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Advection-Is that what you call it?

In my line of work I spend a fair amount of time analyzing,designing, optimizing, and describing heat transfer paths.  Depending on the device and environment under study different modes of heat transfer are considered.  If I am talking about an IC or a sealed enclosure the mechanisms of heat transfer that could be relevant are radiation, convection, and conduction, listed in no particular order.  If I am talking about an enclosure that is vented I like to include an additional mode that I refer to as advection.  Even as I type that word my spell checker is confused and wants to offer up convection.  When I say advection I am referring to that bit of heat that is carried out with the flow.  For a forced convection system, those which have fans for instance, advection through the vents accounts for 90%+ of the heat removal.  For a natural convection system a pie chart of the various modes of heat transfer from the enclosure might look like this:

heattransferpaths1
Clearly in this case the heat is leaving this enclosure primarily due to convection and radiation.  Heat conduction through the stand-offs, and the heat leaving through the vents (advection) are insignificant.  It is important though, I believe, to break out the part that is leaving with the fluid.  There are situations where it may seem viable to increase the size or the number of vents in the enclosure because in our minds we can visualize the air swooping in to pick up the heat and jet out the other side.  The reality is that often times it makes no difference and to communicate that I break it out as a separate term.

Am I the only one who calls it advection?!?!  Based on a quick search on the web for definitions of advection it would seem so.  Convection seems to be the catch-all word to cover this kind of heat transfer.

I am curious what you call it.

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About John Wilson

John WilsonJohn Wilson joined Mentor Graphics Corporation, Mechanical Analysis Division (formerly Flomerics Ltd) in 1999. John has worked on or managed more than 100 thermal and airflow design projects. His modeling and design knowledge range from Electronics Cooling IC packaging level to Data Centers and Clean Rooms. He has extensive experience in IC package level test and analysis correlation through his work at Mentor Graphics' San Jose based Thermal Test Facility. He is currently the Consulting Engineering Manager, WRO in the Mechanical Analysis Division. Visit John R Wilson's Blog

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Hi John, Great article! I think of advection a little bit differently. If you have some cold water and you want to make it boil and you have some very hot rocks you could put the rocks into the water. This movement of heat with the rocks as the medium is what I would call advection. The dictionary doesn’t support this but it seems that advection is not a steady state thing, more of a one time transient movement of heat.

Joe Proulx
3:23 PM Nov 5, 2009

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