Boiling to Keep Cool...?

iStock-1081367188When something is boiling that means it’s hot, right?  That’s not necessarily the case to some researchers, including thermal engineers at Advanced Cooling Technologies. Experts in Pumped Two Phase Cooling (P2P) intentionally design cooling systems so that the working fluid that cools the hot device boils when it comes in contact with it. 

They do this because they want the vapor to help take the heat away. The principle that these engineers are taking benefit from is ‘the heat of vaporization’, also known as latent heat.  The heat of vaporization is the energy that must be added to the substance, typically a liquid, to transform a portion of that substance into a vapor. In other words, for a working fluid near its boiling point, one can keep adding heat without increasing the temperature of either the heat source or the working fluid.  The additional heat is being absorbed as the working fluid begins boiling and transforming from a pure liquid to a liquid/vapor mixture.  A visual of the P2P effect can be seen in the video, where the vapor bubbles are created as the working fluid passes over the heat source below.  The bubbles assist in removing the heat.

 

That’s cool (haha), but so what?  Well, in most cases this heat of vaporization effect offers a 2-4x increase in heat transport capability, compared to conventional liquid cooling systems.  This means P2P can remove a lot more heat.  Additionally, the required flow rates for P2P systems are significantly reduced, requiring much smaller pumps.  In one example of cooling an 80kW heat source, converting from a pumped liquid system to P2P, the required fluid flow rate was reduced 80% resulting in a 95% power savings!  Even cooler, well designed P2P systems boil uniformly across the heat source resulting in uniform temperature distribution, which is critical in many sensitive high-powered laser applications. 

 So, the next time you’re in the kitchen preparing for nice cup of tea, maybe think how cool that boiling water is!