Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “thermal flexibility”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Performance of Conformable Phenolic Impregnated Carbon Ablator in Aerothermal Environments

Conformable Phenolic Impregnated Carbon Ablator, a cousin of Phenolic Impregnated Carbon Ablator (PICA), was developed at NASA Ames Research Center as a lightweight thermal protection system under the Fundamental Aeronautics Program. PICA is made using a brittle carbon substrate, which has a very low strain to failure. Conformable PICA is made using a flexible carbon substrate, a felt in this case. The flexible felt significantly increases the strain to failure of the ablator. PICA is limited by its thermal mechanical properties. Future NASA missions will require heatshields that are more fracture resistant than PICA and, as a result, NASA Ames is working to improve PICA's performance by developing conformable PICA to meet these needs. Research efforts include tailoring the chemistry of conformable PICA with varying amounts of additives to enhance mechanical properties and testing them in aerothermal environments. This poster shows the performance of conformable PICA variants in arc jets tests. Some mechanical and thermal properties will also be presented.

ablative materials↗
NASA NTRS2004

Nano-casted Metal Oxide Aerogels as Dual Purpose Structural Components for Space Exploration

NASA missions and space exploration rely on strong, ultra lightweight materials. Such materials are needed for building up past and present space vehicles such as the Sojourner Rover (1997) or the two MERs (2003), but also for a number of components and/or systems including thermal insulators, Solar Sails, Rigid Aeroshells, and Ballutes. The purpose of my internship here at Glenn Research Center is to make dual purpose materials; materials that in addition to being lightweight have electronic, photophysical and magnetic properties and, therefore, act as electronic components and sensors as well as structural components. One type of ultra lightweight material of great interest is aerogels, which have densities ranging from 0.003 g/cc to 0.8 g/cc . However, aerogels are extremely fragile and, as a result, have limited practical applications. Recently, Glenn Research Center has developed a process of nano-casting polymers onto the inorganic network of silica-based aerogels increasing the strength 300 fold while only increasing the density 3 fold. By combining the process of nano-casting polymers with inorganic oxide networks other than silica, we are actively pursuing lightweight dual purpose materials. To date, thirty different inorganic oxide aerogels have been prepared using either standard sol-gel chemistry or a non-alkoxide method involving metal chloride precursors and an epoxide; epichlorohydrin, propylene oxide or trimethylene oxide, as proton scavengers. More importantly, preliminary investigations show that the residual surface hydroxyl groups on each of these inorganic oxide aerogels can be successfully crosslinked with urethane. In addition to characterizing physical and mechanical properties such as density, strength and flexibility, each of these metal oxide aerogels are being characterized for thermal and electronic conductivity and magnetic and optical properties.

Vassilaras, Plousia E.↗
NASA NTRS1984

Thermal performance of FRSI/graphite epoxy materials for the Orbiter TPS application

Radiant tests have been conducted to evaluate the performance of the Flexible Reusable Surface Insulation (FRSI) when bonded to Graphite/Epoxy (G/E) honeycomb sandwich structures. The results from this study indicate reasonable agreement with the baseline FRSI properties that existed prior to this test program. An updated Thermal Math Model (TMM) prediction technique was developed, with the use of the well-defined boundary conditions, which appears to be valid in analyzing the complex heat transfer associated with the honeycomb structure. The updated TM analysis of flight data resulted in good agreement of predicted temperatures with flight data for bondline responses of Orbiter FRSI/GE TPS applications.

