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In an earlier study,1 values of the thermal-conductivity (viscosity) cross section for argon deduced from velocity distributions measured near the centerline of a free jet deviated unexpectedly from the temperature dependence predicted for low temperatures. Subsequently, the molecular-beam sampling system and data-reduction procedures used in that study were upgraded and the measurements were repeated. Cross-section values were obtained at temperatures more than an order of magnitude below the normal condensation temperature of argon. The temperature dependence of the deduced effective hard-sphere diameter is in good agreement with the predicted dependence, but the magnitudes are about 10 percent less then the predicted values.

The kinematic boundary condition has a profound effect on the velocity field in a flow channel. This effect will be studied with respect to an extensional rheometer of planar extensional flow.

In general, dynamic seals can be categorized into four basic types, shaft, face, labyrinth, blade tip or their combinations. The flow field for the shaft or cylindrical seal is simplest to describe and the tip seal is the most complex due to a combination of axial flow around the blade and circumferential flow over the tip.

The stability of seals, bearings, and shaft dampers depends critically on the pressure profiles within clearance passages. The pressure profiles which provide the restoring forces and stiffness in some passages are critically dependent on inlet geometry and fluid stagnation pressure and temperature. In nearly all cases, simple geometries or combinations of simple geometries are used.

The first part of a sodium seeded free jet expansion (from the orifice to about 20 nozzle diameters downstream) is illuminated with light from a single mode CW dye laser and the spatial distribution of the resulting fluorescence is measured. Results for different carrier gases (Ar, Ne, He, N2) and different stagnation pressures (1–20 Torr.mm) have been obtained. At the highest stagnation pressures the fluorescence intensity distributions are in good agreement with the prediction from MOC calculations, a qualitative analysis of the deviations at lower stagnation pressures is given.

The spatial distribution of Sodium dimers (Na2) is studied experimentally in the first part of a free jet expansion of Sodium vapour, using laser induced fluorescence. Angular intensity profiles have been measured for several (v,J) — states of the molecules. Their features turn out to be very different, depending on the values of v,J and the stagnation pressure P0. These results allow to get some insight in the various relaxation- and freezing-processes taking place in the expansion.

Nowadays inelastic collisions with the energy exchange of a rotational motion of molecules attract a wide attention of researcher (eg., see recent review1). Supersonic expansion of gas in nozzles or free jets is one of the most suitable methods of investigation of rotational relaxation that explains the appearance of a great number of experimental works related to this topic. In the experiments on the rotational relaxation in free jets various diagnostics methods are used, however, a more detailed information on rotational relaxation has been obtained with the use of the electron-beam diagnostics.

In the past, hypersonic aerodynamics has been concerned primarily with continuum flow. For ballistic re-entry vehicles, it was established in earlier studies [1] that most of the problems which tend to define the vehicle occur at altitudes below 200,000 ft, where the flow is substantially a continuum one. However, lifting re-entry from satellite orbits and any type of space re-entry may give rise to significant aerodynamic problems at altitudes between 200,000 and 500,000 ft. Although the forces are low, they act over relatively long periods of time and may have a lasting effect on the motions of the vehicle and, consequently, its design. Perhaps even more important is the necessity of knowing and understanding the ionized wake characteristics for low radar cross-section vehicles.

The work reported here is part of a series of experiments [1–5] conducted in recent years at the NASA Lewis Research Center involving two-phase choked flow of liquid cryogens. The essential characteristics of these experiments were that the initial stagnation conditions were always single-phase and subcooled and that the pressure drop in the flow passage was always to a level below saturation. A wide range of stagnation parameters from well below to above the thermodynamic critical state were examined. The work covered a variety of fluids and geometric openings. The present study deals with a sharp-edged orifice. The literature on two-phase choked flow has been surveyed by Hsu [6], Henry et al. [7] and Smith [8].

The design of refrigeration machinery and other low-temperature process systems often calls for accurate sizing of variable area control devices which are subject to two-phase flow. It has been recognized for some time that with large pressure gradients these elements frequently may operate in a regime characterized by “critical” or mass limited flow quite similar to that observed for a single vapor phase. Thus, if we consider the case where saturated liquid escapes through an orifice from a high-pressure surrounding into a low-pressure reservoir, it will be noted that at first the flow rate increases uniformly as the receiver pressure is lowered. Soon, however, a point will be reached where the mass flux of the escaping stream achieves a maximum, which then cannot be exceeded by further decreasing the outlet pressure. It is this situation, applied to the particular fluid systems of oxygen and nitrogen, which has been the subject of the present study.

The critical discharge of fluids is of interest in a variety of industries: transportation, nuclear power, desalinization, aeronautics, and astronautics, to cite a few. The interest stems primarily from venting requirements and flow measurements, but includes such novel techniques as the production of hydrogen.