscopy (AES)~Used to study surfaces for material sciences.

-Secondary ion mass spectrometry (SIMS)

~Measure the composition of thin films and solids.

-Thermal desorption spectroscopy (TPD)

~Measure adsorption binding energy.

-Angle resolved photoemission spectroscopy (ARPES)

~ Analyze the density and distribution of electrons.

-Particle accelerators

-Atomic Physics Experiments involving cold atoms


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THE MCLEOD GAUGE

Sensitive to condensed

vapors

Measures pressures for

0.0013 to 13.3 Pa Electronic vacuum

gauges are now more

common, but the McLeod

Gauge is often used to calibrate

them.

Absolute Pressure below 133 Pa

when using The Mcleod Gauge. Example of The McleodGauge


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PIRANI GAUGE

Measures thermal conductivity of a gas

Range of pressure is between 0.1 to 100 Pa

Schematic of Pirani gauge

Pirani gauge arrangement to compensate for

change in ambient temperature


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>Medium Pressure

SensorsBarometer

Manometer


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BAROMETER

One common application of the

manometer is the barometer

The barometer measures

atmospheric pressure This barometer uses a reference

gas separated from the

atmosphere by a liquid

If the atmospheric pressure

changes, the reference gas

expands/contracts

Static pressure gauge

Basic barometer


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MANOMETER

The manometer consists of a

tube filled with liquid of

known density.

A pressure difference across

the tube causes the liquid toshift position

The change in position can be

measured to give the pressure

Best suited to static pressuremeasurement

Difficult to use for small

pressure changes, unsuitable

for very large pressures

Basic manometer


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MANOMETER TOPOLOGIES


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Cont


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>High Pressure

SensorsBourdon-tube Gauge

Schrader Gauge


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BOURDON-TUBE GAUGE

Invented by Eugene

Bourdon in 1849

Can be used to measure

pressures up to 100,000 psi Uses an elastic tube as

its primary element

The tube straightens out

with increasing pressure,

moving the pointer via

mechanical links

Measures static pressure

Commercial Bourdon tube gauge


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SCHRADER GAUGE

Uses a piston connected to a

spring

Simple & sturdy construction

Not particularly accurate Common use is in simple tyre

pressure gauges

Performs better than

bourdon-tube under dynamic

loads


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>Calibration ofPressure Sensors


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CALIBRATION

The most common way to calibrate pressure sensors is

with a dead-weight tester

Has accuracy in the 0.005% to 0.1% range

Allows pressure tests up to 10kBar (~145,000 psi)


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>Elastic Deformation

Sensors Bellow Gauges

Diaphragm Gauge

Piezoresistive Pressure Sensor

Linear Variable Differential transformer (LVDT)

pressure transducers

Bridgman Gauge


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Piezoresistive Pressure Sensor

Piezoresistive consist of a silicon

diaphragm with a semiconductor strain

gauge bonded to the diaphragm.

Advantages:

- High sensitivity

- Good linearity at constant temperature.


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LINEAR VARIABLE DIFFERENTIAL

TRANSFORMER (LVDT) PRESSURE

TRANSDUCERS

The motion of a diaphragm sensed by a Linear Variable

Differential Transformer or (LVDT).


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BRIDGMAN GAUGE

The wire is typically Manganin (84% Cu, 12%Mn, 4%Ni).

Resistance is less affected by temperature change.

Resistance can respond to variations in pressure in the

megahertz range.

The total resistance of the wire is about 100 and is

usually employed in a Wheatstone bridge.

Accuracy of 0.1%

Such gauges require frequent calibration.

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