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粒徑大小的測定蒺藜(催乳食谱原文)
儿童舞蹈音乐How methods and instruments have kept pace with changing technology
There are many methods and instruments available for drop size data collection. Since repeatable test results are esntial in comparing nozzle performance data, it is esntial to u testing procedures that take into account all of the potential variables in the sampling technique for both methods and instrumentation.
By spraying water into a pan of oil and shuttering the spray, it is possible to count and size individual drops using a microscope. This technique is still ud by some rearchers. Problems with this method involve drop coalescence, inadequate sample size and the fact that very small drops will be deflected away from the oil by air currents at the surface due to the spray velocity. Also, larger drops can and do break-up from impacting the surface.
The same type of method is ud when spraying a dye onto a stationary card, or water onto liquid nsitive paper. Again, the small drops might be deflected away from the target and the large drops can break-up from the impact. Data collected by the "intrusive" methods
depends on a number of uncontrolled variables making such test results generally non-repeatable.
While drop size data was being collected in the early 1950's using methods such as flash photography, probably the first real breakthrough in drop sizing technology was the development in 1961 of an automated imaging analyzer (Figure 5).1
1 The Electronic Imaging Analyzer was developed at Spraying Systems Co. by Dr. Verne Dietrich and built by the Dage Division of TRW, Michigan City, Indiana. The design was awarded U.S. Patent 3275733 in September of 1966, and is currently in its cond generation.
Basically, the Electronic Imaging Analyzer incorporates the spatial measurement technique using a strobe light to illuminate the spray and record the image with a vidicon tube. The image is scanned, and the drops are sized and parated into different class. Resulting data can be mathematically corrected using velocity data to give a flux distributi
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on. Sources of error early in the development of this device included blurring, depth of field variations and vidicon tube saturation. The sources were recognized and corrected.
The imaging type analyzer is still actively promoted by some nozzle manufacturers. The limited availability of this type of instrument, however, prevents independent rearchers and other interested members of the drop size analyzer community from verifying data arrived at from a particular test or comparing performance from similar designs.
More recently the development of commercially available drop size analyzers makes it feasible to verify drop size results by independent sources. This new breed of analyzers incorporates lars, special optics and digital circuitry to minimize imaging error. Some of the more commonly recognized manufacturers of lar measurement instruments include Malvern, Particle Measuring Systems (PMS), and Aerometrics. The following is an analysis of three of their instruments.
沙发哪个品牌好Malvern Particle Analyzer
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The Malvern Analyzer, which is considered a spatial sampling device, utilizes the fact that a spray drop will cau lar light to scatter through an angle dependent on the diameter of the drop (e Figure 6). The scattered light intensity is measured using a ries of micircular photo diodes. Theoretically, the distance of the individual photo diodes from the centerline of the lar and the intensity functions are all that are needed to calculate the drop size distribution. A curve-fitting program is ud to convert the light intensity distribution into any of veral empirical drop size distribution functions. Since the Malvern has some lf-diagnostics, potential sources of error are easier to identify. The instrument must be aligned and calibrated periodically using reticle slides with known etched drop distributions.
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Perhaps the biggest source for error with this type of instrument is multiple light scattering. If the spray is too den, there is a possibility that the scattered light from one drop might be scattered again by other drops further down the beam axis. The Malvern is equipped with an "obscuration level" indicator which can be ud to determine if the spray is too den, but such a determination is often difficult. To circumvent this in the lab, the technician typically moves the nozzle farther away or us special shielding to permit only a portion of the spray to enter the sample area.
Particle Measuring Systems
Particle Measuring Systems, also know as PMS, produces instruments known as Optical Array Probes. The PMS Optical Array Probe is a flux sampling instrument (e Figure 7). As the drops pass through the sampling plane, the drops are sized and counted providing information which can be ud to determine velocity. The two-dimensional grey scale OAP can provide drop measurement in two ranges, 100 and 6200 microns and 200 to 12,400 microns, and is currently the most sophisticated offered by PMS.
