MEASUREMENT OF PRESSURE.

Shantilal shah engineering college. NAME:SARIYA ARTI ENROLL.NO: SUB:FLUID MECHANICS. BRANCH :CIVIL. SEM: 3 rd

Overview Pressure (P ) expresses the magnitude of normal force (F-N) per unit area (A-m 2 ) applied on a surface. Units: Pa(= N/m 2), psi(=lbf/in 2 ), bar (=10 5 Pa=100 kPa), mbar (=100 Pa=1 hPa), atm (=101.3 kPa), mmHg (or Torr), in Hg, etc. Note: For every Unit:=hectoUnit=100 Unit 3

Pressure Measuring Devices Bourdon Gage: Applications: tire pressure, pressure at the top or along the walls of tanks or vessels Principles: change in curvature of the tube is proportional to difference of pressure inside from that outside the tube

Where P abs : Absolute pressure P atm : Atmospheric pressure (standard is: kPa = psi=760 mmHg=29.92 in Hg) P gage : Gage pressure 5

Pressure Measuring Devices Strain Gage 6 Applications: Sensors for internal combustion engines, automotive, research etc. Principles: ∆ P  ∆ Resistance  ∆ Voltage

Pressure Measuring Devices Quartz Gage 7 Applications: measurements with high accuracy, good repeatability, high resolution. e g. Quartz Clock Principles: ∆ Pressure  ∆ Charge  ∆ Voltage Piezoelectric transducers

Pressure Measuring Devices U-tube Manometer 8 Air Water Manometer Mercury Water Manometer Applications: air pressure, pipe pressure, etc.

UT Manometer Applet 9

RELATIONSHIP BETWEEN PRESSURES: 1.ABSOLETE PRESSURE. 2.GAUGE PRESSURE. 3.VACUUM PRESSURE.

1.ABSOLUTE PRESSURE: It is defined as the pressure which is measured with reference to absolute vacuum pressure. Mathematically: absolute pressure=atmospheric pressure + gauge pressure.

2.GAUGE PRESSURE It is defined as the pressure which is measured with the help of a pressure measuring instrument in which the atmospheric pressure is taken as datum. The atmospheric pressure on the scale is marked as zero.

3.Vacuum pressure: It is defined as the pressure below the atmospheric pressure. Vacuum pressure=atmospheric pressure – absolute pressure.

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