GP313-PROCESS INSTRUMENTATION & CONTROL

PETROCHEMICAL ENGINEERING DEPARTMENT

PREPARED BY:MOHD TAUFIK REZZA BIN MOHD FOUDZIJun 2011

Pressure Measurement

Pressure

Type of Pressure Measurement

Evaluation

Hydrostatic Pressure

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BuoyancyMeasuring

Instruments

Applications

PRESSURE• Pressure units are a measure of force

acting over unit area.• It is most commonly expressed in

pounds per square inch (psi) or sometimes pounds per square foot (psf) in English units; or Pascals (Pa) in metric units, which is the force in Newtons per square meter (N/m²).

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Pressure = Force, F Area, A

Pressure = Force, F Area, A

Exercise2.1

HYDROSTATIC PRESSURE

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Which the vessels above have high pressure?

A B C

= Mass density of fluid in kilograms per cubic meter (metric) or slugs per cubic foot (British) =Weight density of fluid in Newton per cubic meter (metric) or pounds per cubic foot (British)

HYDROSTATIC PRESSURE

• A vertical column of fluid exerts a pressure due to the column’s weight.

• The relationship between column height and fluid pressure at the bottom of the column is constant for any particular fluid (density) regardless of vessel width or shape.

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Exercise2.2, 2.3

SPECIFIC WEIGHT TABLEFORWARD

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TYPE OF PRESSURE MEASUREMENT

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Absolute Pressure

Gauge Pressure

Atmosphere Pressure

Vacuum Pressure

PRESSURE CONVERSIONFORWARD

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Exercise2.5, Extra

BUOYANCY FORWARD

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•Buoyancy is the upward force exerted on an object immersed or floating in a liquid. •The weight is less than it is in air, due to the weight of the displaced fluid. The upward force on the object causes the weight loss, called the buoyant force, and is given by:

where B = The buoyant force in pounds y = The specific weight in pounds per cubic footV = the volume of the displaced liquid in cubic feet.

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BUOYANCY

Exercise2.6, 2.7

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PASCAL LAW

The pressure applied to an enclosed liquid (or gas) is transmitted to all parts of the fluid and to the walls of the container.

Exercise2.8

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Manometer

MEASURING INSTRUMENTS

Exercise2.9, 2.10

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Diaphragms, Capsules, and Bellows

MEASURING INSTRUMENTS

The devices that change their shape when pressure is applied.

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Capsules

MEASURING INSTRUMENTS

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Bellow

MEASURING INSTRUMENTS

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Bourdon Tube

MEASURING INSTRUMENTS

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Differential Pressure

Transmitter

MEASURING INSTRUMENTS

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Applications

Measuring process vessel clogging

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Applications

Measuring positive gauge pressure

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Applications

Measuring vacuum

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EXERCISE 2.1

The liquid in a container has a total weight of 152 kN, and the container has a 8.9 m² base. What is the pressure on the base?

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EXERCISE 2.2 & 2.3

What is the depth in a lake, if the pressure is 0.1 MPa?

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What is the pressure at the base of a water tower that has 35m of head?

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EXERCISE 2.5 & EXTRA

What pressure in psi corresponds to 98.5 kPa?

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The atmospheric pressure is 14.5 psi. If the absolute pressure is 2,865.6 psfa, what isthe gauge pressure?

What is the gauge pressure in (a) kPa, and (b) N/cm², at a distance 5.5 ft below thesurface of a column of water?

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EXERCISE 2.6 & 2.7

What is the buoyant force on a plastic cube with 2.5m sides, floating in water, if three-quarters of the block is submerged?

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What is the apparent weight of a 3.7m³ block of wood totally immersed in acetone? Assume the specific weight of wood is 8.5 kN/m³.

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EXERCISE 2.8

In figure below, if the area of the small piston AS is 8.2 in²,and the area of the large piston AL is 2.3 ft², what is the force FL on the large piston, if the force FS on the small piston is 25N?

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EXERCISE 2.9 & 2.10

The liquid in a manometer has a specific weight of 8.5 kN/m³. If the liquid rises 83 cm higher in the lower pressure leg, what is difference in the pressure between the higher and the lower legs?

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What is the liquid density in a manometer, if the difference in the liquid levels in the manometer tubes is 1.35m, and the differential pressure between the tubes is 7.85 kPa?