Numeričko istraživanje efekata poroznih svojstava i debljine sloja na performance protonske izmjenjivačke membrane gorive ćelije

In this study, fluid flow and concentration distribution on the cathode side of a Proton Exchange Membrane Fuel Cell were numerically analyzed. The problem domain consists of a cathode gas flow channel, cathode gas diffusion layer and cathode catalyst layer. The governing equations, continuity, momentum and concentration equations were discritized by the control volume method and solved using a computer program based on SIMPLE algorithm. Simulations were made for different values of gas diffusion layer porosity, catalyst layer porosity and the ratio of the cathode gas diffusion layer thickness to the gas flow channel height. Using the results of these simulations, the effects of these parameters on flow, oxygen concentration and current density distribution were analyzed. It is observed that increasing the porosities of the gas diffusion layer and catalyst layer increases the current and power densities. The increase in the porosity of the gas diffusion layer also increases the oxygen concentration in both gas diffusion and catalyst layers but decreases the oxygen concentration in gas flow channel. Simulations also showed that increasing porosity of the catalyst layer increases the oxygen concentration in a catalyst layer but decreases the oxygen concentration in a gas flow channel and gas diffusion layer. It is also seen that the effect of the gas diffusion layer porosity is more dominant on cell performance compared to the catalyst layer porosity. The analysis of the effect of the ratio of the cathode gas diffusion layer thickness to the gas flow channel height on the cell performance showed that the increasing ratio of the cathode gas diffusion layer thickness to the gas flow channel height decreases the current and power densities. An analysis of the data obtained from simulations also shows that increasing the ratio of the cathode gas diffusion layer thickness to the gas flow channel height increases the oxygen concentration in the gas flow channel but decreases the oxygen concentration in both gas diffusion and catalyst layers.U ovom radu je numerički analizirano strujanje fluida i raspodjela koncentracije protonske izmjenjivačke membrane na katodnoj strani gorive ćelije. Problemska domena se sastoji od kanala katode kroz koji struji plin, difuznog sloja plina na strani katode kao i katodnog katalitičkog sloja. Generalne jednadžbe, jednadžbe kontinuiteta, jednadžbe količine gibanja i jednadžbe koncentracije su diskretizirane metodom kontrolnog volumena i riješene koristeći računarski program koji je baziran na algoritmu SIMPLE. Simulacije su napravljene za različite vrijednosti poroznosti difuzijskog sloja na strani plina, poroznosti katalitičkog sloja i omjera debljine difuzijskog sloja na strani plina i visine kanala kroz koji struji plin. Koristeći rezultate ovih simulacija, analizirani su efekti ovih parametara na strujanje, koncentraciju kisika i raspodjelu gustoće struje. Uočeno je da se s povećavanjem poroznosti difuzijskog sloja na strani plina i katalitičkog sloja, povećava se jakost struje i snage. Povećavanjem poroznosti difuzijskog sloja na strani plina, povećava se i koncentracija kisika i u difuzijskom sloju na strani plina i u katalitičkom sloju, ali se smanjuje koncentracija kisika u kanalu kroz koji struji plin. Simulacije su također pokazale da povećavanjem poroznosti u katalitičkom sloju povećavaju u njemu koncentraciju kisika, ali smanjuje se koncentracija kisika u kanalu strujanja plina kao i u difuzijskom sloju na strani plina. Također je uočeno da je efekt poroznosti u difuzijskom sloju na straniplina bitno utjecajniji na performanse gorive ćelije od poronosti kataltičkog sloja. Analiza efekta omjera debljine difuzijskog sloja na strani plina na katodi i visine kanala kroz koji struji plin na performance gorive ćelije je pokazala da se povećavanjem debljine difuzijskog sloja plina na katodi u odnosu na visinu kanala, smanjuje jakost struje i gustoću snage. Analiza podataka dobivena simulacijom također pokazuje da se povećavanjem omjera debljine difuzijskog sloja plina na strani katode prema visini kanala, povećava koncentraciju kisika u kanalu strujanja plina ali smanjuje koncentraciju kisiku i u dufuzijskom sloju plina i katalitičkom sloju

Numeričko istraživanje efekata poroznih svojstava i debljine sloja na performance protonske izmjenjivačke membrane gorive ćelije

