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Fluid flow measurements
Published in Amithirigala Widhanelage Jayawardena, Fluid Mechanics, Hydraulics, Hydrology and Water Resources for Civil Engineers, 2021
Amithirigala Widhanelage Jayawardena
Laser Doppler anemometer (LDA), sometimes referred to as laser Doppler velocitometer (LDV) is a non-invasive method of measuring velocities in flowing liquids and gases, especially in a laboratory environment. The technique has been well established about three decades ago and has the advantages of being able to give spatial and temporal high resolution and does not need calibration. The technique also has the capability to measure reversing flows. The components of an LDA system consist of a continuous wave laser, transmitting optics and a signal processor. The velocity information comes from light scattering from particles carried in the fluid. Fluids normally have particles naturally, but gases need to be seeded with particles. The particles, which can be solids (powder) or liquids (droplets), typically have sizes ranging from 1 to 10 μm.
Photoacoustic Spectroscopy
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
The constant, C, is a measure for the efficiency of the conversion of the PA-generated pressure into an electronic signal (Sigrist, 1994). Light scattering by particles or gas molecules does not directly influence the PA signal, since it does not lead to local heating. However, light can be scattered onto the walls of the PA cell and particularly on the microphone, where it gets absorbed and generates a PA signal by itself. One of the challenges of PA cell design is the suppression of this background signal.
Geometry of Purple Membranes in Aqueous Medium
Published in Stoyl P. Stoylov, Maria V. Stoimenova, Molecular and Colloidal Electro-Optics, 2016
Thus the conclusion obtrudes itself that the fast relaxation process is connected with changes in PM geometry, induced by the external electric field. The difference in EOE decay in the two methods is due to the high sensitivity of light scattering to particles’ geometry as opposed to the low sensitivity of dichroism. The smaller relative share of the fast process at dichroism suggests a change in curvature but not a change in chromophore orientation.
Evaluation of a Portable Aerosol Collector and Spectrometer to measure particle concentration by composition and size
Published in Aerosol Science and Technology, 2019
Changjie Cai, Larissa V. Stebounova, David W. Peate, Thomas M. Peters
For the two-mode aerosol, mass concentrations detected with the photometer were low (0.003 ± 0.001 mg/m3) in all stages (Figure 4a) because of the limitations of photometer for measuring mass concentrations. The photometer uses the Mie theory of light scattering of particles and the built-in optical parameters (e.g., light wavelength and detection angle) (Görner, Bemer, and Fabries 1995). Therefore, the mass concentration measured with the photometer is a function of the main aerosol parameters including the refractive index, particle density, particle size, etc. For metal fume, Sousan et al. (2017) found that mass concentrations measured with a photometer were highly linear (correlation coefficient r = 0.99) with those measured gravimetrically, but were severely underestimated (slope of 0.2 ± 0.01; photometer concentrations were five times lower than gravimetric mass concentrations). In addition, the photometer does not measure the mass concentration of ultrafine mode particles because the photometer only responds to particles larger than 100 nm (as reported by the manufacturer).