Detailed Description of the Fluidized Bed Mixing and Heat Transfer by Means of Eulerian Multi-Fluid Numerical Simulations

2020 ◽  
Author(s):  
Muhammad Ali Uzair ◽  
Francesco Fornarelli ◽  
Sergio Mario Camporeale ◽  
Marco Torresi
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Granular Flow ◽  
Fluid Model ◽  
Gas Velocity ◽  
Uniform Temperature ◽  
Temperature Dependent ◽  
Commercial Code ◽  
Temperature Dependent Properties ◽  
Superficial Gas Velocity

Abstract The hydrodynamics and heat transfer of a binary mixture of sand and biomass in a fluidized bed have been numerically investigated. The Eulerian multi-fluid model MFM incorporating kinetic theory of granular flow was used to numerically investigate fluidized bed. A commercial code has been used together with user-defined functions to correctly predict the hydrodynamics and the heat transfer. Numerical results were validated against the experiment in terms of pressure drop across the bed and concentration of biomass at different heights of the bed. Influence of additional parameters, such as superficial gas velocity and sand sizes on hydrodynamics were investigated. Additionally, heat transfer in the fluidized bed was also studied highlighting the influence of the temperature dependent properties of air on the results. The present results reveal that better mixing is achieved for smallest sand size, also promoting more uniform temperature of biomass.

CFD-DEM Numerical Simulation and Experimental Validation of Heat Transfer and Two-Component Flow in Fluidized Bed

2017 ◽  
Vol 16 (1) ◽  
Author(s):  
Feihong Guo ◽  
Zhaoping Zhong
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Fluidized Bed ◽  
Quartz Sand ◽  
Thermal Imager ◽  
Gas Velocity ◽  
Bed Height ◽  
Two Component ◽  
Superficial Gas Velocity ◽  
Infrared Thermal Imager

AbstractBased on the improved computational fluid dynamics and discrete element method (CFD-DEM), heat transfer and two-component flow of biomass and quartz sand have been studied from experiments and numerical simulation in this paper. During experiments, the particle temperature and moving images are respectively recorded by infrared thermal imager and high speed camera. With the increase of the velocity, the mixing index (MI) and the cooling rate of the particles are rising. Due to larger heat capacity and mass, the temperature of biomass drops slower than that of quartz sand. Fictitious element method is employed to solve the incompatibility of the traditional CFD-DEM where the cylindrical biomass are considered as an aggregation of numerous fictitious sphere particles arranged in certain sequence. By the comparison of data collected by infrared thermal imager and the simulated results, it can be concluded that experimental data is basically agreement with numerical simulation results. Directly affected by inflow air (25℃), the average temperature of particles in the bed height area (h>30 mm) is about 3 degrees lower than that of the other heights. When the superficial gas velocity is larger, the fluidization is good, and the gas temperature distribution is more uniform in the whole area. On the contrary, bubbles are not easy to produce and the fluidization is restricted at lower superficial gas velocity. Gas-solid heat transfer mainly exists under the bed height of 10 mm, and decreases rapidly on fluidized bed height. The mixing index (MI) is employed to quantitatively discuss the mixing effectiveness, which first rises accelerate, then rising speed decreases, finally tends to a upper limit.

scholarly journals Simulation of Three-dimensional Vibrated Fluidized Bed Dryer Using Distinct Element Method

2019 ◽  
Vol 7 (2) ◽  
Author(s):  
S. Wongsiriwan ◽  
Thongchai Rohitatisha Srinophakun ◽  
Pakon Laopreecha
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Particle Motion ◽  
Distinct Element ◽  
Distinct Element Method ◽  
Drying Rate ◽  
Gas Velocity ◽  
Fluidized Bed Dryer ◽  
Vibrated Fluidized Bed ◽  
Superficial Gas Velocity

The particle motion, temperature behavior, and drying rate of particle inside a vibrated fluidized bed dryer were numerically investigated in this work. In the simulation, the Distinct Element Method (DEM) based on the Newton’s second law of motion was used to solve the particle motion. The physical aspects of fluid motion and heat transfer were obtained by applying Computational Fluid Dynamics (CFD) technique. For the drying of particle, only the constant rate period was considered in order to save the computational time. Programming was developed in Standard-C language and using MATLAB to visualize the results. In the simulation, 2,000 particles with stiffness 800 N m-1 were simulated in a rectangular bed. The developed model was validated with an experimental result of Gupta et al. [1]. The program was then used to study the effect of superficial gas velocity (U0), frequency of vibration (f) and amplitude of vibration (a) in fluidized bed dryer. At low velocities and no vibration of bed,  articles in the bed were not fluidized but smoothly circulated. Thus, the heat transfer occurred only near the orifice. When superficial gas velocity increased, the fluidization of the particles was observed. The fluidization and drying rate improved with increased in superficial velocity for both vibrated fluidized bed and stationary bed. With introducing of vibration, the fluidization behavior of the particle was improved. The particles in the bed were well mixed and also increased the drying rate. From the simulation results, increasing of frequency and amplitude could not significantly improve rate of drying.

