Showing papers on "Critical ionization velocity published in 1974"
TL;DR: In this paper, the stability of a gas jet in a surrounding viscous liquid is studied and an expression for the critical velocity at which the jet becomes unstable in a returning viscous fluid is developed.
Abstract: The stability of a gas jet in a surrounding viscous liquid is studied. An expression is developed for the critical velocity at which the jet becomes unstable in a returning viscous liquid. The stability analysis is made to correspond with the geometrical configuration of gas jets and liquid columns similar to those observed near the peak pool boiling heat flux. The critical velocity of the gas jet is then used to obtain the functional form of the peak heat flux on flat plates and cylindrical heaters. The expressions are compared with original observations of the peak heat flux in very viscous liquids on flat plate, and cylindrical, heaters at both earth-normal, and elevated, gravities.
32 citations
TL;DR: In this article, Doppler-shifted third sound in unsaturated helium II films is used to measure critical flow velocities, which exhibit a well defined maximum as a function of film thickness and at this maximum are considerably higher than those usually found in film flow.
Abstract: Critical flow velocities measured by Doppler-shifted third sound in unsaturated helium II films are shown to exhibit a well-defined maximum as a function of film thickness and at this maximum to be considerably higher than those usually found in film flow. In addition the critical velocity is strongly temperature dependent below the maximum and relatively temperature independent above.
25 citations
TL;DR: In this article, the instability of the wave was treated and a correlation of critical velocity at which the liquid film becomes unstable was derived, which was compared with the previous experimental expression of a flooding velocity in a wetted column and some discussions were made.
Abstract: It has been reported that, in the counter-current annular two-phase flow where a liquid film flows down along the wall of vertical tube and gas flows up in the core, instability of liquid film results not from reversal of flow of liquid under surface shear but from instability of the wave occurring on the surface of liquid film. From this viewpoint, the instability of the wave was treated and a correlation of critical velocity at which the liquid film becomes unstable was derived. Critical heat fluxes of the two-phase thermosyphon for pure water, ethyl-alcohol, nhexane and carbon-tetrachloride as the working fluids were correlated and comparatively good agreement was obtained. In addition, the correlation derived was compared with the previous experimental expression of a flooding velocity in a wetted column and some discussions were made.
23 citations
TL;DR: It is likely that the velocity limitation observed in some types of rotating plasmas is caused by an enhanced plasma-neutral gas interaction at the end walls bounding the plasma in the magnetic field direction as mentioned in this paper.
Abstract: It is likely that the velocity limitation observed in some types of rotating plasma devices is caused by an enhanced plasma-neutral gas interaction at the end walls bounding the plasma in the magnetic field direction. If the mechanism underlying the interaction is due to some process which forms anomalous azimuthal electric fields, a short-circuit of the latter would eliminate the velocity limitation If these predictions are true, new possibilities will open up in the use of rotating plasmas. In particular, the power losses due to ions and electrons escaping from a hot isotropic plasma through the magnetic mirror ends can then be kept small enough to balance the thermonuclear power at technically realizable beta values, plasma densities, and magnetic field strengths. At the same time such a strong confinement can only be achieved by very large centrifugal forces, rotational velocities and applied voltages, the technical feasibility of which has to be further examined.
21 citations
TL;DR: In this paper, the first observation of objects moving through He II with equilibrium drift velocities beyond the Landau critical velocity vc, for roton creation was reported, with T about 0.4 K, P = 25 bar, F = 2 kV/cm.
Abstract: We report the first observation of objects moving through He II with equilibrium drift velocities v beyond the Landau critical velocity vc,for roton creation. With T about 0.4 K, P = 25 bar, F =2 kV/cm, (v - vc) for negative ions is larger than a theoretical prediction by a factor of about 10^5. The vortex-ring nucleation rate is found to decrease with F above 300 V/cm, thus resolving apparent inconsistencies between earlier experiments.
19 citations
TL;DR: In this article, the critical mass for stability against radial pulsations in rotating, homogeneous main-sequence stars was found to be greater than in the case of no rotation, and it was shown that critical mass rises steeply with increasing concentration of angular momentum to the center of the star.
Abstract: The critical mass for stability against radial pulsations in rotating, homogeneous main-sequence stars is found to be greater than in the case of no rotation. Analytic and detailed numerical models show that the critical mass rises steeply with increasing concentration of angular momentum to the center of the star. For uniform rotation near breakup velocity at the star's equator the critical mass is about 850 solar masses if an electron-scattering opacity is used, or about 5000 solar masses if the opacities of Cox and Stewart are used. For nonuniform rotation with a constant ratio of centrifugal force to gravity in the star, the critical mass becomes 'infinite' long before breakup velocity is attained. The relevance of the present results to several observational problems is noted.
15 citations
TL;DR: In this paper, the authors investigated the influence of tangential gas flow on the time required for a laser beam of given intensity to burn through a metal sheet, and derived an interpolation formula that predicts an intermediate velocity for which the time for burnthrough is a minimum.
