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At least 1,225 records · Page 68

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NASA NTRS1985

Gel Precursors as Glass and Ceramic Starting Materials for Space Processing Applications Research

The crystallization kinetics and glass forming ability of reluctant glass formers is investigated. This could ultimately aid the formation of bulk samples of unique glass compositions outside of normal glass forming regions allowing the optimization of certain properties of the glass. One important aspect of processing in space is the containerless undercooling of molten substances. Theoretically, the extent of undercooling can be greatly enhanced by solidifying in the absence of heterogeneous nucleation resulting from contact with crucibles or molds. Techniques were established for the measurement of crystallization kinetics and critical cooling rates. The glass formation ability and crystallization kinetics of Ga2O-43CaO and several Al2O3-CaO compositions were measured. An apparatus was set up to measure the temperature of spherical samples on a thermocouple at large cooling rates. The time and temperature of nucleation is recorded and the probability of nucleation at various cooling rates can be measured.

Downs, R. L.↗

NASA NTRS1985

Glass Formation in Reluctant Glass Formers

The crystallization kinetics and glass forming ability of reluctant glass formers is investigated. This could ultimately aid the formation of bulk samples of unique glass compositions outside of normal glass forming regions allowing the optimization of certain properties of the glass. One important aspect of processing space is the containerless undercooling of molten substances. Theoretically, the extent of undercooling can be greatly enhanced by solidifying in the absence of heterogeneous nucleation resulting from contact with crucibles or molds. Techniques were established for the measurement of crystallization kinetics and critical cooling rates. The glass formation ability and crystallization kinetics of Ga2O-43CaO and several Al2O3-CaO compositions were measured. An apparatus was set up to measure the temperature of spherical samples on a thermocouple at large cooling rates. The time and temperature of nucleation is recorded and the probability of nucleation at various cooling rates can be measured.

Ethridge, E. C.↗

NASA NTRS1985

Airflow calibration of a bellmouth inlet for measurement of compressor airflow in turbine-powered propulsion simulators

The development of turbine-powered propulsion simulators for high-speed wind tunnel models requires a bellmouth inlet which can accurately measure compressor-inlet airflow. A bellmouth inlet was instrumented with total pressure probes, static pressure probes, and thermocouples for airflow measurement. The bellmouth flowmeter against a critical venturi flowmeter was calibrated. The calibration was done at four inlet pressures ranging from 58 to 114 kPa. The bellmouth discharge coefficient varied as a function of bellmouth-throat Mach number. Over the range of Reynolds number and Mach number tested the Reynolds number was not a significant influence on the discharge coefficient. The overall accuracy of the bellmouth inlet as a flowmeter was estimated to be + or - 0.5% of the flowmeter reading.

Smith, S. C.↗

NASA NTRS1983

HOST liner cyclic facilities

The HOST Liner Cyclic Program is utilizing two types of test apparatus, rectangular box rigs and a full annular rig. To date two quartz lamp cyclic box rigs have been tested and a third is to begin testing in late October 1983. The box rigs are used to evaluate 5x8 inch rectangular linear samples. A 21 inch diameter outer liner simulator is also being built up for testing beginning in April 1984. All rigs are atmospheric rigs. The first box rig, a three 6-kVA lamp installation, was operated under adverse conditions to determine feasibility of using quartz lamps for cyclic testing. This work was done in December 1981 and looked promising. The second box rig, again using three 6-kVA lamps, was operated to obtain instrumentation durability information and initial data input to a Finite Element Model. This limited test program was conducted in August 1983. Five test plates were run. Instrumentation consisted of strain gages, thermocouples and thermal paint. The strain gages were found to fail at 1200 F as expected though plates were heated to 1700 F. The third box rig, containing four 6-kVA lamps, is in build up for testing to begin in late October 1983. In addition to 33 percent greater power input, this rig has provision for 400 F backside line cooling air and a viewing port suitable for IR camera viewing. The casing is also water cooled for extended durability.

Schultz, D.↗

NASA NTRS1985

Turbine blade and vane heat flux sensor development, phase 2

The development of heat flux sensors for gas turbine blades and vanes and the demonstration of heat transfer measurement methods are reported. The performance of the heat flux sensors was evaluated in a cylinder in cross flow experiment and compared with two other heat flux measurement methods, the slug calorimeter and a dynamic method based on fluctuating gas and surface temperature. Two cylinders, each instrumented with an embedded thermocouple sensor, a Gardon gauge, and a slug calorimeter, were fabricated. Each sensor type was calibrated using a quartz lamp bank facility. The instrumented cylinders were then tested in an atmospheric pressure combustor rig at conditions up to gas stream temperatures of 1700K and velocities to Mach 0.74. The test data are compared to other measurements and analytical prediction.

