4" shotgun design - 3/8 or 1/4?

[kiwistiller]

I'm going to be making a couple of shotgun (shell and tube, crossflow) condensers in 4" shell. I have to decide between using 3/8" or 1/4" tubes. Any opinions? Currently leaning towards 1/4" because I should be able to get a greater number of tubes and greater surface area (right?), and it is a fair bit cheaper.

[MuleKicker]

+1. surface area is the game. if you take .25X3.14(pi) = .785 .325X3.14 = 1.020. That is only .235" difference on the circumference per tube. take that number times the difference of 3/8 to 1/4 tubes that you can fit in your shotgun. That will give you your answer.

[LWTCS]

+1 more on the 1/4"

Where are you gonna land the shot gun Kiwi?

For dephalaging or product?

[kiwistiller]

Both I'm sick of hearing my pump strain away trying to force water through my 3/4 over 1/2 liebig. the product one maybe scaled back to 2.5" shell though. I would normally be leary of the top baffle of the water jacket pooling slightly and smearing cuts, but this build will have a heads reservior and eventually an E-ARC component, so heads are stuck in the reservoir / bleed off with LM, and tails aren't allowed up the column - no cuts to smear.
Cheers guys

[ozone39]

Correct me if I'm wrong on this but to find surface area is Circumference x length... C=2(pi)r..R=radius. So 2(3.14)x(.125)=.785.... 2(3.14)x(.1875)=1.1775... take this and multiply by the length of tubing for total surface area. But just in circumference area alone you would get 1.1775-.785 = .39..Just in circumferential area you gain more than 3/8"...That a pretty substantial gain in area for only an 1/8" diameter increase in tube size..Two tubes of 3/8" = 3 tubes of 1/4" in surface area.... (.785) x 3 = 2.355"...... (1.1775)x 2 = 2.335"...kinda funny how that math worked out between these two sizes..

[HookLine]

I am a little confused. You running vapour or coolant through the tubes?

[kiwistiller]

I understand your confusion, because I'm planning on doing both - two condensers. One is a reflux condenser, coolent in the tubes. that one is definitely 4". The other is a product condenser, will either going to be 4" or 2.5", and will have distilate in the tubes. Ok by the looks of it I need to sort out the number of tubes, and that should answer my question.

[HookLine]

Coolant in the tubes = 1/4" or 3/8"

Vapour/condensate mix in the tubes = 3/8"

[kiwistiller]

Could you explain that for me hook? why does the product condenser need bigger tubes?

[HookLine]

There is a real risk that 1/4" tubes cannot empty liquid fast enough, and capillary action will clog up the tube, which can result in hot distillate being spat out the top of the condenser, and unstable condenser performance.

[kiwistiller]

Ah ok, but this isn't an issue for a product condenser right? Just imagine it instead of the liebig in a VM

[rad14701]

You could actually also have flooding issues with the reflux condenser, which will be knocking down 100% of the vapor during the equilibrium stage... I'd think 3/8" would be more efficient overall and would require less tubes for the same amount of cooling, which also equates to less solder joints... 1/4" tube has 2/3 the surface area of 3/8" tube so you would need 33% more 1/4" tubes to achieve the same cooling as 3/8"...

Never mind... Re-read your last post, kiwidistiller, and see that the reflux condenser will have coolant in the tubes rather than vapor/condensate... The size differences are still valid, however...

[HookLine]

Ah ok, but this isn't an issue for a product condenser right? Just imagine it instead of the liebig in a VM

I was talking about a shotgun style reflux condenser, where the vapour is travelling upwards into the path of the falling condensate (ie in opposite directions). If you are using it for a VM product condenser that might be different, where the vapour is coming in the top and the condensate is falling out the bottom (ie vapour and condensate are travelling in the same direction.

[kiwistiller]

after playing around in some design software, I'm opting for 3/8" for both. Have a neat idea of channeling the water in the product condenser as well, will provide detail when I build it. cheers all.