Norman, I.↗
NASA NTRS1995

A polyimide molecular composite

A polyimide is a hard and sturdy thermoplastic made from the combination of tetracarboxylic dianhydrides and diamines in a polar aprotic solvent. A series of polyimide blends comprising of a tough moldable, wholly aromatic polyimide and a highly crystalline rigid polyimide were prepared. The flexible polyimide was based on LaRC-SI with a 2% offset, and the rigid polyimide as based on para-phenylenediamine and biphenyltetracarboxylic dinnhydride encapped with pthalic anhydride. The polyimide blends were cast as films and cured at 100, 200, and 300 C in air. These films were characterized by finding their glass-transition temperature, melting temperature, coefficient of thermal expansion, tensile modulus, tensile strength, and percent elongation. These characterizations found out which polyimide blend had exceptional mechanical and thermal properties. Experimental results showed the following: (1) A blend with increasing amounts of flexible polyimide produced a better film; (2) A blend with increasing amounts of rigid polyimide produced a brittle film; (3) LaRC-SI (2% offset) tended to phase separate during film casting; (4) Most of the films produced were brittle; and (5) There was an inability to obtain mechanical and thermal properties due to having brittle film. These conclusions demonstrate the difficulty in producing a polyimide blend comprising two physically distinct polyimides. Combining a polysmide with a poly(amic acid) thermosett could be the next phase of research in polyimide synthesis.

Hart, Aprill J.↗
NASA NTRS2014

Performance of a Multifunctional Space Evaporator-Absorber-Radiator (SEAR)

The Space Evaporator-Absorber-Radiator (SEAR) is a nonventing thermal control subsystem that combines a Space Water Membrane Evaporator (SWME) with a Lithium Chloride Absorber Radiator (LCAR). The LCAR is a heat pump radiator that absorbs water vapor produced in the SWME. Because of the very low water vapor pressure at equilibrium with lithium chloride solution, the LCAR can absorb water vapor at a temperature considerably higher than the SWME, enabling heat rejection sufficient for most EVA activities by thermal radiation from a relatively small area radiator. Prior SEAR prototypes used a flexible LCAR that was designed to be installed on the outer surface of a portable life support system (PLSS) backpack. This paper describes a SEAR subsystem that incorporates a very compact LCAR. The compact, multifunctional LCAR is built in the form of thin panels that can also serve as the PLSS structural shell. We designed and assembled a 2 ft² prototype LCAR based on this design and measured its performance in thermal vacuum tests when supplied with water vapor by a SWME. These tests validated our models for SEAR performance and showed that there is enough area available on the PLSS backpack shell to enable rejection of metabolic heat from the LCAR. We used results of these tests to assess future performance potential and suggest approaches for integrating the SEAR system with future space suits.

Izenson, Michael G.↗
NASA NTRS1978

Thermal Barrier Coatings

Thermal barrier coatings offer gas turbines one way to reach fuel flexibility and improved efficiency. Test/analytical results are encouraging for this young technology.

Grisaffe, S. J.↗
NASA NTRS1987

Concept of adaptive structures

The concept of adaptive structures is brought up in connection with the need in ultra lightweight structural systems to maintain desired properties and configurations without human intervention when subjected to dynamic, thermal, and other environmental forces. Examples are large antenna structures and flexible robotic structures. In the both cases such adaptivity would allow less massive structural members to be employed under normal loading conditions. During special circumstances when unusually large loads are encountered, temporary stiffening would allow the use of less sturdy structures, resulting in large savings in their cost, and in increasing their mobility and efficiency. Within the framework of a finite-dimensional representation of structural dynamics, the adaptivity can be implemented by the dependence of the stiffness matrix (k) upon the expected load (Q), or expected (programmed) changes in configurations, i.e., (k) = (k(t)) where the dependence upon time is programmed in advance. In order to sustain unexpected loads the adaptive structure can be provided by feedback force control, or by a parametrical stiffness control.

Zak, Michail↗
NASA NTRS2000

Advanced Space Suit Insulation Feasibility Study

For planetary applications, the space suit insulation has unique requirements because it must perform in a dynamic mode to protect humans in the harsh dust, pressure and temperature environments. Since the presence of a gaseous planetary atmosphere adds significant thermal conductance to the suit insulation, the current multi-layer flexible insulation designed for vacuum applications is not suitable in reduced pressure planetary environments such as that of Mars. Therefore a feasibility study has been conducted at NASA to identify the most promising insulation concepts that can be developed to provide an acceptable suit insulation. Insulation concepts surveyed include foams, microspheres, microfibers, and vacuum jackets. The feasibility study includes a literature survey of potential concepts, an evaluation of test results for initial insulation concepts, and a development philosophy to be pursued as a result of the initial testing and conceptual surveys. The recommended focus is on microfibers due to the versatility of fiber structure configurations, the wide choice of fiber materials available, the maturity of the fiber processing industry, and past experience with fibers in insulation applications