scholarly journals Mixing Characteristics of Binary Mixture with Biomass in a Gas-Solid Rectangular Fluidized Bed

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 2011
Author(s):  
Guiying Wu ◽  
Bangting Yu ◽  
Yanjun Guan ◽  
Xuehui Wu ◽  
Kai Zhang ◽  
...  
Keyword(s):  
Binary Mixture ◽  
Fluidized Bed ◽  
Binary Mixtures ◽  
Silica Sand ◽  
Mixture Composition ◽  
Inert Material ◽  
Gas Velocity ◽  
Mixing Characteristics ◽  
Superficial Gas Velocity ◽  
Initial Packing

Aiming to better understand the biomass pyrolysis and gasification processes, a detailed experimental study of the mixing characteristics is conducted in a fluidized bed with binary mixtures. Rapeseed is used as biomass, and silica sand or resin as inert material. The effect of mixture composition, initial packing manner, and superficial gas velocity on the concentration distribution is investigated in a rectangular fluidized bed by means of photography and sampling methods. The results show that the mixture composition plays an important role in the axial solids profile of binary mixtures. The mixing behavior of binary mixture is dominated by the bubble movement. The axial distribution of binary mixtures becomes uniform with increasing superficial gas velocity, whilst no obvious effect of initial packing manner is observed in this study.

Internal Laminar Heat Transfer With Gas-Property Variation

1971 ◽  
Vol 93 (4) ◽  
pp. 432-440 ◽  
Author(s):  
T. B. Swearingen ◽  
D. M. McEligot
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Bulk Temperature ◽  
Parallel Plates ◽  
Temperature Dependent ◽  
Property Variation ◽  
Constant Wall Heat Flux ◽  
Mixed Mean ◽  
Two Dimensional Flow ◽  
Temperature Dependent Properties

The results of a numerical investigation of internal laminar heat transfer to a gas with temperature-dependent properties are reported. In this investigation the authors obtained numerical solutions to the coupled partial differential equations of continuity, energy, momentum, and integral continuity describing the two-dimensional flow of perfect gas between heated parallel plates. A sequence of numerical solutions was obtained for the case of constant wall heat flux with a fully developed velocity profile at the start of the heated section and pure forced convection. The results may be summarized by Nu=Nuconst.prop.+0.024(Q+)0.3(Gzm)0.75f·Rem=24(Twall/Tbulk) where the subscript “m” refers to properties evaluated at the local mixed-mean (or bulk) temperature.

CFD Studies on the Heat Transfer Characteristics of a Horizontal Single-Tube in Fluidized Bed Heat Exchanger

2011 ◽  
Vol 374-377 ◽  
pp. 183-186
Author(s):  
Cong Shen ◽  
Jian Xiang Guo ◽  
Lin Li ◽  
Jin Fei Sun
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Fluidized Bed ◽  
High Performance ◽  
Fluid Model ◽  
Two Phase ◽  
Scaling Properties ◽  
Single Tube ◽  
Industrial Sectors ◽  
Two Fluid Model

The fluidized-bed heat exchanger is widely used in various industrial sectors with the high performance of its heat transfer, ability to adapt working conditions, anti-scaling properties and many other advantages. This paper takes a horizontal single-tube in fluidized-bed heat exchanger and the fluidized low-temperature smoke around the tube as the objects of study. Euler-Euler two-fluid model is taken in use. Heat transfer between gas-solid two-phase flows and water in single-tube is simulated. The temperature field and general heat transfer coefficient is analyzed by simulated graphics.

Influence of Fluidization Velocity on Bed Defluidization in Fluidized Bed Combustors

2005 ◽  
Author(s):  
Mohammad R. Golriz ◽  
Morgan Eriksson ◽  
Marcus O¨hman ◽  
Anders Nordin ◽  
Rainer Backman
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Large Scale ◽  
Particle Diameter ◽  
Operating Conditions ◽  
Biomass Combustion ◽  
Gas Velocity ◽  
Fluidization Velocity ◽  
Significant Difference ◽  
Superficial Gas Velocity

Effects of superficial gas velocity and bed particle size on bed defluidization during biomass combustion were investigated. Sampled bed particles from four different large-scale circulating- and bubbling fluidized bed combustors, using biomass as fuel, were collected and analyzed. The bed particles from each fluidized bed unit were divided into small and large particle size fractions. The results indicate no significant difference in elemental compositions between small and large coated bed particles but the ratio of coating thickness to the mean particle diameter was higher for the small particles compared to the large ones. Controlled fluidized bed agglomeration tests revealed strong influence from fluidization velocity on initial defluidization temperatures at lower velocities, but little effect at higher velocities. Influence of bed particle size on initial defluidization temperature varied depending on operating conditions. Finally, a model based on viscous flow sintering is proposed for the relation between agglomeration temperature and superficial gas velocity. The model predictions are in good agreement with experimental data.

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