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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Single-Phase Dielectric Fluid Thermal Management for Power-Dense Automotive Power Electronics

This paper describes the design and performance of a dielectric fluid cooling concept for automotive power electronics. The concept combines a low-thermal-resistance package (which eliminates metalized ceramic substrates) with a high-performance convective cooling strategy (slot jets impinging on finned surfaces). Modeling was first used to design the cooling system to maximize thermal performance and minimize pumping power. Additionally, a prototype was then fabricated, and experiments were conducted to validate the model predictions using three fluids at various fluid flow rates (16.7 cm 3 /s [1 L/min] to 68.3 cm 3 /s [4.1 L/min]) and inlet temperatures (30C and 70C). The final design was compact (120-cm 3 total volume, including heat exchanger and conceptual power modules) and cooled 12 devices (e.g., silicon carbide). The validated model was then used to predict the junction-to-fluid thermal resistance and pumping power for various conditions, including 40C fluid temperature. The results predict thermal resistance values as low as 19 mm 2 K/W are possible using the dielectric fluid cooling approach. The dielectric fluid cooling system is predicted to provide thermal resistance and pumping power values that are approximately 56% and 90% lower, respectively, compared to an automotive power electronics cooling system.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2018

Design and Test of Wendelstein 7-X Water-Cooled Divertor Scraper

Heat load calculations have indicated the possible overloading of the ends of the water-cooled divertor facing the pumping gap beyond their technological limit. The intention of the scraper is the interception of some of the plasma fluxes both upstream and downstream before they reach the divertor surface. The scraper is divided into six modules of four plasma facing components (PFCs); each module has four PFCs hydraulically connected in series by two water boxes (inlet and outlet). A full-scale prototype of one module has been manufactured. Development activities have been carried out to connect the water boxes to the cooling pipes of the PFCs by tungsten inert gas internal orbital welding. This prototype was successfully tested in the GLADIS facility with 17 MW/m2 for 500 cycles. The results of these activities have confirmed the possible technological basis for a fabrication of the water-cooled scraper.

Boscary, J.↗
DOE OSTI2019

‘Birth defects’ of photosystem II make it highly susceptible to photodamage during chloroplast biogenesis

High solar flux is known to diminish photosynthetic growth rates, reducing biomass productivity and lowering disease tolerance. Photosystem II (PSII) of plants is susceptible to photodamage (also known as photoinactivation) in strong light, resulting in severe loss of water oxidation capacity and destruction of the water-oxidizing complex (WOC). The repair of damaged PSIIs comes at a high energy cost and requires de novo biosynthesis of damaged PSII subunits, reassembly of the WOC inorganic cofactors and membrane remodeling. Employing membrane-inlet mass spectrometry and O 2 -polarography under flashing light conditions, we demonstrate that newly synthesized PSII complexes are far more susceptible to photodamage than are mature PSII complexes. We examined these ‘PSII birth defects’ in barley seedlings and plastids (etiochloroplasts and chloroplasts) isolated at various times during de-etiolation as chloroplast development begins and matures in synchronization with thylakoid membrane biogenesis and grana membrane formation. We show that the degree of PSII photodamage decreases simultaneously with biogenesis of the PSII turnover efficiency measured by O 2 -polarography, and with grana membrane stacking, as determined by electron microscopy. Our data from fluorescence, Q B -inhibitor binding, and thermoluminescence studies indicate that the decline of the high-light susceptibility of PSII to photodamage is coincident with appearance of electron transfer capability Q$_A^-$ → QB during de-etiolation. This rate depends in turn on the downstream clearing of electrons upon buildup of the complete linear electron transfer chain and the formation of stacked grana membranes capable of longer-range energy transfer.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Stagnation region heat transfer augmentation at very high turbulence levels

