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

State of Fluids Liquids Gases – equation of state Any physical quantity is function of temperature T and pressure P Ideal gas - air February 27, 2019

State Quantities Temperature – thermometers Pressure – manometers Both STATIC – flowing fluid Total (stagnation) static February 27, 2019

High velocities T – static temperature T0 – total (stagnation) temperature Adiabatic Compression February 27, 2019

Temperature on a sensor We measure recovery temperature For February 27, 2019

Pressure February 27, 2019

Pressure Units Pascal [Pa = N/m2] mm H2O (9.81 Pa) mm Hg, Torr (133.322 Pa) bar (106 dyn/cm2 = 105 Pa) atm (1.0133 x 105 Pa) – sea level at (kgf/cm2 = 0.981 x 105 Pa) – tech. atm. psi (Pound-force per square inch = 6895 Pa) February 27, 2019

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 February 27, 2019

Liquid Column Water k = 9.8 Alcohol k = 7.6 Mercury k = 133 February 27, 2019

Technology Elastic parts Deformation indication Bourdon tubes Diaphraghms Bellows Deformation indication Mechanical Piezoresistive strain gauge Capacitive Electromagnetic Piezoelectric Optical Potentiometric … February 27, 2019

Bourdon tubes Sealed tubes February 27, 2019

Elastic elements February 27, 2019

Capacitance measuring Robust Linear Precise Stable Big Low frequency February 27, 2019

Piesoresistive diaphragms High sensitivity High frequencies Small Temperature influence Nonlinear Fragile February 27, 2019

Pressure scanners Piesoresistive Up to 64 sensors Electronics February 27, 2019

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. February 27, 2019

Pressure-Sensitive Paints Qualitative Only high pressures α high velocities Surface pressure distribution February 27, 2019

Temperature February 27, 2019

Methods Thermal expansivity Electrical sensors Optical methods February 27, 2019

Method of thermal expansivity Liquid in Glass Thermometers Filled System Thermometers Bimetallic Thermometers February 27, 2019

Electrical sensors Thermocouples Resistance Temperature Detectors (RTDs) Thermistors (THERMal resISTORS) February 27, 2019

Thermocouples + Cheep Small, small inertia Big range - Small sensitivity Worse precision Reference February 27, 2019

Resistance Temperature Detectors platinum: 0.0038 + Precision, stability Simple Range (50-1000K) - Bigger Price wire 2w, 3w, 4w film February 27, 2019

Thermistors Semiconductors (oxids of Mn, Ni, Co, Cu, Fe, Ti) Steinhart-Hart equiation + Sensitivity - Nonlinear Low temp (upto 300°C) February 27, 2019

Optical Methods Liquid crystals Radiation Thermometers (RTs) Thermal Imaging (Thermography) Laser-Induced Fluorescence Rayleigh scattering Temperature of surface!!! Temperature of fluid February 27, 2019

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 February 27, 2019

Radiation Thermometers (infrared) Non-contact sensors Electromagnetic radiation received Range -40 °C to 3000 °C February 27, 2019

Thermal Imaging Infrared range of the electromagnetic spectrum (9 000–14 000nm) Black body radiation law (Planck) SURFACE !!! February 27, 2019

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

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