bluuebunny/crossref_metadata_2025 huggingface dataset:
Facilitation contributes to Mediterranean woody plant diversity but does not shape the diversity–productivity relationship along aridity gradients
Authors: Rey Pedro J. , Alcántara Julio M. , Manzaneda Antonio J. , Sánchez‐Lafuente Alfonso M.
Published: March 2016

The diversity–productivity relationship (humped‐back model (HBM)) and the stress‐gradient (SGH) hypotheses may be connected when productivity is limited primarily by aridity. We analytically connect both hypotheses and assess the contribution of facilitation to woody plant richness along the aridity gradient of the Western Mediterranean floristic region.

We monitored regeneration niches of woody plants, obtaining rarefied species richness and plant relative interaction indices in 54 forests and scrublands in a 1750‐km geographical range across Spain, Morocco and the Canary Islands.

We verified the monotonic increase in facilitation with aridity postulated by SGH and the humped‐shape pattern of species richness expected from HBM, which became manifest after expanding the aridity gradient or crossing vegetation types. Along the gradient, interaction balance turned into facilitation earlier in forest than in scrublands. The effects of aridity and interaction balance on species diversity were additive rather than interdependent.

Facilitation is an important driver of woody species richness at macroecological scales because it added up to diversity in most sites, with enhanced contribution with increased stress. The HBM was not shaped by species interactions. Results suggest that facilitation may act in Mediterranean vegetation buffering against critical transitions between states allowing woody plant communities to cope with the rise in aridity expected with global warming.
Decomposing the Ins and Outs of Cyclical Unemployment
Authors: Bachmann Ronald , Sinning Mathias
Published: March 2016

This paper analyses the contribution of the composition of the pool of employed and unemployed individuals to labour market dynamics in different phases of the business cycle. Using individual‐level data from the Current Population Survey (CPS), we decompose differences in employment status transition rates between upswings and downturns into explained and unexplained parts. We find that the duration of unemployment contributes to explaining unemployment outflows to employment and observe that its initially positive contribution turns negative in deep recessions. Composition effects play an important role for unemployment outflows to non‐participation but dampen the cyclicality of unemployment inflows from employment.
Anesthetic care and perioperative complications in children with Sanfilipo Syndrome Type A
Authors: Cingi Elif C. , Beebe David S. , Whitley Chester B. , Belani Kumar G.
Published: March 2016

Background

Patients with mucopolysaccharidoses (MPS) are generally considered high risk for anesthesia care, owing to disease‐related factors. Sanfilippo syndrome type A (MPS IIIA) is the most frequently occurring MPS. Anesthesia‐specific information for MPS IIIA is not readily available in the literature.

Objectives

To report post hoc analyses on anesthesia care and outcomes from a 2‐year study of the natural history of patients with untreated MPS IIIA (NCT01047306).

Methods

Subjects were ≥1 year of age, developmental age ≥1 year, and without significant central nervous system impairment (other than that due to MPS IIIA) or issues that would preclude study procedures. Procedures requiring general anesthesia included brain/abdominal magnetic resonance imaging, lumbar puncture, and echocardiography. Sedation, intubation, and extubation procedures as well as postoperative airway problems were recorded at baseline and 6, 12, and 24 months of age.

Results

Twenty‐five patients (baseline age, 13–220 months) received a total of 94 general anesthetics. Patients successfully received oral sedation prior to 76 of 94 anesthetics. No patients required airway intervention or oxygen supplementation during sedation. All anesthesia providers described facemask ventilation and endotracheal intubations as ‘easy’. All subjects were successfully extubated after completion of the procedures. No patients required reintubation. Six (24%) patients had episodes of postoperative airway problems: wheezing (7/94, 7.4%), croup (6/94, 6.4%), and laryngospasm (2/94, 2.1%).

Conclusion

We found no change in the modified Cormack–Lehane intubation grades in 25 Sanfilippo syndrome type A children over the 2‐year study period.
Global Host Partner Perspectives: Utilizing a Conceptual Model to Strengthen Collaboration with Host Partners for International Nursing Student Placements
Authors: Underwood Margot , Gleeson Judith , Konnert Candace , Wong Katherine , Valerio Bautista
Published: March 2016

Objectives

Collaboration in international nursing student placements requires equitable partnerships between global partners to address areas of shared importance, such as equity and justice in health promotion. This qualitative study was the first to use the Leffers and Mitchell Conceptual Model for Partnership and Sustainability in Global Health to elicit global host partners' perspectives regarding effective collaboration for Canadian community health nursing placements in the Dominican Republic.

Design and Sample

Focus group and semi‐structured interview methodology was conducted with Dominican Republic (Dominican and Haitian) host partners (n = 23) about the engagement processes and host partner factors for effective partnership.

Results

Dominican (83%) and Haitian (17%) participants, comprised similar numbers of male and female adults aged 18–60 years (mean age = 36 years), represented the full range of the Dominican Republic host partners (e.g., teachers, health professionals). Interpretive analysis revealed themes that included (1) the unique role of the cultural broker; (2) relational collaboration in a collective society; (3) reciprocal approaches that honor local expertise; and (4) contextual socioeconomic and cultural factors that influence partnerships.

