scholarly journals Evaluation of flow schemes for near-neutral pH electrolytes in solar-fuel generators

2017 ◽  
Vol 1 (3) ◽  
pp. 458-466 ◽  
Author(s):  
Meenesh R. Singh ◽  
Chengxiang Xiang ◽  
Nathan S. Lewis
Keyword(s):  
Design Principles ◽  
Operating Conditions ◽  
Solar Fuel ◽  
Efficient Operation ◽  
Neutral Ph ◽  
Active Flow

Operating conditions and design principles for the efficient operation of solar-fuel generators with active flow of near-neutral pH electrolytes.

Evaporator Superheat Regulation via Emulation of Semi-Active Flow Control

2009 ◽  
Author(s):  
Matthew Elliott ◽  
Bryan P. Rasmussen
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Control Device ◽  
Operating Conditions ◽  
Limiting Factor ◽  
Efficient Operation ◽  
Control Approach ◽  
Active Feedback ◽  
Vapor Compression Cooling ◽  
Active Flow

Proper regulation of evaporator superheat is essential to ensuring safe and efficient operation of vapor compression cooling systems. Typical mechanical control devices may behave poorly under transient disturbances or as operating conditions vary, degrading system performance. Electronic expansion valves partially alleviate these problems by allowing more sophisticated control approaches, but frequent valve adjustments raise concerns about device longevity. A cascaded control approach to superheat regulation has been shown to provide significant improvements in superheat control, utilizing a hybrid of mechanical (passive) and electronic (active) feedback devices. This paper examines the emulation of a semi-active flow control device using a MEMs based actuator with high bandwidth, few moving parts, and no risk of fatigue failure. Experimental evaluation reveals this to be a comparable approach to the hybrid valve design. Moreover, further examination reveals that actuator characteristics are the limiting factor in achieving similar levels of performance using standard electronic valves.

scholarly journals An electrochemical engineering assessment of the operational conditions and constraints for solar-driven water-splitting systems at near-neutral pH

2015 ◽  
Vol 8 (9) ◽  
pp. 2760-2767 ◽  
Author(s):  
Meenesh R. Singh ◽  
Kimberly Papadantonakis ◽  
Chengxiang Xiang ◽  
Nathan S. Lewis
Keyword(s):  
Water Splitting ◽  
Operating Conditions ◽  
Electrochemical Engineering ◽  
Efficient Operation ◽  
Operational Conditions ◽  
Neutral Ph

Identified operating conditions and constraints for efficient operation of solar-driven water-splitting systems at near-neutral pH.

"Recent Patents on the Triboelectrostatic Separation of Fly Ash"

2019 ◽  
Vol 13 ◽  
Author(s):  
Haisheng Li ◽  
Wenping Wang ◽  
Yinghua Chen ◽  
Xinxi Zhang ◽  
Chaoyong Li
Keyword(s):  
Fly Ash ◽  
Power Plants ◽  
High Efficiency ◽  
Separation Efficiency ◽  
High Reliability ◽  
Operating Conditions ◽  
Security Requirements ◽  
Unburned Carbon ◽  
Efficient Operation ◽  
Triboelectrostatic Separation

Background: The fly ash produced by coal-fired power plants is an industrial waste. The environmental pollution problems caused by fly ash have been widely of public environmental concern. As a waste of recoverable resources, it can be used in the field of building materials, agricultural fertilizers, environmental materials, new materials, etc. Unburned carbon content in fly ash has an influence on the performance of resource reuse products. Therefore, it is the key to remove unburned carbon from fly ash. As a physical method, triboelectrostatic separation technology has been widely used because of obvious advantages, such as high-efficiency, simple process, high reliability, without water resources consumption and secondary pollution. Objective: The related patents of fly ash triboelectrostatic separation had been reviewed. The structural characteristics and working principle of these patents are analyzed in detail. The results can provide some meaningful references for the improvement of separation efficiency and optimal design. Methods: Based on the comparative analysis for the latest patents related to fly ash triboelectrostatic separation, the future development is presented. Results: The patents focused on the charging efficiency and separation efficiency. Studies show that remarkable improvements have been achieved for the fly ash triboelectrostatic separation. Some patents have been used in industrial production. Conclusion: According to the current technology status, the researches related to process optimization and anti-interference ability will be beneficial to overcome the influence of operating conditions and complex environment, and meet system security requirements. The intelligent control can not only ensure the process continuity and stability, but also realize the efficient operation and management automatically. Meanwhile, the researchers should pay more attention to the resource utilization of fly ash processed by triboelectrostatic separation.

