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CHEMICAL
ENGINEERING
120B
Homework 4 
due Friday,
February 18, 2011
1. A drop of water at 25 C is thrown onto a hot copper frying pan. How hot must the frying pan be in order for
the drop to 'sizzle' (boil a thin layer) on contact?
2. Consider a plate of thickness
d
and thermal diffusivity
CY.
One edge (z = 0) is heated in an oscillatory fas hion,
with
T(z
= 0,
t)
=
To coswt
J~
(e
iwt
) .
The other end is insulating
(dT/dz
= 0 at z =
d).
[,(1)
a. Before doing any detailed calculations, from dimensional or scaling arguments, figure out a frequency where the
solution will change qua litatively. That is  above a certain frequency scale, the temperature in the plate will look
a certain way, 'whereas below that frequency scale, it looks completely different. What do you expect will happen?
Describe it physically in terms of how long it conduction takes.
(to)
b. Nondimensionalize the differential equations, choosing z =
d(, T
=
Toe,
and
t
=
i/w,
where
t,
(),
and ( are
dimensionless variables. v"hat dimensionless parameter appears? \\'hat does it correspond to?
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This note was uploaded on 12/29/2011 for the course CHE 120B taught by Professor Zasadinski during the Fall '10 term at UCSB.
 Fall '10
 Zasadinski

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