Category Archives: Thermal Design

Understanding how fluid boils in tiny “microchannels” gives engineers another tool to cool high-power electronics

Yesterday we let everyone know about “Understanding Boiling Heat Transfer: a “how to” article from ATS Thermal Labs“.  Hopefully you had a chance to look at our “how to” article as a basic understanding of this important concept.  And there’s relatively new research in this space that’s worth a look as well.

As reported in Purdue University News,  out at Purdue University’s labs, Indiana’s 21st Century Research and Technology Fund has provided $1.9 million to Purdue and Delphi Corp. in Kokomo, Ind., to help commercialize an advanced cooling system using boiling die-electric liquid in microchannels to cool electronic components in hybrid and electric cars.

Tannaz Harirchian, a doctoral student on the project noted that:

One big question has always been, where is the transition from macroscale boiling to microscale boiling?  How do you define a microchannel versus a macrochannel, and at what point do we need to apply different models to design systems? Now we have an answer.

Here is an abstract of the work being done:

ABSTRACT

Boiling Heat Transfer and Flow Regimes in Microchannels – a Comprehensive Understanding

Suresh V. Garimella and Tannaz Harirchian

Cooling Technologies Research Center
School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University

Although flow boiling in microscale passages has received much attention over the last decade, the implementation of microchannel heat sinks operating in the two-phase regime in practical applications has lagged due to the complexity of boiling phenomena at the microscale. This has led to difficulties in predicting the heat transfer rates that can be achieved as a function of the governing parameters. From extensive experimental work and analysis conducted in recent years in the authors’ group, a clear picture has emerged that promises to enable prediction of flow boiling heat transfer over a wide parameter space. Experiments have been conducted to determine the effects of important geometric parameters such as channel width, depth, and cross-sectional area, operating conditions such as mass flux, heat flux and vapor quality, as well as fluid properties, on flow regimes, pressure drops and heat transfer coefficients in microchannels. High-speed flow visualizations have led to a detailed mapping of flow regimes occurring under different conditions. In addition, quantitative criteria for the transition between macro- and micro-scale boiling behavior have been identified. These recent advances towards a comprehensive understanding of flow boiling in microchannels are summarized here.

There’s more on the boil at Purdue University and the applications for the research are far-reaching beyond cooling just automotive electronics.  Click to “New findings could help hybrid, electric cars keep their cool” so you can have a read of the Purdue University News Article with links to the research.

Understanding Boiling Heat Transfer: a “how to” article from ATS Thermal Labs

With the advent of hybrid automobiles as well as high powered electronics, we are seeing more and more environments in which the heat flux in components is exceeding 1000w/c2. High heat transfer cooling mechanisms are needed to bring their junction temperatures to acceptable operating levels. One of the promising methods for high capacity cooling is boiling heat transfer. ATS Labs has put together a tutorial around that topic to provide a base level of information to help the thermal engineering professional and interested others understand this important topic. You can access it here:
Understanding Boiling Heat Transfer for Electronics Thermal Management

LED Lighting Needs Good Thermal Design for Long Life

Over at Electronics Weekly, Adrian Rawlinson has a nice article on the necessity of LED lighting to have good thermal design. While LED lights are cool on the surface, the electronics that drive them are hot! Heat sinks and good thermal design are a necessity.

Adrian notes, among other things that:

  • LED Lights are moving into the 35W range giving them almost blinding brightness and the commensurate is hot
  • LED’s are driven by electronics and that means IC’s. The basic thermal building block here is junction temperature. And that has to be managed somehow for the electronics and therefor the light to have a reasonable service life.

There’s alot more worth reading in his article, “Good Thermal Design Extends LED Lifetimes”

ATS has done quite a bit of work in this area as well, through our work with Lemnis Lighting cooling 75W LED and our being an LED partner with Digi-Key we’ve applied the basics of thermal design to LED with great success.

ATS has an article we published in QPedia on Thermal Design for LED Lighting we’d invite our readers to view, you can find it at: “Cooling High Power LED’s“

Cavity up or cavity down? The case of the failed system and how up front thermal design could have saved it.

“It is always nice to read a success story but from a professional point of view I find failure stories more interesting. They are often truly sad but they do push things forward. Experience is also to a large extent based on mistakes made. A thermal designer that has a large stack of failure stories is therefore well equipped for the job.”   With that introduction, we invite you to read about this particular failure and what can be learned to make your next design more thermally sound and more likely to succeed.  Please click to, “Not a Success Story” at Frigus Primore to learn how the wrong choice in cavity type for a semiconductor impacted an entire system (and what you can do differently!)

The fallacy of the drop in replacement heat sink

Sometimes we get requests for heat sinks that go something like this:

Requester: “I need a heat sink that looks like [insert other manufacturer here].  Can you like, just cross it over? You know, anything will do as long as it looks kinda like what I need”

ATS Engineer: “Okay, so is this heat sink you need going on a CPU, or a DSP?

Requester: “Umm, its hot, I know that.  Really hot”

ATS Engineer: “Okay, well we can work with that.  Can you tell  us if there is a fan near the device?

Requester: “We  have a big fan, really big. Lots of air moving in that box now let me tell you”.

ATS Engineer: “Right then. We’ve got a super hot chip and a hurricane worth of air moving around, do I have that right?”

Requester: “Yes, exactly!”

What we have exactly is a sincere request but not a whole lot of information by which to be helpful.

The fact is, drop in replacement heat sinks rarely are.  There are many vectors of design when doing a thermal design. Slapping any old heat sink on and attaching a giant fan may simply not work or be way too expensive.

So what to do?

Well, to the rescue is ATS with our handy ATS Heat Sink Questionnaire.  We use this all the time and it is ideal for us (and likely for other engineers too) to gleen the key data necessary to start coming up with the right heat sink, heat sink attach, and thermal interface material necessary to cool a projects hot processor.

We love to hear from our customer’s toughest problems because out of 4000 different heat sink designs we probably have something off the shelf to make  your CPU or other hot thingy cool, reduce the size of your hurricane force fan, and give you a more cost effective and elegant solution.