double helix condenser -- how flat is too flat?

[CooknBrew]

So just how much flattening is ok? There are no full on kinks anywhere, but the inside coil especially seems like halfway flattened.

Do I just have to hook it up to water and see if it comes out good? Is there a way to gauge if you have enough pressure? (aside from making a run and seeing if it knocks down vapor?)

Thanks

[olddog]

What size tube are you using, will water pass through it OK, as long as its not too flat, all you have done is change the diameter from a circle to an elipse, and the volume should be the same.



OD

[CooknBrew]

it is 1/4" od. I havent gotten to hook it up yet, so I dont know how good is the flow... I will try to hook it up in the next day or so and post results.
Thank you-

[ScottishBoy]

Just blow through one end. If its seriously bad, you will have a difficult time blowing, but it will probably be fine. I got a little flattening in mine too and it works great. In an effort to conserve water I run a very small flow. The water that comes out of my exit hose is usually bath water warm.

[rad14701]

In reality most folks run more water through their condensers than required... You should only need to run a couple of liters per minute through it at most in order to maintain 100% reflux... I have never run more than 1 liter per minute, and usually just over half a liter per minute, but the more heat you run the more coolant you'll need...

[CooknBrew]

Ah, good news then, SB! The "blow test" was succesful
Thank you gentlemen- and thanks for giving me a good baseline for judging the flow, Rad.
Soon to hook it up!

[HookLine]

This is how much the tube on the inner coil flattens on my double coils (1/4" tube, inner mandrel 16 mm diameter). I cleaned up the cut to remove any lip on the tube.

This much flattening is not only no problem, it might actually slightly increase condensing efficiency by reducing the average distance between the coolant and the tube wall (the heat exchange surface). Wouldn't want to go much flatter than that though, it will start reducing the maximum flow rate and increasing back pressure, which is not so good for pumps in a recycling coolant system. Trade offs.

Coil tube flattening.jpg (10.68 KiB) Viewed 4593 times

Rad is right. For a 2" reflux column, the coolant flow rate shouldn't need to be more than about a litre per minute. Usually around half that. Well below the maximum flow rate these coils can handle.

[CooknBrew]

Thats a good pic Hook.... I'm tempted to cut open my coil just to see what it looks like...

Anyhow, I attached 1 side of the coil to the water pump - why only 1? -
Well, I got 2 compression fittings that would connect my 1/4" OD coil to the 1/4" ID tube, and had so much trouble with them I just decided to solder the two tubes directly together. I only had time to do the one side....

I let the coil drain the water into a measuring vessel and it comes out at a rate of 1/2 litre per minute. Would it be faster if the other side of the coil were hooked up to a return tube and created a pulling/siphon type effect?
The pump by itself pushes out about 1 litre per 30 seconds.

I am readying myself mentally to go get another piece of coil and do it again....

*edit: Nevermind all that! I got less stupid and hooked it up directly to a faucet, and away we go! I am giddy like a school girl. I got about 1 1/2 litres in a minute and I could have gone faster.

[HookLine]

[squidd]

Hookline,

As the coil is flatened, efficiency increases up to a point and then decreases.

Q1 At what a/b ratio does max efficiency occur ?
Q2 At what a/b ratio is the efficiency the same as that for the unflatenned coil ?

Just an academic exercise.

Regards,
squidd

[Titus-a-fishus]

Thanks for both the question and answers, very informative.

There is also another benefit of the tube flattening.
It means you can use larger diameter tube to wrap the 1/4 copper around.
That is a benefit if you don't have 16mm pipe as the inner.... I used 19mm and 32 as the outer (from memory).
Plenty of room left in a 50mm column.

Cheers
TAF