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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Advanced Multi-Dimensional Capacitance Sensors Based Subsea Multiphase Mass Flow Meter to Measure and Monitor Offshore Enhanced Oil

This innovation is based on advanced multi-dimensional extensions of ECVT sensors that involve ECVT, Displacement Current Phase Tomography (DCPT), Maxwell-Wagner-Sillars polarization effect (MWS), and velocimetry which exploit the variation of electric properties between the oil, water, and gas coming out of the well. Capacitance sensors are embedded on the inside of a pipe spool and placed in-line with the subsea oil line piping on the extraction end of the well. The difference in dielectric, dielectric loss, surface polarization, and velocity of each phase are used in the multi-dimensional algorithm to measure the volume fraction, distribution, velocity, mass flow rate, and flow regime of the mixture moving through the pipe.

02 PETROLEUM↗
DOE OSTI2023

Propellant Mass Gauging in a Spherical Tank under Micro-Gravity Conditions Using Capacitance Plate Arrays and Machine Learning

Propellant mass gauging under micro-gravity conditions is a challenging task due to the unpredictable position and shape of the fuel body inside the tank. Micro-gravity conditions are common for orbiting satellites and rockets that operate on limited fuel supplies. Capacitance sensors have been investigated for this task in recent years; however, the effect of various positions and shapes of the fuel body is not analyzed in detail. In this paper, we investigate this with various fill types, such as annular, core-annular, and stratified fills at different positions. We compare the performance among several curve-fitting-based approaches and a machine-learning-based approach, the latter of which offers superior performance in estimating the fuel content.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Locating the electrical junctions in Cu(In,Ga)Se 2 and Cu 2 ZnSnSe 4 solar cells by scanning capacitance spectroscopy

Here, we determined the electrical junction (EJ) locations in Cu(In,Ga)Se 2 (CIGS) and Cu 2 ZnSnSe 4 (CZTS) solar cells with ~20-nm accuracy by developing scanning capacitance spectroscopy (SCS) applicable to the thin-film devices. Cross-sectional sample preparation for the SCS measurement was developed by high-energy ion milling at room temperature for polishing the cross section to make it flat, followed by low-energy ion milling at liquid nitrogen temperature for removing the damaged layer and subsequent annealing for growing a native oxide layer. The SCS shows distinct p-type, transitional, and n-type spectra across the devices, and the spectral features change rapidly with location in the depletion region, which results in determining the EJ with ~20-nm resolution. We found an n-type CIGS in the region next to the CIGS/CdS interface; thus, the cell is a homojunction. The EJ is ~40 nm from the interface on the CIGS side. In contrast, such an n-type CZTS was not found in the CZTS/CdS cells. The EJ is ~20 nm from the CZTS/CdS interface, which is consistent with asymmetrical carrier concentrations of the p-CZTS and n-CdS in a heterojunction cell. Our results of unambiguously determination of the junction locations contribute significantly to understanding the large open-circuit voltage difference between CIGS and CZTS.

14 SOLAR ENERGY↗
DOE OSTI2024

Reducing Ohmic Resistances in Membrane Capacitive Deionization Using Micropatterned Ion-Exchange Membranes, Ionomer Infiltrated Electrodes, and Ionomer-Coated Nylon Meshes

Membrane capacitive deionization (MCDI) is an emerging water desalination platform that is compact, electrified, and does not require high-pressure piping. Herein, highly conductive poly(phenylene alkylene) ion-exchange membranes (IEMs) are micropatterned with different surface geometries for MCDI. The micropatterned membranes increase the interfacial area with the liquid stream leading to a 700 mV reduction in cell voltage when operating at constant current (2 mA cm -2 ; 2000 ppm NaCl feed) while improving the energy normalized adsorbed salt (ENAS) value by 1.4 times. Combining the micropatterned poly(phenylene alkylene) IEMs with poly(phenylene alkylene) ionomer-filled electrodes reduces the cell voltage by 1000 mV and improves the ENAS values by 2.3 times relative to the base case. This reduction in cell voltage allows for higher current density operation (i.e., 3–4 mA cm -2 ) . The reduction in cell voltage is ascribed to the ameliorating ohmic resistances related to ion transport at the membrane-process stream interface and in the carbon cloth electrode. Finally, porous ionic conductors are implemented into the spacer channel with flat and micropatterned IEM configurations and ionomer infiltrated electrodes. For the configuration with flat IEMs, the porous ionic conductor improves ENAS values across the current density regime (2–4 mA cm -2 ), while for micropatterned IEMs it gets improved only at 4 mA cm -2 .

