The Effect of Forced Convection on Mass and Heat Transfer During Single Coal Particle Combustion

2019 ◽  
Author(s):  
Lele Feng ◽  
Yang Zhang ◽  
Yuxin Wu ◽  
Kailong Xu ◽  
Hai Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Oxygen Concentration ◽  
Turbulent Mixing ◽  
Coal Combustion ◽  
Coal Particle ◽  
Flame Temperature ◽  
Particle Diameter ◽  
Particle Combustion ◽  
Mass And Heat Transfer

Abstract MILD coal combustion is one of promising technologies for clean coal utilization due to uniform heat flux and low NOx emission, while the effect of turbulent mixing on single coal particle combustion under high temperature and low oxygen concentration remains to be studied for micron level particles. In this paper, a 1-D transient coal combustion model was applied to describe mass and heat transfer around a single particle, and the effect of forced convection was modeled to represent turbulent mixing according to similarity analysis. Based on that, effect of particle Reynolds number (Rep) on single coal particle combustion was investigated at various temperature (Ta), oxygen concentration (xO2) and particle diameter (d0). As Rep increases, ignition time (ti) decreases quickly at first and then decreases slowly. ti of larger particle is more sensitive to Rep. As Rep increases, flame temperature (Tf) for 40 μm coal particle decreases, while Tf for 80 μm coal particle barely changes, and that for 160 μm coal particle increases a little. The recommended d0 for MILD coal combustion is smaller than 80 μm. As xO2 decreases from 21% to 5%, ti apparently increases and Tf decreases. ti at lower Ta is more sensitive to Rep. Tf decreases with increasing Rep when Ta < 1200 K. But it appears the opposite trend at Ta = 1600 K. The recommended Ta for MILD coal combustion is lower than 1400 K, while it cannot be too low considering the burnout of char particle.

An Experimental Investigation on Forced Convection Heat Transfer From a Cylinder Embedded in a Packed Bed

1994 ◽  
Vol 116 (1) ◽  
pp. 73-80 ◽  
Author(s):  
K. Nasr ◽  
S. Ramadhyani ◽  
R. Viskanta
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Particle Diameter ◽  
Packed Bed ◽  
Spherical Particles ◽  
Theoretical Equation ◽  
Convection Heat ◽  
Forced Convection Heat Transfer

Forced convection heat transfer from a cylinder embedded in a packed bed of spherical particles was studied experimentally. With air as the working fluid, the effects of particle diameter and particle thermal conductivity were examined for a wide range of thermal conductivities (from 200 W/m K for aluminum to 0.23 W/m K for nylon) and three nominal particle sizes (3 mm, 6 mm, and 13 mm). In the presence of particles, the measured convective heat transfer coefficient was up to seven times higher than that for a bare tube in crossflow. It was found that higher heat transfer coefficients were obtained with smaller particles and higher thermal conductivity packing materials. The experimental data were compared against the predictions of a theory based on Darcy’s law and the boundary layer approximations. While the theoretical equation was moderately successful at predicting the data, improved correlating equations were developed by modifying the form of the theoretical equation to account better for particle diameter and conductivity variations.

scholarly journals Simulation of a continuous plug-flow fluidised bed dryer for rough rice

2014 ◽  
Vol 27 (2) ◽  
pp. 115-124
Author(s):  
Apolinar Picado ◽  
Rafael Gamero
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Transport Coefficients ◽  
Plug Flow ◽  
Particle Diameter ◽  
Fluidised Bed ◽  
Gas Temperature ◽  
Rough Rice ◽  
Mass And Heat Transfer ◽  
Solid Temperature

In this study, a mathematical model to simulate the drying of rough rice in a continuous plug-flow fluidised bed dryer ispresented. Equipment and material models were applied to describe the process. The equipment model was based on thedifferential equations obtained by applying mass and energy balances to each element of the dryer. Concerning the materialmodel, mass and heat transfer rates in a single isolated particle were considered. Mass and heat transfer within the particles wasdescribed by analytical solutions with constant effective transport coefficients. To simulate the dryer, the material model wasimplemented in the equipment model in order to describe the whole process. Calculation results were verified by comparisonwith experimental data from the literature. There was very good agreement between experimental data and simulation. Theeffects of gas temperature and velocity, particle diameter, dry solid flow and solid temperature on the drying process wereinvestigated. It was found that the changes in gas velocity, dry solids flow and solid temperature had essentially no effect ondrying behaviour.DOI: http://dx.doi.org/10.5377/nexo.v27i2.1947