Conclusions

Future research and implications at the individual, community, and policy levels are discussed.
Origin and mechanism of crassulacean acid metabolism in orchids as implied by comparative transcriptomics and genomics of the carbon fixation pathway
Authors: Zhang Liangsheng , Chen Fei , Zhang Guo‐Qiang , Zhang Yong‐Qiang , Niu Shance , Xiong Jin‐Song , Lin Zhenguo , Cheng Zong‐Ming (Max) , Liu Zhong‐Jian
Published: March 2016

Crassulacean acid metabolism (CAM) is a CO2 fixation pathway that maximizes water‐use efficiency (WUE), compared with the C3/C4 CO2 pathway, which permits CAM plants to adapt to arid environments. The CAM pathway provides excellent opportunities to genetically design plants, especially bioenergy crops, with a high WUE and better photosynthetic performance than C3/C4 in arid environments. The information available on the origin and evolution of CAM is scant, however. Here, we analyzed transcriptomes from 13 orchid species and two existing orchid genomes, covering CAM and C3 plants, with an emphasis on comparing 13 gene families involved in the complete carbon fixation pathway. The dosage of the core photosynthesis‐related genes plays no substantial role in the evolution of CAM in orchids; however, CAM may have evolved primarily by changes at the transcription level of key carbon fixation pathway genes. We proposed that in both dark and light, CO2 is primarily fixed and then released through two metabolic pathways via known genes, such as PPC1, PPDK and PPCK. This study reports a comprehensive comparison of carbon fixation pathway genes across different photosynthetic plants, and reveals the importance of the level of expression of key genes in the origin and evolution of CAM.
Performance of Air Gap Membrane Distillation Unit for Water Desalination
Authors: Khalifa Atia E. , Lawal Dahiru U. , Antar Mohamed A.
Published: March 2016

Due to water scarcity in the Arabic gulf region, water desalination technologies are considered extremely important. The present work represents a fundamental study on the effect of basic operating and design variables on the flux of an air gap membrane distillation (AGMD) unit for water desalination. The flat sheet, channeled air gap membrane distillation module was designed and manufactured locally. The effect of feed flow rate, feed temperature, coolant water temperature, the air gap width, and the water salinity on the module flux are investigated. Analytical model for heat and mass transfer is used to predict the flux and the model results are compared to the experimental ones. Results showed that the technique has good potential to be used for water desalination. The permeate flux is increased by increasing feed flow rate, feed temperature, decreasing the air gap width, decreasing coolant temperature, and decreasing salinity of feed water. For a given feed flow rate, the width of the air gap and the feed water temperature are found to be the most effective parameters in increasing the distillate flux. Predicting the permeate flux with analytical models for heat and mass transfer showed good agreement with experimental results.
Development of a Novel Two-Stage Heat Pump Clothes Dryer
Authors: Cao Tao , Ling Jiazhen , Hwang Yunho , Radermacher Reinhard
Published: March 2016

An energy efficient two-stage heat pump clothes dryer (HPCD) was successfully developed. This new dryer utilizes three advanced technologies: vapor injection cycle, compact heat exchanger and brushless direct current (BLDC) fan motor. An in-house heat exchanger design tool – CoilDesigner was utilized to design and optimize the evaporator and condenser in the vapor injection cycle. One electric clothes dryer (CD) from U.S. market was selected as the baseline product, and one hybrid HPCD from European market was selected as the best state-of-the-art commercial product in terms of energy efficiency. These two commercial products and the constructed two-stage HPCD prototype were tested according to the Department of Energy (DOE) dryer test standards. Experimental evaluation revealed that the two-stage HPCD achieved 59% energy savings and improved energy factor (EF) by 143% as compared to the electric dryer. It also achieved 25% energy savings and improved EF by 33% as compared to the hybrid HPCD. This implied that the two-stage HPCD could save energy up to 42 TW·h annually if this technology is fully deployed to replace all U.S. electric CDs. Cost analysis indicates that the payback period of the two-stage HPCD is only 2.2 years as compared to the electric dryer with bottom cabinet. Therefore, the two-stage HPCD is an economically competitive greener option.
Reduction Behavior of Iron Oxide for Chemical-Looping Hydrogen Generation in a Compact Fluidized Fuel Reactor
Authors: Chen Shiyi , Xue Zhipeng , Wang Xiang , Xu Changchun , Wang Dong , Xiang Wenguo
Published: March 2016

Chemical-looping hydrogen generation (CLHG) integrates chemical-looping combustion (CLC) and the steam-iron process. It is a process for hydrogen production with inherent CO2 separation. CLHG includes three reactors: a fuel reactor, a steam reactor and an air reactor, with iron oxide as oxygen carrier. This paper presents a compact fluidized fuel reactor for CLHG to produce reductive FeO with CO2 sequestration. An iron ore as oxygen carrier was tested, and CO and syngas were used as fuels. The results showed that through this compact fuel reactor, reductive FeO for further hydrogen generation was obtained and a high concentration CO2 was separated at the outlet of the fuel reactor. The influence of riser temperature, bubble fluidized bed temperature and Fe2O3/CO ratio on the bed performance was investigated. It revealed that the bubble fluidized bed temperature and Fe2O3/CO ratio had a significant impact on the fuel conversion while the effect of riser temperature was marginal. The iron ore exhibited good reactivity and no agglomeration was found in the experiment.
Time Domain Modeling and Power Output for a Heaving Point Absorber Wave Energy Converter
Authors: Pastor Jeremiah , Liu Yucheng
Published: March 2016

