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Journal articleShevchenko I, Berloff P, 2016,
Eddy Backscatter and Counter-Rotating Gyre Anomalies of Midlatitude Ocean Dynamics, Fluids, Vol: 1, ISSN: 2311-5521
This work concerns how two competing mechanisms – eddy backscatter and2 counter-rotating gyre anomalies – influence the midlatitude ocean dynamics, as described by3 the eddy-resolving quasi-geostrophic (QG) model of wind-driven gyres. We analysed dynamical4 balances and effects of different eddy forcing components, as well as their dependencies on5 increasing vertical resolution and decreasing eddy viscosity and found that the eastward jet6 and its adjacent recirculation zones are maintained mostly by the eddy forcing via the eddy7 backscatter mechanism, whereas the time-mean eddy-forcing component plays not only direct8 jet-supporting but also indirect jet-inhibiting role. The latter is achieved by inducing zonally9 elongated anticyclonic/cyclonic Counter-rotating Gyre Anomaly (CGA) in the subpolar/subtropical10 gyre. The indirect effect of CGAs on the eastward jet is found to be moderate relative to the dominant11 eddy backscatter mechanism. We also found that the higher is the vertical baroclinic mode, the12 weaker is its backscatter role and the stronger is its CGA-driving role. Although the barotropic and13 first baroclinic modes are the most efficient ones in maintaining the backscatter, the higher, up to the14 fifth baroclinic modes also have significant but reverse impact that reduces the backscatter
Journal articleBiton M, Yufit V, Tariq F, et al., 2016,
Enhanced Imaging of Lithium Ion Battery Electrode Materials, Journal of the Electrochemical Society, Vol: 164, Pages: A6032-A6038, ISSN: 0013-4651
In this study we present a novel method of lithium ion battery electrode sample preparation with a new type of epoxy impregnation,brominated (Br) epoxy, which is introduced here for the first time for this purpose and found suitable for focused ion beam scanningelectron microscope (FIB-SEM) tomography. The Br epoxy improves image contrast, which enables higher FIB-SEM resolution (3Dimaging), which is amongst the highest ever reported for composite LFP cathodes using FIB-SEM. In turn it means that the particlesare well defined and the size distribution of each phase can be analyzed accurately from the complex 3D electrode microstructureusing advanced quantification algorithms.The authors present for the first time a new methodology of contrast enhancement for 3D imaging, including novel advancedquantification, on a commercial Lithium Iron Phosphate (LFP) LiFePO4 cathode. The aim of this work is to improve the quality ofthe 3D imaging of challenging battery materials by developing methods to increase contrast between otherwise previously poorlydifferentiated phases. This is necessary to enable capture of the real geometry of electrode microstructures, which allows measurementof a wide range of microstructural properties such as pore/particle size distributions, surface area, tortuosity and porosity. Theseproperties play vital roles in determining the performance of battery electrodes.
Journal articleBladon AJ, Short KM, Mohammed EY, et al., 2016,
Payments for ecosystem services in developing world fisheries, FISH AND FISHERIES, Vol: 17, Pages: 839-859, ISSN: 1467-2960
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ReportMechleri E, Staffell I, Lawal A, et al., 2016,
Evaluation of Process Control Strategies for Normal, Flexible and Upset Operation Conditions of CO2 Post Combustion Capture Processes, 2016/07
This project focuses on performing an evaluation of process control strategies for normal and flexible operation conditions of CO2 post-combustion capture (PCC) processes. PCC is a promising, near-term technology for large-scale deployment for the decarbonisation of the power generation and other sectors. However, the integration of this technology imposes a well-known efficiency penalty on the power plant with which it is integrated. Once an optimal process design has been identified, this energy penalty can be somewhat reduced via application of an appropriate control strategy to the PCC plant. An appropriate process control strategy is also fundamental to guarantee the safety and feasibility of the process under flexible operating conditions that the power plants may be subject to.The aim of this project is to develop the process control strategy, to select appropriate control variables for a PCC process, and design efficient control structures for operation of a post-combustion capture process with minimum energy requirements for coal and natural gas power plants. The control structures are developed for power plant operating ranges of around 50% to 100% load.
