Laser diffraction meter

Previous measurements of variation in droplet size in spray flames have been carried out by flash microphotography (3). In this study, variation in droplet size was measured using a recently developed laser diffraction meter (8). This technique provides the average size of droplets and the size distribution across the entire spray for a height equal to that of the laser light beam. 

The laser diffraction meter consists of a parallel monochromatic light beam, 7 mm in diameter, from a 5-mW helium-neon laser, transmitted across the spray. Light diffracted by droplets and particles produces a Fraunhofer diffraction pattern. Light from the diffraction pattern is collected by 31 semicircular photosensitive rings, and the hght energies... 

Measiurements in the isothermal spray using the laser diffraction meter are shown in Figure 7. Mean droplet diameter, as a fimction of... 

Figure 7. Mean diameter of droplets and spread of size distribution N in isothermal spray. Measurements were made by laser diffraction meter across the spray at various axial locations.

Measurements of mean size and size distribution of droplets in isothermal sprays by the laser diffraction meter show break-up of large droplets into smaller droplets, followed by preferential vaporization of smaller droplets, resulting in increases in mean droplet diameter and... 

To measure wavelengths, adjust the second lens position to focus the beams on the wall (or screen). Tape sheets of paper to the wall at the 0 and 1 order diffraction positions. Attenuate (or block) the brighter beams, and taking care to avoid the diffracted beams, mark the location of all spots with a nonreflecting pencil. Block the pump laser beam before the cell and measure the x and values of the marks with a meter stick or tape measure as accurately as possible. Other variants of the experiment are possible for example, a reflection rather than transmission diffraction grating conld be employed as the dispersing element for these simple wavelength measnrements. 

Laser diffraction (LD) size analysis is a rapid and convenient non-invasive method used extensively for measuring the droplet size distribution of industrial sprays. LD analysis has been used for non-metered dispenser sprays to study the effects of varying the propel-lants and valve orifices. ... 

AN4 plus laser scattering particle meter (Coulter) was used to measure the sol particle diameter distribution at a 90 angle to the light beam. The material structure and chemistry were characterized by X-ray diffraction (XRD, Rigaku D/MAX-RB), atomic force microscopy (AFM, Nanoscope III), transmission electron microscopy (TEM, JEM2010) and N2 physi-adsorption (Omnisorp-lOOCX). 

The mixtures investigated were composed of ethylene-oxygen and ethylene-air at various equivalence ratios and were injected dynamically into the system at the head-end of the test apparatus. A 3.39-micrometer infrared (IR) He-Ne laser was transmitted across the combustor 2.54 cm upstream of the diffraction plane so that the fuel-oxygen to fuel air interfaces could be located spatially and characterized temporally. The typical mixture transition interface between the fuel-oxygen and fuel-air mixtures was approximately 6 cm in length. All gaseous flow rates were determined from metering orifices. Detonation wave speeds were... 

Jager etal. (1992) used a dilution unit in conjunction with laser diffraction measurement equipment. The combination could only determine, however, CSD by volume while the controller required absolute values of population density. For this purpose the CSD measurements were used along with mass flow meter. They were found to be very accurate when used to calculate higher moments of CSD. For the zeroth moment, however, the calculations resulted in standard deviations of up to 20 per cent. This was anticipated because small particles amounted for less then 1 per cent of volume distribution. Physical models for process dynamics were simplified by assuming isothermal operation and class II crystallizer behaviour. The latter implies a fast growing system in which solute concentration remains constant with time and approaches saturation concentration. An isothermal operation constraint enabled the simplification of mass and energy balances into a single constraint on product flowrate. 

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