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Heat Transfer Mechanism (heat + transfer_mechanism)
Selected AbstractsInfluence of Solid Phase Conductivity and Cellular Structure on the Heat Transfer Mechanisms of Cellular Materials: Diverse Case Studies,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Eusebio Solórzano An analysis on the influence of solid phase thermal conductivity and cellular structure on the heat transfer mechanisms (HTMs) by means of studding diverse case studies combining theoretical and experimental data. The radiation and conduction mechanisms have been analyzed for cellular materials based on insulating and conductive matrixes using similar concepts and models for both types of materials. [source] Survey of heat transfer mechanisms in a slurry bubble columnTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2001Hanning Li Abstract Heat transfer mechanisms in the bulk and distributor regions of a slurry bubble column are investigated based on the measurements of local heat transfer in a 0.28 m diameter Plexiglas column. The gas, liquid and solid phases used are oil-free compressed air, tap water and 35 ,m glass beads. The slurry concentration and superficial gas velocity are varied from 0 to 40 vol% and 0.05 to 0.30 m/s respectively. Measurements have been made with a fast response heat flux probe which provided local instantaneous heat transfer coefficients. The time-averaged heat transfer coefficients in the bulk region were on average about 50% higher than the distributor region of the column. The wall region heat transfer coefficients are well predicted by the correlation of Deckwer et al. (1980). Heat transfer mechanism in column centre can be adequately described by the consecutive film and surface renewal model. Les mécanismes de transfert de chaleur dans le coeur et dans la région du distributeur d'une colonne à bulles à suspensions sont étudiés en mesurant le transfert de chaleur local dans une colonne en plexiglass de 0.28 m. Les phases gazeuse, liquide et solide utilisées sont de l'air cornprimé déhuilé, de l'eau du robinet et des billes de verre de 35 ,m. On a fait varier la concentration des suspensions et la vitesse de gaz superficielle de 0 à 40% en volume et de 0.05 à 0.30 m/s, respectivement. Les mesures ont été faites à l'aide d'une sonde de flux de chaleur à réponse rapide qui fournit les coefficients de transfert de chaleur instantanés locaux. Les coefficients de transfert de chaleur moyennés dans le temps dans le coeur étaient, en rnoyenne, environ 50% supérieurs à ceux de la région du distributeur dans la colonne. Les coefficients de transfert de chaleur de la région de la paroi sont bien predits par la cordation de Deckwer et al. (1980). Le mécanisme de transfert de chaleur au centre de la colonne peut ,tre adéquatement décrit par le modéle de renouvellement de surface et de film consécutif. [source] A quantitative identification technique for a two-dimensional subsurface defect based on surface temperature measurementHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2009Chunli Fan Abstract The inverse identification of a subsurface defect boundary is an important part of an inverse heat conduction problem, and is also the basis for the quantitative development of a nondestructive thermographic inspection technique. For the commonly encountered quantitative thermographic defect identification problem when the test piece is heated from one part of the outer boundary, our previous study showed that some parts of the defect boundary are sensitive to the initial defect boundary prediction of the conjugate gradient method. In this paper, the heat transfer mechanism inside a test piece with this problem is analyzed by building a two-dimensional model. A new method, the multiple measurements combination method (MMCM), is also presented which combines the identification algorithm study with the optimization of the thermographic detection technique to solve the problem. Numerical experiments certified the effectiveness of the present method. The temperature measurement error and the initial prediction of the defect boundary shape have little effect on the identification result. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20251 [source] Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2006A. V. S. S. K. S. Gupta Abstract In the present paper the effect of pressure on bed-to-wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas,solid flow structure and average cross-sectional solids concentration play a dominant role in better understanding of bed-to-wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction ,c' in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed-to-wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed-to-wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed-to-wall heat transfer coefficient variation along the riser height is also reported for different operating pressures. Copyright © 2005 John Wiley & Sons, Ltd. [source] Fundamental heat transfer mechanism between bed-to-membrane water-walls in circulating fluidized bed combustorsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2003B.V. Reddy Abstract In the present work, the fundamental mechanism between bed-to-membrane water-walls in the riser column of a circulating fluidized bed (CFB) combustor is presented. The bed-to-membrane water-wall heat transfer depends on the contributions of particle heat transfer, dispersed phase heat transfer and radiation heat transfer. The fundamental mechanism of particle heat transfer and the effect of fraction of wall exposed to clusters and gas gap thickness between cluster and wall on particle heat transfer coefficient and bed-to-wall heat transfer coefficient are investigated. The influence of operating parameters like cross-sectional average volumetric solids concentration and bed temperature on particle and bed-to-wall heat transfer are also reported. The present work contributes some fundamental information on particle heat transfer mechanism, which is responsible for increasing the bed-to-wall heat transfer coefficient (apart from dispersed phase convection and radiation heat transfer). The details on particle heat transfer mechanism will enable to understand the basic heat transfer phenomena between bed-to-membrane water-walls in circulating fluidized bed combustors in a detailed way, which in turn will aid for better design of CFB combustor units. The particle heat transfer mechanism is significantly influenced by the fraction of wall exposed to clusters and gas gap thickness between clusters and wall. Copyright © 2003 John Wiley & Sons, Ltd. [source] Effect of pressure and temperature on cluster and particle heat transfer in a pressurized circulating fluidized bedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2001B. V. Reddy Abstract The present work reports the influence of pressure and bed temperature on particle-to-wall heat transfer in a pressurized circulating fluidized bed (PCFB). The particle convection heat transfer plays a dominant role in determining the bed-to-wall heat transfer coefficient. So far, no information is reported on the effect of pressure and bed temperature on particle-to-wall heat transfer in a PCFB in the published literature. The present investigation reports some information in this direction. The effect of system pressure and bed temperature are investigated to study their influence on cluster and particle heat transfer. The particle convection heat transfer coefficient increases with system pressure and bed temperature due to higher cluster thermal conductivity. The increase in particle concentration (suspension density) results in greater cluster solid fraction and also the particle concentration near the wall is enhanced. This results in higher cluster and particle convection heat transfer between the bed and the wall. Higher particle convection heat transfer coefficient results in enhanced heat transfer between the bed and the wall. The results will also help to understand the bed-to-wall heat transfer mechanism in a better way in a PCFB. Copyright © 2001 John Wiley & Sons, Ltd. [source] Influence of Solid Phase Conductivity and Cellular Structure on the Heat Transfer Mechanisms of Cellular Materials: Diverse Case Studies,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Eusebio Solórzano An analysis on the influence of solid phase thermal conductivity and cellular structure on the heat transfer mechanisms (HTMs) by means of studding diverse case studies combining theoretical and experimental data. The radiation and conduction mechanisms have been analyzed for cellular materials based on insulating and conductive matrixes using similar concepts and models for both types of materials. [source] Particle scale study of heat transfer in packed and bubbling fluidized bedsAICHE JOURNAL, Issue 4 2009Z. Y. Zhou Abstract The approach of combined discrete particle simulation (DPS) and computational fluid dynamics (CFD), which has been increasingly applied to the modeling of particle-fluid flow, is extended to study particle-particle and particle-fluid heat transfer in packed and bubbling fluidized beds at an individual particle scale. The development of this model is described first, involving three heat transfer mechanisms: fluid-particle convection, particle-particle conduction and particle radiation. The model is then validated by comparing the predicted results with those measured in the literature in terms of bed effective thermal conductivity and individual particle heat transfer characteristics. The contribution of each of the three heat transfer mechanisms is quantified and analyzed. The results confirm that under certain conditions, individual particle heat transfer coefficient (HTC) can be constant in a fluidized bed, independent of gas superficial velocities. However, the relationship between HTC and gas superficial velocity varies with flow conditions and material properties such as thermal conductivities. The effectiveness and possible limitation of the hot sphere approach recently used in the experimental studies of heat transfer in fluidized beds are discussed. The results show that the proposed model offers an effective method to elucidate the mechanisms governing the heat transfer in packed and bubbling fluidized beds at a particle scale. The need for further development in this area is also discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Fluidized Bed Air Drying: Experimental Study and Model DevelopmentTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2003Markus Henneberg Abstract The presented study describes the