Current land-based gas turbines are growing in size producing higher approach flow Reynolds numbers at the leading edge of turbine nozzles. These vanes are subjected to high intensity large scale turbulence. This present paper reports on the research which significantly expands the parameter range for stagnation region heat transfer augmenta-tion due to high intensity turbulence. Heat transfer measurements were acquired over two constant heat flux test surfaces with large diameter leading edges (10.16 cm and 40.64 cm). The test surfaces were placed downstream from a new high intensity (17.4%) mock combustor and tested over an eight to one range in approach flow Reynolds number for each test surface. Stagnation region heat transfer augmentation for the smaller (Re D = 15,625–125,000) and larger (Re D = 62,500–500,000) leading edge regions ranged from 45% to 81% and 80% to 136%, respectively. Furthermore, these data also include heat transfer distributions over the full test surface compared with the earlier data acquired at six additional inlet turbulence conditions. These surfaces exhibit continued but more moderate acceleration downstream from the stagnation regions and these data are expected to be useful in testing bypass transition predictive approaches. This database will be useful to gas turbine heat transfer design engineers. [DOI: 10.1115/1.4032677]

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2016

Field and laboratory evaluations of commercial and next–generation alumina-forming austenitic foil for advanced recuperators

Alumina-forming austenitic (AFA) steels represent a new class of corrosion- and creep-resistant austenitic steels designed to enable higher temperature recuperators. Field trials are in progress for commercially rolled foil with widths over 39 cm. The first trial completed 3000 hrs in a microturbine recuperator with an elevated turbine inlet temperature and showed limited degradation. A longer microturbine trial is in progress. A third exposure in a larger turbine has passed 16,000 hrs. Furthermore, to reduce alloy cost and address foil fabrication issues with the initial AFA composition, several new AFA compositions are being evaluated in creep and laboratory oxidation testing at 650–800 °C and the results compared to commercially fabricated AFA foil and conventional recuperator foil performance.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Unsteady Adjoint of Pressure Loss for a Fundamental Transonic Turbine Vane

High-fidelity simulations, e.g., large eddy simulation (LES), are often needed for accurately predicting pressure losses due to wake mixing and boundary layer development in turbomachinery applications. An unsteady adjoint of high-fidelity simulations is useful for design optimization in such aerodynamic applications. In this paper, we present unsteady adjoint solutions using a large eddy simulation model for an inlet guide vane from von Karman Institute (VKI) using aerothermal objectives. The unsteady adjoint method is effective in capturing the gradient for a short time interval aerothermal objective, whereas the method provides diverging gradients for long time-averaged thermal objectives. As the boundary layer on the suction side near the trailing edge of the vane is turbulent, it poses a challenge for the adjoint solver. The chaotic dynamics cause the adjoint solution to diverge exponentially from the trailing edge region when solved backward in time. This results in the corruption of the sensitivities obtained from the adjoint solutions. An energy analysis of the unsteady compressible Navier–Stokes adjoint equations indicates that adding artificial viscosity to the adjoint equations can dissipate the adjoint energy while potentially maintaining the accuracy of the adjoint sensitivities. Analyzing the growth term of the adjoint energy provides a metric for identifying the regions in the flow where the adjoint term is diverging. Results for the vane obtained from simulations performed on the Titan supercomputer are demonstrated.

Engineering↗
DOE OSTI2017

Using Dynamic Simulation to Evaluate Attemperator Operation in a Natural Gas Combined Cycle With Duct Burners in the Heat Recovery Steam Generator

A generic training simulator of a natural gas combined cycle was modified to match operations at a real plant. The objective was to use the simulator to analyze cycling operations of the plant. Initial operation of the simulator revealed the potential for saturation conditions in the final high pressure superheater as the attemperator tried to control temperature at the superheater outlet during gas turbine loading and unloading. Subsequent plant operational data confirmed simulation results. Multiple simulations were performed during loading and unloading of the gas turbine to determine operational strategies that prevented saturation and increased the approach to saturation temperature. The solutions included changes to the attemperator temperature control setpoints and strategic control of the steam turbine inlet pressure control valve.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2018

