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James

Mon Apr 18 2011, 11:23PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Computer equipment recycle events are a great place to get heatsinks. Dell and other OEM boxes that don't use a separate CPU fan typically have a large heavy aluminum heatsink. The power supplies are a small goldmine of power electronics components too.

cjk2

Tue Apr 19 2011, 03:28AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

Dalus wrote ...

Free can also be very nice

016 by roy.piepers, on Flickr

Just some alu and people wanting to spend some time with it

Are you worried about corrosion due to dissimilar metals touching? Aluminum and the plating on the bottom of the IGBT's?

Patrick

Tue Apr 19 2011, 06:26AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

cjk2 wrote ...

Are you worried about corrosion due to dissimilar metals touching? Aluminum and the plating on the bottom of the IGBT's?

This is a great question, had i not been full of booze i may have asked it myself.

James

Tue Apr 19 2011, 04:59PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

You could use a mixture of water and automotive antifreeze if you're worried about corrosion. The stuff made specifically for alloy engines has corrosion inhibitors to deal with dissimilar metals. The engine in my car has a cast iron block, aluminum head, brass coolant temp sensors, bronze water pump impeller, etc and it's made it ~25 years without corroding.

Ash Small

Tue Apr 19 2011, 05:49PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Using oil would be even better as far as corrosion is concerned, it would also cool it more efficiently (ie run cooler), as long as it isn't too viscous (ie you have sufficient circulation)

EDIT: see post below

Tightmopedman9

Tue Apr 19 2011, 09:26PM

Registered Member #3197 Joined: Tue Sept 14 2010, 04:56PM
Location:
Posts: 19

Ash Small wrote ...

Using oil would be even better as far as corrosion is concerned, it would also cool it more efficiently (ie run cooler), as long as it isn't too viscous (ie you have sufficient circulation)

I don't see how oil would be more effcient at all. Water has a much higher specific heat and it is less compressible. Therefore it would extract more heat and be easier to pump.

Dalus

Tue Apr 19 2011, 09:40PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

At the moment it'll be used open loop. Enough zinc in there to be eaten away first. If I where to run the system for weeks I might consider a closed loop with a heath exchanger and proper coolant.

Ash Small

Tue Apr 19 2011, 10:22PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Tightmopedman9 wrote ...

.
I don't see how oil would be more effcient at all. Water has a much higher specific heat and it is less compressible. Therefore it would extract more heat and be easier to pump.

In my youth I attended a metalwork course where the lectureres took great lengths to impress upon us that 'at the same temperature, oil is colder than water' (I remember the exact words to this day). I remember arguing with them that oil has a greater specific heat capacity than water but is not colder at the same temperature. (this was when we were being taught heat treatment and quenching)

Oil cooling is better than water cooling, ask anyone who rides a Suzuki.

EDIT: see post below, this appears to be incorrect.

Myke

Wed Apr 20 2011, 04:55AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Ash Small wrote ...

I'm pretty sure water has one of the highest specific heat capacities at 4.184 kJ/kg*k^-1... Oils are around 2 kJ/kg*k^-1 from what I see. Oil has a much higher boiling point than water, harder to ionize, and less corrosive which makes it a great coolant.

Ash Small

Wed Apr 20 2011, 10:47AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Myke wrote ...

.
I'm pretty sure water has one of the highest specific heat capacities at 4.184 kJ/kg*k^-1... Oils are around 2 kJ/kg*k^-1 from what I see. Oil has a much higher boiling point than water, harder to ionize, and less corrosive which makes it a great coolant.

From Wikipedea:

"Water is one of the most efficient quenching media where maximum hardness is acquired, but there is a small chance that it may cause distortion and tiny cracking. When hardness can be sacrificed, whale, cottonseed and mineral oils are used. These often tend to oxidize and form a sludge, which consequently lowers the efficiency. The quenching velocity (cooling rate) of oil is much less than water."

It looks like you are correct and my lecturers were wrong. I take back what I said.

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