Controlling Flow

Distillation methods and improvements.

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NormandieStill
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Re: Controlling Flow

Post by NormandieStill »

RC Al wrote: Thu Oct 21, 2021 2:49 am
NormandieStill wrote: Thu Oct 21, 2021 2:21 am Why? What are the thermal properties of the incompressible heat transfer fluid that make it more efficient under pressure?
The only thing that you can do to control the heat transfer rate, is adjust the flow rate. And you can do that on either the inlet or outlet. Water at 3 bar will not hold more energy than water at 1 bar.
Not that it applies much to hobby stills, but millions of automobiles rely on a radiator cap to increase/regulate the pressure of a cars cooling system to raise its boiling point every day, Jus Sayin 8)

Simple solution is to add a ball valve on the input if saftey is the concern

I have bleeds with clear tubing on all my condenser outputs to manage/remove bubbles
Cars don't do that to make the cooling more efficient, they do it make the cooling possible since the heat source is well above the boiling point of water. If your condenser has exceeded 100C (give or take) then you're no longer distilling, you're managing an active fire! ;-)

A ball valve on the input is exactly what I'm suggesting. But not one on the output.
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Re: Controlling Flow

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Indeed it looks nice , thats shaping up to be some if the nicest Copper Porn we’ve seen for a while . :thumbup:

Looking forward to see what happens with the Gantry above the RC .

May I suggest you keep some spare O-rings on hand and replace them regardless every 12months . Leaking garden hose fittings are annoying . I’m thinking of changing mine to ( I think its Pope brand) as they have a double O-ring in them .

Also remember when you pull the hose off , there is a lit of water in the condensers that usually pours all over the floor .Perhaps fit a second valve so you can shut both in and out off before removing hoses.

There are also hose fittings with a check valve in them that stop flow as soon as they are disconnected . That will stop a hose full of water soaking your carpet .
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Re: Controlling Flow

Post by kimbodious »

re hose connectors, I am using 3/4” triclamp fittings then a long tail that connects to garden hoses well away from the still. When it comes to packing up you disconnect from the garden hoses first leaving any drips and dribbles well away from the still.
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Twisted Brick
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Re: Controlling Flow

Post by Twisted Brick »

NormandieStill wrote: Thu Oct 21, 2021 2:21 am
Twisted Brick wrote: Wed Oct 20, 2021 7:45 pm ... condensers are more efficient when run with pressure on the shell side.
Why? What are the thermal properties of the incompressible heat transfer fluid that make it more efficient under pressure?
I think s_s already answered this, and the properties are hydrodynamic (not thermo). Like s_s pointed out, internal pressure provides for a more constant flow and predictable transfer of heat. Placing a valve on the discharge end of the condenser promotes consistency of this pressure and minimizes pressure drop in the shell.
Last edited by Twisted Brick on Sun Oct 24, 2021 9:17 am, edited 1 time in total.
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NormandieStill
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Re: Controlling Flow

Post by NormandieStill »

My personal experience with a simple leibig condensor (16mm in 26mm with a coiled wire wrapped around the inner) is that moving my valve from the outlet to the inlet has made no measurable difference to the performance. But... running in the shed using a 1000L reservoir of water at ambient temperature dropped the temp of the distillate from my stripping run by about 10C compared to running indoors using tap water. Possibly due to the different flow levels, more likely due to the fact that the water is significantly colder at this time of year.

The article is concerned with max pressure for safety, not pressure for optimal heat transfer.

I'm more than happy to be corrected on this, if someone can actually point to the laws of physics or a side-by-side comparison that demonstrates a statistically significant improvement in performance (Either cooling capacity for a given flow-rate, or max capacity). Otherwise it just seems to be obtusely sticking to a (marginally) less safe configuration because... ....that's how everyone else is doing it? :-)
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Re: Controlling Flow

Post by Mr Sippy »

NormandieStill wrote: Sat Oct 23, 2021 12:35 am if someone can actually point to the laws of physics or a side-by-side comparison that demonstrates a statistically significant improvement in performance (Either cooling capacity for a given flow-rate, or max capacity).
These two screencast explain it. Log mean temperature difference is the key. Heat transfer coefficient is the 'squishy' number.
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NormandieStill
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Re: Controlling Flow

Post by NormandieStill »

Mr Sippy wrote: Sat Oct 23, 2021 4:26 am These two screencast explain it. Log mean temperature difference is the key. Heat transfer coefficient is the 'squishy' number.
Interesting talks, but they don't mention pressure. Which is the point I've been trying to make. Water is incompressible (unless you've turned it to steam in which case you have a big problem on your hands). So increasing the water pressure inside the shell is not going to have a significant effect on the ability to cool efficiently unless you're exploiting some side-effect of "low" pressure water flow. Bearing in mind that throttled at the input or not, there is still pressure pushing water through the shell. Unless your input pressure is not able to counter the head pressure due to gravity and friction within the shell in which case you have zero flow. I can't find any description of the physical effect on water of restricting the flow at the end of the shell (this would be considered a "nozzle" IIUC) which could account for an increased performance of a tube-in-shell condenser.

Maintaining higher pressure inside the shell might compress any air bubbles that are present, but won't cause them to be displaced unless you increase the flow-rate.

Until someone shows me where I'm wrong in my reasoning, I maintain that throttling input is equivalent to throttling output in terms of performance with the added security that in the event of a blockage, hot (and thus expanded) water has a clear path to leave where increased pressure will not cause deformation or rupturing of the pipes.

None of which is to say that throttling the outlet is dangerous per se, just that a no-cost gain in safety can be made by throttling the input.
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Re: Controlling Flow

Post by Andrew_90 »

From a safety perspective having the tap on the input would be better, I agree. But not enough of a consideration to replumb mine to the inlet.

The advantage to being on the outlet is that I can pressure test the condensers :mrgreen:
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