View Full Version : I'm geussing this wouldn't work well....
sandman
08-21-2003, 12:23 AM
Alright a mach II can absorb, what like 220 watts?
So, take a 172watt pelt and cool it with the prommy, wouldn't this give you lower temps than just a straight mach II?
I'm basically a complete noob to this whole thing, so I'm just wondering where the flaw is in my thinking?
The efficency of tecs goes down drastically at low temps, not to mention a 172watt tec gives out 275watts of heat + ~100watts from the cpu which is 375watts of total heat which would swamp the mk2.
]JR[
Gary Lloyd
08-21-2003, 03:37 AM
If I were going to cascade a tec and a prommie, I would have the tec cooling the prommie liquid line, helping if not replacing the prommie condenser.
TheDude
08-21-2003, 04:25 AM
I think at some point everyone wonders about cooling a tec with a prommie, but I have never seen it suggested to replace the Prommie's condenser with a tec....very interesting idea!
Gary....how would you go about cooling the liquid line with a tec? Wouldn't you have to change the line in order to contact enough surface area to cool it? Or am I way off in my picture of it? Could you explain it or even better....show a diagram.
And as ]JR[ suggests, what would you do about the hotside of the tec?
Sorry, but I am having trouble visualizing the concept.:(
Gary Lloyd
08-21-2003, 05:35 AM
Cascading phase change systems is no different than stacking tecs. It is using one system to cool another. Stacking/cascading two types of systems is no different. The tec is more efficient at higher temps, and we can air cool the tec to get rid of the heat generated. A tec adds a lot of heat, so it would make more sense to put it on top of the stack. Better to get a bigger heat sink and fan than a bigger phase change system.
We would need a heat exchanger, which would look a lot like an evap block. The idea is to condense the refrigerant below room temp. This would allow us to go to a higher pressure refrigerant such as R404A or maybe even R410A, thus achieving a lower evap temp.
Let's say our prommie uses R134A condensing at 90F. This would give us a high side pressure of about 104 psi. If we switched to R404A and could condense at 104 psi, this would give us a condensing temp of 51F, which a tec might be capable of achieving on our tec condenser. In other words, we could switch to R404A without changing the cap tube or anything else, and possibly reach lower temps than if we changed to R404A along with the cap tube mod (although Bowman does a very efficient mod).
R410A could give us even better results, but everything would have to be heavy duty because of the pressures involved. The R134A compressor may not be able to handle it, even with the reduced high side pressure.
I think im going to have to try this just to be the first ;)
Although i think i would rather eliminate the condensor all together (per say) and use tecs on a different exchanger, my only concerns are can you get a big enough path length across dual 172watt tecs, and how fast can i run when the cooling on the hotsides fail :D
]JR[
Gary Lloyd
08-21-2003, 08:11 AM
You would want a temperature switch that does not allow the phase change system to run unless/until the heat exchanger is cold.
You might use a double faced heat exchanger sandwiched between the two tecs.
TheDude
08-21-2003, 08:17 AM
]JR[
If you really do end up doing this...be sure to post your work. I would really like to see how it comes out. :D
Gary,
Thanks for the clear explanation. I can see it now. :D
sandman
08-21-2003, 09:03 AM
I see......
I figured it would be almost like running a tec with chilled water.
I have another sorta dumb question: why do pelts lose thier efficency at low temps?
Because theyre effectively a really big thermocouple...
]JR[
Popcicle
08-23-2003, 04:26 PM
If the condensor isn't eliminated then aren't
we just dealing with sub-cooling?
Similar to Tom H. using his VC on the condensor
vapor line?
Pops.
Gary Lloyd
08-24-2003, 03:12 AM
If the condensor isn't eliminated then aren't
we just dealing with sub-cooling?
That depends on the capacity and placement of the pelt, the cap tube sizing, and the refrigerant charge.
Eliminating the condenser is irrelevant to the question. It can, and preferably should, stay right where it is.