scholarly journals Non-Stoichiometric Redox Active Perovskite Materials for Solar Thermochemical Fuel Production: A Review

Catalysts ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 611 ◽  
Author(s):  
Anita Haeussler ◽  
Stéphane Abanades ◽  
Julien Jouannaux ◽  
Anne Julbe
Keyword(s):  
Carbon Dioxide ◽  
Solar Energy ◽  
Energy Conversion ◽  
Operating Conditions ◽  
Solar Fuel ◽  
Fuel Production ◽  
Concentrated Solar Energy ◽  
Redox Active ◽  
Conversion Rates ◽  
Wide Range

Due to the requirement to develop carbon-free energy, solar energy conversion into chemical energy carriers is a promising solution. Thermochemical fuel production cycles are particularly interesting because they can convert carbon dioxide or water into CO or H2 with concentrated solar energy as a high-temperature process heat source. This process further valorizes and upgrades carbon dioxide into valuable and storable fuels. Development of redox active catalysts is the key challenge for the success of thermochemical cycles for solar-driven H2O and CO2 splitting. Ultimately, the achievement of economically viable solar fuel production relies on increasing the attainable solar-to-fuel energy conversion efficiency. This necessitates the discovery of novel redox-active and thermally-stable materials able to split H2O and CO2 with both high-fuel productivities and chemical conversion rates. Perovskites have recently emerged as promising reactive materials for this application as they feature high non-stoichiometric oxygen exchange capacities and diffusion rates while maintaining their crystallographic structure during cycling over a wide range of operating conditions and reduction extents. This paper provides an overview of the best performing perovskite formulations considered in recent studies, with special focus on their non-stoichiometry extent, their ability to produce solar fuel with high yield and performance stability, and the different methods developed to study the reaction kinetics.

scholarly journals In Situ EPR Characterization of a Cobalt Oxide Water Oxidation Catalyst at Neutral pH

Catalysts ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 926 ◽  
Author(s):  
Yury Kutin ◽  
Nicholas Cox ◽  
Wolfgang Lubitz ◽  
Alexander Schnegg ◽  
Olaf Rüdiger
Keyword(s):  
Cobalt Oxide ◽  
Water Oxidation ◽  
Large Scale ◽  
Low Cost ◽  
Operating Conditions ◽  
Oxidation Catalyst ◽  
O2 Evolution ◽  
Ligand Field ◽  
Neutral Ph

Here we report an in situ electron paramagnetic resonance (EPR) study of a low-cost, high-stability cobalt oxide electrodeposited material (Co-Pi) that oxidizes water at neutral pH and low over-potential, representing a promising system for future large-scale water splitting applications. Using CW X-band EPR we can follow the film formation from a Co(NO3)2 solution in phosphate buffer and quantify Co uptake into the catalytic film. As deposited, the film shows predominantly a Co(II) EPR signal, which converts into a Co(IV) signal as the electrode potential is increased. A purpose-built spectroelectrochemical cell allowed us to quantify the extent of Co(II) to Co(IV) conversion as a function of potential bias under operating conditions. Consistent with its role as an intermediate, Co(IV) is formed at potentials commensurate with electrocatalytic O2 evolution (+1.2 V, vs. SHE). The EPR resonance position of the Co(IV) species shifts to higher fields as the potential is increased above 1.2 V. Such a shift of the Co(IV) signal may be assigned to changes in the local Co structure, displaying a more distorted ligand field or more ligand radical character, suggesting it is this subset of sites that represents the catalytically ‘active’ component. The described spectroelectrochemical approach provides new information on catalyst function and reaction pathways of water oxidation.

