Dry ice and coldfinger?

[wrudisill]

I imagine this has been brought up before, but I ran a search and nothing came up....

I'm in the process of building my first still, a vapor management, and I've read about how much water is used in cooling.

In other chemistry applications, I've read about people using a "cold finger" with dry ice or a dry ice alcohol mix to condense vapor. I was wondering if this could possibly replace the coil in a vm still. Has anyone ever tried this with any success?

[pHneutral]

@ -78, the water would freeze up around the cold finger and eventually clog the condenser.

[HookLine]

Yup, serious overkill.

[wrudisill]

It seems like there would be a way to construct a coldfinger that wouldn't get that cold...

I think I may buy a small chunk and do some experimenting.

[Dnderhead]

could use CO2 and have cold finger as expansion chamber.

[Ugly]

I've used both dry ice (henceforth "dice") and LN2 for supercooling computer processors while massively overclocking them. Even vapour from air will freeze to the side of a tube with either product in it and requires massive insulation to keep frost from forming. Touch water with these products and you will freeze it immediately. Touch alcohol and it will freeze almost as fast. Both of these solutions are only good for short periods of time.

If you want to get your dice evaporting nicely, add a little bit of acetone to get the vapours rolling.

The key to working something like this out is just the same as for a traditional cooling system - surface area contact, velocity, thermal transfer characteristics of the products all have to be considered. A glob of frozen alcohol will also cool incoming alcohol vapour, the key woudl be to balance the contact area so as not to form a blockage, Anything you build at home can't be circulated - would just have to be a static feed pipe with the dice or LN2 in it I believe.

One of thoughts I had for making a super small condensor also comes from the CPU supercooling process. That's basically taking RV or Auto antifreeze halfway to it's freezing point and then moving it through the pipes of the condensor. The below freezing liquid in storage needs to be held to temperature using a fair sized compressor tuned for the job though. A fridge or water cooler isn't up to the thermal load. Mind you, a small freezer full of the stuff would hold that temperature for a few hours before it started heating up.

The "green" spin off version of this I was thinking about was using an absorption refrigeration technology with an external heat source powered by charcoal. But when I did the thermal load calculations I realized I'd need a fair chunk of anhydrous ammonia and it seems all the meth labs have made getting that stuff fairly difficult.

After all this thinking, I hooked up my water hose and ran a pot of rum.

[rad14701]

Ugly, for the sake of safety, don't consider using or suggest using automotive antifreeze even in a closed loop system where there is a possibility of there being direct contact contamination... Only food grade safe coolants should be used, no matter how good connections are or how well components are cleaned... It's just not worth the risk... We can't stress enough that what we make is consumed by humans and every precaution must be taken to insure the safety of everyone who may sample our product, even if it's just ourselves...

[Ugly]

Ugly, for the sake of safety, don't consider using or suggest using automotive .. SNIP

Noted and quite right. My big still of course produces methanol and I keep forgetting the human ingestion factor.

So in conclusion, stick to RV type non toxic anti freeze if you try using a chiller design.

[rad14701]

So in conclusion, stick to RV type non toxic anti freeze if you try using a chiller design.

Propylene Glycol would be a good choice...

[Ugly]

So in conclusion, stick to RV type non toxic anti freeze if you try using a chiller design.

Propylene Glycol would be a good choice...

Which is exactly what RV antifreeze is. If you want the pure stuff without worrying about what's in it, you can order it from a feed store or a drug store if you are urban.

We've beat that one to death now.

[rad14701]

We've beat that one to death now.

Yup... Back on topic...


ps: Never equated RV to be something like water craft... To my old mind RV means Motor Home, from back before any other Recreational Vehicle was anything but air or water cooled... It was long after I left the industry that RV encapsulated as broad a range of vehicles as it does today... Geez...!!! Ancient at 48...!!! Where's my rocker...???

[Dnderhead]

rad in my day recreational vehicle ,was the old ford I took out on saturday night.

[snuffy]

there's no real advantage to supercold coolant. If the surface of the condenser is below the condensation temperature, it will condense. Temperature differential isn't as important as you might think. it might make a small condenser work a little harder, but that's about it. 1000W is 14C differential at 1 L/min.

Increasing the surface area of the condenser (making a bigger one) or increasing the coolant flow rate will get you more with less effort.

The power handling capacity of a heat exchanger is the product of conductivity, temp differential, surface area, mass velocity (flow rate) divided by wall thickness.

If you're using copper pipe, conductivity and wall thickness are constant, so it gets down to temp differential, surface area and flow rate (of both fluids: vapor and coolant). Most of the design innovation is getting the most surface area in the least volume or length while allowing the free flow of coolant.

Temp differential is the most work with the least payoff.

It seems the most common flaw is inadequate vapor contact with the cooled surface - too much volume for the vapor to occupy per cooled surface area. If you turn a liebig inside out and run the vapor through the coolant jacket, you get less cooling than running it through the central tube because the coolant jacket has more volume for the same contact area.

[wrudisill]

Makes sense...

But I guess using something like dry ice would be beneficial if you were concerned with your water footprint or had water restrictions. Of course the amount of water used could be less than I imagine, seeing as how I've yet to run a still.

I think I might mess around with it a bit, though I must say I'm less keen now that I finally managed to wind my first coil.

[riff42]

I imagine this has been brought up before, but I ran a search and nothing came up....

I'm in the process of building my first still, a vapor management, and I've read about how much water is used in cooling.

In other chemistry applications, I've read about people using a "cold finger" with dry ice or a dry ice alcohol mix to condense vapor. I was wondering if this could possibly replace the coil in a vm still. Has anyone ever tried this with any success?

Normally people don't have dry ice or LN2 handy around the house. Hence the common methods we use here. However, with any new topic, experimentation is key! I would imagine that it would work, just like in standard chem. applications.

I say, take the dry ice, and stick it IN you glass of rum/vodka/whatever. It's interesting!!! AND tasty afterwards.

[HookLine]

Most of the design innovation is getting the most surface area in the least volume or length while allowing the free flow of coolant

Probably the best measure of overall efficiency (for our purposes) is the amount of heat exchange material (by mass) and the volume the condenser occupies, to do a given amount of heat exchange.

[shadow0000]

Dry ice could freeze water? but that is impossible to work out man...




____________________
Scotsman Ice Machine

[Adverse Effects]

dry ice is made of CO2 the last thing you want drifting down in to your column is CO2 gas

just throw the dry ice in to your storage tank and cool that water if you need more cooling

[schnell]

There is only 1 legitimate use for extreme cold, like N2 or Dry ice, related to our hobby on this forum. That is to protect a vacuum pump with a vacuum trap. 100% of the vapors will be trapped.

This would really suck if it was happening in your condensor. It would freeze up the vapor, clog the condensor, and the resulting pressure build up will blow out the weakest part of your boiler wall. This would be by way of explosion, possibly followed by fire.

Bad. Bad. Bad Idea. Dangerous.

The trap is used inline after the condensor/receiver and is essential for vacuum work with pumps, and unnecessary but still good practice when using aspirators. I've used these traps with LN2, dry ice and acetone, etc. They are either self assembled or specially made receivers that freeze out any vapors in the vacuum line that could enter the vacuum pump and destroy the pump. I've seen a big oil pump burst into flames in a chemistry lab from getting solvent fumes dissolved into its oil. Pump seized, failed, and flamed. Twas scary since I was standing a foot from it at the time!

Almost no-one on here is hobbying with vacuum pumps... but if you are drop me a line and we'll discuss the joy's of azeotropic manipulation. In the threads I've only seen a couple posts touch on this technique. It's one of my favorites.