SEARCH · Search NASA
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.
Due to the combined increase in circuit integration and chip power dissipation, there is a rapidly growing demand for solving the thermal management issues of power microelectronics.
The 2017 Electrical and Electronics Technical Team Roadmap [11] proposes aggressive research and development targets aimed at improving power electronics technology to enable the mass-market penetration of electric-drive vehicles. Achieving these aggressive targets will require a decrease in cost (year 2025 cost target: $2.70/kW) and an increase in power density (year 2025 power density target: 100 kW/L) as compared with current on-road technology. Replacing traditional silicon device-based components with more efficient and higher-temperature wide-bandgap (WBG) semiconductor device-based components will enable increased power density. However, meeting the power density target will also require innovative thermal management solutions to increase the heat fluxes dissipated and allow for compact electronics packaging. This project evaluates, designs, and develops thermal management strategies that use dielectric fluid (single-phase heat transfer) as coolants.
The properties, generation, and dissipation mechanisms of acoustic, gravity and Alfven waves are described, whose restoring forces are pressure, buoyancy, and magnetic tension, respectively. For acoustic waves, generation by turbulent convective motions and by the Eddington Valve thermal overstability is discussed, considering the 'five-minute' oscillation; dissipation is possible either by radiation or shocks. Generation of gravity waves by penetrative convective motions and by shear arising from supergranule motions is reviewed, and dissipation due to wave breaking, interaction with the mean horizontal fluid flow, and very severe radiative damping is considered. Attention is given to Alfven wave generation by convective motions and thermal overstability, and to dissipation by mode coupling, wave decay, current dissipation, and particle collisions producing Joule or viscous heating.
We report a new transparent ceramic phosphor for use in LED lighting has been fabricated. The previously reported and optimized narrow-emitting red phosphor, K 2 SiF 6 :Mn 4+ (KSF), has been consolidated into a transparent ceramic phosphor for the first time, accomplished via hot-pressing the feedstock phosphor powder in a die under vacuum. KSF ceramics were fabricated with varying doping concentrations of Mn 4+ and their properties studied. The absorption and emission spectra of the ceramics were identical to the feedstock phosphor powders and are ideal for LED lighting with strong absorption at 450 nm and narrow emission around 630 nm. The absorbance of the ceramics was directly proportional to the doping concentration. The ceramics were excited at various blue light fluxes and their emission intensities measured to study the effect of Mn 4+ concentration on intensity-driven “droop” in the emission output. The ceramics with a lower Mn 4+ doping were more efficient under higher light fluxes due to a decrease in Auger upconversion losses. KSF ceramics can allow a much longer path length of the diode light through the phosphor, as compared to phosphor-in-silicone, enabling the use of low optical absorption and the associated reduced activator concentration. The ceramics are measured to have a thermal conductivity of ~1.0 W/m-K, higher than that of phosphor-in-silicone or phosphor-in-glass. Several of these properties make KSF ceramics potentially desirable for use in white light LEDs. Greater thermal conductivity helps with heat dissipation, the lower surface area of the ceramic compared to the powder minimizes the environmental vulnerability of KSF, and the ability to lower the Mn 4+ concentration reduces Auger recombination losses and mitigates the temperature rise, particularly at higher light flux.
We present a novel perspective on the role of inflation in the production of dark matter (DM). Specifically, we explore the DM production during warm inflation via ultraviolet freeze-in (WIFI). We demonstrate that in a warm inflation (WI) setting the persistent thermal bath, sustained by the dissipative interactions with the inflaton field, can source a sizable DM abundance via the nonrenormalizable interactions that connect the DM with the bath. Compared to the (conventional) radiation-dominated (RD) UV freeze-in scenario for the same reheat temperature (after inflation), the resulting DM yield in WIFI is always enhanced showing a strongly positive dependence on the mass dimension of the nonrenormalizable operator. Of particular interest, for a sufficiently large mass dimension of the operator, the entirety of the DM abundance of the Universe can be created during the inflationary phase. For the specific models we study, we find that the enhancement in DM yield, relative to RD UV freeze-in, is at least an order of magnitude for an operator of mass dimension 5, and as large as 18 orders of magnitude for an operator of mass dimension 10. Our findings also suggest a broader applicability for producing other cosmological relics, which may have a substantial impact on the evolution of the early Universe. Published by the American Physical Society 2024
The 10 September 2025 M w 4.1 earthquake in northeastern Utah, United States, had a focal depth 68 km beneath sea level, which is ∼20–25 km greater than estimates of local crustal thickness, making it a rare example of a continental mantle earthquake (CME). The focal depth is well resolved from arrival-time inversion (nearest station ∼13 km away) and moment tensor inversion of regional waveforms. Similar to other CMEs in the Intermountain West, there were no obvious aftershocks or foreshocks, and the waveforms were enriched in high-frequency energy. Spectral modeling gives a stress drop of ∼80 MPa and a radiation efficiency of ∼0.08, albeit with large uncertainties. The high stress drop and low radiation efficiency are consistent with a dissipative source process such as thermal runaway. Also similar to previous Intermountain West CMEs, the event occurred along the boundary of the Archean Wyoming craton, where pressure–temperature conditions favor ductile deformation. We hypothesize that edge-driven or regional-scale mantle convection produces increased strain rates near the craton boundary that make either conventional brittle failure or thermal runaway feasible at relatively high pressure–temperature conditions. High conductivity inferred around the edge of the craton may suggest that fluids also contribute to CME occurrence.