Journal articlevon Srbik M-T, Marinescu M, Martinez-Botas RF, et al., 2016,
A physically meaningful equivalent circuit network model of a lithium-ion battery accounting for local electrochemical and thermal behaviour, variable double layer capacitance and degradation, Journal of Power Sources, Vol: 325, Pages: 171-184, ISSN: 0378-7753
A novel electrical circuit analogy is proposed modellingelectrochemical systems under realistic automotive operation conditions. The model is developed for a lithium ion battery and is based on a pseudo 2D electrochemical model. Although cast in the framework familiar to application engineers, the model is essentially an electrochemical battery model: all variables have a direct physical interpretation and there is direct access to all states of the cell via the model variables (concentrations, potentials) for monitoring and control systems design. This is the first Equivalent Circuit Network-type model that tracks directly the evolution of species inside the cell. It accounts for complex electrochemical phenomena that are usually omitted in online battery performance predictors such as variable double layer capacitance, the full current-overpotential relation and overpotentials due to mass transport limitations. The coupled electrochemical and thermal model accounts for capacity fade via a loss in active species and for power fade via an increase in resistive solid electrolyte passivation layers at both electrodes. The model's capability to simulate cell behaviour under dynamic events is validated against test procedures, such as standard battery testing load cycles for current rates up to 20 C, as well as realistic automotive drive cycle loads.
Journal articleAlberts G, Gurguc Z, Koutroumpis P, et al., 2016,
Competition and norms: a self-defeating combination?, Energy Policy, Vol: 96, Pages: 504-523, ISSN: 1873-6777
This paper investigates the effects of information feedback mechanisms on electricity and heating usage at a student hall of residence in London. In a randomised control trial, we formulate different treatments such as feedback information and norms, as well as prize competition among subjects. We show that information and norms lead to a sharp – more than 20% - reduction in overall energy consumption. Because participants do not pay for their energy consumption this response cannot be driven by cost saving incentives. Interestingly, when combining feedback and norms with a prize competition for achieving low energy consumption, the reduction effect – while present initially – disappears in the long run. This could suggest that external rewards reduce and even destroy intrinsic motivation to change behaviour.
ReportMechleri E, Rivotti P, Staffell I, et al., 2016,
Evaluation of Process Control Strategies for Normal, Flexible and Upset Operation Conditions of CO2 Post Combustion Capture Processes
Mechleri E, Staffell I, Lawal A, Ramos A, Shah N, Mac Dowell Nclose, 2016, Evaluation of Process Control Strategies for Normal, Flexible and Upset Operation Conditions of CO2 Post Combustion Capture Processes, 2016/07
Journal articleOchoa-Tocachi B, Buytaert W, De Bièvre B, et al., 2016,
Impacts of land use on the hydrological response of tropical Andean catchments, Hydrological Processes, Vol: 30, Pages: 4074-4089, ISSN: 1099-1085
Changes in land use and land cover are major drivers of hydrological alteration in the tropical Andes. However, quantifying their impacts is fraught with difficulties because of the extreme diversity in meteorological boundary conditions, which contrasts strongly with the lack of knowledge about local hydrological processes. Although local studies have reduced data scarcity in certain regions, the complexity of the tropical Andes poses a big challenge to regional hydrological prediction.This study analyses data generated from a participatory monitoring network of 25 headwater catchments covering three of the major Andean biomes (páramo, jalca, and puna), and link their hydrological responses to main types of human interventions (cultivation, afforestation and grazing). A paired catchment setup was implemented to evaluate the impacts of change using a “trading space-for-time” approach. Catchments were selected based on regional representativeness and contrasting land use types. Precipitation and discharge have been monitored and analysed at high temporal resolution for a time period between 1 and 5 years.The observed catchment responses clearly reflect the extraordinarily wide spectrum of hydrological processes of the tropical Andes. They range from perennially humid páramos in Ecuador and northern Peru with extremely large specific discharge and baseflows, to highly seasonal, flashy catchments in the drier punas of southern Peru and Bolivia. The impacts of land use are similarly diverse and their magnitudes are a function of catchment properties, original and replacement vegetation, and management type. Cultivation and afforestation consistently affect the entire range of discharges, particularly low flows. The impacts of grazing are more variable, but have the largest effect on the catchment hydrological regulation. Overall, anthropogenic interventions result in increased streamflow variability and significant reductions in catchmen
Journal articleSarwar W, Engstrom T, Marinescu M, et al., 2016,
Experimental analysis of Hybridised Energy Storage Systems for automotive applications, Journal of Power Sources, Vol: 324, Pages: 388-401, ISSN: 0378-7753
The requirements of the Energy Storage System (ESS) for an electrified vehicle portfolio consisting of a range of vehicles from micro Hybrid Electric Vehicle (mHEV) to a Battery Electric Vehicle (BEV) vary considerably. To reduce development cost of an electrified powertrain portfolio, a modular system would ideally be scaled across each vehicle; however, the conflicting requirements of a mHEV and BEV prevent this. This study investigates whether it is possible to combine supercapacitors suitable for an mHEV with high-energy batteries suitable for use in a BEV to create a Hybridised Energy Storage System (HESS) suitable for use in a HEV. A passive HESS is found to be capable of meeting the electrical demands of a HEV drive cycle; the operating principles of HESSs are discussed and factors limiting system performance are explored. The performance of the HESS is found to be significantly less temperature dependent than battery-only systems, however the heat generated suggests a requirement for thermal management. As the HESS degrades (at a similar rate to a specialised high-power-battery), battery resistance rises faster than supercapacitor resistance; as a result, the supercapacitor provides a greater current contribution, therefore the energy throughput, temperature rise and degradation of the batteries is reduced.
