Compact Air Condenser

[carbohydratesn]

Thicker vanes should have about the same surface area, but more cross-sectional area, than thin vanes. So they should condense about the same amount of vapor, but do a better job of transferring that heat to the heatsinks.

[NgrainD]

I see the way you're thinking: the bigger the highway the more cars can travel down it at one time. Ergo, thicker veins provide that "bigger highway" for heat to travel.
The way I'm thinking: if you heat two pieces of metal to the same temperature, only difference is one piece is half the mass of the other, and you let them both air cool, which will cool faster ?, and which will retain heat longer?.
Not trying to argue, just trying to merge theory and reality in my brain. I know most problems have many theories, and only one solution. I guess I'll just wait and see what swag comes up with, and go from there. Not that I don't believe you. Just brainstorming.
Thank you for your conversation carbohydratesn.
Stay safe, and still well friend.

[Bagasso]

The way I'm thinking: if you heat two pieces of metal to the same temperature, only difference is one piece is half the mass of the other, and you let them both air cool, which will cool faster, and which will retain heat longer.

I think the difference in cooling time would be in large part a function of the heat transfer capacity of the air and not because of the heat transfer capacity of the metal.

In other words, it isn't that the metal won't give up the heat, it's that the air can only absorb so much at a time. Place a fan on it or place it in liquid and the metal has no problem giving up the heat.

[NgrainD]

The way I'm thinking: if you heat two pieces of metal to the same temperature, only difference is one piece is half the mass of the other, and you let them both air cool, which will cool faster, and which will retain heat longer.

I think the difference in cooling time would be in large part a function of the heat transfer capacity of the air and not because of the heat transfer capacity of the metal.

In other words, it isn't that the metal won't give up the heat, it's that the air can only absorb so much at a time. Place a fan on it or place it in liquid and the metal has no problem giving up the heat.

Right, but you put the same fan on both chunks of metal which will cool faster? Bigger? Or smaller?
Where does the greater efficiency lie?

[skow69]

The small one will cool faster. You said you raised them to the same temperature, which means that you added twice as much heat to the bigger one so you will have to extract twice as much. Temperature is a measure of the average heat of an object.

[skow69]

I think the mass of the fins will be inconsequential compared to the surface area for contact. Heat will be drawn off to the outside at a fixed rate that doesn't depend on the mass. So highest efficiency would come from using the most fins possible, which means making them thin.

I find thermodynamics fascinating, but it's not my strongest suit, so I am open to other interpretations.

[Bagasso]

The small one will cool faster. You said you raised them to the same temperature, which means that you added twice as much heat to the bigger one so you will have to extract twice as much. Temperature is a measure of the average heat of an object.

This makes the most sense.

[NgrainD]

Ok, so really were both half right. Where my theory fits is : thinner veins inside would be more efficient, however, I think this is where your theory fits: you would need to double the number of veins inside. Am I getting it?

[carbohydratesn]

Exactly. A very large number of thin vanes would be the best. Tons of surface area, and tons of cross-sectional area to move the heat out.

But if you only have six vanes total, thicker is better. Less surface area to condense vapors on, but still plenty of cross-sectional area.

A few thin vanes would be less effective than either of those.

[Swag]

Interesting discussion. You also have to take into account how quickly the heat can be transferred through the fin to the sink. Can a thin fin transfer as much heat as a thicker one? You also have to wonder if direct exposure to the sink itself is more efficient than heat transferred through a fin. The sink itself is designed to draw heat from a flat surface and up into the fins.
I think a better design for the fins in the chamber would be tapered, with a thin tip and a thicker base.
I can certainly try it both ways: with and without the fins.

[Bagasso]

I think a better design for the fins in the chamber would be tapered, with a thin tip and a thicker base.

If you can't fit more fins into the same space then the tapered fins would have less surface area than untapered fins.

[still_stirrin]

.....You also have to wonder if direct exposure to the sink itself is more efficient than heat transferred through a fin. ....

If this were the case, then a thick slab of material would work better to remove the heat out of the vapor. But what happens actually, is the fin gets hot (temperature is a scaler) and the material conducts heat (a flow of energy) to the substrate with a lower temperature. Temperature is the motive force, analogous to voltage in a power circuit which I'm sure you somewhat understand.

...The (heat) sink itself is designed to draw heat from a flat surface and up into the fins....