The objective of this research is to develop an understanding of how nuclear motions can be used to drive and control photo-induced charge transfer and singlet fission reactions in molecular crystals and thin films. By following the structural evolution of reacting molecules and nanostructures on the timescale of their nuclear motion, we will determine what interplay of nuclear coordinates is most efficient in driving electron transfers, a necessary first step in most photovoltaic and photocatalytic processes. We will identify which nuclear coordinates effectively promote desirable electron transfer processes, or ineffectively dissipate photon energy into unwanted thermal energy, thus guiding the design and implementation of molecular systems tailored for high efficiency processes. Specifically, we aim to identify which nuclear coordinates are responsible for driving electron transfer and singlet fission reactions at different points along the reaction coordinate, particularly in regimes which deviate from Marcus theory predictions. We will do so by investigating systems with electron transfer and singlet fission occurring from non-thermalized states due to strong donor-acceptor electronic coupling. First, we will prove that specific vibrational modes are responsible for charge transfer processes in molecular crystals. Secondly, we will investigate how vibrational coherences and specific nuclear motions can be used to drive high yield singlet fission processes. Finally, we will determine how complex film morphology affects long-range charge transport, a key limiting factor in our ability to make gains in efficiency.
Previous simulations have tested HTS magnets with dissipative flux flow regimens for thermal runaway. My goal was to make a system that would be able to take real world data on this for Quench Detection. My poster will show the design for a PCB I made and the test setup for conducting said experiment.
We present Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of $0^{"}_{.}2$ (60 pc) of CO emission from the Taffy galaxies (UGC 12914/5). The observations are compared with narrowband Paα, mid-IR, radio continuum and X-ray imaging, plus optical spectroscopy. The galaxies have undergone a recent head-on collision, creating a massive gaseous bridge that is known to be highly turbulent. The bridge contains a complex web of narrow molecular filaments and clumps. The majority of the filaments are devoid of star formation, and fall significantly below the Kennicutt–Schmidt relationship for normal galaxies, especially for the numerous regions undetected in Paα emission. Within the loosely connected filaments and clumps of gas we find regions of high velocity dispersion that appear gravitationally unbound for a wide range of likely values of X CO . Like the "Firecracker" region in the Antennae system, they would require extremely high external dynamical or thermal pressure to stop them dissipating rapidly on short crossing timescales of 2–5 Myr. We suggest that the clouds may be transient structures within a highly turbulent multiphase medium that is strongly suppressing star formation. Despite the overall turbulence in the system, stars seem to have formed in compact hotspots within a kiloparsec-sized extragalactic H ii region, where the molecular gas has a lower velocity dispersion than elsewhere, and shows evidence for a collision with an ionized gas cloud. Like the shocked gas in the Stephan's Quintet group, the conditions in the Taffy bridge shows how difficult it is to form stars within a turbulent, multiphase, gas.
Circuit, based on use of power transistors which do not display second breakdown under valve loading, drives inductive loads. Peak voltages, power dissipations, heat sink requirements, and thermal stability considerations can be obtained by theoretical analysis.
Studies of transport mechanisms in the upper atmosphere (diffusion, turbulence, large-scale circulation) are reviewed. A normally turbulent state of the lower thermosphere is inferred from direct observations of tracers and from thermal and composition structure. Viscous dissipation in the thermosphere and energy dissipation in turbulence working against buoyancy are discussed in relation to a critical Richardson number for initiation of turbulence (0.25, as in the stratosphere). But the usefulness of the Richardson criterion is limited when static stability is low, as is the case when strong shear-generated turbulence prevails.
Thirty-five (35) furnace runs were carried out during this quarter, of which 25 produced a total of 120 web crystals. The two main thermal models for the dendritic growth process were completed and are being used to assist the design of the thermal geometry of the web growth apparatus. The first model, a finite element representation of the susceptor and crucible, was refined to give greater precision and resolution in the critical central region of the melt. The second thermal model, which describes the dissipation of the latent heat to generate thickness-velocity data, was completed. Dendritic web samples were fabricated into solar cells using a standard configuration and a standard process for a N(+) -P-P(+) configuration. The detailed engineering design was completed for a new dendritic web growth facility of greater width capability than previous facilities.