42 ENGINEERING↗
DOE OSTI2025

Capacitated p -hub approach for park-and-ride facility location problem under nested logit demand function: polyhedral approaches

By generalizing the unconstrained p-hub approach for the park-and-ride (P&R) facility location problem under the multinomial logit demand function, the capacitated p-hub approach for the problem under the nested logit demand function captures a broader range of real-world cases. To solve this problem optimally, we introduce a mixed-integer linear program and accelerate its solution by enhancing the branch-and-cut procedure. To address the problem at a large scale, we introduce two other polyhedral approaches: variable neighborhood search (VNS) and adaptive randomized rounding (ARR). Downtown areas in Seoul have a high modal share of public transportation and congested road traffic, yet P&R has not been widely implemented. Therefore, we apply the ARR procedure to solve a real-world problem using traffic and geographic data from the Seoul metropolitan area. ARR performs better than VNS and addresses real-world cases. The solutions obtained by ARR present a phased expansion plan that encourages policymakers to start installing a small number of P&Rs immediately.

Capacitated p-hub approach↗
DOE OSTI2024

Prediction of residual stresses in additively manufactured parts using lumped capacitance and classical lamination theory

Several industries are interested in Laser Powder Bed Fusion (L-PBF) Additively Manufactured (AM) metal parts because their designs can be made arbitrarily complex while retaining bulk-type material properties. However, the residual stresses (RS) and distortions caused by the heat gradients inherent to L-PBF processes are detrimental to the structural integrity of the parts and must be taken into consideration during the part design cycle. Predicting the state of stresses in as-built 3D printed parts is a difficult problem that is typically approached with the use of transient thermomechanical Finite Element Models (FEMs). However, the nonlinearities associated with AM processes are difficult to capture in these FEMs without increasing the computational cost of the simulation, limiting their ability to be incorporated into practical design cycles. This work presents a novel analytical framework that combines lumped capacitance nonlinear heat transfer with time dependent classical lamination theory to efficiently and accurately predict RS in as-built L-PBF parts without the need of FEMs. The simulation was compared to Neutron Diffraction (ND) residual strain measurements taken at Oak Ridge National Laboratories (ORNL) as well as Synchrotron X-ray Diffraction (XRD) strain data published by the National Institute of Standards and Technology (NIST). The simulation predictions and the experimental data showed excellent agreement for the in-plane strain directions, and general agreement for the out of plane strain component, highlighting an area where further development can be implemented.

42 ENGINEERING↗
DOE OSTI2018

Seawater desalination by over-potential membrane capacitive deionization: Opportunities and hurdles