Atkinson, W. H.↗

NASA NTRS1986

A numerical and experimental investigation of electrochemical aircraft deicing

This study was composed of three parts. The first part involved the extension of an existing transient two dimensional numerical code for an electrothermal deicer so that it would simulate the situation where a variable thickness ice layer existed at the outer surface. The Enthalpy Method was used to simulate the phase change, and Gauss-Seidel iteration was used to solve the resulting system of finite difference equations. A set of criteria were developed for determining when a variable thickness ice layer had an effect on deicer performance. The second part was the acquisition and analysis of experimental data. The test model was a section of a Bell UH-1H helicopter blade equipped with an electrothermal deicer. A total of fifty-two thermocouples were utilized to document the thermal response of the blade and decier assembly. In the deicing runs, the experimental temperature response data clearly showed when melting, shedding or refreezing occurred. The tests illustrated that the criterion for shedding in the three cases where it did occur was that the abrasion shield interface temperature was 32 to 34 F. The third part concerned the validation of a one dimensional transient thermal model of an electrothermal deicer by comparison of the predictions with the experimental data. The Enthalpy Method was found to effectively model the phase change which occurred, and the ice shedding algorithm employed in the simulation was also evaluated.

Leffel, K. L.↗

NASA NTRS1986

Cryogenic wind tunnels: Problems of continuous operation at low temperatures

The design of a cryogenic wind tunnel which operates continuously, and is capable of attaining transonic speeds at generating pressures of about 3 bars is described. Its stainless steel construction with inside insulation allows for very rapid temperature variations promoted by rapid changes in the liquid nitrogen flow. A comparative study of temperature measuring probes shows a good reliability of thin sheet thermocouples. To measure fluctuations, only a cold wire makes it possible to record frequencies of about 300 Hz. The use of an integral computer method makes it possible to determine the impact of the wall temperature ratio to the adiabatic wall temperature for the various parameters characterizing the boundary layer. These cases are processed with positive and negative pressure gradients.

Faulmann, D.↗

NASA NTRS1986

Research instrumentation for hot section components of turbine engines

Programs to develop research instrumentation for use on hot section components of turbine engines are discussed. These programs can be separated into two categories: one category includes instruments which can measure the environment within the combustor and turbine components, the other includes instruments which measure the response of engine components to the imposed environment. Included in the first category are instruments to measure total heat flux and fluctuating gas temperature. High temperature strain measuring systems, thin film sensors (e.g., turbine blade thermocouples) and a system to view the interior of a combustor during engine operation are programs which comprise the second category. The paper will describe the state of development of these sensors and measuring systems and, in some cases, show examples of measurements made with this instrumentation. The discussion will cover work done at NASA Lewis and at various contractor facilities.

Englund, D. R.↗

NASA NTRS1985

Development and usage of a small-scale V/STOL ground effects simulator

A small scale ground effects simulator for V/STOL aircraft design testing has been built by an American university in association with NASA-AMES. The simulator is used to measure pressures and forces on a wide variety of V/STOL model configurations including generic models which do not represent any particular aircraft. The modes of operation and instrumentation of the simulator are described, and a survey of some recent test results are presented. The basic simulator consists of two parts, an aluminum disk ground plane and a model support. Instrumentation consists of pressure transducers, scanivalves, thermocouples and hot wire anemometers. Test results are presented for single and twin nozzle configurations; a generic V/STOL design, and the Harrier and Grumman 698 combat aircraft models. A black and white photograph of the simulator is provided.

Lord, P. A.↗

NASA NTRS1985

Thermal and sputtered aluminum oxide coatings for high temperature electrical insulation

Aluminum oxide coatings have been investigated as electrically insulating layers for mounting thin film Pt-Pt/Rh thermocouples on gas turbine blade and vane alloys (MAR M200 + Hf and MAR M509). Thermal oxides were grown directly onto NiCoCrAlY and FeCrAlY coatings on these alloys at temperature between 1300 and 1400 K in oxygen partial pressures 10 to the -7th to 2 x 10 to the 4th Pa. Although these thermal oxides exhibited good adherence, analytical characterizations using electron and optical microscopy, as well as X-ray photoelectron spectroscopy showed that they had defects and impurities which limited their insulating ability. The insulating quality of the coating was greatly improved however by reactively sputtering an aluminum oxide film over the thermal oxide. Results are presented on the electrical performance of the 2-5 micron thick composite layers for temperatures up to 1300 K.

