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1243. A survey of flow at low pressures
Classified
abstracts
Classified abstracts on this page 1242-l
1242-1340
248
Editor’s note The label immediately following the title of each item denotes country or origin of publication, that at the end of each abstract indicates country of origin of work (where known).
I. General 14. KINETIC
vacuum THEORY
science
and engineering
OF GASES
14 1242. Monte Carlo calculation of ultra cold neutron flow through long tubes with a realistic angular distribution of reflected neutrons. (GB) Monte Carlo simulations of the flow of particles through tubes are used to study the effects of a theoretically well founded non-specular reflection probability on the transmission of the tubes and the angular distribution of the emerging particles. The theoretical reflection probability used is appropriate for ultra cold neutrons scattering from almost smooth surfaces. The results obtained are compared to those described in earlier work in which approximations to the theoretical reflection law were used. M Brown et al, Vacuum, 25 (2), 1975, 61-64. 14 1243. A survey of flow at low pressures. (GB)
The theory of internal flows at such low pressures that the NavierStokes equations are not valid is reviewed. In the extreme low pressure range (free molecular flow), where the flow rate is independent of pressure, the basic theory is well developed. However, the influence of channel length, cross sectional shape, or surface characteristics have not been totally defined. Slip theory, which extends the low pressure range of the Navier-Stokes equation by modifying the wall boundary conditions, is discussed. The theory provides a good basis for experimental data correlation, but is not adequate to extend the viscous equations into the free molecular range. The empirical methods used to provide a smooth transition from slip to free molecular flow are reviewed, and a method of obtaining an equation for the total flow regime is illustrated. The extensive work in physical gas dynamics is discussed. Boltzmann’s equation which has been solved numerically for small pressure gradients was found to be valid only in the viscous regime near the free molecular flow range. (USA) S L Thomson and W R Owens, Vacuum, 25 (4). 1975,151-156. 16. GASES AND SOLIDS 16 1244. Gas evolution from a solid following de-trapping during tempering. (GB)
and diffusion
The gas evolution rate from the surface of a solid is determined as a function of temperature during controlled heating of the solid, for the case where it is assumed that gas atoms are initially trapped at centres requiring an activation energy E for stimulation into a diffused mode. Diffusion then proceeds with a different activation energy Q. The initial location of atoms is assumed to be a plane, depth ph below the surface and the heating function is assumed to be l/T = l/T, - br. Even in this simplified case it is shown that although the release rate can be expressed as a formal mathematical function of temperature, numerical evaluation is necessary for each value of E, Q, b and pX. G Carter et al, Vacuum, 25 (5), 1975, 197-199. 16 1245. Apparatus for studying the gas permeability
of thin-walled shells.
(USSR) An apparatus for measuring the gas permeability of thin-walled shells is described; it comprises two chambers, one of which holds the sample, together with an electric furnace for heating it to llOO”C, while the other holds the test gas and is furnished with a device for loading the sample by means of a set of standard weights. The pressure in the gas chamber is measured with a standard manometer/
and
vacuum gauge. By means of the loading system, either static or dynamic loads may be applied to the sample. The amount of gas diffusing through the sample is easily determined from the difference between two pressure readings. The constitution of the gas may be verified by means of a mass spectrometer. In order to carry out measurements at very low pressures (lo-’ torr) a magnetic discharge pump is incorporated. A A Goryunov and E S Ermakov, Tr Mosk Inst, Elektron Mashinostroenie, No 42, 1974, 125-128 (in Russian). 16:22 1246. Experimental verification of a method of determining the pressure and rate of gas flow from vacuum devices. (USSR) A differential method of determining the pressure and rate of gas outflow from electronic vacuum devices is described. The apparatus is first evacuated to as high a vaccum as possible, and then one section is filled with air to a pressure several orders of magnitude higher than that in the evacuated section. A controlled leak is set up between the two sections; the rate of change in pressure and gas content is determined either by means of a differential vacuum gauge, or alternatively by a capillary method. Excellent agreement is obtained between the results of the two measuring techniques. On the basis of this agreement a simple reading device is proposed for determining pressures and rates of flow to an accuracy sufficient for practical purposes, and a calibration chart for a typical version is given by way oi example. V A Akonvan and N N Gonzhalov. Tr Mosk Enera _ Inst. No 192. 