This paper presents, assesses, and optimizes a point absorber wave energy converter (WEC) through numerical modeling, simulation, and analysis in time domain. Wave energy conversion is a technology especially suited for assisting in power generation in the offshore oil and gas platforms. A linear frequency domain model is created to predict the behavior of the heaving point absorber WEC system. The hydrodynamic parameters are obtained with AQWA, a software package based on boundary element methods. A linear external damping coefficient is applied to enable power absorption and an external spring force is introduced to tune the point absorber to the incoming wave conditions. The external damping coefficient and external spring forces are the control parameters, which need to be optimized to maximize the power absorption. Two buoy shapes are tested and a variety of diameters and drafts are compared. Optimal shape, draft, and diameter of the model are then determined to maximize its power absorption capacity. Based on the results generated from the frequency domain analysis, a time domain analysis was also conducted to derive the responses of the WEC in the hydrodynamic time response domain. The time domain analysis results allowed us to estimate the power output of this WEC system.
Climate Change Aggravates the Energy-Water-Food Nexus
Authors: Wong Kaufui V. , Chaudhry Sarmad
Published: March 2016

There are regions in the world experiencing the energy-food-water nexus problems. These regions tend to have high population density, economy that depends on agriculture and climates with lower annual rainfall that may have been adversely affected by climate change.

A case in point is the river basin of the Indus. The Indus River is a large and important river running through four countries in East Asia and South Asia: China, India, Afghanistan, and Pakistan.

The region is highly dependent on water for both food and energy. The interlinkage of these three components is the cause for the energy-water-food nexus. The difficulty in effectively managing the use of these resources is their very interdependence. For instance, water availability and policies may influence food production, which is governed by agricultural policies, which will further affect energy production from both water and biofuel sources, which will in turn require the usage of water.

The situation is further complicated when climate change is taken into account. On the surface, an increase in temperatures would be devastating during the dry season for a region that uses up to 70% of the total land for agriculture. There are predictions that crop production in the region would decrease; the Threedegreeswarmer organization estimated that crop production in the region could decrease by up to 30% come 2050.

Unfortunately, the suspected effects of climate change are more than just changes in temperature, precipitation, monsoon patterns, and drought frequencies. A huge concern is the accelerating melting of glaciers in the Himalayas. Some models predict that a global increase in temperature of just 1°C can decrease glacial volume by 50%. The loss of meltwaters from the Himalayan glaciers during the dry season will be crippling for the Indus River and Valley. In a region where up to 90% of accessible water is used for agriculture, there will be an increased strain on food supply. This will further deteriorate the current situation in the region, where almost half of the world’s hungry and undernourished people reside. While the use of hydropower to generate electricity is already many times lower than the potential use, future scarcity of water will limit the potential ability of hydropower to supply energy to people who already experience less than 50% access to electricity.

In the current work, suggestions have been put forward to save the increased glacier melt for current and future use where necessary, improve electricity generation efficiency, use sea water for Rankine power cycle cooling and combined cycle cooling, and increase use desalination for drinking water. Energy conservation practices should also be practiced. All of these suggestions must be considered to address the rising issues in the energy-water-food nexus.
A CFD Simulation Analysis of the Water Volumetric Fraction Distribution in the Runner of a Turgo Type Turbine Designed With an Integrated Dimensional Methodology
Authors: Clarembaux Correa Jorge Luis , de Andrade Jesús , Croquer Sergio , Asuaje Miguel
Published: March 2016

Our previous work, on development of a design methodology inspired in the analysis of One-Dimensional and Three-dimensional Theories [1], allowed to obtain a Turgo Type Turbine (TTT) bucket using 8 geometric parameters as a function of the jet diameter, and Rankine Ovoids potential flow. CFD models under steady state regime [2] made possible to verify deduced expressions for torque, output power and hydraulic efficiency. In this paper, the effects of the water volumetric fraction distribution in the runner have been included, which are significantly conclusive to understand the runner hydrodynamic behavior and highlighted several optimizations to the performance equations that could be considered as a potential novelty for these turbines. In the same way, an influence study of nozzle parameters determined that the most profitable performance is achieved for an absolute velocity angle coming from the jet of 19.8°. Finally, several differences in the flow distribution in the runner were evaluated through a non-steady state regime CFD simulation, when comparing with the steady state.
Fixed Bed Solid Fuel Combustor for the Purpose of Testing Solid Biomass Emissions Properties
Authors: Apprill Bob , Coen Logan , Gessler Brian , Mattson Jonathan , Depcik Christopher
Published: March 2016

