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Heat and mass transfer in packed beds
01 Jan 1982-
About: The article was published on 1982-01-01 and is currently open access. It has received 215 citations till now. The article focuses on the topics: Mass transfer.
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TL;DR: In this article, the phenomenology and fundamental thermodynamics of magnetocaloric materials are discussed, as well as the hysteresis behavior often found in first-order materials.
Abstract: Magnetocaloric materials with a Curie temperature near room temperature have attracted significant interest for some time due to their possible application for high-efficiency refrigeration devices. This review focuses on a number of key issues of relevance for the characterization, performance and implementation of such materials in actual devices. The phenomenology and fundamental thermodynamics of magnetocaloric materials is discussed, as well as the hysteresis behavior often found in first-order materials. A number of theoretical and experimental approaches and their implications are reviewed. The question of how to evaluate the suitability of a given material for use in a magnetocaloric device is covered in some detail, including a critical assessment of a number of common performance metrics. Of particular interest is which non-magnetocaloric properties need to be considered in this connection. An overview of several important materials classes is given before considering the performance of materials in actual devices. Finally, an outlook on further developments is presented.
463 citations
TL;DR: TauFactor is a MatLab application for efficiently calculating the tortuosity factor, as well as volume fractions, surface areas and triple phase boundary densities, from image based microstructural data, without requiring high computational power.
244 citations
TL;DR: In this article, the authors summarize the key aspects of packed-bed thermal energy storage systems and compare the performance of different types of thermal storage systems, including two-tank molten salt technology and thermal stratification.
183 citations
Cites background from "Heat and mass transfer in packed be..."
...This contribution is not the same in axial and radial directions (respectively parallel and perpendicular to flow direction) and is given by (Wakao and Kaguei, 1982):...
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...Effective thermal conductivity The effective thermal conductivity of packed beds has been investigated with various approaches by many authors and quite exhaustive reviews can be found in the literature (Kaviany, 1995; Tsotsas and Martin, 1987; Van Antwerpen et al., 2010; Wakao and Kaguei, 1982)....
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...This contribution is not the same in axial and radial directions (respectively parallel and perpendicular to flow direction) and is given by (Wakao and Kaguei, 1982): λmix,z λf = 0,5 · Re · Pr (28) λmix,r λf = 0,1 · Re · Pr (29) According to equations (28) and (29), effective conductivity of the…...
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...The effective thermal conductivity of packed beds has been investigated with various approaches by many authors and quite exhaustive reviews can be found in the literature (Kaviany, 1995; Tsotsas and Martin, 1987; Van Antwerpen et al., 2010; Wakao and Kaguei, 1982)....
[...]
TL;DR: In this article, a simple model for estimating the emissivity of the surface of a powder bed by knowing only the bed porosity and its solid emissivities is presented, and the model is compared with experimental measurements for powder beds of alumina, silicon carbide, and iron.
Abstract: A simple model for estimating the emissivity of the surface of a powder bed by knowing only the bed porosity and its solid emissivity is presented. Estimates by the model are compared with experimental measurements for powder beds of alumina, silicon carbide, and iron. Agreement within the uncertainty of the measurements of ±10% is obtained. A view factor that adopts the predicted emissivity of the powder beds into its term is suggested for the calculation of the conductivity by radiation. For the prediction of the thermal conductivity of the powder beds, the authors compared the existing models in literature. They rederived the Zehner-Schlunder equation (1970) and made some modifications to it. Comparison of predictions by this equation with 424 measured values shows the predictions to be accurate to within a ±30% relative error.
178 citations
TL;DR: In this paper, the authors used a laser-diffraction technique to determine the interfacial area per unit gas volume, a.k.a. KL, for a synthesis-gas fermentation.
