Partitioned time-stepping scheme for an MHD system with temperature-dependent coefficients
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S S Ravindran↗
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High Temperature - Thin Film Strain Gages Based on Alloys of Indium Tin Oxide
A stable, high temperature strain gage based on reactively sputtered indium tin oxide (ITO) was demonstrated at temperatures up to 1050 C. These strain sensors exhibited relatively large, negative gage factors at room temperature and their piezoresistive response was both linear and reproducible when strained up to 700 micro-in/in. When cycled between compression and tension, these sensors also showed very little hysteresis, indicating excellent mechanical stability. Thin film strain gages based on selected ITO alloys withstood more than 50,000 strain cycles of +/- 500 micro-in/in during 180 hours of testing in air at 1000 C, with minimal drift at temperature. Drift rates as low as 0.0009%/hr at 1000 C were observed for ITO films that were annealed in nitrogen at 700 C prior to strain testing. These results compare favorably with state of the art 10 micro-m thick PdCr films deposited by NASA, where drift rates of 0.047%/hr at 1050 C were observed. Nitrogen annealing not only produced the lowest drift rates to date, but also produce the largest dynamic gage factors (G = 23.5). These wide bandgap, semiconductor strain sensors also exhibited moderately low temperature coefficients of resistance (TCR) at temperatures up to 1100 C, when tested in a nitrogen ambient. A TCR of +230 ppm/C over the temperature range 200 C < T < 500 C and a TCR of -469 ppm/C over the temperature range 600 C < T < 1100 C was observed for the films tested in nitrogen. However, the resistivity behavior changed considerably when the same films were tested in oxygen ambients. A TCR of -1560 ppm/C was obtained over the temperature range of 200 C < T < 1100 C. When similar films were protected with an overcoat or when ITO films were prepared with higher oxygen contents in the plasma, two distinct TCR's were observed. At T < 800 C, a linear TCR of -210 ppm/C was observed and at T > 800 C, a linear TCR of -2170 DDm/C was observed. The combination of a moderately low TCR and a relatively large gage factor make these semiconducting oxide films promising candidates for the active strain elements in high temperature thin film strain gages, particularly in applications where static strain measurement is desired.
Gregory, Otto J.↗
Temperature dependence of the NO super plus plus e dissociative- recombination-rate coefficient.
NO dissociative-recombination rate coefficient temperature dependence, assuming constant transition probability at potential crossing
Hansen, C. F.↗
Estimates of Doppler coefficients for in-pile thermionic reactor materials
Temperature coefficients of reactivity due to Doppler broadening of resonances in materials for in-pile thermionic reactor materials
TEMPERATURE MEASUREMENT↗
Latching solenoid for cryogenic valves
Pull-in and Delatching Coils of cryogenic solenoid contain copper and low-resistance, low-temperature-coefficient alloy to limit current at low temperatures.
Wang, W. S.↗
Nondestructive testing of electro thermal devices
This paper describes the results of a recent investigation into 'thermal time constant' nondestructive testing of high reliability electrical fuses. The use of established nondestructive test technology for examining the quality and firing characteristics of electro-explosive devices has been successfully applied to the inspection and prediction of the functional performance of electrical fuses. The technique requires application of a low level current pulse to the electrical fuse with an oscilloscope display of the curve as generated by the temperature coefficient of resistance feedback. The heating curve of temperature vs time is composed of one predominant thermal time constant, which is the product of the test unit's thermal capacity and thermal resistance. It has been found that the quality of the individual electrical fuse, for instance, the relative condition of the critical internal weld or solder joint, can be examined nondestructively.
Earnest, J. E., Jr.↗
Self-regulating proportionally controlled heating apparatus and technique
A self-regulating proportionally controlled heating apparatus and technique is provided wherein a single electrical resistance heating element having a temperature coefficient of resistance serves simultaneously as a heater and temperature sensor. The heating element is current-driven and the voltage drop across the heating element is monitored and a component extracted which is attributable to a change in actual temperature of the heating element from a desired reference temperature, so as to produce a resulting error signal. The error signal is utilized to control the level of the heater drive current and the actual heater temperature in a direction to reduce the noted temperature difference. The continuous nature of the process for deriving the error signal feedback information results in true proportional control of the heating element without the necessity for current-switching which may interfere with nearby sensitive circuits, and with no cyclical variation in the controlled temperature.