1974, 1151i18 (in Russian). ’ 16:22 1247. On measuring the pressure and rate of gas removal from an electrical vacuum device in the course of evacuation. (USSR) Methods of determining the current pressure in an electrical vacuum device during its evacuation and also the rate of evolution of gas inside the device, as well as the rate of gas removal are discussed. The pressure and gas flow may in fact be determined to a moderate accuracy by means of a simple reading sensor operating in conjunction with any pumping system and taking account of the transient nature of the evacuation process. A schematic description of the device is presented, together with a series of working equations used to determine the quantities in question in terms of some simple differential pressure measurements. Initial tests indicate that for most practical purposes the accuracy of this device is entirely adequate. VA Akopyan, Tr Mosk Energ Znst, No 192,1974,113-l 15 (in Russian). 16 1248. An apparatus for estimating the sorption properties of a gas absorber. (USSR) An apparatus enabling the activity of a getter to be determined by two independent techniques (the volumetric method and the slow leak principle) is described; it consists basically of a high-vacuum pumping system, a measuring section, and a device for the measured inflow of the test gas. The rate of sorption is determined from the readings of two manometers, which are periodically recalibrated. The test samples are in the form of sections of metal strip 0.1 mm thick and 10 cm2 in area, the active powder being deposited on these by a plasma-arc method. The gas-supply systems are of conventional chemical form, protected from contamination by liquid-nitrogen traps. By means of a simple switching system, gas mixtures may also be admitted to the measuring section. Reproducibility of the results is of the order of 10%. V E Visloukh and G D Glebov, Trudy Mosk Znst Elektron Mashinostroenie, No 42, 1974, 15-21 (in Russian). 453
abstracts
Classified abstracts on this page 1242-l
1242-1340
248
Editor’s note The label immediately following the title of each item denotes country or origin of publication, that at the end of each abstract indicates country of origin of work (where known).
I. General 14. KINETIC
vacuum THEORY
science
and engineering
OF GASES
14 1242. Monte Carlo calculation of ultra cold neutron flow through long tubes with a realistic angular distribution of reflected neutrons. (GB) Monte Carlo simulations of the flow of particles through tubes are used to study the effects of a theoretically well founded non-specular reflection probability on the transmission of the tubes and the angular distribution of the emerging particles. The theoretical reflection probability used is appropriate for ultra cold neutrons scattering from almost smooth surfaces. The results obtained are compared to those described in earlier work in which approximations to the theoretical reflection law were used. M Brown et al, Vacuum, 25 (2), 1975, 61-64. 14 1243. A survey of flow at low pressures. (GB)
The theory of internal flows at such low pressures that the NavierStokes equations are not valid is reviewed. In the extreme low pressure range (free molecular flow), where the flow rate is independent of pressure, the basic theory is well developed. However, the influence of channel length, cross sectional shape, or surface characteristics have not been totally defined. Slip theory, which extends the low pressure range of the Navier-Stokes equation by modifying the wall boundary conditions, is discussed. The theory provides a good basis for experimental data correlation, but is not adequate to extend the viscous equations into the free molecular range. The empirical methods used to provide a smooth transition from slip to free molecular flow are reviewed, and a method of obtaining an equation for the total flow regime is illustrated. The extensive work in physical gas dynamics is discussed. Boltzmann’s equation which has been solved numerically for small pressure gradients was found to be valid only in the viscous regime near the free molecular flow range. (USA) S L Thomson and W R Owens, Vacuum, 25 (4). 1975,151-156. 16. GASES AND SOLIDS 16 1244. Gas evolution from a solid following de-trapping during tempering. (GB)
and diffusion
The gas evolution rate from the surface of a solid is determined as a function of temperature during controlled heating of the solid, for the case where it is assumed that gas atoms are initially trapped at centres requiring an activation energy E for stimulation into a diffused mode. Diffusion then proceeds with a different activation energy Q. The initial location of atoms is assumed to be a plane, depth ph below the surface and the heating function is assumed to be l/T = l/T, - br. Even in this simplified case it is shown that although the release rate can be expressed as a formal mathematical function of temperature, numerical evaluation is necessary for each value of E, Q, b and pX. G Carter et al, Vacuum, 25 (5), 1975, 197-199. 16 1245. Apparatus for studying the gas permeability
of thin-walled shells.