Fossil fuels place a large strain on the environment due to the pollution produced through their extraction and usage. One method to reduce societal fossil fuel usage is through co-combustion of coal with woody biomass. However, overproduction of this biomass may lead to significant environmental deterioration. A potential sustainable substitute for the woody biomass is in the form of dried algae. Because the emission characteristics of algae combustion are unknown, a simple dry mass combustor was constructed, including necessary instrumentation, as part of an undergraduate design class with the goal of a more thorough characterization of algae’s combustion properties. The combustor is a simple and affordable design, in keeping with the classes’ principles of sustainability through a focus on energy, environment, and economy. The combustor consists of a flow controller that sends air into a metallic plenum, where modulations in flow are reduced before it is sent to a steel pipe for combustion. This paper describes the concepts involved in the design of this combustor, and preliminary assessment efforts employing the system when testing biomass pellets. Testing showed combustion efficiency greater than 98%, and the data clearly illustrates three separate phases to the reaction process, with rapid changes in emissions and temperature punctuating the ends of these phases.
Technoeconomy of Different Solid Oxide Fuel Cell Based Hybrid Cycles
Authors: Rokni Masoud
Published: March 2016

Gas turbine, steam turbine and heat engine (Stirling engine) is used as bottoming cycle for a solid oxide fuel cell plant to compare different plants efficiencies, CO2 emissions and plants cost in terms of $/kW. Each plant is then integrated with biomass gasification and finally six plants configurations are compared with each other. Technoeconomy is used when calculating the cost if the plants.

It is found that when a solid oxide fuel cell plant is combined with a gas turbine cycle then the plant efficiency will be the highest one while if a biomass gasification plant is integrated with these hybrid cycles then integrated biomass gasification with solid oxide fuel cell and steam cycle will have the highest plant efficiency.

The cost of solid oxide fuel cell with steam plant is found to be the lowest one with a value of about 1030$/kW.
Combustion Characteristics of Spray Flames of Diesel and Palm Methyl Ester at Lean Inlet Conditions
Authors: Richichi Michael S. , Parthasarathy Ramkumar N. , Gollahalli Subramanyam R.
Published: March 2016

Palm Methyl Ester (PME) is an attractive alternate fuel to petroleum diesel because it can be produced from a renewable source, is close to being carbon-neutral in the environment, and has many properties similar to those of petroleum fuels. Although a few engine studies have been completed using PME, basic studies on the combustion of PME sprays are limited. Hence, the objective of this investigation was to study the combustion characteristics of spray flames of PME and diesel at three equivalence ratios: 0.4, 0.6 and 0.8. The liquid fuel was atomized and combusted with air in a heated environment; the coflow air temperature was maintained at 65% of the midpoint of the boiling point range of the fuels. The equivalence ratio was changed by altering the fuel flow rate, while maintaining the atomizing and coflow air flow rates constant, thus maintaining the gas velocity field invariant. The PME flames were shorter and less luminous than the diesel flames and had significant near-burner homogeneous-gas-phase reaction zones. The global CO emission index of the PME flames was higher than that of diesel flames at equivalence ratios of 0.4 and 0.6. The NO emission index of the PME flames was almost twice that of the diesel flames. The in-flame concentration profiles highlighted the effects of the significant fuel-bound oxygen content in PME.
A New Concept for Power Grid Stabilization Using a Motor-Assisted Variable Speed Gas Turbine System
Authors: Kusumi Naohiro , Hino Noriaki , Thet Aung Ko
Published: March 2016

As the penetration ratio of renewable energy sources becomes larger, the fluctuations of grid load also become larger and larger because of the intermittent generation of wind power and photovoltaic power. These fluctuations cause instability of voltage and frequency in the power grid.

Recently, there has been considerable research into solving these challenges, leading to development such as batteries, flywheels, and improved flexibility of thermal power plants. The batteries and the flywheels are confronted with the challenge of high initial cost for the Mega-Watt class. Improving flexibility for the thermal power plants is effective, but this improvement has several limitations such as load-follow operation capability under mechanical constraints and frequency regulation within governor-free regulating capacity.

To overcome these problems, we propose a new gas turbine system named Motor-assisted Gas Turbine (MAGT). MAGT is composed of a two-shaft gas turbine: one free turbine shaft is connected to a synchronous generator rotating at a constant speed, and the other compressor shaft is coupled to an inverter-fed motor controlled at variable speed. The motor and inverter capacity is appropriate: about 5–10 % that of the gas turbine. MAGT improved the reaction rate corresponding to the load fluctuation by changing the speed of the compressor. Since the motor’s shaft, which has a compressor and a high pressure turbine, rotates at high speed and those masses are considerable, it has rotational energy of about several kWh. This energy could be charged and discharged through the converter that controls the motor speed, the same as for flywheels. This response could be much faster than conventional gas turbines, which contain huge amounts of working gas. MAGT controls its rotational energy in seconds and controls gas turbine power in minutes; thereby it improves response totally. Moreover, by assisting the compressor by using motor power, MAGT can increase gas turbine power output. Since the density of air decreases with as temperature increase, the mass of working gas is reduced. Thus, the fuel input must accordingly be reduced to suppress the combustion temperature without damaging turbine blades. As a result, power output is reduced. In such cases, a motor-assisted compressor can increase working gas. That allows more fuel input.

