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How cold will they get?

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Depends. Current applied to the device will produce heat on one side and cold on the other side, from 30 to 100° C  difference between the two sides, or even more depending on the device and how it's set up. A good heat sink is recommended. Modules can be mounted in parallel to increase the heat transfer effect or can be stacked to achieve high differential temperatures.

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Modules can be mounted in parallel to increase the heat transfer effect or can be stacked to achieve high differential temperatures.

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sorry for the double post but I've always heard stacking TEC's dosn't give any benifit at all and its pretty useless ... I'm not 100% sure though but I know I've heard it somewhere

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If you used a ice water filled aluminuim box for the heatsink, you would be able to achieve temperatures cool enough to liquify anyhydrous ammonia ? For the sake of a bit of wasted electricity !

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If you have a "Potted" peltier it seems possible (potting protects the electrics inside the peltier) but anhydros NH3 only has to be colled to -33°c correct? you can buy peltiers with enough DeltaT to achieve that no problems.

Also don't forget that one side is HOT and the other COLD so by placing it in a bath of ice water, you ARE cooling it by however many degrees on one side but the HOT side is the same temp, just opposite (eg, -30 on one side, +30 on the other) so that might defeat the purpose.

I'm only 95% sure on this however, so if someone has some experience with it, feedback would be greatly appriciated.

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New/old ways that work are: for cooling down to -70°C and if you have an supply of pressured air: the "Wirbelrohr", aka "vortex tube" aka "Ranque-Hilsch Resonator". Quite noisy if not properly insulated, but ya need only an compressor. No moving parts at all. How it works? Answer the question and get the Nobel-Price..... (this is no joke!)

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Funny thing about that statement, Mr. Smith didn't get a Nobel prize for writing this in Scientific American, his explanation makes perfect sense to SWIL



Three factors determine the performance of the Hilsch tube: the setting of the stopcock, the pressure at which air is admitted to the nozzle, and the size of the hole in the washer. For each value of air pressure and washer opening there is a setting of the stopcock which results in a maximum difference in the temperature of the hot and cold pipes. When the device is properly adjusted, the hot pipe will deliver air at about 100 degrees Fahrenheit and the cold pipe air at about -70 degrees (a temperature substantially below the freezing point of mercury and approaching that of "dry ice"). When the tube is adjusted for maximum temperature on the hot side, air is delivered at about 350 degrees F. It must be mentioned, however, that few amateurs have succeeded in achieving these performance extremes. Most report minimums on the order of -10 degrees and maximums of about +140 on the first try.
Despite its impressive performance, the efficiency of the Hilsch tube leaves much to be desired. Indeed, there is still disagreement as to how it works. According to one explanation, the compressed air shoots around the spiral and forms à high-velocity vortex of air. Molecules of air at the outside of the vortex are slowed by friction with the wall of the spiral. Because these slow-moving molecules are subject to the rules of centrifugal force, they tend to fall toward the center of the vortex.
The fast-moving molecules just inside the outer layer of the vortex transfer some of their energy to this layer by bombarding some of its slow-moving molecules and speeding them up, The net result of this process is the accumulation of slow-moving, low-energy molecules in the center of the whirling mass, and of high-energy, fast-moving molecules around the outside. In the thermodynamics of gases the terms "high energy" and "high velocity" mean "high temperature." So the vortex consists of a core of cold air surrounded by a rim of hot air.
The difference between the temperature of the core and that of the rim is increased by a secondary effect which takes advantage of the fact that the temperature of a given quantity of gas at a given level of thermal t energy is higher when the gas is confined in a small space than in a large one; accordingly when gas is allowed to expand, its temperature drops. In the case of the Hilsch tube the action of centrifugal force compresses the hot rim of gas into a compact mass which can escape only by flowing along the inner wall of the "hot" pipe in a compressed state, because its flow into the cold tube is blocked by the rim of the washer.

The Hilsch tube does make a great cold trap for oil pumps, all that talk about Maxwell's demon was hype

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##### outer sheath - ring clamp not shown

%%%%% flang or other adapter

***** threaded ends of T compression joints

/----
\---- compression nut

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----- inner copper or glass tube

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=||=  T connector


What is being constructed (cheap and OTC) is a coaxial heat exchanger, that will cool a liquid flowing one direction on the outer tube using expanding CO2 gas from the canister on the inner tube flowing in the opposite direction.  Expanding co2 gas is way fucking cold as shit mucho bigtime!  I don't remember what terminal temp for CO2 is, but it hasn't frozen acetone at any flow rate that I have tested. 

I use an 12v oil pump for boat maint. to pump the acetone, but I don't know how long it will last given the noise it is making after about 12 hrs of use.  I am using a 12v solanoid valve from the high performance autoparts store intended for swithing nitrous on/off (120$) to blow bursts of co2 into the exchanger to implement gross temp control.  Lets say to the nearest 10-15deg C, but you won't get much better than that from such a crude control method.  Secondly, I have four speeds that I can drive the circulating pump, but only two are currently used: minimal maintnance flow and full cooling. 

Where the peltier comes in is at the junction between the reaction unit and the cooling setup.  By placing a peltier between the device to be cooled and the cooling system I can adjust with a very fine degree of control the amount of cooling delivered.  I can boost the cooling by running the peltier in the forward mode, or reduce the cooling by running the peltier in the reverse or heating mode.  If I am running the peltier in the reverse mode, I will also slow the coolant flow to minimal maintnance flow.  Peltiers can adjust the temp and direction very quickly, too quickly in fact.  If you don't implement a degree of deliberate histeresis to govern the temp swings, you can destroy the device through thermal stress.  Buy some extras and attach them using thermal lube and screw clamps instead of thermal glue witch requires a chisle for part replacement.

You will also need two temp sensors, one on the peltier and one in the reaction chamber.  By calculating the rate change and change of rate change factors you can quickly identify the dynamic "intentions" of the system.  The peltier sensor change values will freewheel as the coolant modulates and the reaction chamger sensor change values will freewheel as the reaction sinks or sources energy.

So just input it all into your computer and fuck around for a few months and it should all work out!

I have no life!