MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...

The burnout and particle velocity data were used to validate the model. It was
assumed that the particle velocities are always equal to the local gas velocities. This
assumption is commonly accepted for entrained-flow, pulverized-char combustion. Gas
velocity is proportional to gas temperature. The final velocities of particles measured by
Monson (1992) were used to calculate the gas velocity (and hence particle velocity) at
any location between the injection point (x = L) and the collection point (x = 0):
V p (x) = V g (x) = V g (0) T g (x)
T g (0)
where x is the distance from the collection point.
The wall temperatures in the HPCP furnace were not uniform. Three
thermocouple were used by Monson (1992) to measure the wall temperatures at three
locations: x 1 = 1.3 cm, x 2 = 6.4 cm, and x 3 = 16.5 cm. Non-uniform wall temperatures
were correlated using a quadratic equation:
where a =
107
(7.13)
T w (x) = ax 2 + bx + c (7.14)
T1 − T2 −
x1 − x 2
T1 − T3 x1 − x3 x 2 − x3 b = T 1 − T 2
x 1 − x 2
2
c = T1 − ax1 − bx1
− a(x 1 + x 2 )
where T 1, T 2 and T 3 are wall temperatures at axial locations x 1, x 2 and x 3, respectively.
These wall temperature data were from Monson’s experimental records, and to the
author’s knowledge have never been published before. These wall temperature profiles
were used directly in the HP-CBK model. A burning char particle interacts with the non-
uniform wall temperatures through radiative heat transfer. In order to simplify the