Effect of Porosity and Thermal Conductivity of a Porous Transport Layer on Saturation and Thermal Transport in a Low-Temperature Fuel Cell

2013 ◽  
Author(s):  
Vinaykumar Konduru ◽  
Ezequiel Medici ◽  
Jeffrey S. Allen
Keyword(s):  
Thermal Conductivity ◽  
Fuel Cell ◽  
Solid Phase ◽  
Polymer Electrolyte Membrane ◽  
Operating Conditions ◽  
Transport Layer ◽  
Reliable Operation ◽  
Two Phase ◽  
Efficient Operation ◽  
Electrolyte Membrane

Water transport in the Porous Transport Layer (PTL) plays an important role in the efficient operation of polymer electrolyte membrane fuel cells (PEMFC). Excessive water content as well as dry operating conditions are unfavorable for efficient and reliable operation of the fuel cell. The effect of thermal conductivity and porosity on water management are investigated by simulating two-phase flow in the PTL of the fuel cell using a network model. In the model, the PTL consists of a pore-phase and a solid-phase. Different models of the PTLs are generated using independent Weibull distributions for the pore-phase and the solid-phase. The specific arrangement of the pores and solid elements is varied to obtain different PTL realizations for the same Weibull parameters. The properties of PTL are varied by changing the porosity and thermal conductivity. The parameters affecting operating conditions include the temperature, relative humidity in the flow channel and voltage and current density. A parametric study of different solid-phase distributions of the PTL and its effect on thermal, vapor and liquid transport in the PTL under different operating conditions are discussed.

Optimum Efficiencies and Phase Change Temperatures in Latent Heat Storage Systems

1994 ◽  
Vol 116 (1) ◽  
pp. 79-86 ◽  
Author(s):  
S. Aceves-Saborio ◽  
H. Nakamura ◽  
G. M. Reistad
Keyword(s):  
Phase Change ◽  
Latent Heat ◽  
Heat Storage ◽  
Storage Systems ◽  
Broad Class ◽  
Operating Conditions ◽  
Latent Heat Storage ◽  
Efficient Operation ◽  
Basic Model ◽  
Application Potential

This paper presents an analysis of a class of latent heat storage systems (LHSS). The analysis is based on a lumped model (the basic model) that allows a broad class of LHSSs to be completely specified, with only two parameters and a set of operating temperatures, while still retaining the main thermodynamic aspects associated with its operation. Characterization of the performance in this manner permits the broad base application potential of such systems to be viewed. This modeling is in contrast to most studies to date, which employ many parameters to include details of specific systems, and therefore obscure, to a great extent, this broad-based application potential. The basic model is later modified in three ways to analyze operating conditions that either occur in practical units or are desirable for an improved operation of the units. The modifications include, first, the consideration of the LHSS as being formed by many independent phase-change material (PCM) capsules. Second, the possibility of having PCMs with different phase change temperatures filling the capsules. Third, the case when the PCM melts over a temperature range. The results indicate that the efficiency of the basic model represents a higher bound for the efficient operation of LHSSs with negligible sensible storage capacity, and a single PCM. Using multiple PCMs within a LHSS results in higher efficiencies. These efficiencies set higher bounds for efficiency of any sensible or latent heat storage system, and also represent the only possibility for reversible operation of LHSS.

Advanced Cooling With Embedded Heat Pipes for High Power Microelectronics

2009 ◽  
Author(s):  
Victor Adrian Chiriac
Keyword(s):  
Heat Pipe ◽  
Thermal Performance ◽  
Heat Sink ◽  
Heat Pipes ◽  
Optimal Operation ◽  
Operating Conditions ◽  
Peak Temperature ◽  
Transient Temperature ◽  
Efficient Operation ◽  
The Impact