processes and mechanisms of batch fluidized bed drying. The influencing factors of hot air drying are theoretically and experimentally examined, in order to present the relations between temperature and humidity profiles and all other drying parameters. A physical model is presented to facilitate the calculation of the drying processes under defined conditions. Three succeeding drying stages are therefore modeled. Mass and energy balances including all components taking part in the process are formulated. The model clarities the drying process under the assumption of pure heat transfer mechanisms. It does not contain adaptive parameters and takes into account an inactive bypass fraction of the fluidization and drying medium. The evaluation of the model was successful for two fluidized bed plants with nominal widths of 100 mm and 400 mm. The experiments showed sufficient accuracy and transferability of the model to equipment of application-oriented dimensions. On décrit dans la présente étude les procédés et mécanismes de séchage en lit fluidisé discontinu. Les facteurs importants du séchage à air chaud sont examinés de façon théorique et expérimentale dans le but d'expliquer les relations entre les profils de température et d'humidité et tous les autres paramètres de séchage. On présente un modèle physique pour faciliter le calcul des procédés de séchage dans des conditions définies. Trois étapes de séchage consécutives sont modélisées. Les bilans de matière et d'énergie faisant intervenir tous les composants qui prennent part au procédé sont formulés. Le procédé de séchage est modélisé en supposant des mécanismes de transfert de chaleur purs. Il ne comporte pas de paramètres adaptatifs et prend en compte une fraction de dérivation inactive du milieu de fluidisation et de séchage. L'évaluation du modèle s'est avérée concluante pour deux lits fluidisés de largeur nominale de 100 mm et 400 mm. Les expériences montrent une précision et une transférabilité suffisantes du modèle à des équipements de dimensions industrielles. [source] Survey of heat transfer mechanisms in a slurry bubble columnTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2001Hanning Li Abstract Heat transfer mechanisms in the bulk and distributor regions of a slurry bubble column are investigated based on the measurements of local heat transfer in a 0.28 m diameter Plexiglas column. The gas, liquid and solid phases used are oil-free compressed air, tap water and 35 ,m glass beads. The slurry concentration and superficial gas velocity are varied from 0 to 40 vol% and 0.05 to 0.30 m/s respectively. Measurements have been made with a fast response heat flux probe which provided local instantaneous heat transfer coefficients. The time-averaged heat transfer coefficients in the bulk region were on average about 50% higher than the distributor region of the column. The wall region heat transfer coefficients are well predicted by the correlation of Deckwer et al. (1980). Heat transfer mechanism in column centre can be adequately described by the consecutive film and surface renewal model. Les mécanismes de transfert de chaleur dans le coeur et dans la région du distributeur d'une colonne à bulles à suspensions sont étudiés en mesurant le transfert de chaleur local dans une colonne en plexiglass de 0.28 m. Les phases gazeuse, liquide et solide utilisées sont de l'air cornprimé déhuilé, de l'eau du robinet et des billes de verre de 35 ,m. On a fait varier la concentration des suspensions et la vitesse de gaz superficielle de 0 à 40% en volume et de 0.05 à 0.30 m/s, respectivement. Les mesures ont été faites à l'aide d'une sonde de flux de chaleur à réponse rapide qui fournit les coefficients de transfert de chaleur instantanés locaux. Les coefficients de transfert de chaleur moyennés dans le temps dans le coeur étaient, en rnoyenne, environ 50% supérieurs à ceux de la région du distributeur dans la colonne. Les coefficients de transfert de chaleur de la région de la paroi sont bien predits par la cordation de Deckwer et al. (1980). Le mécanisme de transfert de chaleur au centre de la colonne peut ,tre adéquatement décrit par le modéle de renouvellement de surface et de film consécutif. [source] Convection, diffusion, and exothermic zero-order reaction in a porous catalyst slab: Scaling and perturbation analysisAICHE JOURNAL, Issue 10 2009João P. Lopes Abstract The analysis of the interaction between transport phenomena and chemical reaction inside large-pore catalyst particles needs to include intraparticular convection as an additional mass/heat transfer mechanism. In this work, we describe by a 3D regime diagram the global behavior of a permeable catalyst slab, where an exothermic, zero-order reaction is occurring. An order of magnitude estimate for the maximum temperature change is obtained by scaling techniques in each regime of operation. Specific operating regimes of fast mass/heat transport, dominant reaction and strong intraparticular convection, are then studied in more detail using perturbation analysis. The results include approximate concentration and temperature profiles, which allow the estimation of both the effectiveness factor and maximum temperature attained inside the catalyst in these regimes. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | |||||||||||||