The salt removal capacity ( SRC ) of the carbon electrodes in membrane capacitive deionization (MCDI) is limited by the applied potential (<1.6 V). Thus, enhancement of the SRC is essential before applying MCDI to seawater desalination. This study aims at developing a novel MCDI system for seawater desalination by applying over-potential (OP) to enhance ion-adsorption capacity and kinetics, and by reversing the polarity (RP) of electrodes to improve ion-desorption kinetics (hereafter named OP-MCDI-RP) for seawater desalination. At 2.4 V, the OP-MCDI system with mesoporous carbon demonstrated a SRC value of 64.7 mg g –1 when desalting 0.5 M NaCl solution, while the OP-CDI system could only remove 8.2 mg g –1 under identical conditions. Similarly, an OP-MCDI cell using carbon aerogel demonstrated a greater SRC value of 43.4 mg g –1 in comparison with 12.5 mg g –1 achieved in OP-CDI. These results indicate that the OP-MCDI system can directly desalt high salinity water regardless of the electrode material. In contrast to the OP-MCDI system, the OP-MCDI-RP system yields a higher regeneration efficiency by applying a reversed low-voltage. It is shown that, under appropriate operating conditions, the OP-MCDI-RP system reduced the electrical conductivity of a seawater sample of 37 practical salinity units by 99.9%, suggesting that the OP-MCDI-RP system can be employed for seawater desalination. In conclusion, due to the dramatic increase in energy demand and insufficient long-term stability caused by high potential and high salt concentration, however, the OP-MCDI-RP process should be further investigated for potential practical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Selective phosphate removal with manganese oxide composite anion exchange membranes in membrane capacitive deionization

The discharge of excessive phosphorous into water bodies can lead to serious eutrophication threatening aquatic ecosystem. Membrane capacitive deionization (MCDI) is an effective platform for deionizing aqueous streams; however, conventional MCDI is unable to selectively remove targeted ions from a liquid mixture. Here, in this work, we fabricated manganese oxide composite anion exchange membranes (AEMs) for MCDI to enhance phosphate removal selectivity from sodium chloride-sodium dihydrogen phosphate (10:1 M ratio) aqueous mixtures. We systematically investigated several critical factors, such as constant current or voltage operation, applied voltage amount, process stream pH, and manganese oxide (Mn 2 O 3 ) content in the AEM, on phosphate removal efficiency and phosphate selectivity. A trade-off was observed between phosphate removal and selectivity when increasing the cell voltage. Under the best conditions, a MCDI unit with a 20 wt% Mn 2 O 3 composite AEM and a bipolar membrane facilitated high phosphate removal efficiency of ≥ 31.8 % and a phosphate over chloride selectivity of 1.1 while showing stability for at least 30 cycles. To help understand how Mn 2 O 3 composite AEM boosts phosphate selectivity, static electronic structure calculations were performed, and they revelated that hydrogen phosphate absorption on Mn 2 O 3 composite AEM was 314 kcal/mol more exothermic than that on pristine AEM while chloride adsorption on Mn 2 O 3 composite AEM was 2.2 kcal/mol less exothermic than that on a pristine AEM. Overall, this work presents an effective strategy for selectively removing phosphate from model wastewater solutions and the mechanistic understanding that governs ion selectivity in composite ion-exchange membranes used in MCDI.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Numerical modeling of ion transport and adsorption in porous media: A pore-scale study for capacitive deionization desalination

In this report a pore-scale model is presented to simulate the dynamic ion transport and adsorption processes in porous electrodes used for capacitive deionization (CDI). The Stokes equation governing water flow is solved using the lattice Boltzmann method and Nernst-Planck equation describing ion transport is solved using the finite volume method. The ion adsorption process is considered at the surface of carbon electrodes. After validation against analytical solutions and published results, the model is used to study the coupled water flow, ion transport and adsorption in both two-dimensional and three-dimensional porous CDI electrodes at the pore scale. The effect of electrode microstructure, electrical potential and flow velocity on the adsorption processes is quantitatively investigated, and the relative importance of various parameters is determined. The presented model can be a powerful numerical tool to quantitatively analyze ion transport and adsorption in porous electrodes, and may provide useful information for the design and optimization of CDI electrodes and operating conditions for desired desalination efficiency, water throughput and cost.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Hierarchically porous electrospun carbon nanofiber for high-rate capacitive deionization electrodes