Abstract: This paper contains an investigation of the influence of a tangential gas flow on the time required for a laser beam of given intensity to burn through a metal sheet. From a consideration of the hydrodynamics of the liquid metal-gas interface and the time required for an entrained liquid droplet to vaporize, an interpolation formula is derived relating the time required for burnthrough at a given freestream Mach number to that required in the absence of tangential flow, or for flow rates less than the critical velocity at which melt droplets are entrained. The interpolation formula so derived depends only on the thermodynamic properties of the melt, the hydrodynamic properties of the boundary layer and the size of the spot irradiated by the laser beam. The formula predicts an intermediate velocity for which the time for burnthrough is a minimum. Physical explanation of the minimum is given in the text. For limiting cases of very large laser spot size, the reduction in burnthrough time disappears.
14 citations
TL;DR: In this article, the authors measured the energy dissipation, chemical potential difference and temperature difference over a capillary as a function of the steady state mass velocity, generated by a plunger system.
12 citations
TL;DR: In this paper, the authors measured the wall velocity in YFeO 3 single crystal platelets by the bubble collapse method, and the applied pulse width ranges from 100 ns to 7.8 ns and the maximum applied field is 170 Oe.
Abstract: Domain wall velocity in YFeO 3 single crystal platelets is measured by the bubble collapse method. The applied pulse width ranges from 100 ns to 7.8 ns, and the maximum applied field is 170 Oe. The wall velocity increases nearly monotonically with field up to 9000 m/sec, which exceeds the Walker critical velocity of 3600 m/sec estimated by Hagedorn. A weak knee is observed in velocity-field curves at about 4400 m/sec, which appears to be the indication of the Walker peak or critical velocity. The velocity break down theories due to coherent or incoherent precession of magnetization around the drive field analyzed by Slonczewski in high field are not applicable to this material. A possible mechanism in high field appears to be that the wall moves followed by a wake as proposed by Hagedorn and Gyorgy, and recently by Schlomann.
11 citations
TL;DR: In this paper, the dynamics of a rod-shell system simulating nuclear reactor fuel rod bundles subjected to a parallel flow is studied analytically, and it is shown that the natural frequency and critical flow velocity of the coupled rod-fluid shell system are smaller than those of an isolated rod subjected to an axial flow.
11 citations
01 Jan 1974
TL;DR: In this paper, a simple empirical technique for predicting the water current velocity which will initiate one failure mode, i.e., entrainment failure, is presented, where the critical velocity is a function of the specific gravity of the oil and the interfacial tension between oil and water.
Abstract: The proper deployment and utilization of oil-containment barriers depends upon a knowledge of the failure mechanisms of such devices. A simple empirical technique for predicting the water current velocity which will initiate one failure mode, i.e., entrainment failure, is presented. The critical velocity is a function of the specific gravity of the oil and the interfacial tension between the oil and water. (Author)
TL;DR: In this article, it was shown that taking the viscous drag into account leads to a reduction of the critical velocity of a viscoelastic plate, which is the same as in this paper.
Abstract: The method of averaging is used to investigate the flutter of a viscoelastic plate. It is shown that taking the viscous drag into account leads to a reduction of the critical velocity.
TL;DR: In this article, the authors investigated the thermal resistance of He II contained in both metal and glass capillary tubes and observed a curious and highly reproducible fine structure, exhibited only in the metal tubes, can be satisfactorily accounted for by assuming the existence of two distinct distributions of vorticity.
Abstract: In an extensive investigation of the thermal resistance of He II contained in both metal and glass capillary tubes, we have observed a curious and highly reproducible fine structure heretofore not reported. This fine structure, exhibited only in the metal tubes, can be satisfactorily accounted for by assuming the existence of two distinct distributions of vorticity, each described by the Vinen theory. The significant difference in the thermal resistance between glass and metal tubes has serious implications toward critical velocity measurements.
01 Apr 1974
TL;DR: In this paper, the effect of incidence angle on the aerodynamic performance of an uncooled core turbine rotor blade was investigated experimentally in a two-dimensional cascade, and the results of the investigation include blade-surface velocity distribution and overall performance in terms of weight flow and loss for the range of incidence angles and exit velocity ratios investigated.
Abstract: The effect of incidence angle on the aerodynamic performance of an uncooled core turbine rotor blade was investigated experimentally in a two-dimensional cascade. The cascade test covered a range of incidence angles from minus 15 deg to 15 deg in 5-degree increments and a range of pressure ratios corresponding to ideal exit critical velocity ratios of 0.6 to 0.95. The principal measurements were blade-surface static pressures and cross-channel surveys of exit total pressure, static pressure, and flow angle. The results of the investigation include blade-surface velocity distribution and overall performance in terms of weight flow and loss for the range of incidence angles and exit velocity ratios investigated. The measured losses are also compared with two common methods of predicting incidence loss.
