Environmental Conditions Range for Thermal Calculations

When starting a new application, it’s critical that you determine the environmental conditions your end device will live in. Your environmental conditions will affect how easily your product might reach maximum case temperature. Or maybe your user is in contact with your device and you need to design a safe touch temperature.

In many cases, the application is clear on what temperature range your device may be subject to. It may only require straightforward lab conditions (23-25°C at sea level) to perform well. Other times the application may need to accommodate extreme or harsh environments, which will drastically influence the end user’s experience with your product.

Most of the time you, the thermal designer, don’t have the capacity to control what the end user will do. Think of how you treat your poor smartphone all day; you constantly use it throughout the day, so you are generating heat and draining the battery. You may store it in your pocket next to your own body heat and no airflow to help cool it down. While your end application may not have such high demands as a smartphone, the environmental conditions your device will experience are critical to the overall performance and longevity of your end product.

After you have taken a moment to consider what temperature and altitude you expect, you might find that you have a large range of conditions.

Temperature Range might be somewhat difficult to define, since you may have an upper and lower limit. We’ve seen consumer applications that need to survive from high temperature environments around 100°C, outside in the hot desert at 41°C, and other applications that need to function at -40°C. Space applications have a much wider temperature range, depending on sun exposure.

Then the next key is to determine what temperature to use in your simulation or calculations. We recommend using the highest temperature in your range first. If the simulations determine your heat sink cannot perform well enough in this case, then the heat sink is inadequate for your application.

Altitude might not be on our radar for consideration when we’re determining the environmental conditions our products will experience. But altitude defines how much atmosphere is available for heat transfer. Less dense air at higher altitudes decreases the rate of heat dissipation through air cooling, so heat can build up faster but is typically exposed to colder temperatures.

Most consumer applications will be at or near sea level, but you may want to consider higher altitude conditions for cities such Mexico City or Denver, Colorado with significant populations. Many aerospace and defense devices need to withstand higher atmosphere conditions. Products meant for extreme hikers may be another time where altitude is an important parameter to consider.