Cm condensers are too efficient?

[Alchemist75]

It occurred to me that the whole reason folks find even newer cm designs "fiddly" is because the range of adjustment on the RC needle valve is quite literally a hairs bredth of a turn. Now you learn how to work this if you're running a cm and you're fine in the end but I feel like there has to be a way to make things a little less sensitive. My original cm condenser was an exterior coil with a few through condensers leading up to it. I thought I needed to make it counter flow so I fed the whole thing through the top. It was pretty touchy and only needed the top couple coils to be cold to really maintain a high reflux ratio. The vapor speed on my pathologically narrow column still wasn't enough to overpower this inefficient design at full flow so I was happy with it......until the annealed copper coil eventually sprang a leak. I built a new one, a tube and shell "west" condenser with a few through condensers inside it and fed it from the bottom. This one's about 4.75" in length and holds full reflux with all I throw at it, it's also touchy, maybe even more than my first design. It works, I can hit the same abv the old design did, counterflow be damned ( I speculate this design could be used to make PC's at a fraction of the recommended length but don't quote me on that.) . I feel now like maybe the trick to giving greater adjustment range and reducing control sensitivity may boil down to making a much less efficient condenser. The older cm designs use a few through tubes but I wonder if even that might be more than this design truly needs. Perhaps I misunderstand the principals involved here but i theorize that the cm needs more of a dephlegmator in the classic sense i.e. a partial condenser that can only achieve full reflux when the valve is open 100% without having to heat the water feed. So, first, correct my idea here if it's wrong please and then explain why in pornographic detail, the engineering fascinates me. My idea for an ideal cm dephlegmator might be something like 3 narrow through condensers spread further apart, perhaps a very narrow "west" style tube and shell or even more liebig proper that provides only a couple inches of actual cooling surface. You get the picture, something seriously under powered that can only just hold full reflux when completely open. This seems to make sense in my mind because I know both of my RC designs had way more oomph than is required to control take off meaning that anything above a slow trickle will throw the column into full reflux and even cool off the whole top of the column no problem.
Ok, there's my notion, cm condensers need to be less efficient: destroy it or support it. Ready, set, pick it apart!

[shadylane]

May I suggest a dimroth condenser and a little bit of copper mesh.
On my still, it works better than a shotgun dephleg
The dimroth is more compact, easier to build, less likely to leak and has much better throttle response.

[Alchemist75]

So a dimroth on a cm, I assume it would have to be moveable as the vapor typically has to make it past the dephlegmator to get to the take off. Actually, now that I think about it, exactly how would a dimroth work on a cm? My existing dephlegmator is plenty and it's pretty short, I feel like a dimroth would work roughly the same in terms of efficiency, perhaps even more so. So would a dimroth provide a less sensitive control range? That's the aspect of the cm I feel like could brook improvement, less tight control.

[Alchemist75]

step0002.jpg (12.64 KiB) Viewed 4160 times

This is the condenser as is. The guts of the thing aren't visible but it's a tube and shell with three through condensers built into it. The view looking into it from the bottom displays the centering collar that slips on and then there's a bit of scrubby down in there to cause turbulence. The through condensers are just past the scrubby being 3 in total. The functional cooling area, not including the 3 through condensers is 4.75" in length. The vapor tube itself is 3/4" id and the annular flow space inside the condenser jacket is 1/4". It works very efficiently considering its size. It's been done before, nothing new, it's a tube and shell meets cold finger design. Anyway, no problems doing it's job, these are just for reference. The question is: should a cm condenser be LESS efficient so that the coolant control isn't so tight/sensitive?

The reflux condenser I'm using is basically the same concept as the one described here:
viewtopic.php?f=87&t=54946&start=0
Except mine is much shorter, does not use pvc, is open at the top (cm) and has a narrower annular flow space.

[Bushman]

I have a shotgun condenser with a ball valve not needle and have no problems. My shotgun condenser is built different than most in that both water in and out come through the top of the condenser. The tube with the water in goes to the bottom of my dephlagmater and fills the out tube. The tube with the water out is at the top of the dephlagmater so the hot water leaves at the top thus filling the whole dephlagmater. I have 1/2” water tubes and five 3/4” vapor tubes. I can get 100% reflux and when I have equalized my column I have to barley turn the knob to slow down the water flow and then wait a few minutes before I readjust so that I get the take-off rate correct for the type of alcohol I am running. I also readjust it after heads to take off at a bit faster at the hearts so I don’t lose equilibrium.

