There are safety rules for the operation of cryogenic systems designed to avoid the formation of explosive mixtures or solid particles of high-boiling impurities, and one of the problems in cryogenic engineering is to provide the reliable elimination of explosive and high-boiling gas components from closed cavities, ones without through flow, and from dead-end pipes and units. The problem is made more difficult in that it is required to provide replacement of the gas medium guaranteed with a given accuracy for dead-end branches, dead zones in fittings, and dead areas in the cavities of various sensors for which direct gas monitoring is not possible.Basically, two methods are used in industrial gas replacement: flushing and rinsing. When the gas in a blind-end section is replaced by flushing from a central pipeline to which it is attached, it is found [1] that the flushing is effective only for dead-end parts of length not more than 10 times their diameter even when the speed is raised to 2 m/sec, which is clearly inadequate for a pulsed line terminating in a closed cavity.Published data relate only to rinsing large vessels of simple shape [2, 3], so we consider in detail the gas component distribution when rinsing is applied to a pulse tube-closed cavity system.The basic model is a simplified piston one for rinsing with ideal gases and complete mixing ( Fig. 1): the rinsing gas is in a flow pipe, and its pressure varies from Pl (exhaust pressure) to P2 (injection pressure);the concentration Cg of the component to be removed in the rinsing gas is constant and is governed only by the quality of the gas used; -the motion of the rinsing gas in the tube during injection occurs in piston mode: as a straight front without mixing or mass transfer in the contact zone;-the gases mix completely in the closed cavity after injection; -the gases are taken as ideal and as governed by the Clapeyron-Mendeleev equation of state; and -in the pauses between the rinsing stages at pressures Pl (exhaust pause) and P2 (injection pause), the exchange by diffusion in the tube is considered as occurring in an immobile medium and in the one-dimensional space along the tube.Our purposes are not only to obtain working equations but also to select a test for the quantitative evaluation of how the rinsing performs in order to define the efficient rinsing limits. That test and the performance zones allow one to vary the parameters and convert unsuitable techniques to work in the region of efficient performance, with scope for calculation.Usually, the criterion for rinsing performance is taken as pl/P2 , which is quite adequate for large vessels, but when the volume of the tube V t and of the cavity ~c are comparable, one needs to consider Vt/V c as well as pl/p2.Preliminary experiments were performed with various states and various systems differing in parameters, where we took the test for performance as the optimal filling coefficient, which is the proportion of the closed cavity filled by the rinsing gas on injection:in which Mg is the amount...
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