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Validated Model of a Fluid Drop for All Pressures

The report "A Validated All-Pressure Fluid Drop Model and Lewis Number Effects for a Binary Mixture" presents one in a series of theoretical and computational studies of the subcritical and subpercritical behaviors of a drop of fluid and, in particular, a drop of heptane surrounded by nitrogen The study is based on a fluid-drop model in which, among other things, the differences between subcritical and supercritical behaviors are identified with length scales. It is shown that in the subcritical regime and for a large rate of evaporation from the drop, there exists a mass0fraction "Film layer" immediately below the drop surface and the solution of the model equations has a convective-diffusive character. In the supercritical regime, there is no material surface to follow and this introduces an indeterminancy in the boundary conditions. To resolve the indeterminancy, one must follow an arbitrary boundary, which, in this case, is that of the initial fluid drop. The solution has then a purely diffusive character, and from this solution, one calculates the location of the highest density gradient, which location is identified with the optically observable boundary. It is also shown that the classical calculation of the Lewis number gives qualitatively erroneous results at supercritical conditions, but that an effective Lewis number previously defined gives qualitatively correct estimates of the length scales for heat and mass transfer at all pressures.

Posted in: Briefs, TSP, Physical Sciences

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Numerical Index for Quantifying Aircraft Icing Hazards

This index would offer several advantages over the present four-level index. A new method for assessing and communicating aviation in-flight icing hazards has been proposed. This methodology creates a simple numerical index for quantifying hazard severity. The index is traceable to flight-level meteorology and aircraft-specific, icing-induced reductions in aircraft performance. It also provides a connection to a statistical data base of icing meteorology. This system will clarify the terminology used to describe the degree of danger posed by specific meteorological conditions. The relationship between hazard severity and meteorology is related by measured ice accumulation rates observed on a standard airfoil under prescribed conditions. This system has greater fidelity than the existing system and is applicable to all types of air vehicles.

Posted in: Briefs, TSP, Physical Sciences

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DNS of Mixing of Supercritical Heptane and Nitrogen

A report discusses direct numerical simulations (DNS) of a developing mixing layer between nitrogen and heptane initially at different temperatures and initially flowing at different velocities under supercritical conditions. The usual conservation equations for a binary fluid, along with the Peng-Robinson equation of state for the heptane/nitrogen mixture, were solved numerically and the solutions analyzed. Departures from perfect-gas and ideal-mixture conditions were quantified by compression factors and mass-diffusion factors, both of which exhibited decreases from unity.

Posted in: Briefs, TSP, Physical Sciences

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Polarization Recycling for Lighting LCD's More Efficiently

Unpolarized light would be utilized fully, without enlargement of the illuminated area. Two polarization-recycling techniques have been proposed to increase the efficiency of illumination of liquid-crystal display (LCD) panels. The motivation for this proposal lies in the inherent inefficiency of an LCD panel: For proper operation, illumination with polarized light is necessary, but a typical lamp generates unpolarized light. If one simply passes the lamp light through a polarizer on the way to the LCD panel, then one wastes the half of the light that is in the undesired polarization. To increase the efficiency of illumination, one would have to recycle the otherwise wasted light, converting the undesired polarization to the desired one; this is what is meant by "polarization recycling."

Posted in: Briefs, TSP, Physical Sciences

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Fiber-Optic Transducers for Distributed Sensing of Volatiles: An Optical Nose

Volatiles would swell polymers on optical fibers, inducing changes in indices of refraction. The term "optical nose" refers to a fiber-optic chemical sensor of a type that has been proposed to enable distributed measurement of the concentrations of volatile compounds. Optical noses should not be confused with electronic noses, which are single-point sensors based on chemical-induced variations of the electrical resistances of carbon-black/polymer composite films. Optical noses could enable rapid measurement of gas mixtures (e.g., volatile compounds in air) at multiple sensing locations along their lengths, which could be of the order of kilometers. Optical noses could function well in locations where audio- and radio-frequency electromagnetic interference renders electronic noses ineffective. Moreover, it may be easier to fabricate optical noses than to fabricate electronic noses because it would not be necessary to handle carbon black.

Posted in: Briefs, TSP, Physical Sciences

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Rare-Earth Optical Temperature Sensors

These sensors exploit the narrow-band emission peculiar to rare earths. A recently developed type of fiber-optic temperature sensor utilizes narrow-band near-infrared radiation emitted by rare-earth ions. These sensors are suitable for use in harsh environments at temperatures above the maximum (1,700 °C) that Pt/Rh thermocouples can withstand. The maximum operating temperature for these optical temperature sensors can equal or exceed 2,000 °C, the exact values depending on the choice of fiber-optic and rare-earth-containing radiative materials. The minimum temperature measurable by use of a sensor of this type, related to the minimum detectable radiation, has been found to be ≈700 K (≈427 °C).

Posted in: Briefs, TSP, Physical Sciences

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Capacitive Sensor for Measuring Level of Liquid Nitrogen

The liquid is used as a dielectric layer in a parallel-plate capacitor. The feasibility of a capacitive sensor for measuring the level of liquid nitrogen in a container has been demonstrated. The basic sensor design could also readily be adapted to measurement of the levels of cryogenic liquids other than nitrogen.

Posted in: Briefs, Physical Sciences

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