| 1. |
- Eddy, Tyler D., et al.
(författare)
-
Energy Flow Through Marine Ecosystems : Confronting Transfer Efficiency
- 2021
-
Ingår i: Trends in Ecology & Evolution. - : Elsevier BV. - 0169-5347 .- 1872-8383. ; 36:1, s. 76-86
-
Forskningsöversikt (refereegranskat)abstract
- Transfer efficiency is the proportion of energy passed between nodes in food webs. It is an emergent, unitless property that is difficult to measure, and responds dynamically to environmental and ecosystem changes. Because the consequences of changes in transfer efficiency compound through ecosystems, slight variations can have large effects on food availability for top predators. Here, we review the processes controlling transfer efficiency, approaches to estimate it, and known variations across ocean biomes. Both process-level analysis and observed macro-scale variations suggest that ecosystem-scale transfer efficiency is highly variable, impacted by fishing, and will decline with climate change. It is important that we more fully resolve the processes controlling transfer efficiency in models to effectively anticipate changes in marine ecosystems and fisheries resources.
|
|
| 2. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
-
Design of a bench-scale ammonia-SrCl2 thermochemical storage system using numerical modelling
- 2019
-
Ingår i: Eurotherm Seminar #112 - Advances in Thermal Energy Storage. - Lleida. - 9788491441557
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work presents the numerical modelling of a bench-scale thermochemical storage (TCS) system based on the reversible absorption-desorption of ammonia in strontium chloride. The modelling is performed using the ASPEN software and was validated against experimental data from literature on a different TCS system configuration but using the same reaction pair. The modelled TCS system in this work comprises two identical reactors, alternatively operating as absorber or desorber with a storage capacity of 0.5 kWh. The system is designed to store and release heat under 8 bar of NH3 pressure, with the two identical reactors respectively undergoing desorption at 82 °C and absorption at 79 °C. Together with the two reactors, a liquid ammonia storage tank is used as a buffer (10 bar at 25 oC). The desorption half-cycle of the system is made of the desorber (82 °C, 8 bar), a compressor (8-10 bar), a cooler (108-25 °C), a pump (to pump liquid ammonia) and the liquid ammonia storage (25 °C, 10 bar). The absorption half-cycle starts form the liquid ammonia storage tank and goes via an expansion valve (10-8 bar) and then a heater (18-25 °C) towards the absorber (79 °C, 8 bar). In the model, the desorption and absorption are respectively driven by an external heater and cooler, which represent a waste heat source and a heat sink respectively. The efficiency of the TCS system was found to be of 67 % and 61 % for the absorption and desorption half-cycles, respectively. A sensitivity analysis was also conducted to identify optimum operating conditions. In conclusion, this study presents an ammonia-SrCl2 TCS bench-scale system that allows simultaneous heat storage and retrieval, as the basis for the practical construction of the system. This is expected to provide inspiration and operational analysis to accommodate the design of similar TCS systems for storing surplus industrial heat.
|
|
| 3. |
- Gunasekara, Saman Nimali, Dr. 1982-, et al.
(författare)
-
Numerical Design of a Reactor-Heat Exchanger Combined Unit for Ammonia-SrCl2 Thermochemical Storage System
- 2019
-
Ingår i: ISES Solar World Congress 2019. - Germany : International Solar Energy Society. ; , s. 1300-1311
-
Konferensbidrag (refereegranskat)abstract
- This work presents the design of a reactor-heat exchanger combined unit using COMSOL transient simulations in2D for a thermochemical storage (TCS) system of NH3-SrCl2 (absorption-desorption of SrCl2·NH3 and SrCl2·8NH3).TCS with NH3-metal halide reactions is emerging, with many packed-bed reactors often incorporating salt withexpanded graphite (EG) to improve thermal conductivity. Similarly, a packed-bed reactor is chosen here using SrCl2-EG composite, for a reaction pressure of 8 bar, accommodating desorption above 82 ℃ and absorption below 79 ℃.The aim here is to find a simple and cost-effective reactor-heat exchanger (HEX) combined unit to store 0.5 kWhheat (1.1 kg of SrCl2·NH3 forming 1.8 kg of SrCl2·8NH3). From several HEX configurations, the first configurationis modelled here. This is contains three reaction media cylinders (a composite of 87.5% w/w of SrCl2·8NH3 in EG)sandwiching two units of tube-in-tube (TinT) HEXs. A stationary study for the heat transfer fluid (HTF) velocityanalysis is coupled with a time-dependent study for the reaction phenomena, respectively for the salt-alone and salt-EG composite. For 15 hours reaction time, the reaction advancement (above 0.85) was enhanced significantly in thesalt-EG composite, which was only above 0.55 for the salt-only case. The reaction progression is the slowest in thebottom of the innermost reaction media, where the HTF temperature is the lowest. Thus, an additional HEX unitalong the center-axis of the reactor appears suitable to reduce the reaction time. As next, the effect of HEX thickness,number of TinT units, as well as other reactor-HEX configurations will be analyzed to choose the optimal setup.
|
|
| 4. |
- Hirscher, Michael, et al.