The proposed system was evaluated using numerical simulations. The results showed that frequency variations were within ±0.1Hz and the output power was recovered under high ambient temperature.
Performance Evaluation of a Solar Powered Organic Rankine Cycle for Residential or Small Commercial Applications
Authors: Ledbury Emily , Mago Pedro J.
Published: March 2016

Organic Rankine cycles (ORC) are used to convert energy from low temperature heat transfer into electrical energy. In this paper, a model for an hourly solar powered organic Rankine cycle is presented, and the effect of average hourly outdoor temperatures on the system performance is investigated. The solar ORC was modeled and evaluated in Jackson, MS, using five different dry organic working fluids. The purpose of this study is to investigate how hourly temperature change affects the electricity production rates of the solar ORC, as well as to determine the best working fluid for the proposed system. The effect of average hourly outdoor temperatures on the ORC performance is evaluated by modeling the ORC in two locations with the same latitude but different climate conditions. In addition, a parametric analysis to determine how temperature and pressure of the organic working fluid as well as the solar collector area affects the electricity production in the solar ORC is performed. Results show that the ORC produces the most electricity during the middle of the day when the temperatures are the highest and when the solar collectors have the highest efficiency. Furthermore, results also indicate that R-236ea is the working fluid that shows the best performance out of the five organic fluids evaluated.
Design for Integration of a Compact Waste Energy Recovery System for Automobile Engine Exhaust Gas and Coolant
Authors: Mayeed Mohammed S. , Ghiaasiaan S. Mostafa , Luong Thuyen , Ilksoy Erhan
Published: March 2016

In this study, key components of combined cycles designed for waste energy recovery from automobile engines have been virtually designed for being light weight, small sized without compromising strengths, and based on integration with the existing components of an automobile. Originally a simulation was performed to examine the amount of waste energy that could be recovered and the consequential increase in the overall thermal efficiency through the use of Kalina, ethanol and steam cycles using Engineering Equation Solver software under typical engine operating conditions. It was found that steam cycle was better for recovering energy from the exhaust gas at the higher temperature range (689 C to 160 C) and Kalina cycle was better for recovering energy from the exhaust gas and the cooling water at the lower temperature range (122 C to 80 C) among the three cycles. It was found that using this combination of cycles about 5 kW of power could be extracted from the wasted energy. The next thing was to determine the amount of space, weight and design to incorporate a system of cycles like this with an automobile. The combined cycle generation, a process widely used in existing power plants, has become a viable option for automotive applications due to advances in materials science, nanotechnology, and MEMS (Micro-Electro Mechanical Systems) devices. Critical components of the best performing cycles have been designed using computer aided engineering for the minimization of weight and space, and integration with the typical components of an automobile.
Small Hydro Plant Using Archimedes Screw: Modeling and Analysis
Authors: Rohmer Julien , Knittel Dominique , Sturtzer Guy , Flieller Damien , Renaud Jean
Published: March 2016

In this paper we introduce a small hydro plant that uses Archimedes screws. This is an alternate solution to small-scale hydropower as it exploits unused resources such as small rivers or streams. Based on hydrological study, we developped a theoretical static model to estimate the annual energy production depending on flow rate, hydrostatic head and Archimedes screw efficiency variations. Then, we studied the flood and low-water periods in order to exclude harmful climatic events of the annual energy production estimation, used for the Archimedes screw design.
Using the Peng-Robinson Equation of State to Explore Working Fluids for Higher Temperature Organic Rankine Cycles
Authors: Romanin Vincent D. , Rodriguez Alfonso , Toutain Jean , Fereres Sonia
Published: March 2016

Organic Rankine Cycles (ORCs) are primarily used in low-temperature/low-grade heat recovery systems, where water cycles are not efficient enough to economically extract work. For this reason, ORC analysis and ORC fluids have focused on low (< 300 °C) temperatures. Because the Carnot efficiency of a Rankine cycle increases with temperature, the high temperature limit of organic fluids is of interest for exploring the boundary between the economic advantages of organic fluids versus water in Rankine cycles. In this study, the high temperature limit of working fluids and the role of fluid properties on cycle efficiency for critical/subcritical ORCs are investigated. The performance of a wide range of organic fluids is evaluated through the development of thermal property calculator coded in MATLAB using the Peng-Robinson Equation of State (PREOS) and the Design Institute for Physical PRoperties (DIPPR) database correlations for heat capacity. This process allows for the development of an efficient property calculator that allows the rapid characterization of the thermodynamic performance of a large number of working fluids. A regenerative Rankine cycle for organic fluids was compared to a reheated Rankine cycle for water, for temperatures between 100 and 800 °C, with different cycle boundary conditions. The role of working fluid properties such as boiling temperature, critical point, molecular weight, and acentric factor on cycle performance are evaluated. It was found that the limits of efficiency of most of the fluids analyzed results from the limits of the high and low temperature of the cycle. Efficiency improvements due to a combined cycle with two ORCs are also examined. Finally, given the limits and performance of the fluids analyzed, desirable fluid properties for efficient high temperature ORCs are discussed.
Constrained-Equilibrium Modeling of Ethanol Combustion in Air
Authors: Nicolas Ghassan , Janbozorgi Mohammad , Metghalchi Hameed
Published: March 2016