Transient Cold Flow Simulation of Fast Fluidized Bed Fuel Reactors for Chemical-Looping Combustion

Circulating fluidized bed in chemical-looping combustion (CLC) is a recent technology that provides great advantage for gas–solid interaction and efficiency. In order to obtain a thorough understanding of this technology and to assess its effectiveness for industrial scale deployment, numerical simulations are conducted. Computational fluid dynamics (CFD) simulations are performed with dense discrete phase model (DDPM) to simulate the gas–solid interactions. CFD commercial software ansysfluent is used for the simulations. Two bed materials of different particle density and diameter, namely the molochite and Fe100, are used in studying the hydrodynamics and particle behavior in a fuel reactor corresponding to the experimental setup of Haider et al. (2016, “A Hydrodynamic Study of a Fast-Bed Dual Circulating Fluidized Bed for Chemical Looping Combustion,” Energy Technol., 4(10), pp. 1254–1262.) at Cranfield University in the UK. Both the simulations show satisfactory agreement with the experimental data for both the static pressure and volume fraction at various heights above the gas inlet in the reactor. It is found that an appropriate drag law should be used in the simulation depending on the particle size and flow conditions in order to obtain accurate results. Furthermore, the simulations demonstrate the ability of CFD/DDPM to accurately capture the physics of circulating fluidized bed-based CLC process at pilot scale which can be extended to industrial scale projects.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2018

Estimation of Minimum Spouting Velocity in a Rectangular Spouted Bed

Here, a study was conducted to explore the effects of static bed height, nozzle diameter, cone angle, and particle properties on the minimum spouting velocity in a 4 in × 1 in rectangular spouted bed. Tests were conducted with various solids materials (including 871 μm HPDE pellets, 3.2 mm nylon beads, 707 μm glass beads, and 1.5 mm alumina spheres), two gas inlet nozzle diameters, and two cone angles. Experimentally obtained minimum spouting velocities were compared to existing published correlations developed for cylindrical spouted beds. In each case, it was determined that the existing correlations did not adequately predict the minimum spouting velocity for a rectangular spouted bed. A new correlation is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

High-Performance Computing and Analysis-Led Development of High Efficiency Dilute Opposed Piston Gasoline Engine

Pinnacle is developing a multicylinder 1.2 L gasoline engine for automotive applications using high-performance computing (HPC) and analysis methods. Pinnacle and Oak Ridge National Laboratory executed large-scale multidimensional combustion analyses at the Oak Ridge Leadership Computing Facility to thoroughly explore the design space. These HPC-led investigations show high fuel efficiency (~46% gross indicated efficiency) may be achieved by operating with extremely high charge dilution levels of exhaust gas recirculation (EGR) at a light load key drive cycle condition (2000 RPM, 3 bar brake mean effective pressure (BMEP)), while simultaneously attaining high levels of fuel conversion efficiency and low NO x emissions. In this extremely dilute environment, the flame propagation event is supported by turbulence and bulk in-cylinder charge motion brought about by modulation of inlet port flow. This arrangement produces a load and speed adjustable amalgamation of swirl and counter-rotating tumble which provides the turbulence required to support stable low-temperature combustion. At higher load conditions, the engine may operate at more traditional combustion modes to generate competitive power. In this work, the numerical results from these HPC simulations are presented. Finally, further HPC simulations and test validations are underway and will be reported in future publications.