Strange, M. G.↗
A Satellite Borne Cadmium Sulfide Total Corpuscular Energy Detector
The properties of single crystals of cadmium sulfide as radiation detectors are described. It has been found possible to select crystals such that: (a) The ratio of increase of conductivity under irradiation to the rate of absorption of energy in the crystal is substantially independent of particle energy (over the examined ranges of 500 ev to 80 kev for electrons and 5 kev to 180 kev for protons) and of the magnitude of energy flux (over the range from.005 to 10 ergs/cm(sup 2 -sec); and (b) The above ration is substantially the same for protons, electrons, alpha particles, x-rays, and gamma-rays. For a driving voltage of 100 volts, typical crystal yield currents of 10(sup -7) to 10(sup- 6) amperes for each erg/cm(sup 2-sec) of energy absorbed by the crystal. The threshold of such crystal detectors (resulting from dark currents of the order of 10(sup 10 amp) is typically 10(sup -3) ergs/cm(sup 2- sec). For the selected crystals a response-temperature coefficient of -0.25% per degree centigrade is found for the temperature range -50 deg C to + 50 deg C. A description is given of a complete CdS total corpuscular energy detector for the study of geomagnetically trapped radiation by means of a satellite. The detector described has a dynamic range great than 10(sup 4), a solid angle of 10(exp -3) steradian, and a detection threshold of approximately 1 erg/cm(sup 2-sec-sterad). A similar detector employing a small magnet for the selective exclusion of electrons is also described. Noteworthy practical features of these detectors for satellite and space probe experiments are: (a) Use of bare crystals, without covering foils, in order to detect charged particles having energies as low as hundreds of electron volts. (b) Simplicity of electronic auxiliaries. (c) Compactness, lightweight and nechanical ruggedness. (d) Low electrical power requirements; and (e) Conversion of conduction current to the rate of a twostate relaxation oscillator in order to facilitate telemetric transmission of data. A pair of such detectors was flown as part of the s-46 satellite payload on March 23, 1960, but due to vehicular failure an orbit was not achieved and the operation of the CdS detectors was observed for only, six minutes of flight.
Freeman, John W.↗
Aspects of Cool-Flame Supported Droplet Combustion in Microgravity
Droplet combustion experiments performed on board the International Space Station have shown that normal-alkane fuels with negative temperature coefficient (NTC) chemistry can support quasi-steady, low-temperature combustion without any visible flame. Here we review the results for n-decane, n-heptane, and n-octane droplets burning in carbon dioxidehelium diluted environments at different pressures and initial droplet sizes. Experimental results for cool-flame burning rates, flame standoff ratios, and extinction diameters are compared against simplified theoretical models of the phenomenon. A simplified quasi-steady model based on the partial-burning regime of Lin predicts the burning rate, and flame standoff ratio reasonably well for all three normal alkanes. The second-stage cool-flame burning and extinction following the first-stage hot-flame combustion, however, shows a small dependence on the initial droplet size, thus deviating from the quasi-steady results. An asymptotic model that estimates the oxygen depletion by the hot flame and its influence on cool-flame burning rates is shown to correct the quasi-steady results and provide a better comparison with the measured burning-rate results.This work was supported by the NASA Space Life and Physical Sciences Research and Applications Program and the International Space Station Program.
cool flames↗
Three Stage Cool Flame Droplet Burning Behavior of n-Alkane Droplets at Elevated Pressure Conditions: Hot, Warm and Cool Flame
Transient, isolated n-alkane droplet combustion is simulated at elevated pressure for helium-diluent substituted-air mixtures. We report the presence of unique quasi-steady, three-stage burning behavior of large sphero-symmetric n-alkane droplets at these elevated pressures and helium substituted ambient fractions. Upon initiation of reaction, hot-flame diffusive burning of large droplets is initiated that radiatively extinguishes to establish cool flame burning conditions in nitrogen/oxygen “air” at atmospheric and elevated pressures. However, at elevated pressure and moderate helium substitution for nitrogen ( X He > 20%), the initiated cool flame burning proceeds through two distinct, quasi-steady-state, cool flame burning conditions. The classical “Hot flame ” ( ∼1500 K) radiatively extinguishes into a “Warm flame ” burning mode at a moderate maximum reaction zone temperature ( ∼ 970 K), followed by a transition to a lower temperature ( ∼765 K), quasi-steady “Cool flame ” burning condition. The reaction zone (“flame”) temperatures are associated with distinctly different yields in intermediate reaction products within the reaction zones and surrounding near-field, and the flame-standoff ratios characterizing each burning mode progressively decrease. The presence of all three stages first appears with helium substitution near 20%, and the duration of each stage is observed to be strongly dependent on helium substitutions level between 20–60%. For helium substitution greater than 60%, the hot flame extinction is followed by only the lower temperature cool flame burning mode. In addition to the strong coupling between the diffusive loss of both energy and species and the slowly evolving degenerate branching in the low and negative temperature coefficient (NTC) kinetic regimes, the competition between the low-temperature chain branching and intermediate-temperature chain termination reactions control the “Warm” and “Cool ” flame quasi-steady conditions and transitioning dynamics.
Droplet Combustion↗
Implementation of a self-controlling heater
Temperature control of radiation sensors, targets, and other critical components is a common requirement in modern scientific instruments. Conventional control systems use a heater and a temperature sensor mounted on the body to be controlled. For proportional control, the sensor provides feedback to circuitry which drives the heater with an amount of power proportional to the temperature error. It is impractical or undesirable to mount both a heater and a sensor on certain components such as ultra-small parts or thin filaments. In principle, a variable current through the element is used for heating, and the change in voltage drop due to the element's temperature coefficient is separated and used to monitor or control its own temperature. Since there are no thermal propagation delays between heater and sensor, such control systems are exceptionally stable.
