Having some new inventory to work with, that being too much, and basically wanting to get back into benching I've decided to build myself a new cascade.
I decided on two Hitachi 11.5k Btu rotaries, a rather large condenser I've had sitting, four 180cfm 120mm 110vac fans, a Temprite 900 (oh yes), a little blue for desuperheating, a 12 plate HX, a CPEV on the second stage, a hot gas bypass with electric solenoid valve, a small expansion tank, and some normal filter driers, oh and a high pressure cutoff from Danfoss.
After shrouding the big condenser, and putting on the fans, I decided to do a little display, so enjoy, I'll be away this weekend, but expect some more updates early next week!
Oh and a 5ft braided stainless steel flex, with an ancient 1.25" Runmc Stepper on the end!
Wow- Go big or go home- this is the kind of rig I'd be interested in- not a wee one that I can stash under my desk for 24/7 use, but a big bad boy in the basement to hook up to a test system for benchmarking.
Okay a brief explanation and loop order. A cascade systems utilizes more then one refrigeration loop, completely separate. The first loop features one compressor, and the large condenser with four 120mm fans at the front. This condenses a refrigerant in normal condensing range (sub 250psi) at room or slightly above room temperature. This refrigerant will be metered and expanded into the plate heat exchanger (thing with green caps, [four of them]] chilling it. The gas then returns to the compressor to rebegin the loop. The second loop starts off at its compressor, heads to the little blue condenser with fan (to remove excess heat), then into the oil separator (the red cylinder) to remove the oil, and then into the other side of the plate heat exchanger (thing with four caps), here it is chilled to a low temperature (-30 to -40C range), and the refrigerant condenses. This is then metered to the evaporator on the CPU where it expands.
The oil separator in the second stage must remove oil so it doesn't freeze!
The first stage will use r402a and r290, and the second stage will use r1150 (ethylene). Also in this unit will be a hot gas bypass and a CPEV on the second stage. The CPEV is a constant pressure expansion valve; it holds the low side pressure constant, and thus the evaporating temperature, however it is ADJUSTABLE! So I can avoid coldbugs! The hot gas bypass is a simple valve that is linking the evaporator (the cold end) to the hot gas exiting the compressor. By opening this valve hot gas can be shot into the evaporator warming it up :)
This is probably how they work: think of the Ideal gas law:
P=pressure of a gas
n= number of moles of gas
R= a constant (ignore it for conceptual purposes)
T= absolute temperature of the gas
The important part of this is that if you increase pressure the temperature of the gas goes up- so what you do is remove this heat while the gas is still under pressure (in liquid form) using a radiator like device, then when you release the pressure, the temperature of the gas drops to well below where you started as much of the energy was been removed from it. I'm not sure that's how they work, but I assume so.
Last edited by Babrbarossa; March 29, 2008 at 07:11 AM.
To boil water you need heat, to boil anything, you need heat. Even things that boil at room temperature, they take heat from the area around it. The first loop turns a gas into a liquid, that happens to have a boiling point in the -40C range, it then puts it into a lower pressure zone, and so on the PT chart its now a gas, and it boils off. This removes a lot of heat, and causes the area to drop into that temperature range. Now the second stage contains a gas that boils at -104C, its alot harder to liquidize though, and takes the -40C transfered to it, to liquidize it. Then boiled off it makes -104C.
Basically its an exchange of heat, but mostly its about boiling something off that has a low boiling poiint, and that you can condense to begin with.
Some wanted a shot of my workspace. This one is a few weeks old but still does well. Yes its a huge space.
And heres a brazed up first stage, gotta put on some rubber feet if I have any that'll fit, and clean that sucker.