Which cooling design would you take to the next test?
Reassess two cooling options after an electrical budget changes.
The question
A fictional survey aircraft ground prototype needs sensor cooling. The module limit is 2.6 kg and its case temperature limit is 65°C. The initial power allowance is an unconfirmed 20 W.
| Passive spreader | Fan module | |
|---|---|---|
| Mass (kg) | 2.4 | 1.5 |
| Electrical draw (W) | 0 | 18 |
| Estimated case temperature (°C) | 62 | 56 |
The two temperature estimates use the same modeled hot condition.
“Which cooling design would you take to the next test?”
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A strong answer, step by step
Open each step in turn. This is one strong answer, not the only one.
Step 1: How would you compare the options?
What would you do here? Open the move you’d make.
Commit to the fan because it is the lighter option.
Tempting, but it misses something. Power remains unconfirmed. The estimate alone does not settle the design.
Recommend the fan conditionally and state which limit you need to check.
The strong move. This uses the preliminary trade-off and makes its dependency visible.
Reject the passive option because its estimate is warmer.
Tempting, but it misses something. Its 62°C estimate is within the 65°C limit.
See how a strong candidate says it
“Both options fit the planning limits. The fan is lighter and has the lower estimated temperature. I would carry it forward subject to confirmation of usable power.”
Why it works: The comparison depends on three limits and a shared set of conditions.
Step 2: What would you ask the electrical owner?
What would you do here? Open the move you’d make.
Ask for the usable share with the other equipment active.
The strong move. This checks the constraint at the condition in the decision.
Ask only for the total rating of the supply.
Tempting, but it misses something. The total leaves the other equipment’s draw unaccounted for.
Accept 20 W because it is in the first table.
Tempting, but it misses something. The allowance is explicitly awaiting confirmation.
See how a strong candidate says it
“How much power is available to the cooling module when the other equipment runs at the same hot operating condition?”
Why it works: The share available during operation matters more than the preliminary allowance.
Step 3: Which option would you take to the next test?
The electrical owner measures 8 W available for cooling with the other equipment active at the same hot condition. The mass and temperature limits are unchanged.
What would you do here? Open the move you’d make.
Choose the fan because it gives 9°C of estimated thermal margin.
Tempting, but it misses something. The larger thermal margin does not supply the missing electrical power.
Assume the fan can run intermittently and keep its temperature estimate.
Tempting, but it misses something. That changes how the fan works. Its temperature estimate needs a new check.
Advance the passive option and verify the estimated margins in the system.
The strong move. It fits the available power and has positive estimated mass and thermal margins.
See how a strong candidate says it
“The fan needs 10 W more than is available. Take the passive spreader to the next integrated test. The estimate gives 0.2 kg of mass margin and 3°C of thermal margin.”
Why it works: The latest power limit changes which option fits the current system.
Step 4: What could change your choice?
What would you do here? Open the move you’d make.
Verify the selected option in the intended load and mount.
The strong move. This gives evidence for the current recommendation.
Report the passive estimate as a verified result.
Tempting, but it misses something. The packet gives a model estimate. The integrated test is still due.
Remove the fan from all future options.
Tempting, but it misses something. A different verified power allocation would justify another comparison.
See how a strong candidate says it
“Check the passive case temperature and module mass in the representative installation. Reopen the fan option if 18 W is available in that condition and the updated system test supports it.”
Why it works: The next test addresses the estimates that the recommendation depends on.
The answer, in short
- Decision
- Use the passive spreader for the next integrated test.
- Because
- The fan needs 18 W. The current system has 8 W available.
- What would change it
- Representative temperature evidence or a verified change in available power.
Common traps
- Optimizing one measure while missing another limit.
- Comparing a measured power limit with an unchecked assumption.
Check your answer
- Which constraints apply?
- Which values are estimates?
- Why did the recommendation change?
- What would the next test establish?
Last reviewed Nov 11, 2026