Trevino, Luis A.↗
NASA NTRS2013

Performance of a Multifunctional Space Evaporator- Absorber-Radiator (SEAR)

The Space Evaporator-Absorber-Radiator (SEAR) is a nonventing thermal control subsystem that combines a Space Water Membrane Evaporator (SWME) with a Lithium Chloride Absorber Radiator (LCAR). The LCAR is a heat pump radiator that absorbs water vapor produced in the SWME. Because of the very low water vapor pressure at equilibrium with lithium chloride solution, the LCAR can absorb water vapor at a temperature considerably higher than the SWME, enabling heat rejection by thermal radiation from a relatively small area radiator. Prior SEAR prototypes used a flexible LCAR that was designed to be installed on the outer surface of a portable life support system (PLSS) backpack. This paper describes a SEAR subsystem that incorporates a very compact LCAR. The compact, multifunctional LCAR is built in the form of thin panels that can also serve as the PLSS structural shell. We designed and assembled a 2 sq ft prototype LCAR based on this design and measured its performance in thermal vacuum tests when supplied with water vapor by a SWME. These tests validated our models for SEAR performance and showed that there is enough area available on the PLSS backpack shell to enable heat rejection from the LCAR.

Izenson, Michael G.↗
NASA NTRS2019

Increased Flexibility in Polyimide Aerogel Substrates for Conformal, Lightweight Antennas

Polyimide aerogels are desirable for many aerospace applications due to their high porosity, low density, low thermal conductivity, and superior mechanical properties. They have also been demonstrated as lightweight substrates for antennas since they possess very low dielectric constants, approaching one as density decreases. Increasing the flexibility of the aerogel would allow them to be used as conformal antennas for use on aerospace vehicles, leading to significant space and weight savings. In this research, we demonstrate that the flexibility can be increased depending on the polyimide oligomer backbone structures. We have substituted up to 75 mol % of the aromatic diamines typically used in polyimide aerogels with 1, 3-bis (4-aminophenoxy)-2, 2-dimethylpropane (BAPN). Twenty different formulations of polyimide aerogels were synthesized from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and a combination of BAPN and 2,2'-dimethylbenxidine (DMBZ) and cross-linked with 1, 3, 5 triaminophenoxybenzene (TAB). The polymer concentration, n-value, and molar concentration of BAPN and DMBZ were varied to determine an ideal formulation that has both a high bend radius and low dielectric constant. With only aromatic diamines in the backbone, the aerogels are flexible only as very thin films, nominally 0.5 mm thick. Samples containing at least 25 mol % BAPN have higher flexibility in substrates as thick as 2-3 mm and dielectric constants ranging from 1.11-1.26.

Cashman, Jessica↗
NASA NTRS2024

Thermal Modeling and Testing of High-Temperature Refractory Ceramic Insulation Felts

Heat transfer in high-temperature, high-porosity, flexible refractory ceramic fibrous insulation felts is investigated. Heat transfer in these insulation materials consists of combined gas conduction, solid conduction, and radiation modes, with the precise theoretical modeling of the latter two modes being formidable. A semi-empirical model that requires inverse methods and steady-state thermal test data to infer some of the required model parameters is further developed in this study, and applied to five insulation materials for temperatures between 300 K and 1900 K. The steady-state thermal test setup at NASA Langley Research Center with recent modifications to increase its testing capability to 1900 K is discussed. Design considerations to ensure one-dimensional heat transfer in the test setup are described. Test data and corresponding thermal models for alumina and zirconia-based fibrous insulation felts are presented. Furthermore, test data and thermal models on two fibrous insulation samples containing additives to further suppress either radiation or gas conduction modes of heat transfer are presented. Previously published alumina-based insulation data are also re-processed using the updated modeling methodology. The significance of various heat transfer modes in typical insulation samples is discussed and used to provide general guidance on optimum insulation layups.

