where to place cooling water flow control on shotgun

[Bigvalveturbo]

I am building a Shotgun and in the past with my Leibigs i have used a 1/2 sweat on valve to control the water flow. my question is there any advantage to putting the flow control on the colling water exit side of the condenser so that the colling water is under pressure?

for those you who will ask it's a 2 inch with 4 1/2 tubes and 7 plates 38 inches of cooling area. Over kill? Perhaps

[shadylane]

The cooling water flow fills the shotgun from the bottom and drains out the top.

I prefer to have the valve on the cold side, it's less painful than turning a hot valve.
There's also less pressure inside the shotgun jacket and less likely to leak.

[Salt Must Flow]

Having the valve on the cold side allows any gas bubbles to freely escape through the top.

[NZChris]

I put the valve before the inlet hose to minimize pressure on connections and hoses during runs.

[BrewinBrian44]

I put the valve before the inlet hose to minimize pressure on connections and hoses during runs.

^^ this

[Twisted Brick]

The cooling water flow fills the shotgun from the bottom and drains out the top.
I prefer to have the valve on the cold side, it's less painful than turning a hot valve.
There's also less pressure inside the shotgun jacket and less likely to leak.

I like to run my valve on the output (hot) side. Shell and tube heat exchangers like ours achieve a higher overall heat exchange coefficient when operated with shell side pressure. For every S&T unit built, commercial heat exchange manufacturers configure an optimum working design pressure depending on its application. Variables considered are vapor tube thickness, diameter and length, shell length and diameter and coolant flow rate along with number/spacing of and type of baffles and others.

Bigvalveturbo, your baffles have had their tube pitch and cut (open coolant flow area) optimized for a 2” shell and pull additional duty in keeping your vapor tubes aligned while regulating coolant flow across each vapor tube to overcome laminar flow. They also aid in maintaining a consistent pressure level over the length of shell.

The flanges built into each end plate were designed for ease of soldering, but also to overcome the stresses of internal pressure, not that its significant anyway. Over the last 7yrs and many dozens of strip/spirit runs, I have yet to experience a leak either from my shotty itself or any of the coolant hoses and fittings.

While its popular for some members to dismiss shotguns as overkill and claiming they needn't be made of copper or with baffles, taking the time to understand and build the most efficient hobby condenser we can just adds one more area of distilling that helps keep the hobby moving forward. I can safely say that to date, members in 35 states (several states with 7 or 8 members) now rely on shotgun condensers to process their spirits.

This condenser is more than we need most of the time, but late in a run, with a 30gal coolant reservoir of 130F water, it's nice to know one's condenser can overcome the shrinking temp differential and keep knocking down vapor like a champ. I guess thats one of the reasons many of us have looked into methods to cool the steaming exit water created by our most-efficient condensers.

for those you who will ask it's a 2 inch with 4 1/2 tubes and 7 plates 38 inches of cooling area. Over kill? Perhaps

I'm not sure if you plan to make your shotgun 38" long, but my 21" shotty will knock down 11kw without blinking. The vast majority of members who have built their shotties with my plates have opted for 5 baffles in a 21" shell, while only a handful have installed 7 baffles in a 24" shell. Keep in mind that the longer the shell, the heavier it will be, especially when full of coolant.

[Bigvalveturbo]

I like to run my valve on the output (hot) side. Shell and tube heat exchangers like ours achieve a higher overall heat exchange coefficient when operated with shell side pressure. For every S&T unit built, commercial heat exchange manufacturers configure an optimum working design pressure depending on its application. Variables considered are vapor tube thickness, diameter and length, shell length and diameter and coolant flow rate among others.


I'm not sure if you plan to make your shotgun 38" long, but my 21" shotty will knock down 11kw without blinking. The vast majority of members who have built their shotties with my plates have opted for 5 baffles in a 21" shell, while only a handful have installed 7 baffles in a 24" shell. Keep in mind that the longer the shell, the heavier it will be, especially when full of coolant.

Yes 38 inches of cooling length from end cap to end cap 7 baffles. The total over all length is tbd

Additional pressure for better efficiency is what I was wondering about. I am confident that my solder joints will hold. I have yet to decide what to do about the suspended weight of the condenser, for my Liebig all 120inches of it! It ran 60 inches with a u turn and 60 inches back. in order to support it I 3d printed a leg for it, for the weight and to keep it from wobbling. I am thinking something similar here. Think a kick Stand, However with 10 gallons in the pot it should hold the weight with no support anyway.

Thanks for all the input guys! as a high school dropout (a successful one i think) i am definitely an eyeball engineer but i love to hear from guys who are smarter than me!

[Twisted Brick]

Yes 38 inches of cooling length from end cap to end cap 7 baffles. The total over all length is tbd

Additional pressure for better efficiency is what I was wondering about. I am confident that my solder joints will hold. I have yet to decide what to do about the suspended weight of the condenser, for my Liebig all 120inches of it! It ran 60 inches with a u turn and 60 inches back. in order to support it I 3d printed a leg for it, for the weight and to keep it from wobbling. I am thinking something similar here. Think a kick Stand, However with 10 gallons in the pot it should hold the weight with no support anyway.

Thanks for all the input guys! as a high school dropout (a successful one i think) i am definitely an eyeball engineer but i love to hear from guys who are smarter than me!