The rate-controlled constrained-equilibrium technique is used to study the ignition characteristics of mixtures of ethanol/air in an isolated batch reactor. A set of 16 constraints was identified which is able to reproduce the ignition characteristics very well within the specified range of thermodynamics conditions. The detailed kinetic scheme involves 37 species and 238 reactions without nitrogen chemistry.
Developing a Methodology for Comparing the Energy Efficiency of Hydraulic and Traction Elevators
Authors: Bos Jim , Dell Robert , Nemeth Brad , Wei C. S. , Foley William
Published: March 2016

Traction elevators are hoisted by wire rope cables and hydraulic elevators are pushed by pressurized hydraulic fluid. Previous work published in IMEC2013-66663 presented methodologies for only traction elevator energy analysis. Many of the elevators in the USA are hydraulic. An objective and inclusive measurement methodology is needed for comparing energy efficiency of these two elevator systems for a valid cost benefit analysis. In this paper, the necessary requirements for a workable system for energy analysis are presented along with case study results. The previously presented elevator energy equations have evolved from simple kilogram-meters to watt-seconds for a more conventional energy analysis.
Numerical Study of Regenerator Configuration in the Design of a Stirling Engine
Authors: Ferreira Ana C. , Teixeira Senhorinha , Nunes Manuel L. , Martins Luís B.
Published: March 2016

The sustainable development involves the rational use of energy, by satisfying energy demands without compromising the safety of future supply. The use of renewable energy sources together with combined heat and power systems is currently considered a priority in Europe. The market trends are evolving to decentralized energy conversion with the increasing replacement of boilers and other conventional systems by small and micro-scale cogeneration units, able to produce the same amounts of useful energies. Micro scale cogeneration systems have been developed as ideal solutions to meet the energy needs for the building sector. These technologies, which include the Stirling engines, allow the production of high quality electricity and heat, efficiently and close to the final point of use. Stirling engines seem to be a good alternative for residential energy conversion. The main objective of this paper is to study alternative configurations for the regenerator of an alpha Stirling engine and evaluate the overall performance of the system. Numerical simulations were performed via a MatLab® code that includes the thermodynamic cycle analysis accounting for the effects of non-ideal heat exchangers and pumping losses. Based on a previously developed costing methodology, the investment purchase cost for each configuration is also estimated. Results showed that, for mean pressure values above 30 bar, the Stirling engine efficiency is higher for a regenerator with a wired mesh matrix rather than with a wrapped foil matrix. This is due both to better heat transfer and to lower pumping losses with the wired mesh configuration. The capital cost of the system was calculated and showed that the heater and the engine bulk are the most expensive components.
Probabilistic Life Prediction of Hydrogen Steel Pressure Vessels in Industrial Electric Trucks
Authors: Minas Constantinos , Patel Sejalben
Published: March 2016

Fuel cell powered industrial electric trucks are widely used in industry where more than 4000 systems are currently installed, achieving more than 20 million operating hours. The electric trucks are equipped with fuel cell power systems instead of an array of lead-acid batteries, which incorporate a permanently mounted pressure vessel containing compressed hydrogen gas and enabling onboard fueling. Fueling can be performed several times a day subjecting the pressure vessel to a large number of pressure cycles. It is critical to design the pressure vessel to withstand the required number of cycles which is in the thousands, over the life of the fuel cell power system estimated at 20000 hours. Steel pressure vessels which are subjected to hydrogen embrittlement are widely used in this application. In order to ensure the safety of the design, a linear elastic fracture mechanics model was developed in order to predict the life of the steel pressure vessel. The developed model was based on the ASME pressure vessel code section KD-10, which uses fatigue crack growth laws based on the relationship between the fatigue crack growth rate (da/dN) and the cyclic intensity factor (ΔK). Two samples were tested under hydrogen cyclic pressure loading. The experimental data was used to obtain estimates for the crack initiation phase. Statistical data was obtained from several hundred systems of the installed base, in order to determine the distributions of the maximum and minimum pressures the vessel is typically subjected to. The probabilistic LEFM model was used in a Monte Carlo simulation where the maximum and minimum pressure assumed a random value based on the equivalent random generator of their associated statistical distribution that is an extreme distribution and a Johnson SB distribution, respectively. The results indicated an increase by a factor of two, in the number of cycles when compared to the cycle prediction based on a constant R-ratio (maximum/minimum fill pressure). The analysis was repeated with normal distribution random generators which resulted in similar results. The results from this analysis ensure the safety of the steel pressure vessel design.
Multifunctional Load-Bearing Energy Storage Materials
Authors: Westover Andrew S. , Tian John , Bernath Shiva , Oakes Landon , Edwards Rob , Shabab Farhan Nur , Chatterjee Shahana , Anilkumar Amrutur , Pint Cary L.
Published: March 2016