Kreider, K. G.↗

NASA NTRS1985

Real-time SEM studies in controlled reactive atmospheres

A unique scanning electron accessory has been developed that allows the observation of specimens under partial pressures of any gas. The sample is placed in a metal support boat inside a special sample holder. The sample in the boat is imaged on a CRT and is simultaneously recorded on a videotape, allowing the reaction between the sample and the gas to be observed in real time. Sample changes can be seen continuously as the sample is being heated or cooled. This process allows the observation of material transformations such as phase changes as they happen. Temperatures as high as 1000 C have been used and are continuously monitored using a thermocouple with a digital display on the CRT and videotape. X-ray analyses can also be run before and after any reactions. In the study described here, thick-film screen-printing inks using molybdenum/tin compositions as a replacement for silver were developed to be used on terrestrial photovoltaic cells. Pieces were placed on the sample stage and heated in both O2 and H2 atmospheres. The results were used to determine the most effective frits to be used in the thick-film inks.

Gallagher, B. D.↗

NASA NTRS1986

Further development of the dynamic gas temperature measurement system

A compensated thermocouple measurement method was experimentally verified. Dynamic signal content from an atmospheric pressure laboratory burner was measured by the dynamic temperature sensor and a relatively delicate fine-wire resistance thermometer. Compensated data from the two dynamic temperature sensor thermoelements were compared with the compensated fine-wire data in the frequency domain. Absolute differences between spectral line amplitudes measured with different sensors are small relative to the mean temperature and verify the compenation method. Increases in precision of the measurement method require optimization of several factors, and directions for further work are identified.

Elmore, D. L.↗

NASA NTRS1987

Controller for Fast-Acting Furnaces

Circuit slows responses of certain furnace types. Circuit output actuates external power supply, which furnishes heater power to furnace in response to furnace temperature sensed by thermocouple. Temperaturecontrol circuit suppresses temperature oscillations in rapidly responding laboratory furnaces. Ordinarily, such furnaces difficult to control because temperatures change very rapidly with changes in delivered electric power. Ordinary commercial controllers not designed to handle this kind of response.

Williams, R. J.↗

NASA NTRS1987

Measuring Specific Heats at High Temperatures

Flash apparatus for measuring thermal diffusivities at temperatures from 300 to 1,000 degrees C modified; measures specific heats of samples to accuracy of 4 to 5 percent. Specific heat and thermal diffusivity of sample measured. Xenon flash emits pulse of radiation, absorbed by sputtered graphite coating on sample. Sample temperature measured with thermocouple, and temperature rise due to pulse measured by InSb detector.

Vandersande, Jan W.↗

NASA NTRS1987

Fiber-Optic Temperature Sensor

Proposed sensor measures temperatures over wide range, from cryogenic liquids to burning gases. Made in part of optical fibers, sensor lighter in weight than thermocouple and immune to electromagnetic interference. Device does not respond to temperatures elsewhere than at sensing tip. Thermal expansion and contraction of distance between fiber end and mirror alters interference between light reflected from those two surfaces, thereby giving interferometric indication of temperatures.

Maram, Jonathan M.↗

NASA NTRS1987

Meteoritic basalts: The nakhlites, their parental magmas, cooling rates, and equivalents on Earth

Field study in northern Ontario was planned to compare cumulate rocks reported in the literature with the nakhlites in order to study the crystallization rates of the nakhlites and their possible geological settings. Experimental studies have progressed slowly because of the demands of the field work and teaching. The furnace is fully functional, and its thermocouple and oxygen sensor cells are functional and calibrated.

Treiman, Allan H.↗

NASA NTRS1986

Further development of the dynamic gas temperature measurement system. Volume 1: Technical efforts

A compensated dynamic gas temperature thermocouple measurement method was experimentally verified. Dynamic gas temperature signals from a flow passing through a chopped-wheel signal generator and an atmospheric pressure laboratory burner were measured by the dynamic temperature sensor and other fast-response sensors. Compensated data from dynamic temperature sensor thermoelements were compared with fast-response sensors. Results from the two experiments are presented as time-dependent waveforms and spectral plots. Comparisons between compensated dynamic temperature sensor spectra and a commercially available optical fiber thermometer compensated spectra were made for the atmospheric burner experiment. Increases in precision of the measurement method require optimization of several factors, and directions for further work are identified.

Elmore, D. L.↗

NASA NTRS1987

Rapid melt/quench furnace using commercially available hardware

This report describes an off-the-shelf Orbital Tube Welder that can be easily used to melt and resolidify almost any electrically conductive material. This can be done on a KC-135 Aircraft within the microgravity period of one parabola. Melt sizes 3 mm diameter by 10 mm length and larger are feasible with most if not all materials. A highly reproducible, controlled, programmable heat and cool cycle can be provided. Sample measurements would have to be developed and could be as sophisticated or as simple as desired. These could include: optical and thermocouple temperature measurements, Peltier pulser for marking the solidification fronts, dimensional changes and whatever. Sample heat flows could be fixed over a very wide range being limited mostly by the cooling period, the desired sample size, and the 20 sec microgravity period of the KC-135 Aircraft parabola.

Poorman, Richard M.↗