Two-dimensional model of heat transfer in circulating fluidized beds. Part II: Heat transfer in a high density CFB and sensitivity analysis

High-density circulating fluidized beds (CFB) differ in several respects from low-density CFB systems. In high-density CFB risers, solids move upward throughout the entire riser cross-section, and the net downflow of particles at the wall, a commonly observed feature of fast fluidized beds, is absent. Hence there exists a transition regime from the low density to high density CFB where the net particle motion in the vicinity of the wall is changing from downwards to upwards. This was confirmed by experiments carried in a dual-loop high-density CFB facility with concentric-tube heat exchanger installed in the riser. Local suspension-to-wall heat transfer coefficient and suspension temperature distribution below and above the heat exchange section were measured. Experimental results elucidated that particles move both upwards and downwards in the vicinity of the wall for the operation conditions studied. This alternation of direction leads to higher heat transfer coefficients at both ends of the heat exchange.

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Two-dimensional simulation of unsteady heat transfer from a circular cylinder in crossflow

Journal of Fluid Mechanics ◽

10.1017/s0022112006002941 ◽

2007 ◽

Vol 570 ◽

pp. 177-215 ◽

Cited By ~ 21

Author(s):

SALEM BOUHAIRIE ◽

VINCENT H. CHU

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Circular Cylinder ◽

Reynolds Numbers ◽

Boundary Layer Separation ◽

Length Scale ◽

Two Dimensional ◽

Dimensional Model ◽

Transfer Rates ◽

Two Dimensional Model

The heat transfer from the surface of a circular cylinder into a crossflow has been computed using a two-dimensional model, for a range of Reynolds numbers from Re=200 to 15550. The boundary-layer separation, the local and overall heat-transfer rates, the eddy- and flare-detachment frequencies and the width of the flares were determined from the numerical simulations. In this range of Reynolds numbers, the heat-transfer process is unsteady and is characterized by a viscous length scale that is inversely proportional to the square root of the Reynolds number. To ensure uniform numerical accuracy for all Reynolds numbers, the dimensions of the computational mesh were selected in proportion to this viscous length scale. The small scales were resolved by at least three nodes within the boundary layers. The frequency of the heat flares increases, and the width of each flare decreases, with the Reynolds number, in proportion to the viscous time and length scales. Despite the presence of three-dimensional structures for the range of Reynolds numbers considered, the two-dimensional model captures the unsteady processes and produced results that were consistent with the available experimental data. It correctly simulated the overall, the front-stagnation and the back-to-total heat-transfer rates.

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Heat Transfer Characteristics of Two-Dimensional Model of Parallel Louver Fin

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.55.2457 ◽

1989 ◽

Vol 55 (516) ◽

pp. 2457-2464 ◽

Cited By ~ 2

Author(s):

Kenjiro SUZUKI ◽

Tetsuro HAYASHI ◽

Matthew J. SCHUERGER ◽

Atsuo NISHIHARA ◽

Masakatsu HAYASHI

Keyword(s):

Heat Transfer ◽

Two Dimensional ◽

Dimensional Model ◽

Heat Transfer Characteristics ◽

Transfer Characteristics ◽

Two Dimensional Model

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2D Model of Transfer Processes for Water Boiling Flow in Microchannel

ChemEngineering ◽

10.3390/chemengineering5030042 ◽

2021 ◽

Vol 5 (3) ◽

pp. 42

Author(s):

Valery A. Danilov ◽

Christian Hofmann ◽

Gunther Kolb

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Temperature Profiles ◽

Two Dimensional ◽

Dimensional Model ◽

Transfer Processes ◽

Two Dimensional Model ◽

Boiling Flow ◽

Homogeneous Mixture Model ◽

2D Model

The modeling of transfer processes is a step in the generalization and interpretation of experimental data on heat transfer. The developed two-dimensional model is based on a homogeneous mixture model for boiling water flow in a microchannel with a new evaporation submodel. The outcome of the simulation is the distribution of velocity, void fraction and temperature profiles in the microchannel. The predicted temperature profile is consistent with the experimental literature data.

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Two-dimensional model for predicting performance of aerated grit chambersA paper submitted to the Journal of Environmental Engineering and Science.

Canadian Journal of Civil Engineering ◽

10.1139/l09-109 ◽

2009 ◽

Vol 36 (9) ◽

pp. 1567-1578 ◽

Cited By ~ 4

Author(s):

Alex Munoz ◽

Stephanie Young

Keyword(s):

Sensitivity Analysis ◽

Velocity Field ◽

Treatment Plant ◽

Poisson’S Equation ◽

Two Dimensional ◽

Dimensional Model ◽

Poisson's Equation ◽

Design Variables ◽

Predicting Performance ◽

Two Dimensional Model

A two-dimensional model was developed in this study. The model predicts the performance of a full-scale aerated grit chamber for grit removal from wastewater. The model numerically integrates Poisson’s equation, which describes the motion of the liquid induced by the rising air bubbles. The model makes use of finite element algorithms available in Mathcad to solve Poisson’s equation. The model was developed for predicting the velocity field in the chamber. The model was used to perform a sensitivity analysis of the design variables that affect the performance of an existing grit chamber at the Moose Jaw Wastewater Treatment Plant. The results of the sensitivity analysis indicate that predictions of velocity field are highly sensitive to energy transfer efficiency, air flowrate, and particle settling velocity but less sensitive to variations of wastewater flowrate, diffuser depth, and grid spacing.

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