This paper demonstrates our progress on the development of dual function energy storage and structural materials. Such materials require a mechanically robust interface that exists between a conventional bulk material and a nano- or microstructured material that serve to both reinforce a polymer composite and store charge. Our work demonstrates that porous silicon materials, which are etched directly on-wafer, are promising candidates to explore the proof-of-concept of this unique multifunctional device platform. We demonstrate a testing approach that combines an assessment of mechanical properties and electrochemical supercapacitor charge transport properties in real-time, enabling understanding of the mechanical-electrochemical coupling in energy storage structural materials. Our work gives promise to the development of a broad range of energy storage materials that can be dually utilized for load-bearing structural composites in many technological platforms.
A Multilevel Optimization Method for the Design and Operation of Stand-Alone Hybrid Renewable Energy Systems for Multiple Remote Communities
Authors: Contreras Francisco J. , Romero David A. , Amon Cristina H.
Published: March 2016

Recently, there has been increased interest in designing stand-alone Hybrid Renewable Energy Systems (HRES) for remote communities. Several methodologies have been proposed to tackle the design optimization problem, to develop strategies for optimal operation/dispatch, or to address both problems concurrently. So far, however, these methods have been developed only for specific communities or system configurations (e.g., wind-diesel; PV-diesel). In this study, we propose a multilevel design optimization method that considers both optimal component selection and dispatch strategy that can be applied to any community regardless of the available renewable resources, thus overcoming the limitations of previous studies. The new approach considers a wide range of renewable and non-renewable energy technologies, a database of commercially available components, and leverages state-of-the-art methods for solving each optimization subproblem. The novel algorithm was evaluated with a set of meteorological conditions that emulate different remote communities. In addition, two pricing scenarios for diesel are studied to explore how the HRES design is influenced by this parameter.
Parametric Studies of Microstructural Performance Effects in Solid Oxide Cells
Authors: van Zandt Zachary K. , Nelson George J.
Published: March 2016

A distributed charge transfer model has been developed to analyze solid oxide fuel cells and electrolyzers operating in H2-H2O and CO-CO2 atmospheres. The model couples mass transport based on the dusty-gas model, ion and electron transport in terms of charged species electrochemical potentials, and electrochemical reactions defined by Butler-Volmer kinetics. The model is validated by comparison to published experimental data, particularly cell polarization curves for both fuel cell and electrolyzer operation. Parametric studies have been performed to compare the effects of microstructure on the performance of SOFCs and SOECs operating in H2-H2O and CO-CO2 gas streams. Compared to the H2-H2O system, the power density of the CO-CO2 system shows a greater sensitivity to porosity and tortuosity. Analyses of the effects of the pore diameter suggest the H2-H2O and CO-CO2 systems are affected by changes in pore diameter in a similar manner. However, the concentration losses of the CO-CO2 system are significantly higher than those of the H2-H2O system for the pore sizes analyzed. While both systems can be shown to improve in performance with higher porosity, lower tortuosity, and larger pore sizes the results of these parametric studies imply that CO-CO2 systems would benefit more from such microstructural changes. These results further suggest that objectives for tailoring microstructure in solid oxide cells operating in CO-CO2 are distinct from objectives for more common H2-focused systems.
A Web-Accessible Robotics Monitoring System Powered by a Thermoelectric Generator Connected to a Battery
Authors: Dell Robert , Unnthorsson Runar , Wei C. S. , Foley William
Published: March 2016

In small source power generation scenarios in industrial or remote settings a viable small electrical supply for security and monitoring systems is often problematic due to the variability of the energy sources and the stability of the power generated. These small scale systems lack the advantages of a larger power grid. Therefore peak power requirements can be beyond the power generator necessitating energy storage such as batteries. The authors have developed and documented a reliable thermoelectric generator and a test bed. The generator was combined with a battery in order to meet peak power requirements beyond the unassisted range of the generator. This paper presents a test case result with the thermoelectric generator powering a complete web accessible mobile robot system. The robot system can be used for monitoring, physical manipulation of the environment, routine maintenance and in emergencies.
An Energy Harvester From Airflow Induced Vibrations
Authors: Nayyar A. , Stoilov V.
Published: March 2016

This paper presents piezoelectric energy power generator exploiting direct conversion of airflow into mechanical vibrations. The device consists of two tightly coupled parts: a mechanical resonator, which produces high-frequency mechanical oscillation from quasi-constant airflow, and piezoelectric power generator harvesting the energy from the resonator’s motion. The proposed energy harvester allows for locking up the devices lowest natural frequency to the vortex-shedding resonant frequency induced by the ambient energy source. The Energy Harvester demonstrated a peak-to-peak output voltage of 20V at 10Hz, from an input wind velocity of ∼7 m/s.
Comparing High-Performance Computing Techniques for Modeling Structural Impact on Battery Cells
Authors: Gilaki Mehdi , Avdeev Ilya
Published: March 2016

