CM 3120, Transport / Unit Operations 2
Concept Quiz #1
Spring 2009
Mon. Feb. 02, 2009
Closed Book
1. Heat transfer into a semi-infinite solid
The temperature at the boundary of a semi-infinite solid initially at a temperature of To is suddenly raised to a
higher temperature of T1. If the initial temperature is a constant value as shown by the vertical dashed line, use
the diagram below to draw temperature versus distance into the solid at different times, starting at short time
and then for progressively longer times.
∞
qy
t increasing
y
solid
solid
To
T1
Indicate on the diagram above the direction of the conductive heat flux.
Would the conductive heat flux be larger at early times or at later times? Circle which is correct.
Name the analytical solution method for temperature versus distance and time for the problem shown in the
diagram above.
Combination of Variables solution method.
2. Numerical solution for unsteady-state heat transfer
Pick the numerical finite difference solution method from the list below for unsteady-state heat transfer
problems where the temperature at each node is calculated explicitly from known temperatures at adjacent
nodes at the previous time step.
a) Illicit Method
b) Exquisite Method
c) Explicit Method
d) Simplistic Method
3. Fick’s 1st law of diffusion
Write Fick’s 1st law of diffusion for the molecular diffusive flux in the z direction.
𝑁𝐴𝑧 = −𝑐𝐷𝐴𝐵
𝑑𝑥𝐴
𝑑𝑧
4. Diffusion coefficient for species A in a gas
Would the gas phase diffusion coefficient increase with increasing temperature? Yes or No