The results of studies performed at NASA of five space platform design reference missions (DRM) are presented. The DRM's were planned in an effort to eliminate problems, rather than to enhance optimization. A diagram of each payload is included, and the space platform concept is presented with the most important features being a continuous total power supply of 12.5 kW to the payloads at 30 and/or 120 Vdc regulated, a high-rate multiplexer with a total output of 48 Mbps, and and a thermal control system capable of dissipating the platform power output at payload fluid temperatures of 0 C to 3 C. Payload interface requirements were analyzed and appropriate integration hardware was added. Payload viewing characteristics are considered, and resource use is discussed. It is concluded that, in payload applications, efficient use of STS transportation and the platform must be considered.
Bimetallic tips attached to injector posts improve burner performance and reliability. Tip allows excess heat generated at tip to be dissipated circumferentially and axially through thermal conduction.
The relationship between Rankine-Hugoniot solutions and critical Mach numbers is studied. The range of upstream parameters for which the resistivity or thermal conduction provide all the dissipation required by the slow shock Rankine-Hugoniot relations are evaluated. The calculation of the critical Mach number by analyzing the flux of shock catching ions is examined. It is observed that the properties of slow shocks depend on shock normal angle, and the ratio of the sound and Alfven speeds upstream. The Rankine-Hugoniot solutions are applicable to the analysis of spacecraft observations of slow shocks.
This paper is mainly concerned with the nature of volcanic eruptions on Io, taking into account questions regarding the presence of silicates or sulfur as principal component. Attention is given to the generation of silicate magma, the viscous dissipation in the melt zone, thermal anomalies at eruption sites, and Ionian volcanism. According to the information available about Io, it appears that its volcanism and hence its surface materials are dominantly silicic. Several percent of volatile materials such as sulfur, but also including sodium- and potassium-rich materials, may also be present. The volatile materials at the surface are continually vaporized and melted as a result of the high rates of silicate volcanism.
The Shuttle/Centaur high energy upper stage vehicle thermal environments were more severe than previous Centaur vehicle thermal environments, creating need for a new hydrazine fuel line thermal control technique. Constant power heaters did not satisfy power dissipation requirements, because the power required to maintain fuel line thermal control during cold conditions exceeded the maximum power allowable during hot conditions. Therefore, a Raychem Thermolimit self-regulating heater was selected for this application, and was attached to the hydrazine fuel line with Kapton and aluminum foil tapes. Fuel line/heater thermal modeling and subsequent thermal vacuum chamber testing simulated heater thermal performance during all worst-case Shuttle/Centaur thermal environmental conditions. Fuel line temperatures were maintained between the 4C to 71C limits during all analytical and test cases. Finally, the thermal model predictions were correlated with the test data, thereby ensuring that the model would provide satisfactory predictions for future missions and/or vehicles.
Micro-electromechanical systems (MEMS) is an emerging technology for radio frequency (RF) systems because it has the potential to dramatically decrease loss and improve efficiency. In this paper, we address the design and fabrication of novel MEMS switches being developed at NASA Glenn Research Center. Two types of switches are being developed: a microstrip series single pole single throw (SPST) switch and a coplanar waveguide (CPW) series SPST and single pole double throw (SPDT) switches. These are being fabricated as an integral part of 50 Ohm microstrip and CPW RF integrated circuits using microfabrication techniques. The construction of the switch relies on a cantilever beam that is partially supported by a dielectric post. The cantilever beam is electro-magnetically actuated. To decrease stiction, a Si3N4 thin film is deposited over the contact area. Thus, when the switch is closed, the ON-state insertion loss is governed by the parallel plate capacitance formed by the two contacts. The isolation in the OFF-state is governed by the parasitic capacitance when the cantilever is in the up position. RF MEMS switches have been demonstrated with 80% lower insertion loss than conventional solid state devices (GaAs Metal Semiconductor Field Effect Transistors (MESFETs) and Silicon PIN diodes) based switches. For example, a conventional GaAs five-bit phase shifter which is required for beam steering in a phased array antenna has approximately 7 dB of insertion loss at 26.5 GHz where as a comparable MEMS based phase shifter is expected to have only 2 dB of insertion loss. This translates into 56% lower power dissipation and therefore decreases the thermal load on the spacecraft and also reduces the power amplifier requirements. These benefits will enable NASA to build the next generation of deep space science crafts and micro/nano satellites.