Development of filtered Euler–Euler two-phase model for circulating fluidised bed: High resolution simulation, formulation and a priori analyses

Euler–Euler two-phase model simulations are usually performed with mesh sizes larger than the smallscale structure size of gas–solid flows in industrial fluidised beds because of computational resource limitation. Thus, these simulations do not fully account for the particle segregation effect at the small scale and this causes poor prediction of bed hydrodynamics. An appropriate modelling approach accounting for the influence of unresolved structures needs to be proposed for practical simulations. For this purpose, computational grids are refined to a cell size of a few particle diameters to obtain mesh-independent results requiring up to 17 million cells in a 3D periodic circulating fluidised bed. These mesh-independent results are filtered by volume averaging and used to perform a priori analyses on the filtered phase balance equations. Results show that filtered momentum equations can be used for practical simulations but must take account of a drift velocity due to the sub-grid correlation between the local fluid velocity and the local particle volume fraction, and particle sub-grid stresses due to the filtering of the non-linear convection term. This paper proposes models for sub-grid drift velocity and particle sub-grid stresses and assesses these models by a priori tests

A posteriori study of filtered Euler-Euler two-phase model using a high resolution simulation of a 3D periodic circulating fluidized bed

Gas-particle flows in vertical risers are involved in many industrial scale fluidized bed applications such as catalytic cracking, fossil or biomass combustion. Risers flows are often simulated by two-fluid model equations coupled with closures developed in the frame the kinetic theory of granular media. However, two-fluid model discretized over coarse mesh with respect to particle clustering size are performed for large units because of limited computational resources. Now, it is well established that meso-scales cancelled out by coarse mesh simulations have dramatic effect on overall behaviour of flows. This study proposed a sub-grid modeling approach for effective drag force and particle stresses which accounts for the effects of unresolved structures on the resolved flows

Effect of unresolved structures on the Euler-Euler simulation of 3D periodic circulating fluidized of binary mixture

It is well established that small-scale structures have an important effect on the overall hydrodynamic behaviour of dense and circulating fluidized bed. Due to computational constraints, the numerical simulations of practical applications with Euler-Euler two-phase approach are usually performed with relatively coarse mesh with respect to the local segregation of solid. These simulations cancel out the small-scale solid structures. All previous studied attempted to take into account the effect of unresolved structures on the drag force in the case where the particulate phase is monodisperse. This paper is dedicated to analyse the unresolved structures effects on polydisperse gas-solid flow by multi-fluid Eulerian approach. In this study, the binary mixture is conducted by gas at an ambient condition in a 3D periodic circulating fluidized bed. The aim is first to obtain mesh independent results where further mesh refinement is not necessary. Then these results are used to investigate the unresolved structures effects on resolved field by following a priori methodology. In particular, the role of small-scale structures on the momentum transfer by inter-particle collisions is pointed out

Ekolojik temelli bir rekreasyon turizm yeşilyolu planlaması: Erzincan Ekşisu Sazlığı – Altıntepe ve Saztepe Höyükleri güzergahı örneği

Today’s uncontrolled increase in population, irregular urbanization, and technological development screate disconnections in the landscape system. These fragmentations can only be avoided by establishing links. Corridors connect parts of landscape, prevent the landscape parts’ destruction, and create spaces for the continuity of life. Corridor systems are planned not only for ecological but also cultural, historic and recreational usage. In this study, Eksisu Reeds which is located in Üzümlü, Erzincan, and it’s around corridor which covering the historic tumuluses, recreation tourism greenway feasibility which based on ecological basis was investigated. Which included in this context a limit has been established. Within this limit, maps were formed in GIS and current situation analysis was conducted. Then, a survey was conducted with 200 people in the city and as a result of survey, landuse decisions suggested this corridor within the working limits can be planned as an ecologically based recreation tourism greenway. Results showed that, 19.7% of people who live in the city would like to increase picnic areas, 17% would like to have navigation points and 16.8% would like to transform spas into resorts. 18.9% of students would like to increase the number of picnic areas, 16.2% would like to see recreative activities in the pond and 15.5% would like to have navigation points. 51.6% of people who live in the city and 8.4% of students have visited Altıntepe. The greenway planning necessity which examined in this research is supported by the obtained dataGünümüzdeki kontrolsüz nüfus artışı, çarpık kentleşme ve teknolojik gelişmeler gibi pek çok durum peyzaj sisteminde kopmalar meydan getirmektedir. Bu kopmaların önüne ancak oluşturulan bağlantılarla geçilebilmektedir. Koridorlar peyzaj parçalarını birbirine bağlar, küçülüp yok olmasını engeller, canlı yaşamının devamlılığı için alanlar oluşturur. Koridor sistemleri sadece ekolojik amaçlar için değil, kültürel/tarihi ve rekreasyonel kullanımlar için planlanırlar. Bu çalışmada; Erzincan ili Merkez ve Üzümlü ilçe sınırları içerisinde bulunan Ekşisu Sazlıklarını ve çevresindeki tarihi höyükleri içine alan koridorun ekolojik temele dayanan bir rekreasyon turizm yeşilyolu olabilirliği incelenmiştir. Bu bağlamda Ekşisu Sazlıklarını, tarihi höyükleri, çevredeki bazı kırsal yerleşimleri ve rekreasyon alanlarını içine alan bir sınır oluşturulmuştur. Bu sınır dahilinde alanın CBS ortamında haritaları oluşturulmuş ve mevcut durum analizi yapılmıştır. Ardından, kent içinde 200 kişi üzerinde gerçekleştirilen bir anket çalışması sonucunda çalışma alanı sınırları içerisindeki koridorun ekolojik temelli bir rekreasyon turizm yeşilyolu olarak planlanması yönünde öneri alan kullanım kararları verilmiştir. Gerçekleştirilen anket çalışması sonucunda kent halkının %19.7’nin piknik alanlarının arttırılmasını, %17’si seyir noktaları yapılmasını, %16.8’inin kaplıcaların tesislere dönüştürülmesini istedikleri; öğrencilerin ise %18.9’unun piknik alanlarının arttırılmasını, %16.2’si gölette rekreatif faaliyetlere yer verilmesini,%15.5’inin seyir noktaları yapılmasını istedikleri bulunmuştur. Ayrıca anket sonuçlarına göre kent halkının %51.6’sının, öğrencilerin ise %10.3’ünün Altıntepe'den haberdar oldukları, kent halkının %5.4’ünün, öğrencilerin ise %8.4’ünün Altıntepe'yi ziyaret ettikleri görülmüştür. Bu çalışmadan elde edilen veriler, uygunluğu incelenen yeşilyol planlamasının gerekliliğini desteklemektedir