Capacitive deionization (CDI) is a promising technology that has gained interest for the desalination of brackish water. Hierarchically porous carbons are commonly used as electrodes for CDI due to their high surface areas and controlled pore size distributions that maximize ion adsorption capacity and rate. Electrospinning is an effective way of generating carbon nanofibers with high inter-fiber macroporosity that can be further modified to improve surface area, total pore volume, and pore size distribution. This work describes the use of sacrificial mesopore formers in tandem with a micropore etching technique to induce hierarchical porosity in electrospun fibers. Mesopores are formed via the dissolution of silica nanoparticles that are introduced into the fibers during the electrospinning step. After mesopore formation, micropores are etched into the resulting surface through KOH impregnation and thermal activation. This sequential technique creates a hierarchical network of pores from the inherent macroporosity of the fiber network, to the mesopores, and finally micropores to simultaneously maximize surface area and accessibility. Micropore formation is optimized to maximize specific surface area while maintaining physical integrity of the fibers. Further, the combination of mesopores and micropores enables fast ion adsorption rates and capacity. Carbon fiber electrodes fabricated in this method achieve specific surface areas exceeding 1400 m 2 g -1 , with pore volumes exceeding 1.0cc g -1 . The pore size distributions are highly controlled, with 80% of total pore volume coming from pores <20nm in radius. In 500 ppm constant voltage CDI tests, these fiber electrodes obtain a salt adsorption capacity of over 14 mg g -1 at a salt adsorption rate of ~4mg g -1 min -1 , showcasing the high capacity matched with high rate of these easily fabricated, inexpensive materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Capacitive Deionization Using Alternating Polarization: Effect of Surface Charge on Salt Removal

Alternating polarization (AP) at ±1.2/0 V is performed on a capacitive deionization stack assembled with carbon xerogel (CX) electrodes. Long-term testing shows enhanced cycling stability without the formation of inversion peaks. AP also leads to an arch-shaped plot of salt adsorption capacity (SAC) versus cycling time, with the highest SAC of approximately 3 mg (NaCl) g −1 (CX) during this long-term test. Characterization of both the freshly prepared and cycled electrodes depict that AP results in surface charge of all the electrodes being modified from positive to negative character. Here by leveraging balances of electronic, surface, and ionic charges in carbon micropores, it is found that a portion of the electronic charge contributes to the ionic charge for salt adsorption, and another portion is parasitically consumed to balance the surface charge during the charge reconciliation process. When the consumption of electronic charge for charge reconciliation becomes minimal, both the positive and negative surface charges are nearly equivalent on the CX electrode. Under such a condition, the highest SAC values can be achieved for AP testing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Application of the macrohomogeneous line model for the characterization of carbon aerogel electrodes in capacitive deionization

Capacitive deionization (CDI) is a conceivable alternative desalination technology. Among the carbon materials studied as the deionizing electrode, carbon aerogels are a promising material due to their high surface area, structural designability and low resistivity. When evaluating carbons for CDI, their electrochemical properties are a crucial variable making the characterization of such properties vital. We apply a macrohomogenous model to evaluate carbon aerogels activated with CO 2 for various periods and varying Resorcinol/Catalyst, R/C, ratios during synthesis for estimation of their effective surface areas and pore sizes from an electrochemical standpoint. The porosities and structural properties of carbon aerogels were evaluated by nitrogen porosimetry, STEM, SEM and Electrochemical Impedance Spectroscopy (EIS). Results showed that the effective electrochemical surface areas calculated from the EIS were a small fraction of the areas estimated by nitrogen porosimetry, indicating that primarily the mesoporosity was utilized for deionization. Characteristic pore sizes calculated by the model were also close to the mesopore sizes estimated by the nitrogen adsorption isotherms, STEM and SEM measurements. Such results demonstrate the validity and value of the macrohomogenous model for evaluating effective electrochemical properties important for CDI applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Capacitively coupled pickup in MCP-based photodetectors using a conductive metallic anode

