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Report presents study of bubble-count method of measurement of surface or interfacial tension of liquids. In method, gas or liquid pumped at known rate along capillary tube. One end of tube open and immersed in liquid that wets tube. Pumped gas or liquid forms bubbles, detaching themselves from immersed open end of tube, and one measures average period, Pi, for formation and detachment of bubbles.
Glass or ceramic tubes out-of-round sealed effectively by ordinary O-rings in caps of modified hydraulic fittings. In typical connection, O-ring squeezed between two surfaces having inward-opening slants of 5 degrees or 10 degrees. Slanted surfaces force ring inward, compressing it around tube. Connector metal fitting, tightened by hand around O-ring, seals O-ring against tube as much as 1/16 in. out of round. Modified connectors seal glass or ceramic tubes against gas or vacuum leakage in furnaces, vacuum systems, and tubes for glassblowing equipment.
Two improvements in heat-transfer design have been investigated with a view toward increasing the efficiency of refrigerators used to liquefy gases. The improvements could contribute to the development of relatively inexpensive, portable oxygen liquefiers for medical use. A description of the heat-transfer problem in a pulse-tube refrigerator is prerequisite to a meaningful description of the first improvement. In a pulse-tube refrigerator in particular, one of in-line configuration heat must be rejected from two locations: an aftercooler (where most of the heat is rejected) and a warm heat exchanger (where a small fraction of the total input power must be rejected as heat). Rejection of heat from the warm heat exchanger can be problematic because this heat exchanger is usually inside a vacuum vessel. When an acoustic-inertance tube is used to provide a phase shift needed in the pulse-tube cooling cycle, another problem arises: Inasmuch as the acoustic power in the acoustic-inertance tube is dissipated over the entire length of the tube, the gas in the tube must be warmer than the warm heat exchanger in order to reject heat at the warm heat exchanger. This is disadvantageous because the increase in viscosity with temperature causes an undesired increase in dissipation of acoustic energy and an undesired decrease in the achievable phase shift. Consequently, the overall performance of the pulse-tube refrigerator decreases with increasing temperature in the acoustic-inertance tube. In the first improvement, the acoustic-inertance tube is made to serve as the warm heat exchanger and to operate in an approximately isothermal condition at a lower temperature, thereby increasing the achievable phase shift and the overall performance of the refrigerator. This is accomplished by placing the acoustic-inertance tube inside another tube and pumping a cooling fluid (e.g., water) in the annular space between the tubes. Another benefit of this improvement is added flexibility of design to locate the warm heat-rejection components outside the vacuum vessel. The second improvement is the development of a compact radial-flow condenser characterized by a very high heat transfer coefficient and a small pressure drop.
Time-dependent upwind high resolution schemes for solving the Euler equations were developed and applied to simulate 1-D and 2-D transient inviscid gas flows in a shock tube. Using obstacles of different geometries, a series of calculations were carried out to investigate the transient complex shock-wave diffraction phenomena. Shock-wave and objects interactions with shock Mach-number Ms ranging from 2 to 20 were considered. Comparison with analytical and available experimental results indicate good agreement. Display of detailed flow structures including multiple Mach shocks, slip surfaces, and vortex are also given.
Steady-state pressure drop characteristics of normal hydrogen gas flowing through electrically heated small diameter tube - laminar flow instability
Absorption spectra determination of iron and chromium Fermi-Dirac values by shock heated argon tube
The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.
Experimental results of a group of theoretically selected cold cathode materials are presented. These tests indicate Ag-CuO, Cu, and Pt-Cu as three new cold cathode materials for sealed-off CO2 lasers. The power output of a test laser with an Ag-CuO cathode and a gas volume of only 50 cu cm varied from 0.72 W to 1.1 W at 3000 hours and still yields 0.88 W after 8000 hours. Gas discharge tubes with Cu cathodes and a volume of 25 cu cm yield lifetimes in excess of 10,000 hours. Gas analysis results, obtained from a similar tube over a period of 3000 hours, look most promising. A Pt-Cu alloy cathode shows an extremely promising V-I characteristic over a period of 2800 hours.
Experimental results of a group of theoretically selected cold cathode materials are presented. These tests indicate Ag-CuO, Cu and Pt-Cu as three new cold cathode materials for sealed off CO2 lasers. The power output of a test with an Ag-CuO cathode and a gas volume of only 50 cubic centimeters varied from 0.72 W to 1.1 W at 3000 hours and yields still 0.88 W after 8000 hours. Gas discharge tubes with Cu cathodes and a volume of 25 cubic centimeters yield life times in excess of 10,000 hours. Gas analysis results, obtained from a similar tube over a period of 3000 hours, look most promising. A Pt-Cu alloy cathode shows an extremely promising V-I characteristic over a period of 2800 hours.