Simulation aux grandes échelles des lits fluidisés circulants gaz-particule

Les simulations numériques des équations d’Euler deux-fluides réalisé sur des maillages grossiers éliminent les structures fins d’écoulement gaz-solide dans les lits fluidisés. Pour précisément estimer l’hydrodynamique globale de lit, il faut proposer une modélisation qui prend en compte les effets de structure non-résolue. Dans ce but, les maillages sont raffinés pour obtenir le résultat de simulation pleinement résolue ce que les grandeurs statistiques ne modifient plus avec un autre raffinement pour le lit fluidisé périodique dilué gaz-particules sur une géométrie 3D cartésienne et ce résultat est utilisé pour tests "a priori". Les résultats de tests "a priori" montrent que l’équation filtrée de la quantité de mouvement est effectuée mais il faut prendre en compte le flux de la fraction volumique de solide de sous-maille en raison de l’interaction locale de la vitesse du gaz et la fraction volumique de solide pour la force traniée. Nous proposons les modèles fonctionnels et structurels pour le flux de la fraction volumique de solide de sous-maille. En plus, les modèles fermetures du tenseur de sous-maille de la phase dispersée sont similaires aux modèles classiquement utilisés en écoulement turbulent monophasique. Tous les modèles sont validés par test "a priori" et "a posteriori". ABSTRACT : Eulerian two fluid approach is generally used to simulate gas-solid flows in industrial circulating fluidized beds. Because of limitation of computational resources, simulations of large vessels are usually performed by using too coarse grid. Coarse grid simulations can not resolve fine flow scales which can play an important role in the dynamic behaviour of the beds. In particular, cancelling out the particle segregation effect of small scales leads to an inadequate modelling of the mean interfacial momentum transfer between phases and particulate shear stresses by secondary effect. Then, an appropriate modelling ac counting for influences of unresolved structures has to be proposed for coarse-grid simu-lations. For this purpose, computational grids are refined to get mesh-independent result where statistical quantities do not change with further mesh refinement for a 3-D peri-odic circulating fluidized bed. The 3-D periodic circulating fluidized is a simple academic configuration where gas-solid flow conducted with A-type particles is periodically driven along the opposite direction of the gravity. The particulate momentum and agitation equations are filtered by the volume averaging and the importance of additional terms due to the averaging procedure are investigated by budget analyses using the mesh independent result. Results show that the filtered momentum equation of phases can be computed on coarse grid simulations but sub-grid drift velocity due to the sub-grid correlation between the local fluid veloc- ity and the local particle volume fraction and particulate sub-grid shear stresses must be taken into account. In this study, we propose functional and structural models for sub- grid drift velocity, written in terms of the difference between the gas velocity-solid volume fraction correlation and the multiplication of the filtered gas velocity with the filtered solid volume fraction. Particulate sub-grid shear stresses are closed by models proposed for single turbulent flows. Models’ predictabilities are investigated by a priori tests and they are validated by coarse-grid simulations of 3-D periodic circulating, dense fluidized beds and experimental data of industrial scale circulating fluidized bed in manner of a posteriori tests

Non-sendromik dudak damak yarığı hastalarında multidisipliner tedavi: 2 vaka raporu