42 ENGINEERING↗
DOE OSTI2018

Hybrid-Electric Turbocharger and High-Speed SiC Variable-Frequency Drive Using Sensorless Control Algorithm

Electrically assisted engine boosting systems lend themselves to better throttle response, wider effective operating ranges, and can provide the ability to extract excess energy during deceleration and high-load events (and store it in a vehicle's onboard batteries). This can lead to better overall vehicle performance, emissions, and efficiency while allowing for further engine downsizing and increased power density. In this research effort, a hybrid-electric turbocharger, variable-frequency drive (VFD), and novel sensorless control algorithm were developed. An 11 kW permanent-magnet (PM) machine was coupled to a commercial turbocharger via an in-line, bolt-on housing attached to the compressor inlet. A high-efficiency, high-temperature VFD, consisting of custom control and power electronics, was also developed. The VFD uses SiC MOSFETS to achieve high-switching frequency and can be cooled using an existing engine coolant loop operating at up to 105 °C at an efficiency greater than 98%. A digital sliding mode-observer sensorless speed control algorithm was created to command and regulate speed and achieved ramp rates of over 68,000 rpm/s. A two-machine benchtop motor/generator test stand was constructed for initial testing and tuning of the VFD and sensorless control algorithm. A gas blow-down test stand was constructed to test the mechanical operation of the hybrid-electric turbocharger and speed control using the VFD. In addition, a liquid-pump cart was assembled for high-temperature testing of the VFD. Initial on-engine testing is planned for later this year. This paper intends to present a design overview of the in-line, hybrid-electric device, VFD, and performance characterization of the electronics and sensorless control algorithm.

Engineering↗
DOE OSTI2019

Large Eddy Simulation of the Flow Behavior in a Simplified Helical Coil Steam Generator

Large eddy simulation (LES) is conducted for the flow over the shell side of a helical coil steam generator (HCSG) heat exchanger. Simulations are conducted on a simplified experimental test section that represents a one-column region of the helical coils using half-rods. Although the rods are wall-bounded, the flow still exhibits the turbulent characteristics and fluctuations from vortex shedding that one would expect from crossflow around a cylinder. The spectral element, computational fluid dynamics (CFD) code Nek5000, is used to capture the physics, and the results are compared with particle image velocimetry (PIV) measurements. In order to ensure that the turbulence is resolved, analysis is conducted by using the Taylor length scales and normalized wall distance. Sensitivity to the inlet boundary conditions (BCs) and the spatial discretization for different polynomial order solutions are also studied, finding only minor differences between each case. Pressure drop and velocity statistics show reasonable agreement with PIV. Proper orthogonal decomposition (POD) analysis reveals that the primary modes are similar between experiment and simulation, although the LES predicts higher turbulent kinetic energy than does PIV. Overall, the study establishes the resolution and resources required in order to conduct a high-fidelity simulation over 12 helical rods.

Lai, Jonathan K.↗
DOE OSTI2019

A General Study of Counterflow Diffusion Flames for Supercritical CO2 Combustion

Abstract A counterflow diffusion flame for supercritical CO2 combustion is investigated at various CO2 dilution levels and pressures by accounting for real gas effects into both thermal and transport properties. The UCF 1.1 24-species mechanism is used to account the chemistry. The nature of important nonpremixed combustion characteristics such as Prandtl number, thermal diffusivity, Lewis number, stoichiometric scalar dissipation rate, flame thickness, and Damköhler number are investigated with respect to CO2 dilution and pressure. The results show that the aforementioned parameters are influenced by both dilution and pressure; the dilution effect is more dominant. Further, the result shows that Prandtl number increases with CO2 dilution and at 90% CO2 dilution, the difference between the Prandtl number of the inlet jets and the flame is minimal. Also, the common assumption of unity Lewis number in the theory and modeling of nonpremixed combustion does not hold reasonable for sCO2 applications due to large difference of Lewis number across the flame and the Lewis number on the flame drop significantly with an increase in the CO2 dilution. An interesting relation between Lewis number and CO2 dilution is observed. The Lewis number of species drops by 15% when increasing the CO2 dilution by 30%. Increasing the CO2 dilution increases both the flow and chemical timescales; however, chemical timescale increases faster than the flow timescales. The magnitudes of the Damköhler number signify the need to consider finite rate chemistry for sCO2 applications. Further, the Damköhler numbers at 90% sCO2 dilution are very small; hence, laminar flamelet assumptions in turbulent combustion simulations are not physically correct for this application. Also, it is observed that the Damköhler number drops nonlinearly with increasing CO2 dilution in the oxidizer stream. This is a very important observation for the operation of sCO2 combustors. Further, the flame thickness is found to increase with CO2 dilution and reduce with pressure.