Journal articleHills, Florin N, Fennell PS, 2016,
Decarbonising the cement sector: a bottom-up model for optimising carbon capture application in the UK, Journal of Cleaner Production, Vol: 139, Pages: 1351-1361, ISSN: 0959-6526
Industrial processes such as Portland cement manufacture produce a large proportion of anthropogenic carbon dioxide and significantly reducing their emissions could be difficult or expensive without carbon capture and storage. This paper explores the idea of synchronising shutdowns for carbon capture and storage installation with major shutdowns required to refurbish major process units at industrial sites. It develops a detailed bottom-up model for the first time and applies it to the United Kingdom’s cement industry. This research demonstrates that several policy and technology risks are not identified by the top-down models and it highlights the importance of reducing shut-down times for capture plant construction. Failure to do so could increase installation costs by around 10 per cent. This type of approach, which is complementary to top-down modelling, and the lessons learned from it can be applied to other capital- and energy-intensive industries such as primary steel production. It provides important information about what actions should be prioritised to ensure that carbon capture and storage can be applied without extra unnecessary shutdowns which would increase the overall cost of carbon dioxide mitigation and could delay action, increasing cumulative emissions as well.
Journal articleStaffell IL, Rustomji M, 2016,
Maximising the value of electricity storage, Journal of Energy Storage, Vol: 8, Pages: 212-225, ISSN: 2352-152X
Grid-scale energy storage promises to reduce the cost of decarbonising electricity, but is not yeteconomically viable. Either costs must fall, or revenue must be extracted from more of the servicesthat storage provides the electricity system. To help understand the economic prospects forstorage, we review the sources of revenue available and the barriers faced in accessing them. Wethen demonstrate a simple algorithm that maximises the profit from storage providing arbitragewith reserve under both perfect and no foresight, which avoids complex linear programmingtechniques. This is made open source and freely available to help promote further research.We demonstrate that battery systems in the UK could triple their profits by participating in thereserve market rather than just providing arbitrage. With no foresight of future prices, 75-95% ofthe optimal profits are gained. In addition, we model a battery combined with a 322 MW wind farmto evaluate the benefits of shifting time of delivery. The revenues currently available are notsufficient to justify the current investment costs for battery technologies, and so further revenuestreams and cost reductions are required.
Journal articleBin Mamat AMI, Martinez-Botas RF, Rajoo S, et al., 2016,
Design methodology of a low pressure turbine for waste heat recovery via electric turbocompounding, Applied Thermal Engineering, Vol: 107, Pages: 1166-1182, ISSN: 1873-5606
This paper presents a design methodology of a high performance Low Pressure Turbine (LPT) for turbocompounding applications to be used in a 1.0 L “cost-effective, ultra-efficient heavily downsized gasoline engine for a small and large segment passenger car”. Under this assumption, the LPT was designed to recover the latent energy of discharged exhaust gases at low pressure ratios (1.05–1.3) and to drive a small electric generator with a maximum power output of 1.0 kW. The design speed was fixed at 50,000 rpm with a pressure ratio, PR of 1.08. Commercially available turbines are not suitable for this purpose due to the very low efficiencies experienced when operating in these pressure ratio ranges. By fixing all the LPT requirements, the turbine loss model was combined with the geometrical model to calculate preliminary LPT geometry. The LPT features a mixed-flow turbine with a cone angle of 40° and 9 blades, with an inlet blade angle at radius mean square of +20°. The exit-to-inlet area ratio value is approximately 0.372 which is outside of the conventional range indicating the novelty of the approach. A single passage Computational Fluid Dynamics (CFD) model was applied to optimize the preliminary LPT design by changing the inlet absolute angle. The investigation found the optimal inlet absolute angle was 77°. Turbine off-design performance was then predicted from single passage CFD model. A rapid prototype of the LPT was manufactured and tested in Imperial College turbocharger testing facility under steady-state and pulsating flow. The steady-state testing was conducted over speed parameter ranges from 1206 rpm/K0.5 to 1809 rpm/K0.5. The test results showed a typical flow capacity trend as a conventional radial turbine but the LPT had higher total-to-static efficiency, ηt-s in the lower pressure ratio regions. A maximum total-to-static efficiency, ηt-s of 0.758 at pressure ratio, PR ≈ 1.1 was found, no available turbines
Journal articleJones CD, Arora V, Friedlingstein P, et al., 2016,