(USSR) An apparatus for measuring the gas permeability of thin-walled shells is described; it comprises two chambers, one of which holds the sample, together with an electric furnace for heating it to llOO”C, while the other holds the test gas and is furnished with a device for loading the sample by means of a set of standard weights. The pressure in the gas chamber is measured with a standard manometer/
and
vacuum gauge. By means of the loading system, either static or dynamic loads may be applied to the sample. The amount of gas diffusing through the sample is easily determined from the difference between two pressure readings. The constitution of the gas may be verified by means of a mass spectrometer. In order to carry out measurements at very low pressures (lo-’ torr) a magnetic discharge pump is incorporated. A A Goryunov and E S Ermakov, Tr Mosk Inst, Elektron Mashinostroenie, No 42, 1974, 125-128 (in Russian). 16:22 1246. Experimental verification of a method of determining the pressure and rate of gas flow from vacuum devices. (USSR) A differential method of determining the pressure and rate of gas outflow from electronic vacuum devices is described. The apparatus is first evacuated to as high a vaccum as possible, and then one section is filled with air to a pressure several orders of magnitude higher than that in the evacuated section. A controlled leak is set up between the two sections; the rate of change in pressure and gas content is determined either by means of a differential vacuum gauge, or alternatively by a capillary method. Excellent agreement is obtained between the results of the two measuring techniques. On the basis of this agreement a simple reading device is proposed for determining pressures and rates of flow to an accuracy sufficient for practical purposes, and a calibration chart for a typical version is given by way oi example. V A Akonvan and N N Gonzhalov. Tr Mosk Enera _ Inst. No 192. 1974, 1151i18 (in Russian). ’ 16:22 1247. On measuring the pressure and rate of gas removal from an electrical vacuum device in the course of evacuation. (USSR) Methods of determining the current pressure in an electrical vacuum device during its evacuation and also the rate of evolution of gas inside the device, as well as the rate of gas removal are discussed. The pressure and gas flow may in fact be determined to a moderate accuracy by means of a simple reading sensor operating in conjunction with any pumping system and taking account of the transient nature of the evacuation process. A schematic description of the device is presented, together with a series of working equations used to determine the quantities in question in terms of some simple differential pressure measurements. Initial tests indicate that for most practical purposes the accuracy of this device is entirely adequate. VA Akopyan, Tr Mosk Energ Znst, No 192,1974,113-l 15 (in Russian). 16 1248. An apparatus for estimating the sorption properties of a gas absorber. (USSR) An apparatus enabling the activity of a getter to be determined by two independent techniques (the volumetric method and the slow leak principle) is described; it consists basically of a high-vacuum pumping system, a measuring section, and a device for the measured inflow of the test gas. The rate of sorption is determined from the readings of two manometers, which are periodically recalibrated. The test samples are in the form of sections of metal strip 0.1 mm thick and 10 cm2 in area, the active powder being deposited on these by a plasma-arc method. The gas-supply systems are of conventional chemical form, protected from contamination by liquid-nitrogen traps. By means of a simple switching system, gas mixtures may also be admitted to the measuring section. Reproducibility of the results is of the order of 10%. V E Visloukh and G D Glebov, Trudy Mosk Znst Elektron Mashinostroenie, No 42, 1974, 15-21 (in Russian). 453