Experimental and computational study of determining mass transport parameters in vanadium redox flow batteries

Vanadium redox flow batteries are a promising large-scale energy storage technology, but a number of challenges must be overcome for commercial implementation. At the cell level, mass transport contributes significantly to performance losses, limiting VRFB performance. Therefore, understanding mass transport mechanisms in the electrode is a critical step to mitigating such losses and optimizing VRFBs. In this study, mass transport mechanisms (e.g. convection, diffusion) are investigated in a VRFB test bed using a strip cell architecture, having 1 cm2 active area. It is found that diffusion-dominated cells have large current gradients; convection-dominated cells have relatively uniform current distribution from inlet to outlet under a mass transport limited condition. This behavior is attributed to convective mass transport in the electrode. Computational flow simulation is utilized to assess velocity and pressure distributions; experimentally measured in-situ current distribution is quantified for the cell. CFD simulation has shown that the total current in the cell is directly proportional to electrolyte velocity in the electrode. However, maximum achievable current is limited by diffusion mass transport resistance between the liquid electrolyte and the electrode surfaces. The pressure drop arising due to any fluid path outside the channel-electrode region is found to be ineffective and must be minimized to improve overall system efficiency of the VRFB. A three-dimensional, steady-state multiphysics model for VRFB strip cell architecture is further developed to investigate mass transport more fundamentally. Numerical predictions are validated by experimental measurements (polarization curve and current distribution). Diffusion coefficient of the vanadium active species and electrode permeability are found to be the most important parameters affecting electrochemical performance and performance distribution. Carbon paper electrode permeability is investigated both computationally and experimentally. While three-dimensional pore-level Lattice Boltzmann model is adopted to predict electrode permeability, a permeability cell experimental setup is designed to measure carbon paper electrode permeability under different compressions. It is found that permeability is directly proportional to the electrode porosity. While a simulated solid domain considering only the fibers does not predict experimentally measured permeabilities for higher electrode porosities, a composite domain considering both fibers and filler material successfully simulates carbon paper electrode macropore structure

Primjena irizina u pretilih štakora modificira broj mastocita u jajniku, ovarijsku angiogenezu i razine oksitocina

Exercise hormone irisin, a thermogenic adipo-myokine, promotes energy expenditure by white adipose tissue browning. Considering that irisin improves the white adipose tissue metabolic profile and increases whole-body energy expenditure, it is thought that irisin may be a potential new therapeutic target for the treatment of the growing epidemic of obesity. The roles of mast cells and angiogenesis in the pathogenesis of obesity are known, and the importance of loss of mast cell function and antiangiogenic agents in the treatment of obesity has gained prominence in recent years. In addition, the therapeutic efficacy of oxytocin for obesity, by inducing browning and stimulating thermogenesis, is also noteworthy. To understand better the mechanisms involved in the therapeutic effect of irisin on obesity, the present study evaluated the effects of irisin treatment on high-fat diet-induced, obese female rats, focusing on the number of ovary mast cells, and ovarian angiogenesis and serum oxytocin levels. Our findings showed that ovary mast cell numbers, corpus luteum angiogenesis, and vascular endothelial growth factor (VEGF) immunoreactivity in ovarian tissues increased with obesity and then significantly decreased with irisin administration. Also, it was determined that the increased serum oxytocin levels with obesity, increased markedly depending on irisin administration in obese female rats. Taken together, our findings revealed that irisin can well be considered as a potential therapeutic agent in the treatment of obesity by reducing mast cells and angiogenesis, and promoting oxytocin secretion.Hormon vježbanja irizin, termogeni adipomiokin, potiče potrošnju energije posmeđivanjem bijelog masnog tkiva. S obzirom na to da irizin poboljšava metabolički profil bijelog masnog tkiva i povećava potrošnju energije cijelog organizma, smatra se da bi on mogao biti potencijalni novi terapijski cilj u liječenju rastuće epidemije pretilosti. Poznate su uloge mastocita i angiogeneze u patogenezi pretilosti, a posljednjih je godina naglašena i važnost gubitka funkcije mastocita i antiangiogenih lijekova u liječenju pretilosti. Osim toga važna je i terapijska učinkovitost oksitocina kod pretilosti, poticanjem tamnjenja i termogeneze. Kako bi se bolje razumjeli mehanizmi uključeni u terapijski učinak irizina kod pretilosti, u ovom je istraživanju procijenjen učinak liječenja irizinom na pretile ženke štakora koje su hranjene obrocima s visokim udjelom masnoća, pri čemu je naglasak bio na broju mastocita, ovarijskoj angiogenezi i razinama serumskog oksitocina. Naši su rezultati pokazali da se broj mastocita jajnika, angiogeneza žutog tijela i imunoreaktivnost vaskularnog endotelnog faktora rasta (VEGF) u tkivu jajnika povećala s pretilošću i zatim znakovito smanjila primjenom irizina. Ustanovljeno je također da su se serumske razine oksitocina s pretilošću znatno povećale, ovisno o primjeni irizina u pretilih ženki štakora. Sveukupni rezultati pokazuju da irizin doprinosi smanjenju broja mastocita i angiogeneze te potiče lučenje oksitocina. Navedeno ovaj hormon čini potencijalnim terapijskim sredstvom u liječenju pretilosti

