Practical Pressure Measurement Fluid.pptx

Pressure Measurement Fluid Mechanics

1. 1 Definition of Pressure Pressure is defined as the amount of force exerted on a unit area of a substance:

2. 2 ATMOSPHERIC PRESSURE VACUUM PRESSURE GAUGE PRESSURE ABSOLUTE PRESSURE ABSOLUTE ZERO PRESSURE PRESSURE A B RELATIONSHIP BETWEEN PRESSURES 101,325 Pa 0 Pa

3. 3 Measurement of Atmospheric Pressure Atmospheric pressure is measured by a device called a barometer ; P atm = ρ gh

4. 4 It is important to note that the pressure of a fluid can be measured either using: Manometers or Mechanical gauges

5. 5 The pressure of a fluid is measured in Manometers by balancing the column of a fluid by the same or another column of fluid, Whereas, the pressure of a fluid is measured in Mechanical Gauges by balancing the fluid column by spring or dead weight.

6. 6 The mechanical gauges are used for measuring high pressure and where high precision is not required. Some examples of mechanical gauges are as follows: Bourdon Tube Pressure gauge Diaphragm Type Pressure gauge McLeod Gauge Dead Weight Pressure Gauge However, in dealing with low pressure of fluids, we will use manometer only for the measurement of pressure.

7. 7 The simplest manometer used for the measurement of pressure- Piezometer. A Piezometer is the simplest form of Manometer, which is used for the measurement of moderate pressure of a liquid.

8. 8 It consists of a glass tube inserted in the wall of a vessel or of a pipe containing liquid whose pressure is to be measured. The tube extends vertically upwards to such a height that the liquid can freely rise in it without overflowing. The arrangement is shown in the figure.

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11. 11 A simple manometer is the device consisting of a glass tube bent in u shape. One end of the tube is connected to a point at which the pressure of the fluid is to be measured, and the other end is left open to the atmosphere. SIMPLE MANOMETER

12. 12 Positive Gauge Pressure . Vacuum Pressure ρ l ρ Hg ρ Hg ρ l P atm P atm SIMPLE MANOMETER

13. 13 SIMPLE MANOMETER

14. 14 SINGLE COLUMN MANOMETER

15. 15 INCLINED SINGLE COLUMN MANOMETER More Sensitive

16. 16 DIFFERENTIAL MANOMETER ρ 1 ρ g

17. 17 ρ 1 ρ g

18. 18 INVERTED U TUBE DIFFERENTIAL MANOMETER Uses lighter manometric liquid =

19. 19 MICROMANOMETER  

20. 20 Requirements of manometric fluid For Higher pressure measurement Liquids should be immiscible Liquid should have high density Liquid should have low vapor pressure Should not wet glass surface For Lower pressure measurement Liquids should be immiscible Liquid should have low density Liquid should have low vapor pressure Should not wet glass surface

21. 21 Bourdon tube