BREE301Introduction-2

Bourdon tube consists of a hollow metal tube bent

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Bourdon tube : Consists of a hollow metal tube bent like a hook whose end is closed and connected to a dial indicator needle. Pressure transducers : Use various techniques to convert the pressure effect to an electrical effect such as a change in voltage, resistance, or capacitance. Strain-gage pressure transducers: Work by having a diaphragm deflect between two chambers open to the pressure inputs. Piezoelectric transducers : Also called solid- state pressure transducers , work on the principle that an electric potential is generated in a crystalline substance when it is subjected to mechanical pressure.

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Barometer measurement p atm = p vapour + ρ m gL Atmospheric pressure is measured by a device called a barometer ; thus, the atmospheric pressure is often referred to as the barometric pressure . A frequently used pressure unit is the standard atmosphere , which is defined as the pressure produced by a column of mercury 760 mm in height at 0°C ( Hg = 13,595 kg/m 3 ) under standard gravitational acceleration ( g = 9.807 m/s 2 ). negligible
For example if a barometer reads 760 mm Hg, this represents in SI units: P atm = ρ gL

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Example Problem 1 Measuring pressure in a vessel with a U-tube manometer The fluid in the manometer is mercury ( ρ = 13.6 g cm -3 ). The reading on the manometer is 24 cm. Calculate the absolute pressure in the vessel.
P P atm Measurement of Pressure ρ 1 h 1 h 2 ρ 2 P = P atm + ρ 1 gh 1 + ρ 2 gh 2 P = P atm + P gage

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Example Problem 2 The figure here shows a tank within a tank each containing air. The absolute pressure in tank A is 267.7 kPa. Pressure gage A is located inside tank B and reads 140 kPa. The U- tube manometer connected to tank B contains mercury. Determine the absolute pressure inside tank B in kPa and the column length L in cm. The atmospheric pressure surrounding tank B is 101 kPa and g=9.81 m/s 2
Gauge pressure is zero referenced against ambient pressure, so it is equal to absolute pressure (measured) minus atmospheric pressure. P gauge A = P A - P B

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Example Problem 3 A piston/cylinder with cross-sectional area of 0.01 m 2 is connected with a hydraulic line to another piston cylinder of cross-sectional area of 0.05 m 2 . Assume both chambers and the line are filled with hydraulic fluid of 900 kg/m 3 density and the larger second cylinder is 6 m higher up in elevation. With an outside atmospheric pressure of 100 kPa and a net force of 25 kN on the smallest piston, what is the balancing force on the second larger piston?
Determine the total force in kN on the bottom of a 100×50m swimming pool. The depth of the pool varies linearly along its length from 1 m to 4 m. Also, determine the pressure on the floor at the center of the pool, in kPa. The atmospheric pressure is 0.98 bar, the density of the pool water is 998.2 kg/m 3 and the local acceleration of gravity is 9.8 m/s 2 . Example Problem 4