Wow! 38" is a lot! TBH, I cannot comment on how much more cooling power a shotty of that length will provide. It's waaay more than what's needed for knockdown, especially for a 10gal still charge. And besides, in your neck of the woods it shouldn't be difficult to employ colder coolant water.

Interestingly, its a little more complicated than that. More pressure does not translate to more efficiency or higher HXC. The concept of pressure drop (the inherent reduction of pressure caused by friction from surfaces inside the shell) has been studied to death and there is a point where some pressure drop is desirable. Designing the condenser to stay close to that point is the challenge, and admittedly beyond the scope of our shotties. To put it in simple terms, we can get more knockdown power out of our shotties by simply increasing coolant flow rather than adding length to the condenser.

For grins, here is a simple description of pressure drop.

[Salt Must Flow]

I agree, 38" is unnecessarily long. The vast majority of the shotgun would be cool as can be and only the end would be hot. It would practically have steam exiting the water's output. At nearly half that length it would work just the same. I made my shotgun condenser 24" long. During 5500W stripping runs you'll use a higher water flow than when during a spirit run. During a spirit run, it barely uses a trickle of water. Stripping with 11000W I need to turn the flow up, but a longer shotgun wouldn't help much, if at all really. I've even connected two 24" shotguns together and witnessed this for myself. I had to deliberately turn the flow up otherwise it would shoot steam bubbles out of the water's output while the vast majority of the shotguns were cold as can be.

Think about it ... If a 18" shotgun knocks down 100% of the vapor during a stripping run with X water flow, making it any longer wouldn't really help. You could certainly use less water with a longer shotgun, but by the time you have any kind of temp gradient, it's shooting steam out of the other end. To stop that from happening you have to increase water flow which defeats the purpose of having a longer shotgun to begin with.

[shadylane]

Here's a shotgun PC for a keg sized still.
The cooling was designed to connect to water hoses. With the valve on the inlet.
If the valve was on the hot side, it would be too hot to touch.

viewtopic.php?t=49639#top

[NZChris]

I don't know of any science that supports the notion that pressure increases the rate of heat transfer in something like a shotgun or Leibig. If anyone knows of something, I'd like to see it posted here.

[shadylane]

I don't know of any science that supports the notion that pressure increases the rate of heat transfer in something like a shotgun or Leibig. If anyone knows of something, I'd like to see it posted here.

I can't find anything about pressurizing the cooling water.

[Bigvalveturbo]

interesting reading guys, since it is already soldered together and is just waiting a pressure test shortening is not an option at this point. we will have to see how it works, perhaps in the future i will add a third heating element and strip at 17kw (not really)

[Yummyrum]

I have always had the control valve on the outlet .

But , there have been stories on the forum where this has lead to an accident .

Maybe a minor one , but stories have been where coolant flow got stopped or reduced to point where water in Dephleg got so hot that it could not escape , but rather back tracked through the input hose causing it to melt and spray hot water through a burst hose .


Now I’m not convinced that this is a good enough argument for putting the valve on the input side . But it is a valid point along with letting accumulated bubbles escape via an un-interrupted outlet .

[still_stirrin]

The “valve on the inlet” vs “valve on the outlet” question gets asked often and members have different reasons for their solution. But, as a retired “oil patch” engineer, there can be a few concerns for location of flow control valves.

First, the system designer must consider the design working pressure of the vessel, ie - shell and tube heat exchanger. If working pressures are high, then heat transfer may be restricted by pressure drop due to flow through the HEX. And example of this is natural gas and oil production at 15,000 psi (and higher) working pressures. Often pressure drop devices are needed before the HEX to get the pressures down to where the fluids can be appropriately cooled. This makes separation of oil and gas possible.

Note that in a production system, the valves for flow control are “modulated” and typically both upstream and downstream of the high pressure vessels.

Another thing to consider for the placement of the coolant flow control valve is how the valve’s pressure drop will affect the fluid flow through the process vessel, heat exchanger in this case.

If the valve is on the inlet and the source pressure is high (50 psi or higher), closing the valve to limit flow will create a significant pressure drop at the valve which can, and most likely does cause cavitation. This cavitation will upset laminar flow as well as heat transfer stability.

If the valve is located on the outlet, the HEX will always be filled with coolant at the source pressure such that cavitation will not affect heat transfer performance.

Regulating pressure for flows with a lower source pressure, ie - recirculating pump systems is less critical to placement although “dead head” pressure is a concern for centrifugal pumping systems (most common in pond pumps).

A better way to control flow for this type of pumping system is a “return circuit”, a branch from the pump’s discharge connected back to the pump’s inlet with a regulating flow valve in this short closed loop. The return circuit should be at least the same piping diameter as the network piping running to the heat exchangers because the return circuit becomes a “flow divider” of the pump’s flow.

In conclusion, I would (always) recommend putting the flow control valve on the discharge end of the heat exchanger and if access to the valve, ie - for a reflux condenser atop a tall column, I would run piping from the HEX discharge outlet to a remotely located valve where it could be effectively managed. Remember, the heat exchanger and all the piping to/from it will be at the coolant’s source pressure minus any pressure loss through the system due to the flowrate, so it should be “full of liquid”.

I hope this discussion helps a little in the OP’s questions.
ss