Thermal Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Applying for a Thermal Engineer job in the UK? Here is what you are likely to be asked. These questions come from our Thermal Engineer question bank of 12 questions, written for UK employers at mid-level level.

Eight Thermal Engineer interview questions, and what the interviewer is thinking

1. How do you determine whether an electronic component will stay within its junction temperature limit, and what are the main levers for reducing it?

Why they ask: This is the most common thermal design check and shows whether you can combine theory with practical design.

2. When would you use CFD and when would you use a simpler analytical or compact model for thermal analysis? Which tools have you used?

Why they ask: They want to confirm your tool experience and your judgement about the level of modelling.

3. What does a thermal engineer do on a typical day, and what qualities make someone good at the job?

Why they ask: They want to see that you understand the role beyond running simulations.

4. How do you size a fan or select cooling for a ventilated enclosure, and what is the relationship between the fan curve and the system curve?

Why they ask: Forced-air cooling is a standard thermal design task requiring both theory and practical judgement.

5. How do you plan and run a thermal test, and what are the main sources of measurement error?

Why they ask: Validation testing is necessary for correlating models and proving designs, and accuracy matters.

6. How would you cool a sealed enclosure, such as an IP67 unit with no fan, that dissipates a significant amount of power?

Why they ask: This is a classic and challenging thermal design problem for outdoor or industrial equipment.

7. Your simulation predicted a component would pass at 85 degrees, but the prototype test shows it at 102 degrees. What do you do?

Why they ask: They want to see a systematic approach to resolving the gap between model and measurement.

8. Tell me about a time you solved a significant thermal problem in a product or system.

Why they ask: They want evidence that you can diagnose and fix real thermal issues.

A sample answer to question 1

How do you determine whether an electronic component will stay within its junction temperature limit, and what are the main levers for reducing it?

I use the thermal resistance network: junction temperature equals ambient temperature plus power dissipated multiplied by the sum of the resistances from junction to case, case to heatsink through the interface material, and heatsink to ambient. I take the junction-to-case value from the datasheet, the interface material resistance from the supplier's data at the actual clamping pressure, and the heatsink-to-air value from the manufacturer's curves or from a CFD or hand calculation for the actual airflow. I use worst-case ambient and maximum power, then apply a margin, typically 10 to 20 degrees below the rated maximum, or whatever the reliability derating policy specifies. The main levers are reducing the power, improving the interface material and flatness, increasing heatsink area or airflow, spreading heat into a copper plane or heat pipe, and lowering the ambient. I then check the result by simulation and measurement, because datasheet values are idealised.

Common mistake to avoid: Using typical ambient instead of worst case; ignoring interface material resistance

Want the rest?

Full model answers, key points and common mistakes for all 12 questions are on the Thermal Engineer interview questions page. The first five are free, no sign-up needed.