Kamran Daryabeigi↗
NASA NTRS2017

Improvements to Wire Bundle Thermal Modeling for Ampacity Determination

Determining current carrying capacity (ampacity) of wire bundles in aerospace vehicles is critical not only to safety but also to efficient design. Published standards provide guidance on determining wire bundle ampacity but offer little flexibility for configurations where wire bundles of mixed gauges and currents are employed with varying external insulation jacket surface properties. Thermal modeling has been employed in an attempt to develop techniques to assist in ampacity determination for these complex configurations. Previous developments allowed analysis of wire bundle configurations but was constrained to configurations comprised of less than 50 elements. Additionally, for vacuum analyses, configurations with very low emittance external jackets suffered from numerical instability in the solution. A new thermal modeler is presented allowing for larger configurations and is not constrained for low bundle infrared emissivity calculations. Formulation of key internal radiation and interface conductance parameters is discussed including the effects of temperature and air pressure on wire to wire thermal conductance. Test cases comparing model-predicted ampacity and that calculated from standards documents are presented.

Rickman, Steve L.↗
NASA NTRS2017

Improvements to Wire Bundle Thermal Modeling for Ampacity Determination

Abstract - Determining current carrying capacity (ampacity) of wire bundles in aerospace vehicles is critical not only to safety but also to efficient design. Published standards provide guidance on determining wire bundle ampacity but offer little flexibility for configurations where wire bundles of mixed gauges and currents are employed with various external insulation jacket surface properties. Thermal modeling has been employed in an attempt to develop techniques to assist in ampacity determination for these complex configurations. An earlier tool allowed analysis of wire bundle configurations but was constrained to configurations comprised of less than 50 elements. Additionally, for vacuum analyses, configurations with very low emittance external jackets suffered from numerical instability in the solution. A new thermal modeler is presented allowing for larger configurations and is not constrained by low bundle jacket surface infrared emittance calculations. Formulation of key internal radiation and interface conductance parameters is discussed including the effects of temperature and ambient air pressure on wire-to-wire thermal conductance. Test cases comparing model-predicted ampacity and that calculated from standards documents are presented.

Steven L Rickman↗
NASA NTRS1986

Integrated Thermal-structural-electromagnetic Design Optimization of Large Space Antenna Reflectors

The requirements for low mass and high electromagnetic (EM) performance in large, flexible space antenna structures is motivating the development of a systematic procedure for antenna design. In contrast to previous work which concentrated on reducing rms distortions of the reflector surface, thereby indirectly increasing antenna performance, the current work involves a direct approach to increasing electromagnetic performance using mathematical optimization. The thermal, structural, and EM analyses are fully integrated in the context of an optimization procedure, and consequently, the interaction of the various responses is accounted for directly and automatically. Preliminary results are presented for sizing cross-sectional areas of a tetrahedral truss reflector. The results indicate potential for this integrated procedure from the standpoint of mass reduction, performance increase, and efficiency of the design process.

Adelman, H. M.↗
NASA NTRS1978

Continuum models for beam-like and plate-like lattice structures

A simple, rational approach is presented for developing continuum models for large repetitive beam-like and plate-like lattices with arbitrary configurations subjected to static, thermal and dynamic loadings. The continuum models for these structures are shear flexible beams and plates. They account for local effects in the repeating element of the actual structure and are characterized by their thermoelastic strain and kinetic energies from which the equations of motion and constitutive relations can be derived. The procedure for developing the expressions for thermoelastic strain and kinetic energies of the continuum involves introducing basic assumptions regarding the variation of the temperature, displacement and strain components in one or two directions (for plate-like and beam-like lattices) and obtaining effective thermoelastic and dynamic coefficients of the continuum in terms of material properties and geometry of the original lattice structure. The high accuracy of the continuum models developed is demonstrated by means of numerical examples.

Noor, A. K.↗