This is correct. But you're moving the heat from a surface with higher temperature to a surface with lower temperature. Thin blades quickly shed their heat (measured by temperature) along the length of the fin(s). Moving air across the fins takes that heat away by convection. But the heat is conducted through the metal.

....I think a better design for the fins in the chamber would be tapered, with a thin tip and a thicker base...

Bear in mind that the mechanism for heat transfer is temperature difference. So, thin fins will adapt quicker to the difference in temperature. Sure, the "thermal mass" of the fin does have a bearing on its performance. But I'd doubt that tapered fins would be of any benefit. Conduction through the fin is key, so there needs to be some thickness. And copper has much better thermal conductivity than aluminum. But the quicker you can get the fin to temperature, the quicker you can pull heat out of the vapors.

Also keep in mind that the fins inside the box have a complementary function to those outside the box. Inside you want them to "grab" heat....outside you want them to "throw" heat.

Use your aluminum heat sinks as a design guide for how fins are effectively designed. Depth of the fin, the thickness of the fin, fin spacing, and the thickness of the thermal heat sink (massive base).
ss

[Hound Dog]

I don't know the thermodynamics of it but you have it set up just like I was thinking SWAG. I would have to think that thinner fins would transfer heat better but nothing tells the tale like trial and error. If the heavier ones work then you got it. Can't wait to see the results.

[still_stirrin]

OK, so maybe you guys don't trust me (an engineer) to explain the design. I'm attaching a document which outlines the theory and the analysis in heat sink design. Read and learn something....
ss

[carbohydratesn]

I would have to think that thinner fins would transfer heat better but nothing tells the tale like trial and error.

I don't think so. Trial and error in this case is just a waste of time and materials...it's already been done, much more thoroughly than any of us could do it. SS posted a good (but technical) document. There are some well-understood, basic principles at work here.

[Hound Dog]

Trial and error in this case is just a waste of time and materials...

You are right on the technical side of this. But for some it is the challenge of doing something for yourself to see what the results are that makes it fun. Physically doing it makes it a hobby for some while studying scientific results and theories makes it a hobby for others. I am more "hands on gotta see it". While I don't speak for SWAG, I am willing to bet he is too. Hence trial and error.

Heck, we already know a water cooled condenser will work just fine and can be slapped together with just about anything but what fun is that?

[Danespirit]

+ 1 Hound Dog..

I am also more comfortable in the workshop, than at the keyboard..drawing AutoCad and calculating pressuredifferentials for pipes.
Some drawings, never come to paper..everything is "stored" in my photographical memory..the rest i improvise as the project takes form.
" Improvise, adapt, overcome and succeed.."

Edit: Swag...this is a brilliant out of the box thinking..!
I was tampering with something similar, just in stainless, but scraped the idea because i have soooo much other projects going on.

[Swag]

Hah, I did my homework after I opened my mouth, as usual. I read a similar paper from Cisco all about heat sink design and application.
Anyway, I still have to build the copper parts, which means a less than ideal configuration. This would be so much simpler if alcohol and aluminum were better friends. I wonder if any of the coatings they have on heat sinks have good chemical resistance? More homework...

You are right on the technical side of this. But for some it is the challenge of doing something for yourself to see what the results are that makes it fun. Physically doing it makes it a hobby for some while studying scientific results and theories makes it a hobby for others. I am more "hands on gotta see it". While I don't speak for SWAG, I am willing to bet he is too. Hence trial and error.

Heck, we already know a water cooled condenser will work just fine and can be slapped together with just about anything but what fun is that?

Amen brother!

Cheeers

[Swag]

OK, got it all together and tested it out today. I ran the pot still at full tilt for an hour (after boiling was achieved), and the condenser knocked it all down. The water was hot coming out of the thing, but liquid nonetheless.
I fashioned a "trap" in the output tube to make sure no vapor was escaping along with the liquid:



When everything settled down, the flow was a steady stream. I tried to get a picture of it and this was the best I could capture. Not great but you can kind of make it out.



I built the boiler last night out of a milk can I had. I was going to do a stovetop, but the kettle lid I have sucks. Here is the whole rig:



Anyway, my impression was that I could use a little more air flow. Those two fans are adequate, but they're slightly too wide and four properly sized 4" fans would be better. The frame also gets pretty hot so I'm going to stick some sinks on those, which I just happen to have

Cheers

[just sayin]

Swag, congratulation on your successful concept and execution. How much water where you able to condence per hour?
A waterless still condenser opens all kinds of possibilities!