[Alchemist75]

@bushman: like you, I barely have to adjust my reflux valve to change the reflux ratio. Literally just a nudge and maybe that's just the nature of it. It doesn't give me problems at all but I wonder if there isn't a method of making the controls a bit less sensitive. I'm literally running a wee trickle through it to maintain high reflux and it takes very little to push it to full reflux. My RC is a humdinger in terms of it's ability to knock down vapors. Less sensitive control is what I'm chasing here so my theory is that CM condensers might be easier to fine tune if they were somewhat less efficient.....

[Bushman]

I am just the opposite, once I learned how to run my rig being efficient to me is a plus. Before my CM I first built a VM. The CM is so much more versatile allowing me to make any product I want where as the VM was pretty much all neutrals.

[shadylane]

now that I think about it, exactly how would a dimroth work on a cm?

Here's a dimroth and shotgun for a 4" CM
Both clamp on the top of the column and have similar max knock down power.
The dimroth started with more copper tubing, then was cut down until it was barely enough

[Alchemist75]

Oh duh, now that idea makes sense, of course. Mine uses internal cooling area as well, sometimes the obvious eludes me, sorry. I just know I've heard complaints about cms being hard to control and I thought it might in part be an issue of how hair line tight the needle valve controls the RC. The one I use currently is compact but definitely over powered. Maybe that's just the nature of the beast with cms. I may end up tinkering anyway, perhaps running hotter water to the RC would reduce sensitivity, that little puppy gets cold, fast and will literally cool all the plumbing above it in short order.....

[WillieP]

First off, I'm a newbie, so take this for what it's worth.
My thought is that the RC needs to be properly sized to the BTU's/watts that are being put in (same as a PC).
If the RC is way overpowered for the amount of vapor that it has to try to knock down it would need to have just a trickle of coolant moving through it, and with a larger volume of coolant moving through it, it could cool the top of the column.
If you are trying to drive 20mph, it's easy to do with a moped, but really hard to do with a dragster.
Does the sensitivity of your RC seems to adjust better when you throw all the power you have at it?
Hope this made sense!

WillieP

[cranky]

I run a pretty standard shotgun on my packed tower and a CSST dimroth on the flute, with ball valves on both.. The dimroth is a little easier to control but only slightly. I really don't feel either is much of a problem.

[Alchemist75]

First off, I'm a newbie, so take this for what it's worth.
My thought is that the RC needs to be properly sized to the BTU's/watts that are being put in (same as a PC).
If the RC is way overpowered for the amount of vapor that it has to try to knock down it would need to have just a trickle of coolant moving through it, and with a larger volume of coolant moving through it, it could cool the top of the column.
If you are trying to drive 20mph, it's easy to do with a moped, but really hard to do with a dragster.
Does the sensitivity of your RC seems to adjust better when you throw all the power you have at it?
Hope this made sense!

WillieP

You just directly addressed what I theorize about: the cm design might actually benefit from a less efficient condenser. In terms of design my particular cm is of the newer generation with its split coolant lines, appropriate condenser placement, needle valve control, proper centering etc. All great right? Right. Condenser does it's job almost too well. The optimal reflux ratios are achieved with the needle valve almost closed, I base my judgement of reflux on the slight, dripping trickle coming from the RC coolant output line. If I have the valve 100% open it provides far, far more cooling action than it needs. I speculate, perhaps wrongly or rightly, that a much less efficient design would make for looser controls which might grant even finer control of the take off at the PC. Again, a tube and shell only a couple inches long, a few through condensers spread over a wider area, something that requires more from the valve than just a nudge. I'm accustomed to the nudge but maybe there's a way to widen those control parameters. The other approach might be to preheat the water entering the condenser so that greater input is required to achieve full reflux.
Understand that I'm mulling this over in my head, it's not any kind of absolute but it seems intuitive. I've read comments in other places that talk about dephlegmators proper as being fed with warm liquid as opposed to cold. My assumption would be that a greater degree of fine tuning is possible using less efficient cooling means.

[Alchemist75]

What I'm going to try on my next stripping run is pumping hotter water into my system and see what happens when I play with the valve. I'll either prove myself right or wrong and post the results. Maybe too reducing the speed of coolant flow from the tap as well. I tend to run the coolant fast through my rig. Ever since it was suggested that I put scrubbers in the PC I haven't been very precise about coolant flow control. Perhaps a lower flow speed from the tap which is slowed down yet further by the reflux valve might loosten the controls up. You'll have to open the valve much more if the flow heading in is slower......I think.

