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Title: Heat transfer from a horizontal finned tube bundle in bubbling fluidized beds of small and large particles

Abstract

Steady state average heat transfer coefficient measurements were made by the local thermal simulation technique in a cold, square, bubbling air-fluidized bed (0.305 m x 0.305 m) with immersed horizontal finned tube bundles (in-line and staggered) with integral 60{degree} V-thread. Studies were conducted using beds of small (average particle diameter less than 1 mm) sand particles and of large (average particle diameter greater thin 1 mm) particles (raagi, mustard, millet and coriander). The fin pitch varied from 0.8 to 5.0 mm and the fin height varied from 0.69 to 4.4 mm. The tube pitch ratios used were 1.75 and 3.5. The influence of bed particle diameter, fluidizing velocity, fin pitch, and tube pitch ratio on average heat transfer coefficient was studied. Fin pitch and bed particle diameter are the most significant parameters affecting heat transfer coefficient within the range of experimental conditions. Bed pressure drop depends only on static bed height. New direct correlations, incorporating easily measurable quantities, for average heat transfer coefficient for finned tube bundles (in-line and staggered) are proposed.

Authors:
 [1];  [2]
  1. Jayachamaraja College of Engineering, Mysore (India). Dept. of Mechanical Engineering
  2. Indian Inst. of Technology, Madras (India). Dept. of Mechanical Engineering
Publication Date:
OSTI Identifier:
245036
Report Number(s):
CONF-950522-
ISBN 0-7918-1305-3; TRN: IM9627%%402
Resource Type:
Book
Resource Relation:
Conference: 13. international conference on fluidized-bed combustion, Orlando, FL (United States), 7-10 May 1995; Other Information: PBD: 1995; Related Information: Is Part Of 13. international conference on fluidized bed combustion: Proceedings. Volume 1; Heinschel, K.J. [ed.] [Air Products and Chemicals, Inc., Allentown, PA (United States)]; PB: 719 p.
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING NOT INCLUDED IN OTHER CATEGORIES; FLUIDIZED BED HEAT EXCHANGERS; PERFORMANCE; HEAT TRANSFER; ORIENTATION; FINS; PARTICLE SIZE; PARAMETRIC ANALYSIS; GAS FLOW; FLOW RATE; EFFICIENCY; EQUATIONS; EXPERIMENTAL DATA

Citation Formats

Devaru, C.B., and Kolar, A.K.. Heat transfer from a horizontal finned tube bundle in bubbling fluidized beds of small and large particles. United States: N. p., 1995. Web.
Devaru, C.B., & Kolar, A.K.. Heat transfer from a horizontal finned tube bundle in bubbling fluidized beds of small and large particles. United States.
Devaru, C.B., and Kolar, A.K.. Sun . "Heat transfer from a horizontal finned tube bundle in bubbling fluidized beds of small and large particles". United States. doi:.
@article{osti_245036,
title = {Heat transfer from a horizontal finned tube bundle in bubbling fluidized beds of small and large particles},
author = {Devaru, C.B. and Kolar, A.K.},
abstractNote = {Steady state average heat transfer coefficient measurements were made by the local thermal simulation technique in a cold, square, bubbling air-fluidized bed (0.305 m x 0.305 m) with immersed horizontal finned tube bundles (in-line and staggered) with integral 60{degree} V-thread. Studies were conducted using beds of small (average particle diameter less than 1 mm) sand particles and of large (average particle diameter greater thin 1 mm) particles (raagi, mustard, millet and coriander). The fin pitch varied from 0.8 to 5.0 mm and the fin height varied from 0.69 to 4.4 mm. The tube pitch ratios used were 1.75 and 3.5. The influence of bed particle diameter, fluidizing velocity, fin pitch, and tube pitch ratio on average heat transfer coefficient was studied. Fin pitch and bed particle diameter are the most significant parameters affecting heat transfer coefficient within the range of experimental conditions. Bed pressure drop depends only on static bed height. New direct correlations, incorporating easily measurable quantities, for average heat transfer coefficient for finned tube bundles (in-line and staggered) are proposed.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Dec 31 00:00:00 EST 1995},
month = {Sun Dec 31 00:00:00 EST 1995}
}