C4MIP - The Coupled Climate-Carbon Cycle Model Intercomparison Project: experimental protocol for CMIP6, Geoscientific Model Development, Vol: 9, Pages: 2853-2880, ISSN: 1991-9603
Coordinated experimental design and implementation has become a cornerstone of global climate modelling. Model Intercomparison Projects (MIPs) enable systematic and robust analysis of results across many models, by reducing the influence of ad hoc differences in model set-up or experimental boundary conditions. As it enters its 6th phase, the Coupled Model Intercomparison Project (CMIP6) has grown significantly in scope with the design and documentation of individual simulations delegated to individual climate science communities. The Coupled Climate–Carbon Cycle Model Intercomparison Project (C4MIP) takes responsibility for design, documentation, and analysis of carbon cycle feedbacks and interactions in climate simulations. These feedbacks are potentially large and play a leading-order contribution in determining the atmospheric composition in response to human emissions of CO2 and in the setting of emissions targets to stabilize climate or avoid dangerous climate change. For over a decade, C4MIP has coordinated coupled climate–carbon cycle simulations, and in this paper we describe the C4MIP simulations that will be formally part of CMIP6. While the climate–carbon cycle community has created this experimental design, the simulations also fit within the wider CMIP activity, conform to some common standards including documentation and diagnostic requests, and are designed to complement the CMIP core experiments known as the Diagnostic, Evaluation and Characterization of Klima (DECK). C4MIP has three key strands of scientific motivation and the requested simulations are designed to satisfy their needs: (1) pre-industrial and historical simulations (formally part of the common set of CMIP6 experiments) to enable model evaluation, (2) idealized coupled and partially coupled simulations with 1 % per year increases in CO2 to enable diagnosis of feedback strength and its components, (3) future scenario simulations to project how the Earth system will re
Journal articleDessens O, Anandarajah G, Gambhir A, 2016,
Limiting global warming to 2 °C: What do the latest mitigation studies tell us about costs, technologies and other impacts?, Energy Strategy Reviews, Vol: 13-14, Pages: 67-76, ISSN: 2211-467X
There is now a wealth of model-based evidence on the technology choices, costs and other impacts (such as fossil fuel demand) associated with mitigation towards stringent climate targets. Results from over 900 hundred scenarios have been reviewed in the latest Intergovernmental Panel on Climate Change Assessment Report (IPCC AR5) including baseline scenarios under which no mitigation action is taken, as well as those under which different limits to global warming are targeted. A number of additional studies have been undertaken in order to assess the implications of global mitigation action. The objective of the paper is to provide a concise overview and comparison of major input assumptions and outputs of recent studies focused on mitigating to the most stringent targets explored, which means around the 2 °C level of global average temperature increase by 2100. The paper extracts key messages grouped into four pillars: mitigation costs, technology uncertainty, policy constraints, and co-benefits. The principal findings from this comparison are that, according to the models, mitigation to 2 °C is feasible, but delayed action, the absence or limited deployment of any of a number of key technologies (including nuclear, CCS, wind and solar), and limited progress on energy efficiency, all make mitigation more costly and in many models infeasible. Further, rapid mitigation following delayed action leads to potentially thousands of idle fossil fuel plants globally, posing distributional and political economy challenges.
Journal articleMcCarthy N, Chen R, Offer GJ, et al., 2016,
PTFE mapping in gas diffusion media for PEMFCs using fluorescence microscopy, International Journal of Hydrogen Energy, Vol: 41, Pages: 17631-17643, ISSN: 1879-3487
Differentiating between the various polytetrafluoroethylene based structures inside polymer electrolyte membrane fuel cells with a degree of certainty is necessary to optimize manufacturing processes and to investigate possible degradation mechanisms. We have developed a novel method using fluorescence microscopy for distinguishing the origin and location of PTFE and/or Nafion® in Membrane Electrode assemblies and the gas diffusion media from different sources and stages of processing. Fluorescent material was successfully diffused into the PTFE based structures in the GDM by addition to the ‘ink’ precursor for both the microporous layer and the catalyst layer; this made it possible to map separately both layers in a way that has not been reported before. It was found that hot pressing of membrane coated structures resulted in physical dispersion of those layers away from the membrane into the GDM itself. This fluorescence technique should be of interest to membrane electrode assembly manufacturers and fuel cell developers and could be used to track the degradation of different PTFE structures independently in the future.
