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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Cool Flame Quenching

Cool flame quenching distances are generally presumed to be larger than those associated with hot flames, because the quenching distance scales with the inverse of the flame propagation speed, and cool flame propagation speeds are often times slower than those associated with hot flames. To date, this presumption has never been put to a rigorous test, because unstirred, non-isothermal cool flame studies on Earth are complicated by natural convection. Moreover, the critical Peclet number (Pe) for quenching of cool flames has never been established and may not be the same as that associated with wall quenching due to conduction heat loss in hot flames, Pe approx. = 40-60. The objectives of this ground-based study are to: (1) better understand the role of conduction heat loss and species diffusion on cool flame quenching (i.e., Lewis number effects), (2) determine cool flame quenching distances (i.e, critical Peclet number, Pe) for different experimental parameters and vessel surface pretreatments, and (3) understand the mechanisms that govern the quenching distances in premixtures that support cool flames as well as hot flames induced by spark-ignition. Objective (3) poses a unique fire safety hazard if conditions exist where cool flame quenching distances are smaller than those associated with hot flames. For example, a significant, yet unexplored risk, can occur if a multi-stage ignition (a cool flame that transitions to a hot flame) occurs in a vessel size that is smaller than that associated with the hot quenching distance. To accomplish the above objectives, a variety of hydrocarbon-air mixtures will be tested in a static reactor at elevated temperature in the laboratory (1g). In addition, reactions with chemical induction times that are sufficiently short will be tested aboard NASA's KC-135 microgravity (mu-g) aircraft. The mu-g results will be compared to a numerical model that includes species diffusion, heat conduction, and a skeletal kinetic mechanism, following the work on diffusion-controlled cool flames by Fairlie et,al., 2000.

Pearlman, Howard↗
NASA NTRS1991

Model of the Frictional Heating of Inconel 718 and Titanium (ti-6al-4v) in Helium

A computer model of the frictional heating of metals in an inert environment has been developed. The model incorporates the effects of the heat loss from the samples due to conduction, radiation, and convection to the surroundings. This model allows the measured temperatures to be used to determine the amount of heat produced at the interface during the experiment by the sliding contact of two different metallic samples. The results of the simulation for an experiment run at the NASA White Sands Test Facility (WSTF) show that for the same heat production at the interface the heat losses have a significant effect on the temperatures in the samples. But, the heat losses do not significantly affect the different calculated heat flows (or friction coefficients), at the interface, that are necessary to correlate the measured temperatures.

Skowlund, Christopher T.↗
NASA NTRS2007

Catalytic Ignition and Upstream Reaction Propagation in Monolith Reactors

Using numerical simulations, this work demonstrates a concept called back-end ignition for lighting-off and pre-heating a catalytic monolith in a power generation system. In this concept, a downstream heat source (e.g. a flame) or resistive heating in the downstream portion of the monolith initiates a localized catalytic reaction which subsequently propagates upstream and heats the entire monolith. The simulations used a transient numerical model of a single catalytic channel which characterizes the behavior of the entire monolith. The model treats both the gas and solid phases and includes detailed homogeneous and heterogeneous reactions. An important parameter in the model for back-end ignition is upstream heat conduction along the solid. The simulations used both dry and wet CO chemistry as a model fuel for the proof-of-concept calculations; the presence of water vapor can trigger homogenous reactions, provided that gas-phase temperatures are adequately high and there is sufficient fuel remaining after surface reactions. With sufficiently high inlet equivalence ratio, back-end ignition occurs using the thermophysical properties of both a ceramic and metal monolith (coated with platinum in both cases), with the heat-up times significantly faster for the metal monolith. For lower equivalence ratios, back-end ignition occurs without upstream propagation. Once light-off and propagation occur, the inlet equivalence ratio could be reduced significantly while still maintaining an ignited monolith as demonstrated by calculations using complete monolith heating.

Struk, Peter M.↗
DOE OSTI2022

Projection-Based Model Reduction for Coupled Conduction—Enclosure Radiation Systems

We report a projection-based reduced order model (pROM) methodology has been developed for transient heat transfer problems involving coupled conduction and enclosure radiation. The approach was demonstrated on two test problems of varying complexity. The reduced order models demonstrated substantial speedups (up to 185×) relative to the full order model with good accuracy (less than 3% L ∞ error). An attractive feature of pROMs is that there is a natural error indicator for the ROM solution: the final residual norm at each time-step of the converged ROM solution. Using example test cases, we discuss how to interpret this error indicator to assess the accuracy of the ROM solution. The approach shows promise for many-query applications, such as uncertainty quantification and optimization. The reduced computational cost of the ROM relative to the full-order model (FOM) can enable the analysis of larger and more complex systems as well as the exploration of larger parameter spaces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1999