[Manc]

What I'm going to try on my next stripping run is pumping hotter water into my system and see what happens when I play with the valve. I'll either prove myself right or wrong and post the results. Maybe too reducing the speed of coolant flow from the tap as well. I tend to run the coolant fast through my rig. Ever since it was suggested that I put scrubbers in the PC I haven't been very precise about coolant flow control. Perhaps a lower flow speed from the tap which is slowed down yet further by the reflux valve might loosten the controls up. You'll have to open the valve much more if the flow heading in is slower......I think.

Hi Alchemist

I think that you have got the right idea here. I now run my coolant off a pond pump in a 220 litre barrel and with head height etc. It pumps at 1.5 litres a minute fully open and it easy to control with a basic needle valve.

Also I'm not sure if you have thought about this but how about plumbing your RC after your PC in line. So your RC works off the warm water from the PC this is how I do it and find it easy to control.

I've read this thread when first deciding on how to to run my RC it helped can't remember exactly what was in it as it was a while ago but remember it being useful.

viewtopic.php?t=22424

This is just my opinion but hope it helps

Lee

[Alchemist75]

@manc: I have considered exactly what you describe though I'd either have to move the T and add a second control valve or include some kind of blow off because the current RC has a valve built in to the column. Not that hard to do though next time I do a RC I'll put the valve further down the line. A good suggestion actually though it flies somewhat in the face of conventional wisdom. I'm questioning conventional wisdom here anyway so I may just try that after I do some preliminary experiments...now I'm gonna sit and read that thread, looks like it gets interesting.

[Alchemist75]

I wish I could find a thread I found the other day that attempts to address this by placing a second valve between the T and the RC valve. At one point in that thread USGE states that a reduction in RC length helped improved control.....less efficient condenser anyone? I tend to overshoot with condenser designs not really realizing just how little is required especially with the dephleg. Also, Myles suggests running the water path via a coil around some heated element on the still, maybe 1 pass around the top of the boiler.(?) Don't wanna get it too hot....

[NZChris]

You should get more control by reducing the pressure to the valve. My supply is 15psi and I've never had a control problem.

[Alchemist75]

@chris: that's one of the first things I'm going to try. I can reduce flow speed to the RC valve by clamping the inlet hose further down to see if I can adjust the RC a little more finely. Failing that I'll try hot water to see if that works.....then there was the suggestion of actually having two, separately regulated rcs with one being under powered but that would be last ditch

[NZChris]

Restricting the flow with a second valve doesn't have the same effect as reducing the pressure. I use a cheap irrigation pressure reducer I bought at a garden center.

[Alchemist75]

Ok, I'll have to check into that one. I'm sure I can get it locally. My next stripping run should be tomorrow so I'll start playing around with various parameters and see where things end up.

[WillieP]

@chris: that's one of the first things I'm going to try. I can reduce flow speed to the RC valve by clamping the inlet hose further down to see if I can adjust the RC a little more finely.

I'm not a fluid mechanics kind of guy. That being said, I think that there may be a definition issue here.
Pressure is the force behind the fluid.
Volume is the amount of fluid flowing.
They are related but not the same thing. There is also speed of the fluid that comes in to play.

If you are cutting steel with a water jet, you need a very small orifice, very high pressure but very low volume.
But if you are filling a swimming pool, you need a large orifice, low pressure but very high volume

I don't have the answer here, just stating my thoughts out loud.

I'm very interested in this as I am in the design phase of a 3 inch flute myself.
There is a lot of great information in the below link, although I haven't finished reading it all yet.

I've read this thread when first deciding on how to to run my RC it helped can't remember exactly what was in it as it was a while ago but remember it being useful.

viewtopic.php?t=22424

I do not see this as an efficiency problem. I see it as a sizing problem.
If you need 20 horse power, you can use a lawnmower engine with bad piston rings and an out of tune carburetor, or you can use a little pimped out model airplane engine. HP equals amount of work that can be done. (just pulled those numbers and example out my ass)
We have a certain amount of cooling that needs done. We can do it very efficiently with a small RC, or do it less efficiently with a larger RC, but it's about the amount of cooling that needs done compared to the amount of heat being put in.
Just my two cents worth.
Really hope you get it working the way you want.
WillieP

[NZChris]

A method I'm using a lot lately is feeding a condenser from a reservoir 1'-3' above it's inlet. The low head pressure pretty much eliminates the chance of a blown hose to a condenser and flow control is easy.