Journal articleMurray JE, Brindley HE, Bryant RG, et al., 2016,
Enhancing weak transient signals in SEVIRI false color imagery: Application to dust source detection in southern Africa, Journal of Geophysical Research: Atmospheres, Vol: 121, Pages: 10199-10219, ISSN: 2169-897X
A method is described to significantly enhance the signature of dust events using observations from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI). The approach involves the derivation of a composite clear-sky signal for selected channels on an individual time-step and pixel basis. These composite signals are subtracted from each observation in the relevant channels to enhance weak transient signals associated with either (a) low levels of dust emission, or (b) dust emissions with high salt or low quartz content. Different channel combinations, of the differenced data from the steps above, are then rendered in false color imagery for the purpose of improved identification of dust source locations and activity. We have applied this clear-sky difference (CSD) algorithm over three [globally significant] source regions in southern Africa: the Makgadikgadi Basin, Etosha Pan, and the Namibian and western South African coast. Case study analyses indicate three notable advantages associated with the CSD approach over established image rendering methods: (i) an improved ability to detect dust plumes, (ii) the observation of source activation earlier in the diurnal cycle, and (iii) an improved ability to resolve and pinpoint dust plume source locations.
Journal articleAl-menhali A, Menke H, Blunt MJ, et al., 2016,
Pore Scale Observations of Trapped CO2 in Mixed-Wet Carbonate Rock: Applications to Storage in Oil Fields, Environmental Science & Technology, Vol: 50, Pages: 10282-10290, ISSN: 0013-936X
Geologic CO2 storage has been identified as a key to avoiding dangerous climate change. Storage in oil reservoirs dominates the portfolio of existing projects due to favorable economics. However, in an earlier related work (Al-Menhali and Krevor Environ. Sci. Technol. 2016, 50, 2727−2734), it was identified that an important trapping mechanism, residual trapping, is weakened in rocks with a mixed wetting state typical of oil reservoirs. We investigated the physical basis of this weakened trapping using pore scale observations of supercritical CO2 in mixed-wet carbonates. The wetting alteration induced by oil provided CO2-wet surfaces that served as conduits to flow. In situ measurements of contact angles showed that CO2 varied from nonwetting to wetting throughout the pore space, with contact angles ranging 25° < θ < 127°; in contrast, an inert gas, N2, was nonwetting with a smaller range of contact angle 24° < θ < 68°. Observations of trapped ganglia morphology showed that this wettability allowed CO2 to create large, connected, ganglia by inhabiting small pores in mixed-wet rocks. The connected ganglia persisted after three pore volumes of brine injection, facilitating the desaturation that leads to decreased trapping relative to water-wet systems.
Journal articleLiu X, Wu B, Brandon NP, et al., 2016,
Tough ionogel-in-mask hybrid gel electrolytes in supercapacitors with durable pressure and thermal tolerances, Energy Technology, Vol: 5, Pages: 220-224, ISSN: 2194-4288
A primary challenge of gel electrolytes in development of flexible and wearable devices is their weak mechanical performances, including their compressive stress, tensile strength, and puncture resistance. Here we prepare an ionogel-mask hybrid gel electrolyte, which successfully achieves synergic advantages of the high mechanical strength of the mask substance and the superior electrochemical and thermal characteristics of the ionogel. The fabricated supercapacitor can maintain a relatively stable capacitive performance even under a high pressure of 3236 kPa. Meanwhile, with the good thermal stability of the composite gel electrolyte, the solid-state supercapacitor can be operated at high temperatures ranging from 25 °C to 200 °C. The ionogel-mask hybrid gel can be superior tough gel electrolyte for solid-state flexible supercapacitors with durable advantages in both high temperatures and pressures.
Journal articleYu W, Yang Y, Graham N, 2016,
Evaluation of ferrate as a coagulant aid/oxidant pretreatment for mitigating submerged ultrafiltration membrane fouling in drinking water treatment, Chemical Engineering Journal, Vol: 298, Pages: 234-242, ISSN: 1873-3212
Although pre-coagulation can mitigate ultrafiltration (UF) membrane fouling in the treatment of surface waters for drinking water supply, biological activities (‘biofouling’) can induce a continuous increase in membrane fouling. To meet this challenge, potassium ferrate, K2FeO4, a combined oxidant and coagulant, was evaluated as a pre-treatment chemical for controlling submerged UF membrane fouling in water treatment. Ferrate use as an alternative to- (phase 1: ∼23 days), and in combination with- (phase 2: ∼30 days), conventional FeCl3, have been studied using parallel continuous bench-scale submerged membrane systems, using FeCl3 as the reference. The poorer performance of ferrate (alone) as a pre-treatment compared to FeCl3 (phase 1) was the result of a lower coagulation efficiency, which outweighed the beneficial impact of the ferrate on bacterial inactivation. The net reduction in pre-treatment performance led to an increase in the concentration of residual, active bacteria in the membrane tank, and bacteria associated large molecular weight (MW) organic substances, such as extracellular polymeric substances (EPS) or biopolymers, which were the principal cause of the higher rate of membrane fouling observed. In contrast, ferrate performed best as a coagulant aid/oxidant (FeCl3/K2FeO4) (phase 2), with the rate of membrane fouling (increase in transmembrane pressure) 4.5 times lower than conventional FeCl3 pre-treatment. This pre-treatment arrangement resulted in less bacteria (and EPS) and suspended solids in the membrane tank, and less accumulation of materials in the cake layer and within the membrane pores. The results indicated clearly the potential benefit of applying ferrate as a coagulant aid/oxidant with a coagulant, in UF pre-treatment, with the control of bacteria and EPS a key factor in reducing membrane fouling.
