1. Measurement of Pressures and Temperatures
Prof. Václav Uruba
IT ASCR, CTU Praha, UWB Plzeň

2. State of Fluids Liquids Gases – equation of state
Any physical quantity is function of temperature T and pressure P
Ideal gas - air
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3. State Quantities Temperature – thermometers Pressure – manometers
Both STATIC – flowing fluid
Total
(stagnation)
static
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4. High velocities T – static temperature
T0 – total (stagnation) temperature
Adiabatic Compression
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5. Temperature on a sensor
We measure recovery temperature
For
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6. Pressure
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7. Pressure Units Pascal [Pa = N/m2] mm H2O (9.81 Pa)
mm Hg, Torr ( Pa)
bar (106 dyn/cm2 = 105 Pa)
atm ( x 105 Pa) – sea level
at (kgf/cm2 = x 105 Pa) – tech. atm.
psi (Pound-force per square inch = 6895 Pa)
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8. Manometers Types Principles Differential pressure - PSID
Absolute pressure (rel. to ref.) - PSIA
Gauge pressure (rel. to atm.) - PSIG
Vacuum pressure (negative gauge)
Sealed pressure (rel. to atm. at sea level) - PSIS
Principles
Liquid column
Elastic parts
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9. Liquid Column Water k = 9.8 Alcohol k = 7.6 Mercury k = 133
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10. Technology Elastic parts Deformation indication Bourdon tubes
Diaphraghms
Bellows
Deformation indication
Mechanical
Piezoresistive strain gauge
Capacitive
Electromagnetic
Piezoelectric
Optical
Potentiometric …
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11. Bourdon tubes
Sealed tubes
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12. Elastic elements
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13. Capacitance measuring
Robust
Linear
Precise
Stable
Big
Low frequency
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14. Piesoresistive diaphragms
High sensitivity
High frequencies
Small
Temperature influence
Nonlinear
Fragile
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15. Pressure scanners Piesoresistive Up to 64 sensors Electronics
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16. Pressure-Sensitive Paints
Deactivation of photoexcieted molecules of organic luminosphores by oxygen molecules (quenching).
Discovered by H. Kautsky and H. Hirsch in 1935.
Certain materials are luminous when excited by the correct light wavelength.
The luminescence is dependent on air pressure.
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17. Pressure-Sensitive Paints
Qualitative
Only high pressures α high velocities
Surface pressure distribution
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18. Temperature
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19. Methods Thermal expansivity Electrical sensors Optical methods
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20. Method of thermal expansivity
Liquid in Glass Thermometers
Filled System Thermometers
Bimetallic Thermometers
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21. Electrical sensors Thermocouples
Resistance Temperature Detectors (RTDs)
Thermistors (THERMal resISTORS)
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22. Thermocouples + Cheep Small, small inertia Big range -
Small sensitivity
Worse precision
Reference
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23. Resistance Temperature Detectors
platinum: +
Precision, stability
Simple
Range ( K) -
Bigger
Price
wire
2w, 3w, 4w
film
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24. Thermistors Semiconductors (oxids of Mn, Ni, Co, Cu, Fe, Ti)
Steinhart-Hart equiation +
Sensitivity -
Nonlinear
Low temp (upto 300°C)
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25. Optical Methods Liquid crystals Radiation Thermometers (RTs)
Thermal Imaging (Thermography)
Laser-Induced Fluorescence
Rayleigh scattering
Temperature
of surface!!!
Temperature
of fluid
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26. Liquid-crystal temperature-sensitive films
Hydrophobic derivatives of polyvinyl alcohol and cholesteric liquid crystals
Encapsuled (friction)
Temperature -5 to +150°C
Thickness 30-50μm
High sensitivity
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27. Radiation Thermometers (infrared)
Non-contact sensors
Electromagnetic radiation received
Range -40 °C to 3000 °C
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28. Thermal Imaging
Infrared range of the electromagnetic spectrum (9 000–14 000nm)
Black body radiation law (Planck)
SURFACE !!!
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29. PLIF
See more in „Optical methods“
Planar laser-induced fluorescence (planar-LIF) - instant whole-field concentration or temperature maps in liquid flows.
February 27, 2019

30. Rayleigh scattering The Rayleigh signal is dependent on:
See more in „Optical methods“
The Rayleigh signal is dependent on:
Laser intensity
Scattering cross section
Number density
If species composition and pressure are known in the gas the gas temperature can be determined from imaging of the Rayleigh scattering.
February 27, 2019