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1.4 PRESSURE

1.4 PRESSURE. 1.4.1 Pressure in a fluid 1.4.2 The effect of gravity on pressure 1.4.3 The effect of gas temperature on pressure 1.4.4 Propagation of waves 1.4.5 Attenuation of waves. Pressure = Force / Area. Force F 1 Area A 1. Force F 2 Area A 2. F 2 = F 1  A 2 /A 1. Piston.

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1.4 PRESSURE

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  1. 1.4 PRESSURE • 1.4.1 Pressure in a fluid • 1.4.2 The effect of gravity on pressure • 1.4.3 The effect of gas temperature on pressure • 1.4.4 Propagation of waves • 1.4.5 Attenuation of waves

  2. Pressure = Force / Area Force F1 Area A1 Force F2 Area A2 F2 = F1 A2/A1

  3. Piston Cylinder Low Pressure P1 Area A1 Pressure Intensifier High Pressure P2, AreaA2 Seal (O Ring) The pressure is increased by a factor A1/A2 where A2 and A1 are the areas of each end of the piston. Force = P1A1 = P2A2 therefore P2 = A1 P1 A2

  4. 1.4 PRESSURE • 1.4.1 Pressure in a fluid • 1.4.2 The effect of gravity on pressure • 1.4.3 The effect of gas temperature on pressure • 1.4.4 Propagation of waves • 1.4.5 Attenuation of waves

  5. Pressure and depth The pressure at a depth h metres below an open surface of a liquid is given by: where  is the density (1000 kg/m3 for water) and g is 9.81 m/s2.

  6. Units of Pressure 0.99 Atmospheres = 1 Bar = 100 kPa (kilo Pascal) = 0.1 N/mm2 = 10 m water head

  7. Mercury Barometer Sealed End Vacuum Pressure in mm of mercury Approx 1 m. Would be 10 m for water Mercury Open End

  8. 1.4 PRESSURE • 1.4.1 Pressure in a fluid • 1.4.2 The effect of gravity on pressure • 1.4.3 The effect of gas temperature on pressure • 1.4.4 Propagation of waves • 1.4.5 Attenuation of waves

  9. Ideal Gas Equation There is an approximate equation which may be used to calculate the change in pressure in a gas when it is heated. The "ideal gas equation" is: where: P1, V1, and T1 are the pressure, volume and temperature before the change and P2 etc. are the values for after the change. Note that T must be in Kelvin, not centigrade.

  10. 1.4 PRESSURE • 1.4.1 Pressure in a fluid • 1.4.2 The effect of gravity on pressure • 1.4.3 The effect of gas temperature on pressure • 1.4.4 Propagation of waves • 1.4.5 Attenuation of waves

  11. L2 Weight Bar. L1 Schematic diagram of movement of an element of a solid The force on the weight will cause it to accelerate: F=ma where: F is the force = stress  area m is the mass = Al1 and a is the acceleration Thus: F = EyA/l2 The solution to this "simple harmonic motion"

  12. Progress of a wave on a solid Movement of a wave. Pressures at time T and T+T. The velocity of the wave is the frequency  the wavelength Displacement y Position x

  13. Definitions for waves • Frequency in the number of complete cycles per second • Wavelength is the distance from a point on a wave to the identical point on the next wave • Velocity = frequency  wavelength

  14. Pressure waves in a solid • E = Young's modulus • v = pulse velocity • d = density •  = Poisson's ratio

  15. Ultrasonic testing

  16. Our Ultrasonic Test Machine

  17. Elastic deformation of fluid We define the bulk modulus B as follows:

  18. 1.4 PRESSURE • 1.4.1 Pressure in a fluid • 1.4.2 The effect of gravity on pressure • 1.4.3 The effect of gas temperature on pressure • 1.4.4 Propagation of waves • 1.4.5 Attenuation of waves

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