Journal articleAllen RT, Hales NM, Baccarelli A, et al., 2016,
Countervailing effects of income, air pollution, smoking, and obesity on aging and life expectancy: population-based study of U.S. Counties, Environmental Health, Vol: 15, ISSN: 1832-3367
BackgroundIncome, air pollution, obesity, and smoking are primary factors associated with human health and longevity in population-based studies. These four factors may have countervailing impacts on longevity. This analysis investigates longevity trade-offs between air pollution and income, and explores how relative effects of income and air pollution on human longevity are potentially influenced by accounting for smoking and obesity.MethodsCounty-level data from 2,996 U.S. counties were analyzed in a cross-sectional analysis to investigate relationships between longevity and the four factors of interest: air pollution (mean 1999–2008 PM2.5), median income, smoking, and obesity. Two longevity measures were used: life expectancy (LE) and an exceptional aging (EA) index. Linear regression, generalized additive regression models, and bivariate thin-plate smoothing splines were used to estimate the benefits of living in counties with higher incomes or lower PM2.5. Models were estimated with and without controls for smoking, obesity, and other factors.ResultsModels which account for smoking and obesity result in substantially smaller estimates of the effects of income and pollution on longevity. Linear regression models without these two variables estimate that a $1,000 increase in median income (1 μg/m3 decrease in PM2.5) corresponds to a 27.39 (33.68) increase in EA and a 0.14 (0.12) increase in LE, whereas models that control for smoking and obesity estimate only a 12.32 (20.22) increase in EA and a 0.07 (0.05) increase in LE. Nonlinear models and thin-plate smoothing splines also illustrate that, at higher levels of income, the relative benefits of the income-pollution tradeoff changed—the benefit of higher incomes diminished relative to the benefit of lower air pollution exposure.ConclusionsHigher incomes and lower levels of air pollution both correspond with increased human longevity. Adjusting for smoking and obesity reduces estimates of the benefi
Journal articlePropp K, Marinescu M, Auger DJ, et al., 2016,
Multi-temperature state-dependent equivalent circuit discharge model for lithium-sulfur batteries, Journal of Power Sources, Vol: 328, Pages: 289-299, ISSN: 1873-2755
Lithium-sulfur (Li-S) batteries are described extensively in the literature, but existing computational models aimed at scientific understanding are too complex for use in applications such as battery management. Computationally simple models are vital for exploitation. This paper proposes a non-linear state-of-charge dependent Li-S equivalent circuit network (ECN) model for a Li-S cell under discharge. Li-S batteries are fundamentally different to Li-ion batteries, and require chemistry-specific models. A new Li-S model is obtained using a ‘behavioural’ interpretation of the ECN model; as Li-S exhibits a ‘steep’ open-circuit voltage (OCV) profile at high states-of-charge, identification methods are designed to take into account OCV changes during current pulses. The prediction-error minimization technique is used. The model is parameterized from laboratory experiments using a mixed-size current pulse profile at four temperatures from 10 °C to 50 °C, giving linearized ECN parameters for a range of states-of-charge, currents and temperatures. These are used to create a nonlinear polynomial-based battery model suitable for use in a battery management system. When the model is used to predict the behaviour of a validation data set representing an automotive NEDC driving cycle, the terminal voltage predictions are judged accurate with a root mean square error of 32 mV.
Journal articleFennell PS, Zhang Z, Hills T, et al., 2016,
Spouted Bed Reactor for kinetic Measurements of Reduction of Fe2O3 in a CO2/CO Atmosphere Part I - Atmospheric Pressure Measurements and Equipment Commissioning, Chemical Engineering Research & Design, Vol: 114, Pages: 307-320, ISSN: 1744-3563
A high pressure and high temperature spouted bed reactor, operating in fluidisation mode, has been designed and validated at low pressure for the study of gas-solid reaction kinetics. Measurements suggested the bed exhibited a fast rate of gas interchange between the bubble and particulate phases. Pressurised injection of the particles to the bottom of the bed allowed the introduction of solid reactants in a simple and controlled manner. The suitability of the reactor for the purpose of kinetic studies was demonstrated by investigation of the intrinsic kinetics of the initial stage of the reduction of Fe2O3 with CO over multiple cycles for chemical looping.Changes of pore structure over the initial cycles were found to affect the observed kinetics of the reduction. The initial intrinsic rate constant of the reduction reaction (ki) was measured by using a kinetic model which incorporated an effectiveness factor. The uncertainty arising from the measurement of particle porosity in the model was compensated for by the tortuosity factor. The average activation energy obtained for cycles three to five was 61 ± 8 kJ/mol, which is comparable with previous studies using both fluidised beds and thermogravimetry.