TL;DR: A rotating plasma experiment has been built which produces a stable, reproducible, super-magnetosonic flow in highly ionized argon as mentioned in this paper, which is used to model some aspects of the solar wind flow past bodies in the solar system.
Abstract: A rotating plasma experiment has been built which produces a stable, reproducible, super-magnetosonic flow in highly ionized argon. The rotation is produced by a radial electrical discharge across a vertical magnetic field. A preheat discharge gives uniform starting conditions for the flow. The flow velocity exceeds the limit predicted for argon by the Alfven critical velocity theory. Magnetosonic mach numbers up to 2.0 and flow times of 0.5 msec are obtained. The VORTEX plasma is used to model some aspects of the solar wind flow past bodies in the solar system.
01 May 1974
TL;DR: In this paper, the authors presented a technique for the economic selection of a slurry pipeline with the aid of a computer, where only the pipeline and its prime movers are considered.
Abstract: A technique is presented for the economic selection of a slurry pipeline with the aid of a computer. Mathematical models for the flow of homogeneous slurries are utilized. Only the pipeline and its prime movers are considered. Slurry flow properties are first obtained from rheology and/or pipeline data measurements. A rheological model is then selected for the slurry. It must be emphasized that the accuracy of the method is affected by the accuracy of the slurry flow-property data. Approximate cost parameters may be selected from data for plain and lined pipes, centrifugal and positive displacement pumps, motors and engines. Cost data for the purchase, operation and maintenance of slurry pipelines are also included. A total cost equation for the ownership and operation of a slurry pipeline system is then established. The complexity of the equation is a function of the rheological model selected to describe the slurry. The equation is solved with the aid of a computer for several combinations of pipeline diameters and throughputs to yield minimum total annual cost for the system. A mean velocity is then computed to give the required throughput. The velocity is constrained by an upper and lower bound. A high velocity is undesirable from an energy consumption viewpoint and if pipeline wear is possible. On the other hand, the velocity must exceed the deposition velocity for a heterogeneous suspension or the critical velocity for a homogeneous suspension. There is no guarantee that the velocity developed by this method will lie within the constraints applied, nor that the constraints are even known. This is particularly true for heterogeneous slurries. An important feature of the method is the ease with which the variables can be adjusted to measure the sensitivity of the total cost to the variables.
01 Jan 1974
TL;DR: In this article, the effect of incidence angle on the aerodynamic performance of an uncooled core-turbine rotor blade was investigated experimentally in a two-dimensional cascade, and the results of two methods of estimating incidence loss 1 were compared to the mea-sured loss.
Abstract: SUMMARYThe effect of incidence angle on the aerodynamic performance of an uncooled coreturbine rotor blade was investigated experimentally in a two-dimensional cascade. Thecascade test covered a range of incidence angles from -15 to 15 in 5-degree incre-ments and a range of pressure ratios corresponding to ideal exit critical velocity ratiosof 0. 6 to 0. 95. The principal measurements were blade-surface static pressure andcross-channel surveys of exit total pressure, static pressure, and flow angle. IThe shape of the inlet portion of the blade-surface velocity distribution changed sig-nificantly at large incidence angles. This effect was confined to the first 30 percent ofthe blade axial chord. At an ideal exit critical velocity ratio of 0. 7. kinetic energy loss| l ifor all nonzero incidence angles was higher than it was for zero incidence. The highestloss occurred at a positive incidence of .15°. jThe results of two methods of estimating incidence loss 1 were compared to the mea-sured loss. Estimated losses based on the assumption that the normal component of theinlet velocity is lost were generally too high. Losses estimated according to the methodof Ainley and Mathieson were in generally good agreement with the measured loss.INTRODUCTIONThe NASA Lewis Research Center has been involved in investigations of the perfor-mance of turbine blading for advanced aircraft engines. The high-bypass-ratio turbofanis one of these advanced engines. This engine has a multistage fan drive turbine and ahigh-speed, high-pressure, high-temperature core engine. The core engine turbine ischaracterized by short blade heights (high hub-tip radius ratio) and comprehensivecooling to cope with very high turbine inlet temperatures. The complicated and difficultto manufacture cooling provisions make it desirable to use constant-section, untwisted
01 Jan 1974
TL;DR: In this article, the non-linear analysis of axially moving mass has been presented and it is shown that upto a certain critical value of the transport velocity, the characteristic is similar to that of the stationary state.
Abstract: In this paper the non-linear analysis of an axially moving mass has been presented. It is shown that upto a certain critical value of the transport velocity,the characteristic is similar to that of the stationary state. At the critical velocity, it departs from its non-linear behaviour and the vibration mode is the same as that of the linear case with zero transport velocity. For transport velocities greater than the critical, the non-linear period T .N decreases as the initial tension and the flexural parameter mu increases. These conclusions are not borne out in a linear analysis.