prressure measurement
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Pressure MeasurementTRANSCRIPT
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?