Journal articleGschwend FJ, Brandt A, Chambon CL, et al., 2016,
Pretreatment of Lignocellulosic Biomass with Low-cost Ionic Liquids., Jove-Journal of Visualized Experiments, Vol: 114, ISSN: 1940-087X
A number of ionic liquids (ILs) with economically attractive production costs have recently received growing interest as media for the delignification of a variety of lignocellulosic feedstocks. Here we demonstrate the use of these low-cost protic ILs in the deconstruction of lignocellulosic biomass (Ionosolv pretreatment), yielding cellulose and a purified lignin. In the most generic process, the protic ionic liquid is synthesized by accurate combination of aqueous acid and amine base. The water content is adjusted subsequently. For the delignification, the biomass is placed into a vessel with IL solution at elevated temperatures to dissolve the lignin and hemicellulose, leaving a cellulose-rich pulp ready for saccharification (hydrolysis to fermentable sugars). The lignin is later precipitated from the IL by the addition of water and recovered as a solid. The removal of the added water regenerates the ionic liquid, which can be reused multiple times. This protocol is useful to investigate the significant potential of protic ILs for use in commercial biomass pretreatment/lignin fractionation for producing biofuels or renewable chemicals and materials.
Journal articleAbolghasemi M, Piggott MD, Spinneken J, et al., 2016,
Simulating tidal turbines with multi-scale mesh optimisation techniques, Journal of Fluids and Structures, Vol: 66, Pages: 69-90, ISSN: 1095-8622
Embedding tidal turbines within simulations of realistic large-scale tidal flows is a highly multi-scale problem that poses significant computational challenges. Here this problem is tackled using actuator disc momentum (ADM) theory and Reynolds-averaged Navier-Stokes (RANS) with, for the first time, dynamically adaptive mesh optimisation techniques. Both k-ω and k-ω SST RANS models have been developed within the Fluidity framework, an adaptive mesh CFD solver, and the model is validated against two sets of experimental flume test results. A brief comparison against a similar OpenFOAM model is presented to portray the benefits of the finite element discretisation scheme employed in the Fluidity ADM model. This model has been developed with the aim that it will be seamlessly combined with larger numerical models simulating tidal flows in realistic domains. This is where the mesh optimisation capability is a major advantage as it enables the mesh to be refined dynamically in time and only in the locations required, thus making optimal use of limited computational resources.
Journal articleWu B, Parkes MP, de Benedetti L, et al., 2016,
Real-time monitoring of proton exchange membrane fuel cell stack failure, Journal of Applied Electrochemistry, Vol: 46, Pages: 1157-1162, ISSN: 1572-8838
Uneven pressure drops in a 75-cell 9.5-kWe protonexchange membrane fuel cell stack with a U-shaped flowconfiguration have been shown to cause localised flooding.Condensed water then leads to localised cell heating, resultingin reduced membrane durability. Upon purging of the anodemanifold, the resulting mechanical strain on the membranecan lead to the formation of a pin-hole/membrane crack and arapid decrease in open circuit voltage due to gas crossover.This failure has the potential to cascade to neighbouring cellsdue to the bipolar plate coupling and the current densityheterogeneities arising from the pin-hole/membrane crack.Reintroduction of hydrogen after failure results in cell voltageloss propagating from the pin-hole/membrane crack locationdue to reactant crossover from the anode to the cathode, giventhat the anode pressure is higher than the cathode pressure.Through these observations, it is recommended that purging isavoided when the onset of flooding is observed to preventirreparable damage to the stack.
ReportHolt J, Leach A, Mumford JD, et al., 2016,
Development of probabilistic models for quantitative pathway analysis of plant pest introduction for the EU territory, Parma, Italy, Publisher: European Food Safety Authority, 2016:EN-1062
This report demonstrates a probabilistic quantitative pathway analysis model that can be used in risk assessment for plant pest introduction into EU territory on a range of edible commodities (apples, oranges, stone fruits and wheat). Two types of model were developed: a general commodity model that simulates distribution of an imported infested/infected commodity to and within the EU from source countries by month; and a consignment model that simulates the movement and distribution of individual consignments from source countries to destinations in the EU. The general pathway model has two modules. Module 1 is a trade pathway model, with a Eurostat database of five years of monthly trade volumes for each specific commodity into the EU28 from all source countries and territories. Infestation levels based on interception records, commercial quality standards or other information determine volume of infested commodity entering and transhipped within the EU. Module 2 allocates commodity volumes to processing, retail use and waste streams and overlays the distribution onto EU NUTS2 regions based on population densities and processing unit locations. Transfer potential to domestic host crops is a function of distribution of imported infested product and area of domestic production in NUTS2 regions, pest dispersal potential, and phenology of susceptibility in domestic crops. The consignment model covers the several routes on supply chains for processing and retail use. The output of the general pathway model is a distribution of estimated volumes of infested produce by NUTS2 region across the EU28, by month or annually; this is then related to the accessible susceptible domestic crop. Risk is expressed as a potential volume of infested fruit in potential contact with an area of susceptible domestic host crop. The output of the consignment model is a volume of infested produce retained at each stage along the specific consignment trade chain.
