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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 19 records

All sources NASA NTRS DOE OSTI

NASA NTRS1989

Carbon/Carbon Panels Cooled By Heat Pipes

Durable and reusable high-temperature carbon/carbon heat-pipe structure operates at temperatures above 3,000 degree F (1,649 degree C) in vacuum or inert environment and up to 2,800 degree F (1,537 degree C) in oxidizing environment. New concept combines high-temperature heat-pipe and carbon/carbon technologies to extend both thermal structural capabilities of refractory-metal heat pipes and maximum heat-flux capability of carbon/carbon structures. Uses refractory-metal heat pipes embedded within carbon/carbon structure. Walls of heat pipes thin and contain working fluid (lithium or sodium) of heat pipe. Carbon/carbon acts as primary load-carrying part of structure. Heat pipes help to eliminate local hotspots and associated thermal gradients and stresses and to reduce peak surface temperatures of carbon/carbon to levels within capability of oxidation-resisting system.

Camarda, Charles J.↗

NASA NTRS2008

Oxidation of Carbon/Carbon through Coating Cracks

Reinforced carbon/carbon (RCC) is used to protect the wing leading edge and nose cap of the Space Shuttle Orbiter on re-entry. It is composed of a lay-up of carbon/carbon fabric protected by a SiC conversion coating. Due to the thermal expansion mismatch of the carbon/carbon and the SiC, the SiC cracks on cool-down from the processing temperature. The cracks act as pathways for oxidation of the carbon/carbon. A model for the diffusion controlled oxidation of carbon/carbon through machined slots and cracks is developed and compared to laboratory experiments. A symmetric cylindrical oxidation cavity develops under the slots, confirming diffusion control. Comparison of cross sectional dimensions as a function of oxidation time shows good agreement with the model. A second set of oxidation experiments was done with samples with only the natural craze cracks, using weight loss as an index of oxidation. The agreement of these rates with the model is quite reasonab

Jacobson, N. S.↗

NASA NTRS1995

Eddy-Current Detection Of Cracks In Reinforced Carbon/Carbon

Investigations of failures of components made of reinforced carbon/carbon show eddy-current flaw-detection techniques applicable to these components. Investigation focused on space shuttle parts, but applicable to other parts made of carbon/carbon materials. Techniques reveal cracks, too small to be detected visually, in carbon/carbon matrix substrates and in silicon carbide coates on substrates. Also reveals delaminations in carbon/carbon matrices. Used to characterize extents and locations of discontinuities in substrates in situations in which ultrasonic techniques and destructive techniques not practical.

Christensen, Scott V.↗

DOE OSTI2023

Design of a novel carbon/carbon composite microvascular solar receiver

Solar thermal power tower systems are the primary technology being proposed for solar electricity from thermal energy. Operational limits on these towers are often driven by mechanical properties under significant thermal loads, particularly at the receiver where incoming flux is converted to thermal energy. While the solar receiver’s efficiency is largely driven by its optical properties, thermomechanical stresses on the receiver limits the operational envelope. One pathway to higher efficiency is greater allowable solar fluxes on the receiver but novel materials are required. The present study uses computational fluid dynamics to describe a parametric design space for a microvascular carbon/carbon composite solar receiver as a new material option for high flux solar receivers. Simulations are conducted for different microvascular geometries considering the role of material properties and heat transfer fluids, for the impact on thermal efficiency, and allowable strain. Results show that microscale receiver modules made of the proposed carbon/carbon composite could achieve thermal efficiencies over 90% and full-scale receivers can achieve up to 85% thermal efficiency for the design explored considering realistic strain limits, flux levels, and material properties. These values are highly dependent on the heat transfer fluid pairing, the through plane thermal conductivity of the carbon/carbon composite, the path architecture of the microscale receiver, and the incident solar flux profiles.

14 SOLAR ENERGY↗

NASA NTRS1986

Carbon/Carbon Pistons for Internal Combustion Engines

Carbon/carbon piston performs same function as aluminum pistons in reciprocating internal combustion engines while reducing weight and increasing mechanical and thermal efficiencies of engine. Carbon/carbon piston concept features low piston-to-cylinder wall clearance - so low piston rings and skirts unnecessary. Advantages possible by negligible coefficient of thermal expansion of carbon/carbon.

Taylor, A. H.↗

NASA NTRS1995

Carbon/Carbon Grids For Ion Sources

Ion-extraction grids made of carbon/carbon composites used in spacecraft ion engines and industrial ion sources in place of molybdenum grids. In principle, carbon/carbon grids offer greater extraction efficiency and longer life. Grid fabricated by mechanical drilling, laser drilling, or electrical-discharge machining of array of holes in sheet of carbon/carbon. Advantages; better alignment and slower erosion.