Engineering↗
DOE OSTI2020

Measurements of Density and Sound Speed in Mixtures Relevant to Supercritical CO2 Cycles

Abstract The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO2) power cycles. Direct-fired sCO2 cycles are a promising technology for the future power generation systems. The working fluid of sCO2 cycles will be near and above critical point of CO2. One of the challenges is that the simulation of mixtures should consider real gas behavior. Expected operating conditions of Allam cycles reach up to 300 bar and 1000 °C. Characterizing the mixtures at the extreme conditions is an important issue in current researches and industrial applications. Thermophysical properties of mixtures may be beyond the valid range of the widely used database such as NIST REFPROP. Experimental data of mixture properties in the literature are limited which is necessary to develop high-fidelity design tools for sCO2 power cycles. We measured the density and sound speed of several multi-component mixtures. A temperature-controlled high-pressure test cell was used for the density measurements. Sound speed was measured by resonant frequency detection using an external speaker and a piezoelectric pressure sensor. Mixtures studied in this work include carbon dioxide, methane, oxygen, and water vapor. Properties of pure CO2 were measured to show the validity of our technique. Compositions were selected to be close to frozen mixtures at the inlet, mid-progress, and exhaust conditions of a model sCO2 combustor in the previous numerical simulation work. Corresponding reaction progress variables (RPV) were RPV = 0, 0.5, and 1. Temperature and pressure conditions of experiments are 310–450 K and 0–150 bar. In our study, density and sound speed from the NIST REFPROP database agree with experimental measurements within the range of our measurement uncertainties.

Energy & Fuels↗
DOE OSTI2021

Evaluating the Effects of Transient Purge Flow on Stator-Rotor Seal Performance

Abstract As modern engine designs target higher efficiencies through increased turbine inlet temperatures, critical turbine components are at increased risk of damage from conditions exceeding material melting temperatures. In particular, improperly designed underplatform hardware components are susceptible to damage when hot main gas path flow is ingested into the stator-rotor cavity. While all turbines inherently experience transients during operation, a majority of publicly available turbine studies have been executed using steady operating conditions or inherently transient “blowdown” rigs. For this reason, routine transient events are not well understood. To address this need, the present study utilized a combined experimental and computational approach. The test article is a continuous-duration, one-stage test turbine operating with true-scale engine hardware and seal geometries at engine-representative flow conditions. The nature of the continuous-duration facility uniquely supports the direct assessment of transient events through its ability to transition between steady-state operating conditions. The effects of a transient purge flow were investigated in this study to identify general trends for transient events in a full-scale engine. Results from multiple measurement techniques in the wheelspace region show an interdependence of transient purge flow with a thermal lag of the underplatform hardware. Through experiments conducted at different coolant-to-main gas path temperature ratios, the use of pressure measurements as an indicator of fully purged behavior was introduced, and a thermally driven influence on rim seal performance was quantified. The computational results show good agreement with experimental pressure measurements and provide insight into the physical mechanisms that drive the relationship between pressure and sealing effectiveness measurements observed for the tested geometry.

Engineering↗
DOE OSTI2021

The Effect of Pressure on NO x Entitlement and Reaction Timescales in a Premixed Axial Jet-In-Crossflow