Analysis and Testing of High Temperature Fibrous Insulation for Reusable Launch Vehicles

Analytical models were developed to model the heat transfer through high-temperature fibrous insulation used in metallic thermal protection systems on reusable launch vehicles. The optically thick approximation was used to simulate radiation heat transfer through the insulation. Different models for gaseous conduction and solid conduction in the fibers, and for combining the various modes of heat transfer into a local, volume-averaged, thermal conductivity were considered. The governing heat transfer equations were solved numerically, and effective thermal conductivities were calculated from the steady-state results. An experimental apparatus was developed to measure the apparent thermal conductivity of insulation subjected to pressures, temperatures and temperature gradients representative of re-entry conditions for launch vehicles. The apparent thermal conductivity of an alumina fiber insulation was measured at nominal densities of 24, 48 and 96 kg/cu m. Data were obtained at environmental pressures from 10(exp 4) to 760 torr, with the insulation cold side maintained at room temperature and its hot side temperature varying up to 1000 C. The experimental results were used to evaluate the analytical models. The best analytical model resulted in effective thermal conductivity predictions that were within 8% of experimental results.

Daryabeigi, Kamran↗
DOE OSTI2020

Structural, Electronic, and Thermal Properties of CdSnAs 2

Structural, electrical, and thermal properties of CdSnAs 2 , with analyses from temperature-dependent transport properties over a large temperature range, are reported. Phase-pure microcrystalline powders were synthesized that were subsequently densified to a high-density homogeneous polycrystalline specimen for this study. Temperature-dependent transport indicates n-type semiconducting behavior with a very high and nearly temperature independent mobility over the entire measured temperature range, attributed to the very small electron effective mass of this material. The Debye model was successfully applied to model the thermal conductivity and specific heat. Furthermore, this work contributes to the fundamental understanding of this material, providing further insight and allowing for investigations into altering this and related physical properties of these materials for technological applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1975

Hypersonic engine airplane integration

A summary of the research activities is presented along with the design and analysis of an integrated scramjet engine which utilizes heat conduction flames. The scramjet engine model described was tested at a freestream Mach number of 4.0 by personnel at the General Applied Science Laboratory. The research effort was primarily concerned with the interpretation and analysis of the experimental data. The mixing tests were conducted with cold ambient air, while the combustion tests were conducted with hot vitiated air. The purpose of the cold mixing tests was to determine the degree of mixedness of the fuel at the ignitor station so as to certify if the fuel injection conditions and fuel injectors locations were properly selected to give a uniform fuel concentration profile at the ignitor station. A second objective was to assess the influence of the fuel injection on the inlet flow. Several fuel injection configurations were tested.

Source record↗
NASA NTRS1984

Simulation of solidification in a Bridgman cell

The Hg/Cd/Te solidification in a Bridgman cell was thermally analyzed by Continuum's VAST code. The energy equation is solved in an axisymmetric, quasi steady domain for both the molten and solid alloy regions. Alloys composition is calculated by a simplified one dimensional model to estimate its effect on melt thermal conductivity and, consequently, on the temperature field within the cell. Solidification is assumed to occur at a fixed temperature of 979 K. Simplified boundary conditions are included to model both the radiant and conductive heat exchange between the furnace walls and the alloy. Calculations are performed to show how the steady state isotherms are affected by: (1) the hot and cold furnace temperatures; (2) boundary condition parameters; and (3) the growth rate which affects the calculated alloy's composition.

Dakhoul, Y. M.↗
NASA NTRS1986

Thermal-capillary analysis of small-scale floating zones Steady-state calculations

Galerkin finite element analysis of a thermal-capillary model of the floating zone crystal growth process is used to predict the dependence of molten zone shape on operating conditions for the growth of small silicon boules. The model accounts for conduction-dominated heat transport in the melt, feed rod and growing crystal and for radiation between these phases, the ambient and a heater. Surface tension acting on the shape of the melt/gas meniscus counteracts gravity to set the shape of the molten zone. The maximum diameter of the growing crystal is set by the dewetting of the melt from the feed rod when the crystal radius is large. Calculations with small Bond number show the increased zone lengths possible for growth in a microgravity environment. The sensitivity of the method to the shape and intensity of the applied heating distribution is demonstrated. The calculations are compared with experimental observations.

