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Heat transfer in a membrane assisted bubbling fluidized bed with immersed horizontal tubes
International Journal of …, 2005
The effect of gas permeation through horizontally immersed membrane tubes on the heat transfer characteristics in a membrane assisted fluidized bed operated in the bubbling fluidization regime was investigated experimentally. Local time-averaged heat transfer coefficients from copper tubes arranged in a staggered formation with the membrane tubes to the fluidized bed were measured in a square bed (0.15 m x 0.15 m x 0.95 m). Glass particles (75-110 micrometer) were fluidized with air distributed via a porous plate, where the ratio of gas fed or removed through the membrane bundles and the porous plate distributor was varied. The experimental results revealed that high gas permeation rates through the membranes strongly decreased the heat transfer coefficient at high superficial gas velocities for tubes at the top of the tube bundle, which was attributed to the reduced mobility and increased bubble hold up and/or dilution of the emulsion phase, reducing overall heat capacity.
Heat transfer in a membrane assisted fluidized bed with immersed horizontal tubes
The effect of gas permeation through horizontally immersed membrane tubes on the heat transfer characteristics in a membrane assisted fluidized bed operated in the bubbling fluidization regime was investigated experimentally. Local time-averaged heat transfer coefficients from copper tubes arranged in a staggered formation with the membrane tubes to the fluidized bed were measured in a square bed (0.15 m x 0.15 m x 0.95 m). Glass particles (75-110 micrometer) were fluidized with air distributed via a porous plate, where the ratio of gas fed or removed through the membrane bundles and the porous plate distributor was varied. The experimental results revealed that high gas permeation rates through the membranes strongly decreased the heat transfer coefficient at high superficial gas velocities for tubes at the top of the tube bundle, which was attributed to the reduced mobility and increased bubble hold up and/or dilution of the emulsion phase, reducing overall heat capacity. In the d...
1. Abstract The present research deals with the heat transfer between a bubbling fluidized bed and a single tube exchanger. Theoretical estimates of the heat transfer coefficient have been obtained by adopting a computation procedure from the literature. Experimental data have been produced with a dedicated test facility. The results confirm the high heat transfer coefficient that establishes in a bubbling fluidized bed (up to 200 Wm -2 K -1) and, thus, the suitability for a simple coupling between a fluidized bed and external devices for power generation. Among other advantages of the fluidized bed (FB) technology for combustion, the large heat exchange coefficients in the bed and the capacity to keep clean the submerged surface are relevant when the heat extraction from the bed is the main requirement of the process [1]. This is the case of the co-generation of heat and power at small scale from FB combustion of solid fuels, also including wastes or residual materials. Liquid, vap...
Computational study of heat transfer in a bubbling fluidized bed with a horizontal tube
AIChE Journal, 2011
A combined approach of discrete particle simulation and computational fluid dynamics is used to study the heat transfer in a fluidized bed with a horizontal tube. The approach is first validated through the good agreement between the predicted distribution and magnitude of local heat transfer coefficient with those measured. Then, the effects of inlet fluid superficial velocity, tube temperature and main particle properties such as particle thermal conductivity and Young's modulus are investigated and explained mechanistically. The relative importance of various heat transfer mechanisms is analyzed. The convection is found to be an important heat transfer mode for all the studied conditions. A large convective heat flux corresponds to a large local porosity around the tube, and a large conductive heat flux corresponds to a large number of particle contacts with the tube. The heat transfer is enhanced by the increase of particle thermal conductivity while it is little affected by...
Effect of Fins on Heat Transfer of Horizontal Immersed Tube in Bubbling Fluidized Beds
2009
— Steady state time averaged local heat transfer coefficient measurements were made by the local thermal simulation technique in a cold bubbling fluidized bed with horizontally immersed tube initially with no fin and then with three fixed annular fins of constant thickness. Silica sand of mean particle diameter 307 μm and 200 μm were used as the bed materials. The results indicate that although the heat transfer coefficient falls with the use of fins, the total heat transfer rises as the result of the greater surface area. Increasing the particle diameter reduces the heat transfer coefficient not only for unfinned horizontal tube but also for annular finned horizontal tube at the same conditions of fluidized bed. Based on the experimental data, correlations are proposed for predicting heat transfer coefficient from fluidized bed to horizontally immersed tubes with and without fins. Index Terms — Annular fin, Bubbling fluidized bed, Heat transfer.
Experimental Thermal and Fluid Science, 1995
• The experimental results of an investigation involving particle size effects on the heat transfer for a horizontal tube located in the splash zone of a high-temperature bubbling fluidized bed are reported. This article is the second of a series [1] that investigates specific operating parameters of bubbling fluidized beds. The array of experimental conditions for this work involved three particle sizes, of nominal 1.1, 2, and 2.9 mm in diameter; four bed temperatures, 700, 810, 908, and 1003 K; and three tube locations,-127, 64 and 406 mm relative to the tube centerline to nonfluidized bed surface. The tube locations are representative of a tube totally immersed in the bed, located in the splash zone, and located in the freeboard, respectively. Convective and blackbody radiative heat transfer coefficient variations are presented as functions of the nondimensionalized velocity ratio and of the particle size for the 1003-K case. Maximum convective and blackbody radiative heat transfer coefficients are tabulated for the other temperatures and particle sizes. The tube outside diameter was 51 mm, and the superficial velocity was varied from near-minimum fluidization conditions (Umf) to over 2 Umf.
Numerical prediction of heat transfer between a bubbling fluidized bed and an immersed tube bundle
Heat and Mass Transfer, 2004
In this paper a numerical analysis of the heat transfer between a bubbling fluidized bed of mono-dispersed glass beads of Geldart type B and an immersed heated tube bundle is investigated. The numerical procedure is based on a solution of the mass, momentum and energy equations of both phases with an Eulerian approach. Different physical models for the thermal transport coefficient of the solid phase were used. The results are compared with new experimental data. The numerical and the experimental results show a strong correlation between fluid dynamics and heat transfer similar to the packet theory of Mickley and Fairbanks (1955).
Effect of annular fins on heat transfer of a horizontal immersed tube in bubbling fluidized beds
Powder Technology, 2005
Experiments were conducted in a bubbling air-fluidized bed to investigate the effect of annular fins of constant thickness on heat transfer. Steady state time averaged local heat transfer coefficient measurements were made by the local thermal simulation technique in a cold bubbling fluidized bed (90 mm ID, 260 mm tall) with horizontally immersed tube initially with no fin and then