The transient thermal behavior of a complex testing system including multiple fans, a mixing enclosure, Cu inserts and a leaded package dissipating large amounts of power over short time durations is evaluated via numerical simulations. The system performance is optimized with heat sink/fan structure for device efficient operation under constant powering. The study provides meaningful understanding and prediction of a transient powering scenario at high powering levels, evaluating the impact of alternative cooling fan/heat pipe configurations on the thermal performance of the system. One design is chosen due to its effective thermal performance and assembly simplicity, with the package embedded in heat sink base with multiple (5) heat pipes. The peak temperature reached by the modified design with 4 cooling fans is ∼95°C, with the corresponding Rja thermal resistance ∼0.58°C/W. For the transient study (with embedded heat pipes and 4 fans), after one cycle, both peak temperature (at 45 s) and the end temperature (at 49 s) decrease as compared to the previous no heat pipe/single fan case (especially the end temperature reduces by ∼16%). The temperature drop between peak and end for each cycle is ∼80.2°C, while the average power per transient cycle is ∼31.27W. With this power, the design with 5 perpendicular heat pipes, 4 fans and insert reaches a steady state peak temperature of ∼98°C. Applying the superposition principle, the maximum transient temperature after a large number of operating cycles will not exceed ∼138.1°C, satisfying the thermal budget under the current operating conditions. The benefit of the study is related to the possibility to extract the maximum/minimum temperatures for a real test involving a large number of heating-cooling cycles, yet maintaining the initial and peak temperatures within a certain range for the optimal operation of the device. The flow and heat transfer fields are thoroughly investigated: using a combination of numerical and analytical study, the thermal performance of the device undergoing large number of periodic thermal cycles is predicted. Further comparison between measurement and simulation results reveals good agreement.

Control-Oriented Modeling of a Solid-Oxide Fuel Cell Stack Using an LPV Model Structure

2009 ◽  
Author(s):  
Borhan M. Sanandaji ◽  
Tyrone L. Vincent ◽  
Andrew Colclasure ◽  
Robert J. Kee
Keyword(s):  
Fuel Cell ◽  
Solid Oxide Fuel Cell ◽  
Parametric Method ◽  
Operating Conditions ◽  
Solid Oxide ◽  
Model Structure ◽  
Oxide Fuel ◽  
Efficient Operation ◽  
Fuel Cell Stack ◽  
Starting Point

For efficient operation, as well as to avoid operating conditions that can cause damage, fuel cells require a control system to balance fuel and air supply and electrical load. The need to maintain signal constraints during operation, combined with importance of unmeasured variables such as internal stack temperature or fuel utilization, indicate the need for control-oriented models that can be used for estimation and model predictive control. In this paper, we discuss the development of a control-oriented dynamic model of a solid oxide fuel cell stack. Using a detailed physical model as a starting point, we demonstrate the utility of a linear parameter varying (LPV) model structure as a mechanism for model reduction. A novel feature is a non-parametric method for determining the scheduling functions in this model.

Fuel Nozzle Performance Analysis Using Laser Techniques and Combustion Chamber With Optical Access

2006 ◽  
Author(s):  
G. R. Pucher ◽  
P. R. Underhill ◽  
W. D. Allan ◽  
G. Wang ◽  
S. Guy
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Scattered Light ◽  
Laser Sheet ◽  
Video Camera ◽  
Operating Conditions ◽  
Cross Sectional ◽  
Efficient Operation ◽  
Spray Pattern ◽  
Optical Access

Correct functioning of fuel nozzles is paramount to the efficient operation of gas turbine engines. Nozzles exhibiting poor distribution of droplets can be detrimental to combustion and overall engine life due to the creation of hot spots and potential for torching. The traditional technique of assessing nozzle performance involves operation in stagnant air conditions. Fuel spray is collected in the subdivided bins of a mechanical patternation system to determine spray symmetry. Recent improvements in spray analysis involve the use of laser light sheets to illuminate specific ‘slices’ of sprays in either cross sectional or axial planes. Typically, scattered light from the intersection of a laser sheet and a spray is recorded by a digital video camera, and images are averaged and corrected to determine the quality of the spray pattern. Such optical means of assessing spray quality provide great improvement over conventional means in terms of speed, convenience, and information retrieved. Nonetheless, data obtained in stagnant air conditions do not give an indication of spray geometry within combustion chambers under realistic operating conditions of airflow and combustion. This paper describes a project which applied laser-based optical patternation in a T-56 gas turbine combustion chamber rig with optical access under realistic flow conditions. As such, nozzle spray pattern was observed for various air and fuel flows in both cross sectional and plume (chamber axial) orientations. A deliberately damaged nozzle was also assessed for comparison with a good nozzle. Using optical filtration, spray patterns were observed under operationally representative combustion conditions.

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