Abstract: Synthesis-gas fermentations have typically been gas-to-liquid mass-transfer-limited due to low solubilities of the gaseous substrates. A potential method to enhance mass-transfer rates is to sparge with microbubble dispersions. Mass-transfer coefficients for microbubble dispersions were measured in a bubble column. Oxygen microbubbles were formed in a dilute Tween 20 solution using a spinning disk apparatus. Axial dispersion coefficients measured for the bubble column ranged from 1.5 to 7.2 cm2/s and were essentially independent of flow rate. A laser-diffraction technique was used to determine the interfacial area per unit gas volume, a. The mass-transfer coefficient, KL, was determined by fitting a plug-flow model to the experimental, steady-state, liquid-phase oxygen-concentration profile. The KL values ranged from 2.9 x 10(-5) to 2.2 x 10(-4) m/s. Volumetric mass-transfer coefficients, KLa, for microbubbles with an average initial diameter of 60 microns ranged from 200 to 1800 h-1. Enhancement of mass transfer using microbubbles was demonstrated for a synthesis-gas fermentation. Butyribacterium methylotrophicum was grown in a continuous, stirred-tank reactor using a tangential filter for total cell recycle. The fermentation KLa values were 14 h-1 for conventional gas sparging through a stainless steel frit and 91 h-1 for microbubble sparging. The Power number of the microbubble generator was determined to be 0.036. Using this value, an incremental power-to-volume ratio to produce microbubbles for a B. methylotrophicum fermentation was estimated to be 0.01 kW/m3 of fermentation capacity.
164 citations
References
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TL;DR: TauFactor is a MatLab application for efficiently calculating the tortuosity factor, as well as volume fractions, surface areas and triple phase boundary densities, from image based microstructural data, without requiring high computational power.
244 citations
TL;DR: In this article, the authors summarize the key aspects of packed-bed thermal energy storage systems and compare the performance of different types of thermal storage systems, including two-tank molten salt technology and thermal stratification.
183 citations
TL;DR: In this article, a simple model for estimating the emissivity of the surface of a powder bed by knowing only the bed porosity and its solid emissivities is presented, and the model is compared with experimental measurements for powder beds of alumina, silicon carbide, and iron.
Abstract: A simple model for estimating the emissivity of the surface of a powder bed by knowing only the bed porosity and its solid emissivity is presented. Estimates by the model are compared with experimental measurements for powder beds of alumina, silicon carbide, and iron. Agreement within the uncertainty of the measurements of ±10% is obtained. A view factor that adopts the predicted emissivity of the powder beds into its term is suggested for the calculation of the conductivity by radiation. For the prediction of the thermal conductivity of the powder beds, the authors compared the existing models in literature. They rederived the Zehner-Schlunder equation (1970) and made some modifications to it. Comparison of predictions by this equation with 424 measured values shows the predictions to be accurate to within a ±30% relative error.
178 citations
TL;DR: In this paper, the authors used a laser-diffraction technique to determine the interfacial area per unit gas volume, a.k.a. KL, for a synthesis-gas fermentation.
Abstract: Synthesis-gas fermentations have typically been gas-to-liquid mass-transfer-limited due to low solubilities of the gaseous substrates. A potential method to enhance mass-transfer rates is to sparge with microbubble dispersions. Mass-transfer coefficients for microbubble dispersions were measured in a bubble column. Oxygen microbubbles were formed in a dilute Tween 20 solution using a spinning disk apparatus. Axial dispersion coefficients measured for the bubble column ranged from 1.5 to 7.2 cm2/s and were essentially independent of flow rate. A laser-diffraction technique was used to determine the interfacial area per unit gas volume, a. The mass-transfer coefficient, KL, was determined by fitting a plug-flow model to the experimental, steady-state, liquid-phase oxygen-concentration profile. The KL values ranged from 2.9 x 10(-5) to 2.2 x 10(-4) m/s. Volumetric mass-transfer coefficients, KLa, for microbubbles with an average initial diameter of 60 microns ranged from 200 to 1800 h-1. Enhancement of mass transfer using microbubbles was demonstrated for a synthesis-gas fermentation. Butyribacterium methylotrophicum was grown in a continuous, stirred-tank reactor using a tangential filter for total cell recycle. The fermentation KLa values were 14 h-1 for conventional gas sparging through a stainless steel frit and 91 h-1 for microbubble sparging. The Power number of the microbubble generator was determined to be 0.036. Using this value, an incremental power-to-volume ratio to produce microbubbles for a B. methylotrophicum fermentation was estimated to be 0.01 kW/m3 of fermentation capacity.
164 citations
TL;DR: In this paper, a comprehensive model of a dual-medium thermocline tank that includes both the heterogeneous filler region as well as the composite tank wall is formulated, and the model accounts separately for the rock and molten-salt regions in view of their different thermal properties.
142 citations