30 Control for Aluminum Production
On the whiteboard Barry was doing heat transfer 101 for them:
Q = U A ΔT
LMTD
where
Q = Heat duty to achieve target temperatures, either to the dry aggregate,
pitch, or the paste, kW.
A = Heat exchange surface area, which can become fouled by burned pitch,
paste, or deposits from HTF, thereby increasing its resistance to heat
transfer signicantly.
U = The overall heat transfer coefcient, which includes any ‘fouled’
surfaces.
ΔT
LMTD
= Log mean temperature difference between the HTF and either the
aggregate, paste, or pitch. If U decreases over time, this temperature
difference must increase in order to transfer Q, in order to meet
thetarget temperatures.
Now Barry was leaning over the drawings and pointing. “ ...