The Impact of the Changing Climate on Fire Activity in Mugla Region

It is a known fact that there is a relationship between forest fires and climate factors. Therefore, researchers have always been interested in revealing this relationship and its level in order to struggle with fires. Today, due to the changing climate in the world, this relationship is in a differentiation process. In many countries, researchers have started to study the relationship between fires and climate factors more often. The reason behind is the fact that, besides the change in climate, there is an obvious change in fire activity. The aim is not only to take the measures against fires, but also to estimate possible future forest fires. In order to reveal the relationship between climate change and forest fires, the effects of temperature, precipitation, relative humidity, wind, insolation, cloudiness, and other climatic factors on forest fires can be examined. In the current study, the Mugla Region has been chosen as the study area because of its high forest fire activity rate. The relationship between the number of fires and the area burned and the relationship between these components and annual temperature, summer temperature, annual precipitation, and summer precipitation averages were analyzed. Moving from the results obtained from the relationship between positive and negative changes, this study examines the effect of changes in precipitation and temperatures on fire activity

The relationship between fire number and burned area in Antalya, Izmir and Mugla regions in Turkey

This study focuses on Antalya, Izmir and Mugla regions, where the highest number of fires were experienced within Turkey. The number and area relationship between the fires were examined together with large fires. Within whole Turkey, these three regions incorporated 55.24\% of the area burned in large fires, in which over 300 ha of land was burned. In terms of the number of fires, Mugla ranked first among these regions and was followed by Izmir. Apart from the number of fires, Antalya, however, had the highest burned area, both in all fires and in large fires. No significant relationship was found between the number and area of fires in all working areas. The fact that most fires were small and that the large fires burnt extremely big areas compared the area per fire, relationship between the number of fires and the area burned. However, when the fires burning an area of over 300 ha in Turkey were considered, there was a strong relationship between the number of fires and the area burned

CLIMATE CHANGE AND FOREST FIRE TREND IN THE AEGEAN AND MEDITERRANEAN REGIONS OF TURKEY

The climate change has significant effects on the fire activity. Fire statistics in Turkey have been kept since 1937. When these records are analyzed, it can be seen that the large fires have been more active in the Mediterranean region after 1990, while the small fires have been active in the Aegean region. When top 5 years, in which large fires are seen in the Mediterranean region, are examined, there is 14.75 times increase in terms of the area burned in fires that occurred after 1990. In the Aegean region, where the number of small fires is at highest, there are no fires before 1990 in the largest five fires in respect of burned area. In the fires that occurred after 1990, 5\% of the forests of the Mediterranean region and 2\% of the forests of the Aegean region have been damaged. In this article, the fire statistics obtained from the General Directorate of Forestry and climate data obtained from General Directorate of Meteorology for the years 1973-2009 were used. The statistical analysis of the fire and climate data of 36 years indicates that the fire activity in both regions has increased

Effect of binder burnout on the sealing performance of glass ceramics for solid oxide fuel cells

WOS: 000323628100098The glass ceramics composite sealants are among few materials suitable for the solid oxide fuel cells (SOFC) due to their high operating temperatures (600 degrees C-850 degrees C). The glass ceramics chemically bond to both the metallic interconnector and the ceramic electrolyte and provide a gas tight connection. A careful and several stages manufacturing procedure is required to obtain a gas tight sealing. In this study, effects of binder burnout process on the sealing performance are investigated employing commercially available glass ceramic powders. The glass ceramic laminates are produced by mixing glass ceramic powders with the organic binders and employing a tape casting method. The laminates are sandwiched between the metallic interconnectors of an SOFC cell. The burnout and subsequent sealing quality are analyzed by measuring leakage rate and final macrostructure of sealing region. The effects of heating rate, dead weight load, solid loading, carrier gas and their flow rates are investigated. It is found that sealing quality is affected from all investigated parameters. While a slower heating rate is required for a better burnout, the mass flow rate of sweep gas must be adequate for removal of the burned gas. The leakage rate is reduced to 0.1 ml min(-1) with 2 degrees C min(-1) + 1 degrees C min(-1) heating rate, 86.25% solid loading, 200 N dead weight load and 500 ml min(-1) sweep gas flow rate. (C) 2013 Elsevier B.V. All rights reserved