In this study, fluid flow and concentration distribution on the cathode side of a Proton Exchange Membrane Fuel Cell were numerically analyzed. The problem domain consists of a cathode gas flow channel, cathode gas diffusion layer and cathode catalyst layer. The governing equations, continuity, momentum and concentration equations were discritized by the control volume method and solved using a computer program based on SIMPLE algorithm. Simulations were made for different values of gas diffusion layer porosity, catalyst layer porosity and the ratio of the cathode gas diffusion layer thickness to the gas flow channel height. Using the results of these simulations, the effects of these parameters on flow, oxygen concentration and current density distribution were analyzed. It is observed that increasing the porosities of the gas diffusion layer and catalyst layer increases the current and power densities. The increase in the porosity of the gas diffusion layer also increases the oxygen concentration in both gas diffusion and catalyst layers but decreases the oxygen concentration in gas flow channel. Simulations also showed that increasing porosity of the catalyst layer increases the oxygen concentration in a catalyst layer but decreases the oxygen concentration in a gas flow channel and gas diffusion layer. It is also seen that the effect of the gas diffusion layer porosity is more dominant on cell performance compared to the catalyst layer porosity. The analysis of the effect of the ratio of the cathode gas diffusion layer thickness to the gas flow channel height on the cell performance showed that the increasing ratio of the cathode gas diffusion layer thickness to the gas flow channel height decreases the current and power densities. An analysis of the data obtained from simulations also shows that increasing the ratio of the cathode gas diffusion layer thickness to the gas flow channel height increases the oxygen concentration in the gas flow channel but decreases the oxygen concentration in both gas diffusion and catalyst layers.U ovom radu je numerički analizirano strujanje fluida i raspodjela koncentracije protonske izmjenjivačke membrane na katodnoj strani gorive ćelije. Problemska domena se sastoji od kanala katode kroz koji struji plin, difuznog sloja plina na strani katode kao i katodnog katalitičkog sloja. Generalne jednadžbe, jednadžbe kontinuiteta, jednadžbe količine gibanja i jednadžbe koncentracije su diskretizirane metodom kontrolnog volumena i riješene koristeći računarski program koji je baziran na algoritmu SIMPLE. Simulacije su napravljene za različite vrijednosti poroznosti difuzijskog sloja na strani plina, poroznosti katalitičkog sloja i omjera debljine difuzijskog sloja na strani plina i visine kanala kroz koji struji plin. Koristeći rezultate ovih simulacija, analizirani su efekti ovih parametara na strujanje, koncentraciju kisika i raspodjelu gustoće struje. Uočeno je da se s povećavanjem poroznosti difuzijskog sloja na strani plina i katalitičkog sloja, povećava se jakost struje i snage. Povećavanjem poroznosti difuzijskog sloja na strani plina, povećava se i koncentracija kisika i u difuzijskom sloju na strani plina i u katalitičkom sloju, ali se smanjuje koncentracija kisika u kanalu kroz koji struji plin. Simulacije su također pokazale da povećavanjem poroznosti u katalitičkom sloju povećavaju u njemu koncentraciju kisika, ali smanjuje se koncentracija kisika u kanalu strujanja plina kao i u difuzijskom sloju na strani plina. Također je uočeno da je efekt poroznosti u difuzijskom sloju na straniplina bitno utjecajniji na performanse gorive ćelije od poronosti kataltičkog sloja. Analiza efekta omjera debljine difuzijskog sloja na strani plina na katodi i visine kanala kroz koji struji plin na performance gorive ćelije je pokazala da se povećavanjem debljine difuzijskog sloja plina na katodi u odnosu na visinu kanala, smanjuje jakost struje i gustoću snage. Analiza podataka dobivena simulacijom također pokazuje da se povećavanjem omjera debljine difuzijskog sloja plina na strani katode prema visini kanala, povećava koncentraciju kisika u kanalu strujanja plina ali smanjuje koncentraciju kisiku i u dufuzijskom sloju plina i katalitičkom sloju

Assessment of 3D velocity vector fields and turbulent kinetic energy in a realistic aortic phantom using multi-point variable-density velocity encoding

ISSN:1097-6647ISSN:1532-429

Advances in Biological Liquid Crystals

Biological Liquid Crystal, a rich set of soft materials with rod-like structures widely existed in nature, possess typical lyotropic liquid crystalline phase properties both in vitro (e.g. cellulose, peptides and protein assemblies), and in vivo (e.g. cellular lipid membrane, packed DNA in bacteria and aligned fibroblasts). Given the ability to undergo phase transition in response to various stimuli, numerous practices have been exercised to spatially arrange biological liquid crystals. In this mini-review, the fundamental understanding of interactions between rod-shaped biological building blocks and their orientational ordering across multiple length scales is addressed. Discussions are made with regard to the dependence of physical properties of non-motile objects on the first-order phase transition and the coexistence of multi-phases in passive liquid crystalline systems. This review also focuses on how the applied physical stimuli drives the reorganization of constituent passive particles for a new steady-state alignment. A number of recent progresses in the dynamics behaviours of active liquid crystals are presented, and particular attention has been given to those self-propelled animate elements, like the formation of motile topological defects, active turbulence, correlation of orientational ordering and cellular functions. Finally, future implications and potential applications of the biological liquid crystalline materials are discussed