Metallurgical and Materials Transactions B

, Volume 44, Issue 1, pp 196–209

A Study of Scrap Heating by Burners: Part II—Numerical Modeling

Article

Abstract

A computational fluid dynamics code was developed to model the heating of a bed of porous steel scrap by combustion gases from a burner. The code accounted for nonuniform void fraction in the bed; turbulent, non-Darcian flow, heat transfer from the gas to the scrap; and radiation. The measured bed porosity values were used in the code. Because steel scrap pieces are very irregular in shape and size, the effective particle diameter was fitted to measurements made in a 1-m3 capacity furnace, as reported in part I. It was found that the lower porosity of the scrap was the most beneficial in increasing the efficiency of heat transfer to the scrap bed because the interfacial area is larger. The effect of particle size was much smaller. It was found that the configurations that increased the residence time or path length of the gases increased the efficiency. The measured porosity of the bed approached unity at the walls, so this provided an easy path for the gas to short-circuit the bed, which limited the effectiveness of decreasing the porosity to increase heat-transfer efficiency. Similarly, simulations of nonuniform scrap distributions reduced efficiency of heat transfer due to short circuiting. The implications of the findings for industrial operations are discussed.

Nomenclature

Abbreviations

ReP

pore Reynolds number

Re

Reynolds number

Subscript

f

fluid

s

solid

Greek

β

thermal expansion coefficient

φ

local porosity

φ

porosity from the far away from the boundary or wall

σ

Stefan–Boltzmann constant

σk

k–ε model constant

σε

k–ε model constant

ρ

Fluid density

ε

dissipation rate of turbulent kinetic energy

μ

fluid viscosity

μeff

effective fluid viscosity

μl

laminar fluid viscosity

μT

turbulent fluid viscosity

νf

kinematic viscosity of the fluid

ΔP

pressure gradient

ΔT

temperature difference between the local and reference temperatures

Roman

a

parameter

b

parameter

AS

surface area

C

specific heat

CP(gas)

specific heat of gas

CP(R)

specific heat of refractory

Cμ

k–ε model constant

Ck

porous media k–ε model constant

dP

particle diameter

E

emissivity

F

drag coefficient or Geometric factor

g

acceleration due to gravity

GK

volumetric rate of turbulent production

hv

volumetric heat transfer coefficient

hfS

heat transfer coefficient between fluid and solid

K

permeability

Keff

effective thermal conductivity

Ks

thermal conductivity of solid

Kr

radiative conductivity

Kf

thermal conductivity of fluid

Kfeff

effective thermal conductivity of fluid

Kseff

effective thermal conductivity of solid

k

turbulent kinetic energy

L

characteristic length

qr

heat flux due to radiation

SK

source term in turbulent kinetic energy equation

Sε

source term in the dissipation rate of turbulent kinetic energy equation

t

time

TS

solid temperature

Tf

fluid temperature

Tflame

flame temperature

Texhaust

exhaust gas temperature

Tambient

ambient temperature

uf

fluid velocity in x-direction

vf

fluid velocity in y-direction

Vd

Darcy velocity

VP

pore velocity

wf

fluid velocity in z-direction

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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2012

Authors and Affiliations

  1. 1.Severstal ColumbusColumbusUSA
  2. 2.Steel Research CentreMcMaster UniversityHamiltonCanada

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