Garner, Charles E.↗

NASA NTRS1998

Oxidative Attack of Carbon/Carbon Substrates through Coating Pinholes

A critical issue with oxidation protected carbon/carbon composites used for spacecraft thermal protection is the formation of coating pinholes. In laboratory experiments, artificial pinholes were drilled through SiC-coatings on a carbon/carbon material and the material was oxidized at 600, 1000, and 1400 C at reduced pressures of air. The attack of the carbon/carbon was quantified by both weight loss and a novel cross-sectioning technique. A two-zone, one dimensional diffusion control model was adapted to analyze this problem. Agreement of the model with experiment was reasonable at 1000 and 1400 C; however results at lower temperatures show clear deviations from the theory suggesting that surface reaction control plays a role.

Jacobson, Nathan S.↗

NASA NTRS2015

Estimation of Surface Temperature and Heat Flux by Inverse Heat Transfer Methods Using Internal Temperatures Measured While Radiantly Heating a Carbon/Carbon Specimen up to 1920 F

The ability to solve the heat conduction equation is needed when designing materials to be used on vehicles exposed to extremely high temperatures; e.g. vehicles used for atmospheric entry or hypersonic flight. When using test and flight data, computational methods such as finite difference schemes may be used to solve for both the direct heat conduction problem, i.e., solving between internal temperature measurements, and the inverse heat conduction problem, i.e., using the direct solution to march forward in space to the surface of the material to estimate both surface temperature and heat flux. The completed research first discusses the methods used in developing a computational code to solve both the direct and inverse heat transfer problems using one dimensional, centered, implicit finite volume schemes and one dimensional, centered, explicit space marching techniques. The developed code assumed the boundary conditions to be specified time varying temperatures and also considered temperature dependent thermal properties. The completed research then discusses the results of analyzing temperature data measured while radiantly heating a carbon/carbon specimen up to 1920 F. The temperature was measured using thermocouple (TC) plugs (small carbon/carbon material specimens) with four embedded TC plugs inserted into the larger carbon/carbon specimen. The purpose of analyzing the test data was to estimate the surface heat flux and temperature values from the internal temperature measurements using direct and inverse heat transfer methods, thus aiding in the thermal and structural design and analysis of high temperature vehicles.

Pizzo, Michelle↗

NASA NTRS1995

(abstract) Unidirectional Carbon/Carbon for Ion Engine Optics

Conventional ion engine optical grids are made from hydroformed molybdenum. Carbon/carbon has been utilized in place of molybdenum because of its lower sputter yield, which contributes a greatly increased engine life, and for its low cte, which allows more efficient engine operation. The requirements for this material are that it must have high stiffness, very tight dimensional tolerances, and can be optimized for an hexagonal hole pattern with a very high open area friction. The carbon/carbon for this application was fabricated from unidirectional tape prepreg, using pitch fiber, and was processed to a very high temperature. The use of unidirectional tape allowed for a sufficient number of plies to be used to generate a balanced three directional layup within the thickness constraints of the material, as well as providing strength and stiffness over that normally seen with fabric based carbon/carbons.

ion engine carbon/carbon unidirectional tape prepr↗

NASA NTRS1991

Erosion of carbon/carbon by solar wind charged particle radiation during a solar probe mission

The possible erosion of a carbon/carbon thermal shield by solar wind-charged particle radiation is reviewed. The present knowledge of erosion data for carbon and/or graphite is surveyed, and an explanation of erosion mechanisms under different charged particle environments is discussed. The highest erosion is expected at four solar radii. Erosion rates are analytically estimated under several conservative assumptions for a normal quiet and worst case solar wind storm conditions. Mass loss analyses and comparison studies surprisingly indicate that the predicted erosion rate by solar wind could be greater than by nominal free sublimation during solar wind storm conditions at four solar radii. The predicted overall mass loss of a carbon/carbon shield material during the critical four solar radii flyby can still meet the mass loss mission requirement of less than 0.0025 g/sec.

Sokolowski, Witold↗

NASA NTRS1992

Smooth-Surfaced Carbon/Carbon Reflector Panels

Surface-densification technique integral to fabrication of reflective, lightweight, low-outgassing radio-antenna-reflector panels including carbon/carbon surface laminates supported by carbon/carbon core structures. Densification prevents "print-through" of carbon fibers on surface. When properly densified, surface polished to smooth finish.