Studies on Coal Ignition and Combustion Characteristics

2017 ◽  
Author(s):  
Xue Chen ◽  
MingYan Gu ◽  
XianHui He ◽  
Dan Yan ◽  
Jimin Wang ◽  
...  
Keyword(s):  
Oxygen Concentration ◽  
Coal Particle ◽  
Gas Flow ◽  
Ignition Time ◽  
Particle Diameter ◽  
Combustion Characteristics ◽  
Gas Temperature ◽  
Flow Temperature ◽  
Particle Ignition ◽  
Coal Particles

A 2-D numerical model of flow, heat transfer, and combustion of coal particles in a laminar gas flow at O2/CO2 atmosphere was developed based on the Eulerian-Lagrangian methodology. The gas-phase combustion was modeled using the GRI-Mech 3.0. The motion of coal particles was simulated using a trajectory model. The model was employed to study the coal ignition time, temperature and mass changes. The effects of particle diameter, the flow temperature and oxygen concentration on the ignition time and the combustion characteristics of coal particles were also investigated. The results obtained show that smaller size particle experiences a shorter ignition time with a higher coal temperature. A higher gas temperature leads to a shorter coal particle ignition time; increasing the flow temperature the difference in the ignition time of different sized coal particles decreases. The coal particle ignition time is decreased when the oxygen concentration is increased.

Numerical Simulation of Laminar Forced Convection Heat Transfer of Two Square Prisms Inside Nanofluids

2012 ◽  
Author(s):  
S. M. H. Jayhooni ◽  
M. H. Nowzari ◽  
K. Jafarpur ◽  
A. Abbasi Baharanchi
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Base Fluid ◽  
Convection Heat Transfer ◽  
Particle Diameter ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Volumetric Concentration ◽  
Forced Convection Heat Transfer ◽  
High Particle

Forced convection heat transfer for steady free stream flow past two isothermal prisms inside different nanofluids has been studied numerically. Nanofluids have been consisted of Al2O3 and CuO nanoparticles with different particle diameters (dnp = 30nm and 100nm) and different particle volumetric concentrations (0% < φ < 4%). Besides, water is used as base fluid for all nanofluids. In this research the recent correlations are used for viscosity and thermal conductivity of nanofluids. The correlations are function of temperature and particle volumetric concentration. The present numerical simulations have been performed for Pe < 200 in which the flow is steady and laminar. The results show that the heat transfer coefficients for all nanofluids are higher than the base fluid (water). These enhancements are more considerable in high Peclet numbers and high particle volumetric concentrations. In addition, among the tested nanofluids, the CuO/water with 4% particle volumetric concentration and 100nm particle diameter finds to be the best nanofluid to increase the heat transfer. The effect of nanofluids on increasing heat transfer is lower for second prism as compared with the first one.

Turbulent Mixing of Two Immiscible Fluids

2003 ◽  
Author(s):  
Thierry Lemenand ◽  
Pascal Dupont ◽  
Dominique Della Valle ◽  
Hassan Peerhossaini
Keyword(s):  
Heat Transfer ◽  
Turbulent Mixing ◽  
Driving Force ◽  
Process Intensification ◽  
Immiscible Fluids ◽  
Manufacturing Industries ◽  
Batch Processes ◽  
Global Trend ◽  
Process Plants ◽  
Mass And Heat Transfer

The global trend in chemical and manufacturing industries is towards improved energy efficiency, cleaner synthesis, reduced environmental impact and smaller, safer, multifunctional process plants. Such concerns are the driving force for the intensification of batch processes, which are being replaced with continuous high-intensity in-line mass- and heat-transfer equipment. In this context the process intensification (PI) approach, in which the fluid dynamics of the process is matched to the reaction in order to improve selectivity and minimize the byproducts, takes on particular importance.