In this study, we have investigated feasibility of using commercial explicit finite element code LS-DYNA on massively parallel super-computing cluster for accurate modeling of structural impact on battery cells. Physical and numerical lateral impact tests have been conducted on cylindrical cells using a flat rigid drop cart in a custom-built drop test apparatus. The main component of cylindrical cell, jellyroll, is a layered spiral structure which consists of thin layers of electrodes and separator. Two numerical approaches were considered: (1) homogenized model of the cell and (2) heterogeneous (full) 3-D cell model. In the first approach, the jellyroll was considered as a homogeneous material with an effective stress-strain curve obtained through experiments. In the second model, individual layers of anode, cathode and separator were accounted for in the model, leading to extremely complex and computationally expensive finite element model. To overcome limitations of desktop computers, high-performance computing (HPC) techniques on a HPC cluster were needed in order to get the results of transient simulations in a reasonable solution time. We have compared two HPC methods used for this model is shared memory parallel processing (SMP) and massively parallel processing (MPP). Both the homogeneous and the heterogeneous models were considered for parallel simulations utilizing different number of computational nodes and cores and the performance of these models was compared. This work brings us one step closer to accurate modeling of structural impact on the entire battery pack that consists of thousands of cells.
Modeling of a Piezoelectric Energy Harvester Mounted on a Quick-Return Mechanism
Authors: Endeshaw Haileyesus , Alemayehu Fisseha , Ekwaro-Osire Stephen
Published: March 2016

Piezoelectric materials are being used to harvest mechanical energy from ambient vibration and convert it to electrical energy. They are mainly used to power miniature wireless sensors such as accelerometers, tachometers and proximity probes, which are commonly used for machine monitoring applications. However, exciting a piezoelectric cantilever with its resonance frequency for maximum power output remains to be a challenge. This is because the natural frequency of piezoelectric cantilevers is much higher than the common ambient vibrations. This study answers the research question: “Does a quick-return mechanism enhance the power output of a piezoelectric energy harvester?” For this purpose, analytical methods were employed to model a piezoelectric energy harvester mounted on a quick-return mechanism. The proposed mechanism was able to generate approximately 13.5mW of power, which is 35%–75% greater than the existing designs. A study on the working frequency range of the harvester for maximum power output was employed by varying the dimensional parameters of the quick-return mechanism. It was determined that by varying the dimensions of the quick return it is possible to harvest maximum power at a range of excitation frequencies. It was demonstrated that the system can effectively produce the maximum power when excited at frequencies ranging from 2rad/s to 46rad/s.
Multi Objective Optimization of Direct Coupling Photovoltaic-Electrolyzer Systems Using Imperialist Competitive Algorithm
Authors: Maroufmashat Azadeh , Sayedin Farid , Sattari Sourena
Published: March 2016

Photovoltaic-electrolyzer systems are one of the most promising alternatives for obtaining hydrogen from a renewable energy source. Determining size and the operational conditions are always a key issue while coupling directly renewable electricity sources to PEM electrolyzer. In this research, the multi objective optimization approach based on an imperialist competitive algorithm (ICA), which is employed to optimize the size and the operating conditions of a directly coupled photovoltaic (PV)-PEM electrolyzer. This allows the optimization of the system by considering two different objectives, including, minimization of energy transfer loss and maximization of hydrogen generation.

Multi objective optimization of PV/EL system predicts a maximum hydrogen production of 7930 gr/yr for energy transfer loss of 16.48 kWh/yr and minimum energy transfer loss of 5.21 kWh/yr at a hydrogen production rate of 7760 gr/yr for a the given location and the PV module.
Role of GDL Surface Wettability and Operating Conditions in Liquid-Water Removal From NSTF Catalyst Layers
Authors: Das Prodip K. , Santamaria Anthony D. , Weber Adam Z.
Published: March 2016

Proton-exchange-membrane fuel cells (PEMFCs) are becoming the center of attention as an alternative power source for automotive and stationary applications due to their ability to produce high power densities under rapid load changes. Even though a significant amount of research on PEMFCs has been conducted over the last few decades, the cost associated with platinum (Pt) catalyst remains a barrier for their commercialization. For instance, the US Department of Energy has a target to reduce the use of Pt in PEMFCs to 0.125 mg/cm2 or less, while maintaining rated stack power densities. A path to achieve this target is the use of thin catalyst-layers (CLs), such as nanostructured thin-film (NSTF) CLs [1]. Figure 1 shows a SEM image of NSTF CL showing the catalyst coated whiskers on a microstructured substrate after sputter coating with a PtCoMn alloy. The lengths of the whiskers are in the order of a few microns; however, the thickness of an NSTF CL inside a PEMFC sandwich is often in the range of 500 nm. Due to its submicron thickness, NSTF CL has low liquid-water capacity which can make low temperature operation a challenge. At low temperatures, NSTF CLs experience severe water flooding [2]. Unfortunately, sometimes low-temperature operation is unavoidable and for rapid startup relatively high current densities may be necessary. Therefore, a successful water balance is required to avoid water-flooding in the NSTF CLs.