Schmitigal, Wesley P.↗

NASA NTRS1993

Micromechanics of crenulated fibers in carbon/carbon composites

The influence of crenulated noncircular fibers on the micromechanical stress states due to a transverse strain and to a temperature change in carbon/carbon composites is examined using the finite element method. Stresses at the interface of both fully bonded and fully disbonded fibers having two crenulation amplitudes and with two fiber volume fractions are presented. In each case, these interface stresses are compared to stresses at the interface of circular fibers which have the same degree of disbond and fiber volume fraction and are under the same loading conditions. For the disbonded cases, deformed meshes showing locations of fiber/matrix contact are also included. In addition to the interface stress states, selected composite properties are also computed and compared in each case examined. Interest in studying noncircular fibers stems from a desire to increase the transverse properties of carbon/carbon by introducing a mechanical interlocking between the fiber and the matrix. Results presented here indicate that this interlocking does in fact occur. Evidence from the interface stress data suggests, however, that any possible advantage of this interlocking may be outweighed by the disadvantage of stress concentrations which arise at the interface due to the crenulated geometry of the fibers.

Carapella, E. E.↗

NASA NTRS1996

Thermochemical Degradation Mechanisms for Reinforced Carbon/Carbon Panels on the Space Shuttle

The wing leading edge and nose cone of the space shuttle are fabricated from a reinforced carbon/carbon material (RCC). This material attains its durability from a diffusion coating of silicon carbide (SiC) and a glass sealant (ref. 1). During reentry, this material is subjected to an oxidizing high-temperature environment. Joint work between the Ohio State University and the NASA Lewis Research Center led to a survey of potential degradation mechanisms of the reinforced carbon/carbon (RCC) material at high temperatures

Source record↗

NASA NTRS2007

Oxidation Through Coating Cracks of SiC-Protected Carbon/Carbon

The oxidation of SiC-protected carbon/carbon through machined slots and naturally occurring craze cracks in the SiC was studied. The slot and crack geometries were characterized, and the subsurface oxidation of the carbon/carbon substrate at temperatures of 1000 to 1300 C in air was assessed using weight change, x-ray computed tomography, and optical microscopy of sections. Rate constants were derived from these measurements and compared with a two-step diffusion control model of carbon oxidation. Oxidation kinetic measurements on both the specimens with machined slots and with naturally occurring craze cracks showed good agreement with the model.

Jacobson, Nathan S.↗

NASA NTRS2007

Oxidation Through Coating Cracks of SiC-Protected Carbon/Carbon

Jacobson, Nathan S.↗

NASA NTRS2008

Oxidation Through Coating Cracks of SiC-Protected Carbon/Carbon

Jacobson, Nathan S.↗

DOE OSTI2024

Vascular Carbon/Carbon composites for concentrated solar power

Due to their exceptional mechanical and thermal properties under high temperature conditions, for the first time, a novel vascular (embedded channels) Carbon/Carbon (C/C) composite was developed for use as a modular concentrated solar power (CSP) gas receiver. The fabrication process involves the combination of the vaporization of sacrificial component (VaSC) technique with conventional methods to produce C/C composites with well preserved channels. Different heat treatments were evaluated together with X-ray diffraction (XRD) analysis to determine optimal fabrication conditions that maintains the material and channel’s integrity. Mechanical testing confirms that structural integrity is maintained, with statistical analyses indicating no compromise in flexural strength or modulus. Furthermore, this research introduces an innovative pathway for efficient CSP gas receivers, which can bridge the gap towards improved energy generation efficiency in next-gen CSP plants through higher operating temperatures with the use of C/C composites.

14 SOLAR ENERGY↗

DOE OSTI2022

Prediction of curing kinetics of resorcinol‐added resole phenolic resins using differential scanning calorimetry for the fabrication of carbon/carbon composites

Phenolic resins are commonly used as carbon precursors for the fabrication of carbon/carbon composites due to their high carbon yield and aromatic nature. To decrease curing times, acid catalysts are generally used, but the addition of resorcinol was found to have a similar effect while being incorporated into the resin matrix with no contamination or corrosion issues. In this work, the curing kinetics of pure, 10, 20, and 30 wt% resorcinol-added phenolic resins were investigated through differential scanning calorimetry. Heating rates of 0.5, 1, 2.5, and 5°C min -1 were used with several curing models to predict isothermal curing. Averaged mean absolute error (MAE) for the isoconversional mathematical approaches namely Kissinger–Akahira–Sunose (MAE = 12.9 min), Flynn–Wall–Ozawa (15.8 min), and Vyazovkin (14 min) show that these methods provide the best predictions, attributed to their adoption of an activation energy that depends on the extent of cure (E a (α)). The Kissinger method (MAE = 36 min), which depends only on peak temperature with a constant activation energy assumption, and the data noise sensitive Friedman model (MAE = 1144.7 min) provide the least accurate results. Thermogravimetric analysis revealed that resorcinol decreases the curing times by up to 71% without lowering carbon yield.

36 MATERIALS SCIENCE↗