Design Guidelines for High Performance Industrial Furnaces - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 310

Heated surface (C)

Furnace wall,
reflection surface (R)

Furnace wall,
reflection surface (R)

There exists no
heat radiation
by gas

Heating surface (H)

FIGURE 5.68 Heat transfer in furnace in case of no radiation combustion gas.

TABLE 5.23
Comparison and Model of φ CH and φ CG
φ CH φ CG

Furnace Furnace that has no radiation gas in furnace,

such as a radiant tube heat treatment
furnace, electric heating furnace, etc.

Furnace that has radiation combustion gas
in furnace, such as direct heating furnace

Model
equations

A
A

1 1 1 1

1 1 1

= +

C

1 + 1

= + 1

φ ε ε

*

φ

*

ε

F F CH H H C

CG G

CH

CG

*

FFF F

A
A

*

=+

* * RC *

F = ε

G

×

CH CH RH *

1- F

CG g

RR T

F

=+ FF

RC

ε = 0

CH RH g

1 F A

A

1

RR

1 +

R

A
A

1

= F

C

1 +

T

ε

CH

g

F

G RC

A C = area of heated surface A T = total surface area of furnace wall

A H = area of heating surface A G = surface area of gas body

ε C = emissivity of heated surface A R = area of reflection surface

ε H = emissivity of heating surface ε g = emissivity of gas

F ij = shape factor
F ij * = shape factor under consideration of

gas radiation
F ij * = shape factor under consideration of

--

both gas radiation and reflecting

surface