The 15 psi regulator between the mains and the distillery has stopped the annoying hose blowouts I'd been having and I currently use that for the RC supply.

[Alchemist75]

A method I'm using a lot lately is feeding a condenser from a reservoir 1'-3' above it's inlet. The low head pressure pretty much eliminates the chance of a blown hose to a condenser and flow control is easy.

The 15 psi regulator between the mains and the distillery has stopped the annoying hose blowouts I'd been having and I currently use that for the RC supply.

So do you use a pump to circulate your water or are you feeding the reservoir from a tap?

[Alchemist75]

Fortunately I don't have hose blowouts, everything is pretty firmly assembled and can handle pretty high coolant input which is how I typically run it. I have had the outlet hose from the PC blast off like a rocket a couple times from the pressure but I keep it clamped down anymore lol

[NZChris]

I don't recirculate.

Reservoirs are topped up from the mains via the 15 psi reducer and solenoid valves.

[Alchemist75]

Just fired her up for the strip, let's see if I can tweak things a bit.....

[Alchemist75]

So here's what I gathered fooling with a couple variables:
Attempting to slow input from the tap before hitting the RC valve had little if any effect other than forcing me to open up the valve more to maintain full reflux. No obvious changes to control sensitivity.
Increasing the water flow temperature had a somewhat more observable effect giving more wiggle range with take off though not enough to be earth shattering. Part of the problem I had there was that despite separate plumbing, both RC and PC use the same water source so I lost some efficiency at the PC. It did seem to confirm the suspicion however that a less efficient dephlegmator does allow a certain degree of greater fine tuning so I believe my initial theory was correct.
Another noticable side effect of using the RC in the unpacked column was that I had pulled 64-65% abv at the 2 liter mark. That's the highest I've yet achieved on a stripping run (not that it matters terribly). Typically it drops below 40% by that point though I was able to pull another 200 ml before that happened so I guess it flattened the run a bit.
My conclusion: hotter input to dephlegmator reduces efficiency granting slightly finer control. Makes me want to play around with Myles idea of having two separate rcs, one to hold at full reflux and a second, underpowered one to tune the take off rate......that'll have to wait though, maybe on my next build.

[Yummyrum]

Alchemist75
I’m hearing you . CM ‘s are a royal pain in the backside to control . So many variables to balance .
Before I’d started on my flute I had seen how guys were experimenting with different lengthed deflags to try to optimize the control . Longer ones were better at full reflux with high powers but shorter ones gave better and less fiddly control in the typical operating range .
I come up with an idea of an adjustable height deflag that would touch both bases .
Never got to try it but have wondered how it would work . viewtopic.php?f=87&t=72107#p7537809
The idea was that I adjust the level of water in the deflag to simulate a short deflag or a long one . The problem is in a short deflag , the vapour simply blasts past the cool copper tubes so fast that it doesn’t have a chance to condense . Flow rate adjustment was really a mute point .

Since then what I have come to realize is that the lag between adjustment and product flow change is largely due to the volume of water in the deflag . Squeezing the most pipes and having the most minimal water area will allow for minimal lag time and minimal touchy control of flow .
So in short my deflag is a shitty design . Too much water and not enough pipes .

Further on I am realizing that the whole CM control is a bad way to go and am now running my flute with a VM head with is way more reliable and has reduced my adjustment lag time from minuates to seconds . Just sayin

[WillieP]

Further on I am realizing that the whole CM control is a bad way to go and am now running my flute with a VM head with is way more reliable and has reduced my adjustment lag time from minuates to seconds . Just sayin

Yummy,
Would you mind explaining the "VM head" please.
Are we talking a 'coil being moved up and down to act as a valve' or a 'physical' valve?
I currently have a 2 inch ccvm, and am designing a 3 inch flute build. I've never thought of using anything but the classic dephag on top of the flute. More info please.

Didn't mean to Jack the thread, happy to PM Yummy if you don't want this on here.

Cheers,
WillieP

[HDNB]

so i use a SS deflag. it is very inefficient and cannot hold full relux with room temp recirc water. I can get more reflux with colder water (installed an intercooler on the recirc system for this)

using a gate valve on the (bottom) input of the RC there is a distinct no reflux and full (well, the most i can get) reflux the balance of reflux is evenly graduated between within about not quite 1 full turn of the gate valve. i can acheive 50-80 abv on a 10% mash with 1 or 2 ABV resolution by turning the gate valve within this range....so i think your theory of inefficiency relating to tuning accuracy is valid.