Physical Sciences

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.

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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."

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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.

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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).

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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.

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Microelectromechanical Sensors Based on Magnetoresistance

These would offer advantages over similar sensors based on quantum-mechanical tunneling of electrons. Microelectromechanical sensors based on magnetoresistance have been proposed. Like other microelectromechanical sensors, these would be used to measure physical quantities that can be made to manifest themselves in small mechanical displacements. Potential applications for microelectromechanical sensors include accelerometers, magnetometers, bolometers, pressure sensors, seismometers, Golay cells, and microphones. Potential markets include the aerospace, biomedical, semiconductor, automotive, and defense industries.

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Model of Pyrolysis of Biomass in a Fluidized-Bed Reactor

Complex dynamics and heat transfer are represented more realistically than in prior models. A mathematical model has been formulated to describe the pyrolysis of biomass in a bubbling fluidized-bed reactor. The reactor is a vertical cylinder that contains a mixture of biomass particles and sand. Superheated steam enters the reactor through holes in the bottom and flows out freely at the top. The sand is a high heat capacity medium used for heating the biomass. The biomass particles, initially at room temperature, are introduced into the already hot reactor and become heated primarily through contact with the sand. Upon reaching a threshold temperature, the biomass particles undergo chemical reactions, the gaseous products of which are carried away by the flow of steam. The "bubbles" are regions of the fluidized bed that are mostly devoid of particles; these regions occur as a result of the interaction of the turbulent gaseous flow with the particles.

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