Duranceau, J. L.↗
NASA NTRS1986

Crystal growth and furnace analysis

A thermal analysis of Hg/Cd/Te solidification in a Bridgman cell is made using Continuum's VAST code. The energy equation is solved in an axisymmetric, quasi-steady domain for both the molten and solid alloy regions. Alloy composition is calculated by a simplified one-dimensional model to estimate its effect on melt thermal conductivity and, consequently, on the temperature field within the cell. Solidification is assumed to occur at a fixed temperature of 979 K. Simplified boundary conditions are included to model both the radiant and conductive heat exchange between the furnace walls and the alloy. Calculations are performed to show how the steady-state isotherms are affected by: the hot and cold furnace temperatures, boundary condition parameters, and the growth rate which affects the calculated alloy's composition. The Advanced Automatic Directional Solidification Furnace (AADSF), developed by NASA, is also thermally analyzed using the CINDA code. The objective is to determine the performance and the overall power requirements for different furnace designs.

Dakhoul, Youssef M.↗
NASA NTRS1987

Large-scale volcano-ground ice interactions on Mars

In the present investigation of Martian volcano-ground ice interaction processes, a numerical model is developed that encompasses conductive heat transport, surface radiation, heat transfer to the atmosphere, and H2O phase-changes in an ice-rich permafrost over which lave flows erupt, followed by the intrusion of sills. An examination is made of the two large scale interaction regions formed near Aeolis Mensae and near the volcano Hadriaca Patera, northeast of Hellas. The inferred channel discharges are compared to discharge rates calculated for lava-ground ice interactions, showing that meltwater (probably accumulated under the surface) was rapidly released at a discharge rate that was limited by soil permeability. The volcano-ground ice interactions have been an important Martian geologic process, and could account for the palagonites constituting the Martian dust.

Squyres, Steven W.↗
NASA NTRS1990

Calorimetric determination of thermal parameters for the Li/BrCl in SOCl2 (BCX) chemistry

The heat capacity of a Li-BCX DD-cell was found to be dependent on its state of charge by drop calorimetry measurements. The method of drop calorimetry involves measuring the energy (joules) gained or lost from a sample that is transferred from a bath at temperature A to one at temperature B. The thermoneutral potential is defined as the cell potential where the cell electrochemical reactions are neither exothermic nor endothermic. A Hart scientific calorimeter system, Model No. S77XX, designed for heat conduction calorimetry and drop calorimetry was used. Calorimetric analysis yielded a thermoneutral potential of 4.14 volts and a cell heat capacity dependent on the state of charge.

Darcy, Eric C.↗
NASA NTRS1993

A novel pulse technique for thermal diffusivity determination of high-temperature levitated materials - Inverse analysis and experimental set-up

In order to determine the thermal diffusivity of materials at high temperatures, a two-step extended flash technique, which is applicable to levitated spherical samples, is proposed. The containerless flash method is modeled as an axisymmetric transient conduction heat transfer problem within the sphere subjected to a radiative boundary condition on its surface. The problem of nonlinearity which arises from the radiative heat transfer boundary condition is solved by replacing it with the measured time-dependent surface temperature data, thus giving rise to an 'Inverse Analysis'. Upon obtaining the analytic solution for the temperature field, the determination of the thermal diffusivity turns into a minimization problem, whereby the difference between the actual surface boundary condition and the analytic solution is minimized. In performing the proposed experiments, there is a need to undertake a cool-down experiment which should be governed by the lumped parameter analysis.

Shen, F.↗
NASA NTRS1996

Evaluation of Temperature Gradient in Advanced Automated Directional Solidification Furnace (AADSF) by Numerical Simulation

A numerical model of heat transfer using combined conduction, radiation and convection in AADSF was used to evaluate temperature gradients in the vicinity of the crystal/melt interface for variety of hot and cold zone set point temperatures specifically for the growth of mercury cadmium telluride (MCT). Reverse usage of hot and cold zones was simulated to aid the choice of proper orientation of crystal/melt interface regarding residual acceleration vector without actual change of furnace location on board the orbiter. It appears that an additional booster heater will be extremely helpful to ensure desired temperature gradient when hot and cold zones are reversed. Further efforts are required to investigate advantages/disadvantages of symmetrical furnace design (i.e. with similar length of hot and cold zones).