Strange, M. G.↗
Small Mercury Ion Clock for On-board Spacecraft Navigation
I.Small Ion Clock Approach and Heritage: a) No lasers, uwave cavities, cryogenics, atomic beams, etc. b) Ions are electrically shuttled between separate optical and microwave traps. II. Each trap is optimized for its task: quadrupole for optical state selection; multi-pole for microwave clock. a) Very good stability shown in USNO. Timescale running "open loop." III. "Open loop" operation means no self-measurements of frequency offsets: (Zeeman, ion temperature,... etc.) a) Fewer parts and procedures, produces stable output continuously. IV. Ion clock is not so sensitive to temperature fluctuations a) Measured u:nshielded temperature coefficient of few 10(exp -15) per C. b) No bulky temperature isolation needed.
Prestage, John D.↗
Characterization of path effects on the properties of balloon films
The effect of stress and temperature path on the mechanical properties of a balloon film material (Astrofilm E2) have been studied using two techniques. The first technique is based on uniaxial tensile measurements of prestrained strips of the film as a function of temperature. Data are analyzed in terms of two temperature coefficients, defined here as a stiffness coefficient and a strength coefficient; and by comparing the areas under the stress-strain curves. The second technique investigated the effect of stress and temperature path on inflated cylinders of the same material. The changes in the mechanical properties due to preconditioning in the biaxial stress state were evaluated using the ball burst test. Preliminary findings indicate that the material is stress and temperature path dependent. Changes in stiffness coefficient, draw strength and toughness were measured and discussed. The above techniques may be suitable to document path dependent changes, and to discriminate among films of different manufacture.
Said, Magdi A.↗
Temperature dependence of association of diatomic ions in diatomic gases
The present study compares the experimental rate coefficient temperature dependences for the association of diatomic ions in diatomic gases with the results of model calculations in which it is assumed that the stabilization of the initially formed unstable association complex occurs through the formation of a 'supercomplex'. The acceptable degree of agreement obtained between model and experimental data for the cases of four sample reactions, on the basis of a minimum of plausible assumptions, indicates that earlier theoretical models furnishing an accurate description of the formation and destruction of the association complex, but failing to reproduce experimental data, inadequately treated the temperature dependence of the stabilization step.
Johnsen, R.↗
Low temperature latching solenoid
A magnetically latching solenoid includes a pull-in coil and a delatching coil. Each of the coils is constructed with a combination of wire materials, including material of low temperature coefficient of resistivity to enable the solenoid to be operated at cryogenic temperatures while maintaining sufficient coil resistance. An armature is spring-based toward a first position, that may extend beyond the field of force of a permanent magnet. When voltage is temporarily applied across the pull-in magnet, the induced electromagnetic forces overcome the spring force and pulls the armature to a second position within the field of the permanent magnet, which latches the armature in the pulled-in position. Application of voltage across the delatching coil induces electromagnetic force which at least partially temporarily nullifies the field of the permanent magnet at the armature, thereby delatching the armature and allowing the spring to move the armature to the first position.
Wang, W. S.↗
Thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity
Computer simulation of steady-state axisymmetrical heat transfer and fluid flow was conducted to study thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity. The effects of key variables on the extent of thermocapillary flow in the melt zone, the shapes of melt/solid interfaces and the length of the melt zone were discussed. These variables are: (1) the temperature coefficient of surface tension (or the Marangoni number), (2) the pulling speed (or the Peclet number), (3) the feed rod radius, (4) the ambient temperature distribution, (5) the heat transfer coefficient (or the Biot number), and (6) the thermal diffusivity of the material (or the Prandtl number).
Lan, C. W.↗
Connection between variations of the atmosphere temperature profile and variations of the meson component intensity
The influence of temperature effects on intensity variations of the cosmic ray meson component were studied. The connection between the temperature variation delta T and the intensity variation delta I was established by using the temperature coefficient density technique. To realize how many devices are needed on the Earth for predicting the temperature variation of the atmosphere profile with a reasonable accuracy, IO isobaric levels and IO were calculated. The set of initial elements of the cosmic ray mesons are varied and it is shown that the matrix of the coefficients B sub ij is rather sensitive to their choice. It is found that if for the calculations of the atmospheric temperature variations the model is used, the number of meson components, essentially exceeding 3, should be considered.
Blokh, Y. L.↗
Electrical Conductivity of HgTe at High Temperatures
The electrical conductivity of HgTe was measured using a rotating magnetic field method from 300 K to the melting point (943 K). A microscopic theory for electrical conduction was used to calculate the expected temperature dependence of the HgTe conductivity. A comparison between the measured and calculated conductivities was used to obtain the estimates of the temperature dependence of Gamma(sub 6)-Gamma(sub 8) energy gap from 300 K to 943 K. The estimated temperature coefficient for the energy gap was comparable to the previous results at lower temperatures (less than or equal to 300 K). A rapid increase in the conductivity just above 300 K and a subsequent decrease at 500 K is attributed to band crossover effects. This paper describes the experimental approach and some of the theoretical calculation details.
Li, C.↗