Objective: It is intended in this case report to explain the multidisciplinary treatment of 2 non-syndromic cleft lip and palate patients with different approaches, the treatment phases of prosthetic rehabilitation and the results obtained. Case Reports:15-year-old unilateral cleft lip and palate patient and 25-year-old bilateral cleft lip and palate patient was admitted to our clinic with the functional and aesthetic complaints. Orthodontic, surgical and prosthetic treatments were applied Results: With multidisciplinary treatments aesthetic and functional solutions were provided. Aesthetic and functional results were obtained for both cases with fixed restorations. The treatments protocols had no complications. The outcomes were of high quality and brought satisfaction to the patients. Conclusion: Multidisciplinary treatment should be considered in cleft lip and palate patients in order to be able to fully ensure speech and hearing, continuation of occlusion and maxillofacial growth in the normal course and the improvement of physical appearance and psychological state. However, different treatment plans should be considered in its different timing for each case.Amaç: Bu vaka raporunda 2 non-sendromik dudak damak yarıklı vakanın farklı yaklaşımlarla protetik tedavisinin değerlendirilmesi amaçlanmaktadır. Vaka Raporu: 15 yaşında tek taraflı dudak damak yarıklı erkek hasta ve 25 yaşında çift taraflı dudak damak yarıklı kadın hastalarımız kliniğimize estetik ve fonksiyon kaybından dolayı başvurmuşlardır. Ortodontik, cerrahi ve prostodontik yaklaşımlarla hastalara uygulanmıştır. Her iki vakada da sabit protetik restorasyonlar protokolleri uygulanan hastalarımızda herhangi bir komplikasyon gözlemlenmemiştir. Tedaviler yüksek hayat kalitesi ve memnuniyet sağlamıştır. Sonuçlar: Dudak damak yarıklı hastalarda; konuşma, maxillofacial büyümenin normal seyrinde devamı, fiziksel görünüşün arttırılması ve psikolojik durumun düzeltilmesi için multidisipliner yaklaşım gereklidir. zamanlamaları değerlendirilmelidir

Numerical Simulation of Liquid Injection into an Anisothermal Dense Fluidized Bed

Fluidized beds are widely used in reactive industrial processes such as: olefins production, oil cracking or uranium fluorination because of their high efficiency mixing properties. In such processes, the chemical reaction is strongly dependent on the temperature and liquid is injected into the reactor in order to cool it. The experimental data of the time evolution of the gas temperature in an anisothermal dense fluidized bed with a liquid injection provided by INEOS is first compared with the results predicted by a simple model with an assumption of a perfectly mixed fluidized bed (uniform solid and temperature distribution in the bed). The results of this simple model show that the time evolution of the gas temperature is accurately predicted. Additionally, we point out that the wall-to-bed heat transfer plays a crucial role of the gas temperature in the bed. Then, we performed 3-D numerical simulations that let us investigate local interactions between phases and heat transfer with wall. The simulations show that the liquid evaporates quickly and the temperature is in a satisfactory agreement with the experiment data

Particle resolved direct numerical simulation of a liquid–solid fluidized bed: Comparison with experimental data

Particle-resolved direct numerical simulations of a 3-D liquid–solid fluidized bed experimentally investigated by Aguilar-Corona (2008) have been performed at different fluidization velocities (corresponding to a range of bed solid volume fraction between 0.1 and 0.4), using Implicit Tensorial Penalty Method. Particle Reynolds number and Stokes number are O(100) and O(10), respectively. In this paper, we compare the statistical quantities computed from numerical results with the experimental data obtained with 3-D trajectography and High Frequency PIV. Fluidization law predicted by the numerical simulations is in very good agreement with the experimental curve and the main features of trajectories and Lagrangian velocity signal of the particles are well reproduced by the simulations. The evolution of particle and flow velocity variances as a function of bed solid volume fraction is also well captured by the simulations. In particular, the numerical simulations predict the right level of anisotropy of the dispersed phase fluctuations and its independence of bed solid volume fraction. They also confirm the high value of the ratio between the fluid and the particle phase fluctuating kinetic energy. A quick analysis suggests that the fluid velocity fluctuations are mainly driven by fluid–particle wake interactions (pseudo-turbulence) whereas the particle velocity fluctuations derive essentially from the large scale flow motion (recirculation). Lagrangian autocorrelation function of particle fluctuating velocity exhibits large-scale oscillations, which are not observed in the corresponding experimental curves, a difference probably due to a statistical averaging effect. Evolution as a function of the bed solid volume fraction and the collision frequency based upon transverse component of particle kinetic energy correctly matches the experimental trend and is well fitted by a theoretical expression derived from Kinetic Theory of Granular Flows

3D Numerical Simulation of Catalyst Injection into a Dense Fluidized Bed

In this study, the injection of catalyst particles into a dense gas-solid fluidized bed reactor is investigated using the Euler/Euler approach. Numerical simulations of horizontal catalyst+gas mixture injection through a circular-sectioned nozzle have been performed in order to study the effect of the operating conditions of an injector on the flow hydrodynamics. The study is in the context of a larger project to optimize the nozzle geometry. The nozzle is composed of two annular sections, one outer and one inner. Catalyst is injected from the central section of the nozzle with a transport gas called here “gas 1”. Another gas is injected in the outer section: “gas 2”. The results show that the good dispersion of the catalyst depends highly on the ratio of the velocities in the outer and the inner sections of the nozzle