scholarly journals Numerical study of mixing and heat transfer of SRF particles in a bubbling fluidized bed

2019 ◽  
Vol 142 (2) ◽  
pp. 1087-1096
Author(s):  
Mohamed Sobhi Alagha ◽  
Botond Szucs ◽  
Pal Szentannai
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Fluidized Bed ◽  
Present Model ◽  
Numerical Study ◽  
Sand Particle ◽  
Particle Sizes ◽  
Proposed Model ◽  
Bubbling Fluidized Bed ◽  
Good Agreement

AbstractIn this article, numerical investigations on mixing and heat transfer of solid refused fuel (SRF) particles in a bubbling fluidized bed are carried out. The numerical model is based on the Eulerian–Eulerian approach with empirical submodels representing gas–solid and solid–solid interactions. The model is verified by experimental data from the literature. The experimental data include SRF vertical distribution in SRF–sand mixtures of different sand particle sizes ($$d_{\mathrm{pm}} = 654,810$$ d pm = 654 , 810 and 1110 $$\upmu$$ μ m) at different fluidization velocities ($$u/u_{\mathrm{mf}} = 1.2$$ u / u mf = 1.2 –2.0). We proposed magnification of drag force exerted by the gas on SRF particles based on Haider and Levenspiel (Powder Technol 58(1):63–70, 1989) drag coefficient. The proposed model shows good agreement with the experimental data at high fluidization velocities ( $$u/u_{\mathrm{mf}} = 1.5$$ u / u mf = 1.5 –2.0) and poor predictions at low fluidization velocities ($$u/u_{\mathrm{mf}} = 1.2$$ u / u mf = 1.2 –1.5). Heat transfer results showed that the present model is valid and gives good agreement with the experimental data of wall–bed heat transfer coefficient.

scholarly journals A two-stage heat transfer model for the peripheral layers of a grain store

2003 ◽  
Vol 7 (3) ◽  
pp. 147-164
Author(s):  
Alexsandar Antic ◽  
James M. Hill
Keyword(s):  
Heat Transfer ◽  
Present Model ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Two Stage ◽  
Peripheral Layer ◽  
Proposed Model ◽  
Grain Bulk ◽  
Insight Into ◽  
Good Agreement

An understanding of the flow of heat in grain store structures, in particular, within the peripheral layer, is important from many industrial perspectives. To analyse the heat transfer within such regions a mathematical model known as the two-stage heat transfer model is proposed. This model makes a distinction between the air and grain within the grain bulk, and thus takes into consideration the fact that the rate of heat transfer through the grain is different to that through the interstitial air surrounding the grain. Such a model lends itself to a solution via Laplace transforms and approximate analytical results are obtained for small and large times. In addition, the Stehfest numerical algorithm is used for the inversions and very good agreement is obtained between the two approaches. The present model is compared to a previously developed double-diffusivity heat transfer model by the authors, and good agreement is obtained. At present, no experimental data is available to validate the model as it is very difficult to measure the air and grain temperatures separately, particularly in the peripheral layer. The proposed model provides insight into the potential difference existing between the air and grain temperatures.

Numerical Study of the Influence of Horizontal Tube Banks on the Hydrodynamics of a Dense Gas-Solid Bubbling Fluidized Bed

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Sanjib K. Das Sharma ◽  
Ratan Mohan
Keyword(s):  
Fluidized Bed ◽  
Solid Phase ◽  
Numerical Study ◽  
Horizontal Tube ◽  
Particle Interactions ◽  
Tube Bank ◽  
Bubbling Fluidized Bed ◽  
Tube Banks ◽  
Fluidizing Medium ◽  
Good Agreement

Numerical study of the influence of tube-bank on the hydrodynamics of a freely bubbling fluidized bed is relatively less reported in the literature. In this paper, results obtained from CFD study of a two dimensional gas-solid fluidized beds with horizontal tube-bank are compared with the published experimental data (Hull et. al., 1999). A 2-D bed, 1 m high and 0.2 m wide with tubes of diameter 0.026 m was taken for the calculations. Two different tube arrangements of staggered and inline pitch with center-to-center distance of 0.05 m were considered. Air was used as the fluidizing medium and ballotini glass (diameter: 230 mm and density: 2723 kg/m3) was the fluidized material. Air velocities used were 0.15 m/s and 0.187 m/s. The Eulerian-Eularian Two-Fluid CFD model was employed for modeling the momentum equations for both the gas and the solid phase with kinetic theory modification for the solid phase to account for the inter-particle interactions. Hydrodynamic features, such as, bubble size and bubble rise velocity and their variation with height within and outside the tube bank showed good agreement with the data of Hull et al.(1999)

scholarly journals EXPERIMENTAL STUDY ON BED-TO-TUBE HEAT TRANSFER COEFFICIENTS IN BUBBLING FLUIDIZED BED

2021 ◽  
Vol 15 (2) ◽  
pp. 139-149
Author(s):  
Bamiji Zacheous Adewole
Keyword(s):  
Heat Transfer ◽  
Particle Size ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Fluidized Bed ◽  
Particle Sizes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Bubbling Fluidized Bed ◽  
Coconut Shells

The overall bed-to-tube heat transfer coefficients of the blends of Lafia-obi coal and coconut shells have been investigated in a bubbling fluidized bed combustor. Experiments were performed at five different particle sizes of coal (5, 10, 15, 20 and 25 mm) and five different particle sizes of coconut shells (2, 6, 10,14 and 18 mm) for different blend proportions of 10%, 20%, 30%, 40% and 50%. Results obtained showed that the overall bed-to-tube heat transfer coefficient decreased with increasing coconut shell particle size in the blends. Combined effects of high radiation from large particle size of coal (25 mm) and high convection heat from small particle size of coconut shell (2 mm) at blend proportion of 10 and 50% produced the maximum bed-to-tube heat transfer coefficient. Due to the importance of heat exchange in the fluidized bed, it is observed that the contribution of biomass co-firing with coal is significant, hence, co-firing at optimal particle size and biomass blend ratio is imperative for achieving higher bed-to-tube heat transfer in the fluidized bed boiler.