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  • This paper reports the average and reduced coefficients of heat transfer from finned tubes to fluidized beds were measured, and the effects of the fin geometry, type and particle size of bed material and flow conditions on the average heat transfer coefficient determined. The data were obtained in experiments with single finned tubes submerged horizontally in fluidized beds. The measured reduced heat transfer coefficient were used in estimating the effect of the thermal conductivity of the fin.
  • The mixing and segregation behavior of spherical solids between 30 mm and 80 mm in diameter in a bubbling fluidized bed of quartz sand has been investigated. The experimental system used is a cold-air fluidized bed of 0.45 m x 0.45 m bed area and up to 0.6 m bed height. Fuel particles were replaced with metallic spheres of same size and density. A special experimental technique has been developed to locate metallic spheres in three dimensions while operating the fluidized bed. The method utilizes the influence of metallic surfaces of spheres on oscillating magnetic fields. Binary systems fuel-particle/sand havemore » been studied using three different sizes of sand (Geldart B-D) and varying the fluidization velocity and the size, density and volumetric fraction of the large solids. The experimentally evaluated axial concentration profiles have been compared with theoretical considerations based on the model of Gibilaro and Rowe. The segregation of large flotsam solids is described by a segregation parameter which includes the physical characteristics of the solids used. The segregation parameters for the different solids were obtained by fitting model results to the experimentally determined axial segregation patterns.« less
  • In this paper, the flow hydrodynamics in a bubbling fluidized bed with submerged horizontal tube bundle was numerically investigated with an open-source code: Multiphase Flow with Interphase eXchange (MFIX). A newly implemented cut-cell technique was employed to deal with the curved surface of submerged tubes. A series of 2D simulations were conducted to study the effects of gas velocity and tube arrangement on the flow pattern. Hydrodynamic heterogeneities on voidage, particle velocity, bubble fraction, and frequency near the tube circumferential surface were successfully predicted by this numerical method, which agrees qualitatively with previous experimental findings and contributes to a soundermore » understanding of the non-uniform heat transfer and erosion around a horizontal tube. A 3D simulation was also conducted. Significant differences between 2D and 3D simulations were observed with respect to bed expansion, bubble distribution, voidage, and solids velocity profiles. Hence, the 3D simulation is needed for quantitative prediction of flow hydrodynamics. On the other hand, the flow characteristics and bubble behavior at the tube surface are similar under both 2D and 3D simulations as far as the bubble frequency and bubble phase fraction are concerned. Comparison with experimental data showed that qualitative agreement was obtained in both 2D and 3D simulations for the bubble characteristics at the tube surface.« less
  • Experimental data were obtained for the heat transfer coefficient between electrically-heated horizontal tube bundles and square fluidised beds of silica sand and alumina as a function of air fluidising velocity. Heat transfer data for a bundle of tubes are compared with a single tube under otherwise identical conditions, and are compared with existing correlations and theoretical models in the literature for maximum heat transfer coefficient. A correlation for the maximum heat transfer coefficient between horizontal tube bundles and a gas-solid fluidised bed of small particles is proposed which includes the influence of tube pitch in the bundle. This correlation willmore » be particularly useful in the design of a low-rank coal fluidised-bed combustor where crushed coal is burnt in an inert bed of silica sand or alumina of particle size less than 1 mm.« less
  • Experimental data are obtained for heat transfer coefficient between electrically heated horizontal tube bundles (12.7 and 28.6 mm diameter) and square fluidized beds of silica sand (/sup -/d/rho/ = 167 and 504 ..mu..m) and alumina (/sup -/d/rho/ = 259 ..mu..m) as a function of air fluidizing velocity. The staggered tube bundle has its tubes located at the vertices of equilateral triangles with pitch varying between 1.75 to 9 times the tube diameter. Heat transfer data for a bundle of tubes are compared with a single tube under otherwise identical conditions and are compared with the existing correlations and theoretical modelsmore » in the literature for maximum heat transfer coefficient. A correlation for the maximum heat transfer coefficient between horizontal tube bundles and a gas-solid fluidized bed of small particles (75 < Ar < 20 000) is proposed which includes the influence of tube pitch in the bundle. The predicted values of the maximum heat transfer coefficient from the proposed correlation are generally within plus or minus 20% of the experimental data available in the literature when the contribution due to radiation is also included.« less