Journal articleGeen R, Czaja A, Haigh JD, 2016,
The effects of increasing humidity on heat transport by extratropical waves, Geophysical Research Letters, Vol: 43, Pages: 8314-8321, ISSN: 1944-8007
This study emphasizes the separate contributions of the warm and cold sectors of extratropical cyclones to poleward heat transport. Aquaplanet simulations are performed with an intermediate complexity climate model in which the response of the atmosphere to a range of values of saturation vapor pressure is assessed. These simulations reveal stronger poleward transport of latent heat in the warm sector as saturation vapor pressure is increased and an unexpected increase in poleward sensible heat transport in the cold sector. The latter results nearly equally from changes in the background stability of the atmosphere at low levels and changes in the temporal correlation between wind and temperature fields throughout the troposphere. Increased stability at low level reduces the likelihood that movement of cooler air over warmer water results in an absolutely unstable temperature profile, leading to less asymmetric damping of temperature and meridional velocity anomalies in cold and warm sectors.
Journal articleMac Dowell N, Shah N, Staffell I, et al., 2016,
Quantifying the Value of CCS for the Future ElectricitySystem, Energy & Environmental Science, Vol: 9, Pages: 2497-2510, ISSN: 1754-5706
Many studies have quantified the cost of Carbon Capture and Storage (CCS) power plants, butrelatively few discuss or appreciate the unique value this technology provides to the electricity system.CCS is routinely identified as a key factor in least-cost transitions to a low-carbon electricitysystem in 2050, one with significant value by providing dispatchable and low-carbon electricity.This paper investigates production, demand and stability characteristics of the current and futureelectricity system. We analyse the Carbon Intensity (CI) of electricity systems composed of unabatedthermal (coal and gas), abated (CCS), and wind power plants for different levels of windavailability with a view to quantifying the value to the system of different generation mixes. As athought experiment we consider the supply side of a UK-sized electricity system and compare theeffect of combining wind and CCS capacity with unabated thermal power plants. The resultingcapacity mix, system cost and CI are used to highlight the importance of differentiating betweenintermittent and firm low-carbon power generators. We observe that, in the absence of energystorage or demand side management, the deployment of intermittent renewable capacity cannotsignificantly displace unabated thermal power, and consequently can achieve only moderatereductions in overall CI. A system deploying sufficient wind capacity to meet peak demand canreduce CI from 0.78 tCO2/MWh, a level according to unabated fossil power generation, to 0.38tCO2/MWh. The deployment of CCS power plants displaces unabated thermal plants, and whilstit is more costly than unabated thermal plus wind, this system can achieve an overall CI of 0.1tCO2/MWh. The need to evaluate CCS using a systemic perspective in order to appreciate itsunique value is a core conclusion of this study.
Conference paperMechleri E, fennell P, Mac Dowell N, 2017,
Flexible operation strategies for coal- and gas-CCS power stations under the UK and USA markets, 13th Greenhouse Gas Control Technologies (GHGT) conference
Journal articleAlonso Alvarez D, Ekins-Daukes N, 2016,
SPICE modelling of photoluminescence and electroluminescence based current-voltage curves of solar cells for concentration applications, Journal of Green Engineering, Vol: 5, Pages: 33-48, ISSN: 2245-4586
Quantitative photoluminescence (PL) or electroluminescence (EL) experiments can be usedto probe fast and in a non-destructive way the current-voltage (IV) characteristics ofindividual subcells in a multi-junction device, information that is, otherwise, not available.PL-based IV has the advantage that it is contactless and can be performed even in partlyfinished devices, allowing for an early diagnosis of the expected performance of the solarcells in the production environment. In this work we simulate the PL- and EL-based IVcurves of single junction solar cells to assess their validity compared with the true IV curveand identify injection regimes where artefacts might appear due to the limited in-planecarrier transport in the solar cell layers. We model the whole photovoltaic device as anetwork of sub-circuits, each of them describing the solar cell behaviour using the two diodemodel. The sub-circuits are connected to the neighbouring ones with a resistor, representingthe in-plane transport in the cell. The resulting circuit, involving several thousand subcircuits,is solved using SPICE.
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