3 steps to implement passive two-phase cooling in your modern electronics

Is it the end of your air-cooled system?

You are likely using forced air to cool down your high-power electronics today. But no doubt you are starting to notice that for the modern electronics you implement in your system, air is no longer effective. The temperature of your electronics remains too high. And besides that, air entering your system brings impurities (dust, salt fog, …).

You are therefore investigating a new way of cooling in order to:

• reduce the temperature of your high-power device
• not add too much complexity to its integration (no additional infrastructure requirements such as power input, water connection, ...)
• and still ensure reliability and long lifetime during operation

So, is this the end of your air-cooled system?

Not necessarily.

The limitations in that case are not always related to the air itself, but to the location where you exchange the heat. When you bring the air closer to your electronics, the heat exchange area between your heat sink and the air is limited by the size of your electronics and the maximum volume of your package. This therefore limits the maximum power you can dissipate and your ability to manage high heat flux.

This is why, in these cases,  adding passive two-phase liquid cooling is the practical solution :

• to provide high-performance cooling
• to keep integration simple and passive
• to gain more autonomy and avoid the need for your customer to have new infrastructure (power & cooling infrastructure)
• to ensure reliability over time

But how can you implement it?

Here are 3 steps below that help you integrate passive two-phase cooling into your system.

Step 1: Consolidate your thermal specifications clearly

A good practice is to start by gathering detailed information on your system.

Define clearly:

• the heat source
• the cold source
• the cooling environment

I’ve provided you below with a prefeasibility sheet that gives you detailed requirements.

Download the Specifications sheet

At early project stages, all these specifications may not be defined yet. But try to quickly evaluate these key parameters as a priority:

• power to dissipate
• heat density (presence of hotspots or not)
• temperature of your hot source (junction/case)
• temperature of the cold source
• available volume for the overall cooling system

Trick: for the cold source, feel free to think more broadly. If air is a first candidate, another option we may not always consider is a solid surface, such as an existing chassis or wall, which, like air, must be at a lower temperature than your heat source.

See integration example below:

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Step 2: Choose the right two-phase concept

Once your specifications are clearly defined, you need to choose which passive two-phase cooling technology fits your system. The solution you first think of may not always be the one your system needs.

The choice between: Multi-channel heat pipes (MCHP), Loop Heat Pipes (LHP),  Loop Thermosyphons (LTS), Pulsating Heat Pipes,

depends on:

• the form factor of your electronics
• the power to dissipate
• the heat flux

I invite you to check our website to download white papers related to each technology, or to contact us directly for further guidance.

Step 3: Evaluate the performance in your system

Let’s now evaluate the performance of passive cooling within your system. Based on your system specifications and the selected concept, these inputs are used in a thermal chain model . One example is presented below.

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This model:

• simulates the heat path
• evaluates temperatures at multiple levels
• analyzes the evolution of heat flux and heat spreading throughout the system

The resulting case/junction temperature is therefore your target.

With this simulation, we are able to identify where the design of your system can be improved and provide you cost insights.

The Hidden side of Two-phase cooling

If the operation of two-phase cooling brings multiple benefits, one of the main challenges in its implementation is estimating the heat transfer coefficient at the vaporization stage. Bubble formation is a chaotic phenomenon and cannot be fully simulated with traditional thermal models.

To address this challenge, Calyos develops semi-empirical models, combined with FEM analysis, and validated through laboratory testing and numerical tools. However, the most relevant results are faster achieved by combining our two-phase cooling expertise with your in-depth knowledge of your system and application.

What’s next?

Once the prefeasibility is validated, the most exciting part is yet to come.

The vaporization process has the capacity to reduce the temperature of your electronics so effectively that you may reach temperature values much lower than your initial target.

This benefit can be translated into:

• System size reduction
• Fan noise reduction
• Fan power reduction

This is where you can build even more innovation for your customer, simply by being strategic with your thermal management. The application of two-phase cooling however still varies for each component, each application, and each environment.

Feel free to reach out if you have any question regarding your application.

info@calyos-tm.com