(författare)
-
Materials for hydrogen-based energy storage - past, recent progress and future outlook
- 2020
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 827
-
Tidskriftsartikel (refereegranskat)abstract
- Globally, the accelerating use of renewable energy sources, enabled by increased efficiencies and reduced costs, and driven by the need to mitigate the effects of climate change, has significantly increased research in the areas of renewable energy production, storage, distribution and end-use. Central to this discussion is the use of hydrogen, as a clean, efficient energy vector for energy storage. This review, by experts of Task 32, Hydrogen-based Energy Storage of the International Energy Agency, Hydrogen TCP, reports on the development over the last 6 years of hydrogen storage materials, methods and techniques, including electrochemical and thermal storage systems. An overview is given on the background to the various methods, the current state of development and the future prospects. The following areas are covered; porous materials, liquid hydrogen carriers, complex hydrides, intermetallic hydrides, electrochemical storage of energy, thermal energy storage, hydrogen energy systems and an outlook is presented for future prospects and research on hydrogen-based energy storage.
|
|
| 5. |
- Mewton, Nathan, et al.
(författare)
-
Rationale and design of the Cyclosporine to ImpRove Clinical oUtcome in ST-elevation myocardial infarction patients (the CIRCUS trial)
- 2015
-
Ingår i: American Heart Journal. - : Elsevier BV. - 1097-6744 .- 0002-8703. ; 169:6, s. 6-766
-
Tidskriftsartikel (refereegranskat)abstract
- Background Both acute myocardial ischemia and reperfusion contribute to cardiomyocyte death in ST-elevation myocardial infarction (STEMI). The final infarct size is the principal determinant of subsequent clinical outcome in STEMI patients. In a proof-of-concept phase II trial, the administration of cyclosporine prior to primary percutaneous coronary intervention (PPCI) has been associated with a reduction of infarct size in STEMI patients. Methods CIRCUS is an international, prospective, multicenter, randomized, double-blinded, placebo-controlled trial. The study is designed to compare the efficacy and safety of cyclosporine versus placebo, in addition to revascularization by PPCI, in patients presenting with acute anterior myocardial infarction within 12 hours of symptoms onset and initial TIMI flow <= 1 in the culprit left anterior descending coronary artery. Patients are randomized in a 1: 1 fashion to 2.5 mg/kg intravenous infusion of cyclosporine or matching placebo performed in theminutes preceding PCI. The primary efficacy end point of CIRCUS is a composite of 1-year all-cause mortality, rehospitalization for heart failure or heart failure worsening during initial hospitalization, and left ventricular adverse remodeling as determined by sequential transthoracic echochardiography. Secondary outcomes will be tested using a hierarchical sequence of left ventricular (LV) ejection fraction and absolute measurements of LV volumes. The composite of death and rehospitalization for heart failure or heart failure worsening during initial hospitalization will be further assessed at three years after the initial infarction. Results Recruitment lasted from April 2011 to February 2014. The CIRCUS trial has recruited 975 patients with acute anterior myocardial infarction. The 12-months results are expected to be available in 2015. Conclusions The CIRCUS trial is testing the hypothesis that cyclosporine in addition to early revascularization with PPCI compared to placebo in patients with acute anterior myocardial infarction reduces the incidence of death, heart failure and adverse LV remodeling at one-year follow-up.
|
|
| 6. |
- Sadd, Matthew, 1994, et al.
(författare)
-
Visualization of Dissolution‐Precipitation Processes in Lithium–Sulfur Batteries
- 2022
-
Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 12:10
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, light is shed on the dissolution and precipitation processes S8 and Li2S, and their role in the utilization of active material in Li-S batteries. Combining operando X-ray Tomographic Microscopy and optical image analysis, in real-time; sulfur conversion/dissolution in the cathode, the diffusion of polysulfides in the bulk electrolyte, and the redeposition of the product of the electrochemical reaction, Li2S, on the cathode are followed. Using a custom-designed capillary cell, positioning the entire cathode volume within the field of view, the conversion of elemental sulfur to soluble polysulfides during discharge is quantitatively followed. The results show the full utilization of elemental sulfur in the cathode in the initial stage of discharge, with all solid sulfur converted to soluble polysulfide species. Optical image analysis shows a rapid diffusion of polysulfides as they migrate from the cathode to the bulk electrolyte at the start of discharge and back to the cathode in the later stages of discharge, with the formation and precipitation of Li2S. The results point to the redeposition of Li2S on all available surfaces in the cathode forming a continuous insulating layer, leaving polysulfide species remaining in the electrolyte, and this is the process limiting the cell's specific capacity.
|
|
| 7. |
- Sveinbjörnsson, Dadi, et al.
(författare)
-
Ionic conductivity and the formation of cubic CaH2 in the LiBH4–Ca(BH4)2 composite
- 2014
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 211:0, s. 81-89
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract LiBH4–Ca(BH4)2 composites were prepared by ball milling. Their crystal structures and phase composition were investigated using synchrotron X-ray diffraction and Rietveld refinement, and their ionic conductivity was measured using impedance spectroscopy. The materials were found to form a physical mixture. The composites were composed of α-Ca(BH4)2, γ-Ca(BH4)2 and orthorhombic LiBH4, and the relative phase quantities of the Ca(BH4)2 polymorphs varied significantly with LiBH4 content. The formation of small amounts of orthorhombic CaH2 and cubic CaH2 in a CaF2-like structure was observed upon heat treatment. Concurrent formation of elemental boron may also occur. The ionic conductivity of the composites was measured using impedance spectroscopy, and was found to be lower than that of ball milled LiBH4. Electronic band structure calculations indicate that cubic CaH2 with hydrogen defects is electronically conducting. Its formation along with the possible precipitation of boron therefore has an effect on the measured conductivity of the LiBH4–Ca(BH4)2 composites and may increase the risk of an internal short-circuit in the cells.
|
|