We have designed and tested a robust 20×20 cm 2 thin metal film internal anode capacitively coupled to an external array of signal pads or micro-strips for use in fast microchannel plate photodetectors. The internal anode, in this case a 10 nm-thick NiCr film deposited on a 96% pure Al 2 O 3 3 mm-thick ceramic plate and connected to HV ground, provides the return path for the electron cascade charge. The multi-channel pickup array consists of a printed-circuit card or glass plate with metal signal pickups on one side and the signal ground plane on the other. The pickup can be put in close proximity to the bottom outer surface of the sealed photodetector, with no electrical connections through the photodetector hermetic vacuum package other than a single ground connection to the internal anode. Two pickup patterns were tested using a small commercial MCP-PMT as the signal source: 1) parallel 50 Ω 25-cm-long micro-strips with an analog bandwidth of 1.5 GHz, and 2) a 20×20 cm 2 array of 2-dimensional square ‘pads’ with sides of 1.27 cm or 2.54 cm. The rise-time of the fast input pulse is maintained for both pickup patterns. For the pad pattern, we observe 80% of the directly coupled amplitude. For the strip pattern we measure 34% of the directly coupled amplitude on the central strip of a broadened signal. The physical decoupling of the photodetector from the pickup pattern allows easy customization for different applications while maintaining high analog bandwidth.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Investigation of core-annular flow in an industrial scale circulating fluidized bed riser with electrical capacitance volume tomography (ECVT)

There is a paucity of riser data for industrial scale units, particularly with regard to the solids fraction. This is especially true for detailed spatially distributed values. To alleviate this problem, NETL installed a 0.445 m tall electrical capacitance volume tomography (ECVT) sensor 9.66 m from the gas distributor of its industrial size (15.45 m high and 0.3 m diameter) circulating fluidized bed (CFB) cold model. A series of tests were conducted to investigate the gas-solid flow behavior using high density polyethylene (PPE) solids. Static electricity was successfully minimized using Larostat and humidification. Time averaged radial solid fractions profiles are presented and discussed. The time and spatially averaged solid fractions measured by the ECVT agree well with estimates from the pressure drop. The annular thickness was measured and found to increase with increases in the solids flow rate and decrease with increases in the gas velocity. Comparisons of the annular thickness and solids fraction as determined from the ECVT unit were compared to existing correlations. In conclusion, the average error ranged from 13% to 275% which is not surprising since the literature correlations were developed from data on much smaller units and for significantly different particles.

42 ENGINEERING↗
DOE OSTI2020

Optimal conditions for efficient flow-electrode capacitive deionization

One of the current barriers to achieving fast and stable performance for flow-electrode capacitive deionization (FCDI) is determining optimal operating parameters. To date, however, no consensus has been reached for universal conditions for FCDI. Through experimental and modeling approaches in this study, we systematically evaluated the influence of applied potential (V = 1.2–2.4 V) and electrolyte concentration (C0 = 0.05–0.5 M) on the FCDI and electrodialysis (ED) desalination processes. Evaluation indicators include the concentration decrease in the desalinated solution, salt removal rates, pH fluctuations, charge efficiency, and energy consumption. Results demonstrated that the dynamic curves of concentration decrease at 2.0 V nearly overlapped with the response at 1.6 V at certain electrolyte concentrations, while the salt removal rates at 0.2 M salt concentration were the best among all concentrations tested at a range of applied potential. Therefore, it was thus concluded that the optimum conditions for FCDI operation are 1.6 V applied potential and 0.2 M initial salt concentration, under which faradaic reactions are not being triggered, and concentration polarization does not significantly affect ion transfer. Furthermore, a comparative study between FCDI and ED indicated that ED has a different dependence on the electrolyte concentration and applied potential, in which the desalination can be linearly enhanced with increasing potential but greatly limited at high concentrations. Due to the presence of carbon particles in FCDI, the enhanced charge/ion transfer is probably the main reason for the different desalination performance of FCDI and ED. Overall, the optimal operating parameters obtained in this work could be used as basic test conditions for further development of new carbon-based materials for FCDI.