Analysis of Transient Laminar Forced Convection of Nanofluids in Circular Channels

2012 ◽  
Author(s):  
İsmail Ozan Sert ◽  
Nilay Sezer-Uzol ◽  
Sadik Kakac
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Numerical Analysis ◽  
Forced Convection ◽  
Wall Temperature ◽  
Particle Diameter ◽  
Wall Heat Flux ◽  
Transient And Steady State

In this study, forced convection heat transfer characteristics of nanofluids are investigated by numerical analysis of incompressible transient laminar flow in a circular duct under step change in wall temperature and wall heat flux. The thermal responses of the system are obtained by solving energy equation under both transient and steady-state conditions for hydrodynamically fully developed flow. In the analyses, temperature dependent thermo-physical properties are also considered. In the numerical analysis, Al2O3/water nanofluid is assumed as a homogenous single-phase fluid. For the effective thermal conductivity of nanofluids, Hamilton-Crosser model is used together with a model for Brownian motion in the analysis which takes the effects of temperature and the particle diameter into account. Temperature distributions across the tube for a step jump of wall temperature and also wall heat flux are obtained for various times during the transient calculations at a given location for a constant value of Peclet number and a particle diameter. Variations of thermal conductivity in turn, heat transfer enhancement is obtained at various times as a function of nanoparticle volume fractions, at a given nanoparticle diameter and Peclet number. The results are given under transient and steady-state conditions; steady-state conditions are obtained at larger times and enhancements are found by comparison to the base fluid heat transfer coefficient under the same conditions.

scholarly journals Sulfur retention by ash during coal combustion - Part II: A model of the process

2003 ◽  
Vol 68 (3) ◽  
pp. 171-182 ◽  
Author(s):  
Vasilije Manovic ◽  
Borislav Grubor ◽  
Mladen Ilic ◽  
Branimir Jovancicevic
Keyword(s):  
Coal Combustion ◽  
Parametric Analysis ◽  
Coal Particle ◽  
Product Layer ◽  
Coal Rank ◽  
Influence Of Temperature ◽  
Particle Combustion ◽  
Solid Diffusion ◽  
Kinetics Of ◽  
Porous Grains

An overall model for sulfur self-retention in ash during coal particle combustion is developed in this paper. It is assumed that sulfur retention during char combustion occurs due to the reaction between SO2 and CaO in the form of uniformly distributed non-porous grains. Parametric analysis shows that the process of sulfur self-retention is limited by solid diffusion through the non-porous product layer formed on the CaO grains and that the most important coal characteristics which influence sulfur self-retention are coal rank, content of sulfur forms, molar Ca/S ratio and particle radius. A comparison with the experimentally obtained values in a FB reactor showed that the model can adequately predict the kinetics of the process the levels of the obtained values of the SSR efficiencies, as well as the influence of temperature and coal particle size.

Study on Factors Influencing Pulverized Coal Ignition Time

2012 ◽  
Vol 614-615 ◽  
pp. 120-125
Author(s):  
Xiang Gou ◽  
Jin Xiang Wu ◽  
Lian Sheng Liu ◽  
En Yu Wang ◽  
Jun Hu Zhou ◽  
...  
Keyword(s):  
Coal Particle ◽  
Ignition Time ◽  
Flame Temperature ◽  
Particle Diameter ◽  
Pulverized Coal ◽  
Dominant Factor ◽  
Ignition Process ◽  
Heat Absorption ◽  
Convection Heat ◽  
Radiation Heat

Pulverized coal ignition time is one of crucial parameters in coal ignition process. Based on a general heat absorption equation without chemical reaction, this study was focused on some crucial factors which influence pulverized coal ignition time to theoretically explain the mechanism of heat absorption of pulverized coal. The influences of recirculated flue gas (RFG) temperature, flame temperature, primary air temperature, and coal particle diameter on ignition time were discussed. The importance of radiation heat and convection heat was analyzed. The results show that the higher temperatures of RFG, flame, and primary air can lead to the shorter ignition time respectively. The increase of the coal particle diameter greatly increases the ignition time, and as the diameter goes up, the amount of the ignition delay becomes greater. For high accuracy of ignition time calculation, both radiation heat and convection heat should be taken into account. When flame temperature is very high and RFG temperature is very low, radiation is the dominant factor, otherwise convection is more crucial.

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