Heat exchanger for sealed case?

[firtol88]

I'm thinking of building a mini-itx system in a sealed case so it can live outside.

Just wondering if anyone has run into a small heat exchanger set-up Smaller than the 400 BTU model on this page


TIA

 

[Ice Czar]

what is the total heat load?

would this be where compressed air is available?
a vortex tube could be employed

 

[Little Grabbi]

How about running a W/C system with two radiators, one inside, one outside. Might work.

 

[HeThatKnows]

Watercooling it. A big rad outside to dump all the heat, and a small rad inside to keep the internal air from getting too hot.

400 BTU/hr is only 117 watts; that little peltier heat exchanger you linked to won't cut it unless you're using one of Via's CPUs. You'd want the 1500 BTU model. Oh, and those thing use tons of electricity.

 

[firtol88]

Nope no compressed air but I agree that some of those systems look nice.

Water is out because I want to keep it 'retired Father-in-law simple', it's going to be a wireless steaming music reciever. It will be mounted on a dock at my In-laws property, power will come from an existing lighting system (not a problem), I plan on using a via mini-itx or nano-itx board w/ a via CPU.

As for total heat characteristics I have no idea though I think the PSU will be more of a problem than any other individual component. Heat will be an Issue since they live in Louisiana, as would humidity (thus the sealed case). I plan on making some kind of shade to avoid direct sunlight but ambient temps will be in the upper 90s at times. Via lists up to 60+C(140+F) as an acceptable operating environment so if I can keep the case close to ambient it should be OK (never thought I would think of 100F as an acceptable case temp LOL)

I keep going back to 2 Large (3" x 10" x 3") heatsinks epoxied and bolted together one inside and one outside the enclosure but don't think it would offer enough cooling, maybe with a pelt...

Anyway any ideas are welcome... TIA

 

[Ice Czar]

a good read >
General Heat Transfer Guide @ amdmb written specifically about the thermodynamics of computers, and focusing on aircooling
ProCooling Article base well worth a browse, also check the forum and specifically the ProCooling Staff Worklogs

one of the things you can draw from the first article is
The heat transfer through the wall follows a simple equation:
Q=k/L(T1-T2)

my comments below in italics

We can draw some interesting conclusions from this equation. First, heat transfer is proportional to the temperature difference on the object. If the temperature differential doubles, the heat transferred doubles.If the temperature of your air is colder the efficiency increases Second, the conduction coefficient "k" is proportional to heat transfer. If the conduction coefficient doubles, the heat transfer doubles.Applys to the material, generally copper, which has a better conduction coefficient than say aluminum Alternatively, for the same differential temperature, twice as much heat may be transferred. The final observation is "L". As thickness increases, heat transfer decreases. Alternatively, to maintain the same heat transfer through a material twice as thick requires twice the temperature differential.

that happens to be for conduction, but there is a corrallary for convection (transfer from the heatsink to a fluid (air\water\ect)
its known as Newton's Law of Cooling

so what the hell is my point?
whatever thermal solution you have is typically rated with a °C/W rating (Thermal Resistance (Rht) in °C/W actually)

Delta = CPU temp - Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt (CPUw) that the CPU consumes, the HSF will limit the CPU's temperature rise to (C/W x CPUw) plus the temperature at the HSF's fan inlet. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that CPU temp will increase 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

and the lower the Ambient Temperature too
basically the thermal resistance of a given solution changes with the temperature differential, which is why thermal solutions are rated in °C/W which leaves that variable ambient open but gives you a formula

and considering that 400btu\hr = 117.2 Watts.....
think you need to add up approximately what the assorted components are probably going to consume >
CPU Thermal Power In Watts &
takaman's Power Supply Calculator
(those being the theoretical maximum) plus the efficiency of the Power Supply itself (80% meaning 20% is converted to heat) and of course any peltier adds more heat to the load

Then based on the expected ambient, search for a sealed thermal solution with a °C/W rating capable of actually meeting the job description. Offhand Id say your not looking for a smaller exchanger at all, considering the poor heat transfer because the temperature differential is going to be substantially closer than in say.... my room\enclosure (which is at 15C \ 60F with AC ) maybe you should consider a large radiator\stand\enclosure for your dock, you really need to have enough surface area to dissipate thyat heat at a closer differential temperature and thats going to be a challenge

Good Luck

.