[skow69]

I'll bet that doubling the fans will improve the hell out of it. I was going to ask if you pop for the high performance ones, but you probably have a good supply of used.

[Hound Dog]

Congrats! I am glad your plan came together. If it worked with water booze will be a breeze.

[skow69]

I'll bet that doubling the fans will improve the hell out of it. I was going to ask if you pop for the high performance ones, but you probably have a good supply of used.

Which, come to think of it, makes you even more qualified for this question. Are the super-dooper fans worth it? Does the CFM justify the price?

[Swag]

Thanks all, I appreciate your support and excellent suggestions. I don't think it would have worked without the baffles, the water was definitely hot coming out.
I've already stripped the unit down, and I'm re configuring a few things to add more sinks on to the frame. I cut up a larger sink to make strips to fit the 1" frame pieces, as you can see in the pic:

Which, come to think of it, makes you even more qualified for this question. Are the super-dooper fans worth it? Does the CFM justify the price?

It depends on your cooling requirements versus the space you have to mount the fan. You also have to consider if noise is an issue since those fans can get loud. I usually mount more fans to move more air, say, in an equipment enclosure.
The ones I'm using are rated for 88 CFM and only draw 10 watts, not your turbo fan by any means. But then the price was right and they're quiet! I think doubling them up and adding the extra sinks will give me better cooling and more of a margin when the ambient air temp is higher.
You have to keep in mind that we only need to drop the vapor temperature a few degrees in order to condense it. Hot liquid can cool quite well all by itself. I wish I could tell you guys the cooling capacity in watts, but since I have a burner it's difficult. SS asked how much liquid I got in an hour, which would be a very good measurement, but I didn't pay attention and was throwing some out as I went along. I'll keep a better record next time.

Cheers

[skow69]

Actually, you prolly don't need to lower the temp at all, but you do need to remove the latent heat of vaporization. For ethanol it is 846 KJ/Kg, water is 2257 KJ/Kg. When you extract that much energy (measured in Joules or calories) It will change from vapor to liquid at the temperature of boiling.

I am the King of Useless Trivia.

[Swag]

For ethanol it is 846 KJ/Kg, water is 2257 KJ/Kg.

Good to know anyway. I suppose I could do some highly complex calculations to determine the actual heat dissipation potential of my rig, but it's much easier to just see if we have liquid coming out of the business end, and how hot it is. The ambient air temp was around 60-65 degrees F when I did my test. I definitely need more cooling if the ambient is 20 or 30 degrees warmer.

Cheers

[still_stirrin]

Swag,

Be careful with that trap in your product line. All it takes is a little puke, or some blowby sediment to make a bomb. Your system is a pot still (closed vessel) which will already see pressure buildup due to the liquid head in your trap. If you get crud settling in the bottom.....boom!

Just be very careful. If flow slows...you could be in trouble already. Most pot stills are open to atmoshere at the product outlet....no liquid trap needed.

I'm keeping an eye open for your safety.
ss

[Swag]

Thanks for your concern SS. I do have a temp port on the column, and do not plan on using a trap configuration during a normal run. I just wanted to make sure no vapor was passing through for testing purposes.

Cheers

P.s. I also have a scrubbie in the column which would act as a filter to large particles.

[still_stirrin]

......I also have a scrubbie in the column.....which would act as a filter to large particles.

Now, you know from your extensive reading that scrubbies are not needed or effective in a pot still (column), right Swag? You should know this already.

[mason jar]

Great job Swag. It's always good to see someone build something from parts on hand and have it work so
well. I will have to admit, when I saw your first pictures I didn't think something that small would work
very well. Clearly I was wrong

...I suppose I could do some highly complex calculations to determine the actual heat dissipation potential of my rig, but it's much easier to just see if we have liquid coming out of the business end, and how hot it is.

Actually it's very simple to measure the amount of power your condenser is knocking down. Simply do a
WATER-ONLY run and collect some water (doesn't really matter how much) weigh the water (in kilograms!)
and keep track of how much time it took to collect that amount of water. Then calculate the power your
condenser is knocking down using this formula:

power in kW = (evaporation heat of water) x (water weight in kg) / (collection time in seconds)

where the evaporation heat of water is 2257 kJ/kg, as skow mentioned above. I tried this method on my
air condenser and it worked pretty well.

If you can, push your condenser to the point where it doesn't quite knock down all the vapor, then
back the heat off just a little bit and do the measurements. That will tell you what your condenser
can do.