Study on Heat Transfer from a Bubbling Fluidized Bed Combustor to a Membrane Wall

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Paula Neto ◽  
Albina M. Ribeiro ◽  
Carlos Pinho
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Fluidized Bed ◽  
Equivalence Ratio ◽  
Internal Diameter ◽  
Entrainment Rate ◽  
Particle Sizes ◽  
Temperature Range ◽  
Particle Entrainment ◽  
Bubbling Fluidized Bed

The importance of projection and splashing of bubbling bed particles on the heat transfer rate towards a membrane wall heat exchanger placed above the bed was studied.To characterize the heat transferred from a bubbling fluidized bed to a membrane wall heat exchanger placed above the freeboard, a laboratory scale fluidized bed reactor, heated by a 2 kW electric resistance, was used. The reactor, with an internal diameter of 54.5 mm, had two 0.83 m height double pipe heat exchangers placed one above the other. Only the heat exchanger close to the bed surface participated in the heat exchange process. Tests were done without and with combustion.For experiments without combustion the bed was fluidized with air at superficial velocities of 0.2 to 0.5 m/s in the 400-700 °C temperature range. For experiments with combustion, the fluidizing gas was obtained through propane combustion in the bed in 700-720 °C temperature range, for superficial velocities of 0.2 to 0.3 m/s. Five different bed particle sizes were considered: 107.5, 142.5, 180, 282.5 and 357.5 µm.Particle convective heat transfer coefficients were obtained in the range of 2 to 16 W/m²/K and a correlation for the corresponding Nusselt number as a function of the fluidization characteristics and the combustion equivalence ratio is proposed.For the three smaller bed particle sizes, the particle entrainment ratio had a strong influence on the heat transferred towards the membrane wall and the corresponding bed particle entrainment rate was determined and correlated with the fluidization characteristics and the combustion equivalence ratio.

Oscillatory Heat Transfer in a Pipe Subjected to a Laminar Reciprocating Flow

1996 ◽  
Vol 118 (3) ◽  
pp. 592-597 ◽  
Author(s):  
T. S. Zhao ◽  
P. Cheng
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Nusselt Number ◽  
Numerical Study ◽  
Temperature Cycle ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Cycle Space ◽  
Reciprocating Flow

An experimental and numerical study has been carried out for laminar forced convection in a long pipe heated by uniform heat flux and subjected to a reciprocating flow of air. Transient fluid temperature variations in the two mixing chambers connected to both ends of the heated section were measured. These measurements were used as the thermal boundary conditions for the numerical simulation of the hydrodynamically and thermally developing reciprocating flow in the heated pipe. The coupled governing equations for time-dependent convective heat transfer in the fluid flow and conduction in the wall of the heated tube were solved numerically. The numerical results for time-resolved centerline fuid temperature, cycle-averaged wall temperature, and the space-cycle averaged Nusselt number are shown to be in good agreement with the experimental data. Based on the experimental data, a correlation equation is obtained for the cycle-space averaged Nusselt number in terms of appropriate dimensionless parameters for a laminar reciprocating flow of air in a long pipe with constant heat flux.

A comparative study of lead adsorption by activated Khaya Ivoresnsis and Pycanthus Angolensis sawdust

2016 ◽  
Vol 6 (4) ◽  
pp. 593-601
Author(s):  
Chidozie Charles Nnaji ◽  
Stephen Chinwike Emefu
Keyword(s):  
Experimental Data ◽  
Freundlich Isotherm ◽  
Intraparticle Diffusion ◽  
Bulk Liquid ◽  
Timber Species ◽  
Particle Sizes ◽  
Lead Adsorption ◽  
Intraparticle Diffusion Model ◽  
First Order Kinetics ◽  
Good Agreement

Experiments investigating lead adsorption by activated sawdust of different particle sizes of two timber species were conducted. The experimental data were fitted to isothermal and kinetic models. The optimum particle size was 0.85 mm for Khaya ivorensis and 1.18 mm for Pycanthus angolensis. The adsorption of lead by Khaya ivorensis and Pycanthus angolensis conformed to the Langmuir isotherm (0.83 ≤ R2 ≤ 0.96 and 0.86 ≤ R2 ≤ 0.98, respectively) and Freundlich isotherm (0.69 ≤ R2 ≤ 0.97 and 0.94 ≤ R2 ≤ 1.0, respectively). The adsorption process for the two species of timber was controlled by solute transport in the bulk liquid and intraparticle diffusion which was confirmed by good agreement of experimental data with pseudo-first-order kinetics (0.96 ≤ R2 ≤ 1.0 for Khaya ivorensis and 0.9 ≤ R2 ≤ 1.0 for Pycanthus angolensis) and the intraparticle diffusion model (0.9 ≤ R2 ≤ 0.99 for Khaya ivorensis and 0.84 ≤ R2 ≤ 0.97 for Pycanthus angolensis). A new kinetic model was developed with R2 of 0.93 ≤ R2 ≤ 0.99 for Khaya ivorensis and 0.88 ≤ R2 ≤ 1.0 for Pycanthus angolensis.

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