Feature
volume, and an initial air temperature
of 22ºC was assigned to the brick surroundings. The transient model was
run for 14 hours, saving data every
hour. Variations of fluid volume, brick
mesh size, and solver time step were
completed to determine a satisfactory
trade off between accuracy and solve
time. The results of the simulation, and
the corresponding actual data for the
three TC locations, are shown in Figures 2a, 2b, and 2c, respectively.
As shown in the figures, the agreement between the actual TC data and
the simulation results is reasonably
good. The ramp rate from –20º to 0ºC
and the phase change time for each TC
location are close to actual data. As the
phase change time is of critical importance, these initial results are certainly
promising.
To improve upon the simulation,
however, deviations with actual data
must be analyzed and corrected via compounding. In TC locations A and B, for
example, the values of the simulations at
the end of phase change are higher than
actual data, but the slopes appear to be
correct. In location C the shape of the
simulated phase change curve at the end
26
24
22
20
18
16
14
12
Temperature (ºC)
10
8
6
4
2
0
- 2
- 4
- 6
- 8
- 10
-12
- 14
- 16
- 18
- 20
-22
012345
Location A Data: TC 01 03
Location A Data: Node 49537
Ambient Temperature
6 7 8 9 10 11 12 13
Time (hrs.)
78.8
75.2
71.6
68.0
64.4
60.8
57.2
53.6
50.0
46.4
42.8
39.2
35.6
32.0
28.4
24.8
21.2
Temperature (ºF)
17. 6
14.0
10. 4
6. 8
3. 2
-0.4
- 4.0
- 7. 6
14
Figure 2c: Foam Brick Phase Change Data vs. Simulation for TC location “C.” Here the shape of the
simulated phase change curve at the end of phase change is not accurate compared to actual data.
of phase change is not accurate compared with actual data. These deviations
can be explained by considering the
material properties input into the analysis
program. Specifically, the variation in
specific heat with temperature was input
into the program as a “step” function
26
24
22
20
18
16
14
12
Temperature (ºC)
10
8
6
4
2
0
- 2
- 4
- 6
- 8
- 10
-12
- 14
- 16
- 18
- 20
-22
012345
78.8
75.2
71.6
68.0
64.4
60.8
57.2
53.6
50.0
46.4
42.8
39.2
35.6
32.0
28.4
24.8
21.2
Temperature (ºF)
17. 6
14.0
10. 4
6. 8
3. 2
-0.4
- 4.0
- 7. 6
13 14
(one value for solid that is switched to
a different value for liquid).
In reality, the specific heat versus
temperature will be smooth, showing
much more of a curve. As such, the
shape of the transient simulation curve
will tend to “mirror” the specific heat
versus temperature curve input into the
program. Specific heat versus temperature data are being generated at CCT,
as part of the model validation process,
and will be used during future simulation runs to further compound and
validate the model.
Location A Data: TC 01 03
Location A Data: Node 49537
Ambient Temperature
VALIDATION OF FREE
CONVECTION, CONDUCTION,
PAYLOAD GEOMETRY AND
MATERIAL PROPERTIES
Experiments, similar to refrigerant phase change described above, are
being designed to extend the validation
process to:
6 7 8 9 10 11 12
Time (hrs.)
• Free convection.
• Conduction.
• Payload geometry.
• Material properties.
Figure 2b: Foam Brick Phase Change Data vs. Simulation for TC location “B.” Here, and in Figure A, the
values of the simulations at the end of phase change are higher than actual data, but the slopes appear
correct.
Free convection and conduction
experiments will involve the use of