This paper investigates the pressure dependency of a lean premixed jet injected into a lean vitiated crossflow with an experimentally verified detailed chemistry computational fluid dynamics (CFD) model and 53 species considered. Experimental data were taken in an axially staged combustor with an optically accessible test section, allowing the use of particle image velocimetry (PIV) and CH* chemiluminescence techniques as well as point measurement of species concentration, temperature, and pressure. The experimental data cases at one, three, and five atmospheres were selected to describe the flame stabilization dependency on pressure and gain the required knowledge for an extrapolation to engine condition. Simulated exit nitrogen oxide levels were validated with experimental emission data, and a global emission trend for the NO reduction at elevated pressure and constant turbine inlet temperature level was defined. The nitrogen oxide benefit at elevated operating pressure was justified with the significantly smaller flame surface area: the analysis of the simulated spanwise and top-view profiles showed a relatively short receded core flame with nitrogen oxide production in the center at high pressure relative to a longer and larger shear layer flame at atmospheric condition that produced NO toward the inner and outer side of the flame. Furthermore, decomposition of the Damköhler number revealed the strong influence of the reaction timescales with higher reaction rates at elevated pressure, along with a moderate influence of the turbulent timescales, showing higher turbulence intensity in the lee-side recirculation zone at lower pressure.

03 NATURAL GAS↗
DOE OSTI2021

A Method to Design and Optimize Axial Flow Cyclones for Gas–Liquid Separation

This article provides a detailed design guide, optimization, and performance assessment for air–water separation of an axial flow cyclone. Axial flow cyclones (also known as swirl tube demisters, mist eliminators, or Austin–Write cyclones) have a range of applications in several different industries. This method of gas–liquid separation offers many benefits. Among these are high liquid separation efficiencies (near 99%) and an inline design that allows them to be more easily fitted into existing piping structures. Despite these benefits, there are several design parameters that have not been optimized for performance in wastewater purification applications. This research fills the gap in the literature by quantifying the effect of new design parameters on water collection efficiency, η water collection , and the air bypass efficiency, η air bypass , defined as the ratio of the air mass flowrate exiting through the desired air outlet over the inlet air mass flowrate. A set of wide-ranging experiments were conducted to study the effects of gas–liquid flow rates, tube geometry, and relative injection angles to optimize the water collection and air bypass efficiencies. The water collection efficiency exceeded 99.8% when the liquid streamline came in direct contact with the water drainage exit. An empirical correlation was developed to predict the swirl pitch as a function of the above design parameters. Predictions from the correlation were within 10% of the experimental results. The correlation can be used to design highly efficient in-line gas–liquid separators.

Engineering↗
DOE OSTI2021

Additively Manufactured Compliant Hybrid Gas Thrust Bearing for Supercritical Carbon Dioxide Turbomachinery: Design and Proof of Concept Testing

The following paper presents a new type of gas lubricated thrust bearing that utilizes additive manufacturing or also known as direct metal laser melting (DMLM) to fabricate the bearing. The motivation for the new bearing concept is derived from the need for highly efficient supercritical carbon dioxide (sCO2) turbomachinery in the mega-watt power range. The paper provides a review of existing gas thrust-bearing technology, outlines the need for the new DMLM concept, and discusses proof-of-concept testing results. The new concept combines hydrostatic pressurization with individual tilting pads that are flexibly mounted using hermetic squeeze film dampers (HSFD) in the bearing-pad support. This paper describes the thrust-bearing concept and discusses the final design approach. Proof-of-concept testing in air for a 6.8 in. (173 mm) outer diameter thrust gas bearing was performed; with thrust loading, up to 1500 lbs (6.67 kN) and a thrust runner speed of 10krpm (91 m/s tip speed). The experiments were performed with a bent shaft resulting in thrust runner axial vibration magnitudes of 2.9 mils (74 μm) p-p and dynamic thrust loads of 270 lbs (1.2 kN) p-p. In addition, force deflection characteristics and stiffness coefficients of the bearing system are presented for an inlet hydrostatic pressure of 380 psi (2.62 MPa). Results at 10 krpm show that the pad support architecture was able to sustain high levels of dynamic misalignment equaling 6 times the nominal film clearance while demonstrating a unit load-carrying capacity of 55 psi (0.34 Mpa). Gas-film force deflection tests portrayed nonlinear behavior like a hardening spring, while the bearing pad support stiffness was measured to be linear and independent of gas film thickness.

Engineering↗