Bune, Andris V.↗
NASA NTRS1995

One-dimensional hybrid satellite track model for the Dynamics Explorer 2 (DE 2) satellite

A one-dimensional hybrid satellite track model has been developed to calculate the high-latitude thermospheric/ionospheric structure below the satellite altitude using Dynamics Explorer 2 (DE 2) satellite measurements and theory. This model is based on Emery et al. (1985) satellite track code but also includes elements of Roble et al. (1987b) global mean thermosphere/ionosphere model. A number of parameterizations and data handling techniques are used to input satellite data from several DE 2 instruments into this model. Profiles of neutral atmospheric densities are determined from the Mass Spectrometer Incoherent Scatter 1990 (MSIS-90) model and measured neutral temperatures. Measured electron precipitation spectra are used in an auroral model to calculate particle impact ionization rates below the satellite. These rates are combined with a solar ionization rate profile and used to solve the O(+) diffusion equation, with the measured electron density as an upper boundary condition. The calculated O(+) density distribution, as well as the ionization profiles, are then used in a photochemical equilibrium model to calculate the electron and molecular ion densities. The electron temperature is also calculated by solving the electron energy equation with an upper boundary condition determined by the DE 2 measurement. The model enables calculations of altitude profiles of conductivity and Joule heating rate along and below the satellite track. In a first application of the new model, a study is made of thermospheric and ionospheric structure below the DE 2 satellite for a single orbit which occurred on October 25, 1981. The field-aligned Poynting flux, which is independently obtained for this orbit, is compared with the model predictions of the height-integrated energy conversion rate. Good quantitative agreement between these two estimates has been reached. In addition, measurements taken at the incoherent scatter radar site at Chatanika (65.1 deg N, 147.4 deg W) during a DE 2 overflight are compared with the model calculations. A good agreement was found in lower thermospheric conductivities and Joule heating rate.

Deng, Wei↗
NASA NTRS2008

Thermal Capacitance (Slug) Calorimeter Theory Including Heat Losses and Other Decaying Processes

A mathematical model, termed the Slug Loss Model, has been developed for describing thermal capacitance (slug) calorimeter behavior when heat losses and other decaying processes are not negligible. This model results in the temperature time slope taking the mathematical form of exponential decay. When data is found to fit well to this model, it allows a heat flux value to be calculated that corrects for the losses and may be a better estimate of the cold wall fully catalytic heat flux, as is desired in arc jet testing. The model was applied to the data from a copper slug calorimeter inserted during a particularly severe high heating rate arc jet run to illustrate its use. The Slug Loss Model gave a cold wall heat flux 15% higher than the value of 2,250 W/sq cm obtained from the conventional approach to processing the data (where no correction is made for losses). For comparison, a Finite Element Analysis (FEA) model was created and applied to the same data, where conduction heat losses from the slug were simulated. The heat flux determined by the FEA model was found to be in close agreement with the heat flux determined by the Slug Loss Model.

Hightower, T. Mark↗
NASA NTRS1978

Primordial metamorphism of asteroids via electrical induction in a T Tauri-like solar wind

Possible heating mechanisms for an intense thermal cycle in the early solar system are considered, and inductive asteroid heating in a T Tauri environment is examined. Calculations of thermal models based on recent measurements of the electrical conductivity of carbonaceous meteorites are reported which are presumably more representative of actual conditions in the early solar nebula. Asteroidal thermal evolution is computed using a highly simplified code that restricts induction to the dc limit of the TM mode, approximates the complete unipolar-generation differential equation by a simple series-resistance model, and restricts the modeling of thermal conduction to a calculation of heat transfer across a thin planar shell of given thickness increasing with time, which blankets a body assumed to have an isothermal core. A grid of results is obtained for 20 combinations of asteroid radius and solar distance representing the populaton of asteroids. It is found that there is a relative heating maximum with respect to body radius, that this effect is due to the operation of two distinct heating-rate restrictions which have opposite radius dependences, and that the maximum current density is roughly proportional to the inverse of interior radius.

Herbert, F.↗
NASA NTRS2006

Validation Database Based Thermal Analysis of an Advanced RPS Concept

Advanced RPS concepts can be conceived, designed and assessed using high-end computational analysis tools. These predictions may provide an initial insight into the potential performance of these models, but verification and validation are necessary and required steps to gain confidence in the numerical analysis results. This paper discusses the findings from a numerical validation exercise for a small advanced RPS concept, based on a thermal analysis methodology developed at JPL and on a validation database obtained from experiments performed at Oregon State University. Both the numerical and experimental configurations utilized a single GPHS module enabled design, resembling a Mod-RTG concept. The analysis focused on operating and environmental conditions during the storage phase only. This validation exercise helped to refine key thermal analysis and modeling parameters, such as heat transfer coefficients, and conductivity and radiation heat transfer values. Improved understanding of the Mod-RTG concept through validation of the thermal model allows for future improvements to this power system concept.

numerical model↗