Technique and equipment for dispersion analysis of cryosols and suspended microadmixtures in cryogenic liquids
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UDC 66.078.9:661.91
In research related to obtaining and applying cryogenic liquids (helium, hydrogen, oxygen, etc.), particular attention is paid to the heterogenic systems formed in the liquids by admixtures of solidified gases or by other admixtures. The undesirability of the presence of such admixtures and in certain cases actual danger produced by them and their sediments formed in the course of time has obliged experts to study increasingly the physicochemical and hydrodynamic conditions of their formation and subsequent behavior. The basic information required in this case consists of the dimension of the suspended solid particles and their counted or volumetric concentration. If one takes into account the above liquids' extremely low temperatures, the prevailing polydisperse suspended systems often subjected to very intensive convection or other disturbances, the ~iversity of the microadmixtures' chemical characteristics, the wide range of possible concentrations, etc., the complexity in solving the methodologic and equipment problems of such measurements becomes understandable. Preliminary analysis of the microconcentrations in cryogenic liquids has shown that the size-resolution range should amount to approximately 0.i-I00 ~ with a counting concentration in the range of i 9 109-1 I0 s units/cm s, or volumetric concentration of I i0-~-i 10-s%. Optical methods are the most acceptable. Among the known optical methods for measuring the sizes of particles suspended in liquids it is necessary to note the microscopic technique, evaluation of the dispersion-characteristic curves, and optical-displacement spectroscopy. The microscopic suspended particles, and the procedure of carrying out a large
technique provides a direct method for measuring the size and shape of but its resolution is limited by particle sizes of the order of 1-2 ~, obtaining information is very complicated owing to the requirements for number of measurements and their statistical processing.
Evaluation of the microadmixture distribution from their disperslon-characteristic curves is a very complicated and ambiguous mathematical problem, and the procedure in plotting dispersion characteristics is rather protracted, thus impeding considerably the application of this technique in the case of cryogenic liquids. It would appear that the most promising method for investigating microadmixtures consists of the optical-mixing technique [i], namely, its variety entailing a square-law or pulsating-light spectrometer [i, 2]. The first basic difficulty in applying the technique of [i, 2] to cryogenic liquids consists of suppressing the stray reflections of light from the optical cryostat walls. Stray illumination adds to the signal spectrum at the square-law-spectrometer output a signal due to the beating of radiations dispersed by the cryostat walls and the tested particles. In addition to distorting the useful signal, this leads to the shape of the photocurrent spectrum being affected by the convection flux parameters, which cannot be eliminated in pr
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