42 ENGINEERING↗
DOE OSTI2018

Imaging charge carriers in potential-induced degradation defects of c-Si solar cells by scanning capacitance microscopy

We report on nm-resolution imaging of charge-carrier distribution around local potential-induced degradation (PID) shunting defects using scanning capacitance microscopy. We imaged on cross sections of heavily field-degraded module areas, cored out and selected by mm-scale photoluminescence imaging. We found localized areas with abnormal carrier behavior induced by the PID defects: the apparent n-type carrier extends vertically into the absorber to ~1-2 um from the cell surface, and laterally in similar lengths; in defect-free areas, the n-type carrier extends ~0.5 um, which is consistent with the junction depth. For comparison, we also investigated areas of the same module exhibiting the least PID stress, and we found no such heavily damaged junction area. Instead, we found slightly abnormal carrier behavior, where the carrier-type inversion in the absorber did not occur, but the p-type carrier concentration changed slightly in a much smaller lateral length of ~300 nm. These nano-electrical findings may indicate a possible mechanism that the existing extended defects, which may not be significantly harmful to cell performance, can be changed by PID to heavily damaged junction areas.

14 SOLAR ENERGY↗
DOE OSTI2020

Imaging hole-density inhomogeneity in arsenic-doped CdTe thin films by scanning capacitance microscopy

We report nanometer-scale hole-density imaging in As-doped CdTe films by scanning capacitance microscopy (SCM). The hole-density profiling is validated by contrasting a CdTe cross-section sample made by molecular-beam epitaxy with systematically increased As doping in a staircase pattern over the range of 10 15 -10 18 /cm 3 within a single film. In polycrystalline films, the carrier distribution is significantly nonuniform, with inhomogeneity ranging from several hundred nm to several um and hole density varying by one order of magnitude (low 10^16 to low 10 17 /cm 3 ). This nonuniformity is distributed randomly, independent of the grain structure and grain boundaries (GBs). Kelvin probe force microscopy (KPFM) maps the surface potential and is correlated to cathodoluminescence (CL) and SCM by imaging over identical areas. Higher potential and lower CL intensity are found on GBs but not by SCM contrast; this indicates positive GB charging and recombination, but not GB-specific hole-density changes. The overall KPFM potential image is in rough agreement with the SCM carrier distribution and indicates band-edge potential fluctuations. Nonuniform carrier concentration, potential fluctuations, and defect recombination can all cause voltage and performance loss in As-doped CdTe solar technology.

14 SOLAR ENERGY↗
DOE OSTI2016

Energy breakdown in capacitive deionization

We explored the energy loss mechanisms in capacitive deionization (CDI). We hypothesize that resistive and parasitic losses are two main sources of energy losses. We measured contribution from each loss mechanism in water desalination with constant current (CC) charge/discharge cycling. Resistive energy loss is expected to dominate in high current charging cases, as it increases approximately linearly with current for fixed charge transfer (resistive power loss scales as square of current and charging time scales as inverse of current). On the other hand, parasitic loss is dominant in low current cases, as the electrodes spend more time at higher voltages. We built a CDI cell with five electrode pairs and standard flow between architecture. We performed a series of experiments with various cycling currents and cut-off voltages (voltage at which current is reversed) and studied these energy losses. To this end, we measured series resistance of the cell (contact resistances, resistance of wires, and resistance of solution in spacers) during charging and discharging from voltage response of a small amplitude AC current signal added to the underlying cycling current. We performed a separate set of experiments to quantify parasitic (or leakage) current of the cell versus cell voltage. We then used these data to estimate parasitic losses under the assumption that leakage current is primarily voltage (and not current) dependent. Our results confirmed that resistive and parasitic losses respectively dominate in the limit of high and low currents. We also measured salt adsorption and report energy-normalized adsorbed salt (ENAS, energy loss per ion removed) and average salt adsorption rate (ASAR). As a result, we show a clear tradeoff between ASAR and ENAS and show that balancing these losses leads to optimal energy efficiency.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