A numerical integration scheme for quasi-one-dimensional unsteady flows with finite-rate chemistry is developed and demonstrated. The governing Euler and species-conservation equations are derived; the integration method and the spatial and temporal grid embedding techniques are explained; and results for sample problems involving stream-tube flow with one dissociating gas, shock-tube flow with one dissociating gas, and diverging-channel flow with multiple reactions are presented in extensive graphs and briefly characterized. Accuracy comparable to that of globally fine grid solutions is obtained with significant savings in CPU time.
A shock tube's driver gas can apparently provide flow with turbulent bursts. The fluctuations are interpreted using a boundary layer model of contact surface flow and results form a kinetic theory of turbulence. With this, a lower limit of 4 on the ratio of maximum to minimum turbulent intensities in contact surface instabilities has been estimated.
Laser action in gas discharge tubes filled with compounds containing C, N, H or D in presence of hydrogen or deuterium gas
A generalized expression for the nonsteady-state parameter, lag-time, has been obtained from Fick's second law for gas-phase transport through hollow, cylindrical membranes. This generalized expression is simplified for three limiting cases of practical interest: (1) diffusion controlled transport, (2) phase boundary reaction control at the inlet surface, and (3) phase boundary reaction control at the outlet surface. In all three cases the lag-time expressions were found to be inversely proportional only to the diffusion coefficient and functionally dependent on the membrane radii. Finally, the lag-time expressions were applied to experimentally obtained lag-time data for alpha-phase titanium and alpha-phase iron.
A set of perforated tubes disposed at the gas output side of a heat exchanger, in a position not to affect the rate of flow of the air or other gas is described. The tubes are connected to a common manifold which is connected to a sucking device. Where it is necessary to conserve and recirculate the air sucked through the tubes, the output of the manifold is run through a separator to remove the condensate from the gas. The perforations in the slurper tubes are small, lying in the range of 0.010 inch to 0.100 inch. The tubes are disposed in contact with the surfaces of the heat exchanger on which the condensate is precipitated, whether fins or plates, so that the water may be directed to the tube openings by means of surface effects, together with the assistance of the air flow. Only about 5 percent of the air output need be thus diverted, and it effectively removes virtually all of the condensate.
Heat transfer and pressure drop of argon flowing through single tube with internal interrupted fins
Several (111)-oriented, Ga-doped germanium crystals were grown in pyrolytic boron nitride (pBN) containers by the Bridgman and the detached Bridgman growth techniques. Growth experiments in closed-bottom pBN containers resulted in nearly completely detached-grown crystals, because the gas pressure below the melt can build up to a higher pressure than above the melt. With open-bottom tubes the gas pressure above and below the melt is balanced during the experiment, and thus no additional force supports the detachment. In this case the crystals grew attached to the wall. Etch pit density (EPD) measurements along the axial growth direction indicated a strong improvement of the crystal quality of the detached-grown samples compared to the attached samples. Starting in the seed with an EPD of 6-8 x 10(exp 3)/square cm it decreased in the detached-grown crystals continuously to about 200-500/square cm . No significant radial difference between the EPD on the edge and the middle of the crystal exists. In the attached grown samples the EPD increases up to a value of about 2-4 x 10(exp 4)/square cm (near the edge) and up to 1 x 10(exp 4)/square cm in the middle of the sample. Thus the difference between the detached- and the attached-grown crystals with respect to the EPD is approximately two orders of magnitude.
The design and construction of a long path cell for absorption measurements at temperatures ranging from 215-470 K and at pressures from vacuum to 10 atm are described. The cell consists of three concentric stainless-steel tubes; the innermost tube is 6.5-in. in internal diameter, has a volume of about 47 l, and contains White-type optics, six thermocouples, and a gas input tube; and the outermost tube provides a vacuum Dewar around the inner assembly. The optical design and temperature control system for the long path temperature variable cell are examined. The long path cell is applicable for analyzing temperature and pressure dependence of spectra and reaction rates of gases, and the cell has flow and photolysis capabilities for studying transient species and photochemically initiated reactions. A diagram of the cell is provided.
Slip flow of nitrogen gas through long circular tubes, measuring mass flow, pressure drop and cross sectional velocity profiles