## Firebox condenser tube spacing

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• If I m making a firebox condenser with, say, 1/4 OD tubes what is the minimum tube-pitch before cooling becomes ineffective? Is there some theoretical guide
Message 1 of 9 , Jun 1, 2009
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If I'm making a firebox condenser with, say, 1/4" OD tubes what is the minimum tube-pitch before cooling becomes ineffective? Is there some theoretical guide for this? Does it matter as long as they don't touch? I guess another way to look at it is in perforated sheet metal they talk about % open area. Is there a % open area maximum for round tube firebox condensers?

i.e. I can get about 31 tubes in a 2" pipe and 73 in a 3" pipe on a .3125 pitch triangular pattern. 0.3125 pitch - 0.25 tube dia = 0.0625 between tubes (1/16"). I want my generic, detachable output condenser to handle about 15-20KW and to get a reasonable length that's a lot of parallel tubes.

Thanks
Daryl
• ... 15-20KW ??!!? You looking to produce 5 gallons per hour? Not in the hobby range. You need an engineer consultant. Slainte! regards Harry
Message 2 of 9 , Jun 2, 2009
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--- In new_distillers@yahoogroups.com, "daryl_bee" <darylbender@...> wrote:
>
> If I'm making a firebox condenser with, say, 1/4" OD tubes what is the
> minimum tube-pitch before cooling becomes ineffective? Is there some
> theoretical guide for this? Does it matter as long as they don't touch?
> I guess another way to look at it is in perforated sheet metal they talk
> about % open area. Is there a % open area maximum for round tube firebox
> condensers?
>
> i.e. I can get about 31 tubes in a 2" pipe and 73 in a 3" pipe on a
> .3125 pitch triangular pattern. 0.3125 pitch - 0.25 tube dia = 0.0625
> between tubes (1/16"). I want my generic, detachable output condenser to
> handle about 15-20KW and to get a reasonable length that's a lot of
> parallel tubes.
>
> Thanks
> Daryl
>

15-20KW ??!!? You looking to produce 5 gallons per hour? Not in the hobby range. You need an engineer consultant.

Slainte!
regards Harry
• ... This is an output condenser not reflux. Its a common 60,000 BTU hardware store propane heater (~20KW) which I m thinking would be good for a stripper. If I
Message 3 of 9 , Jun 2, 2009
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--- In new_distillers@yahoogroups.com, "Harry" <gnikomson2000@...> wrote:
>
> --- In new_distillers@yahoogroups.com, "daryl_bee" <darylbender@> wrote:
> >
> > If I'm making a firebox condenser with, say, 1/4" OD tubes what is the
> > minimum tube-pitch before cooling becomes ineffective? Is there some
> > theoretical guide for this? Does it matter as long as they don't touch?
> > I guess another way to look at it is in perforated sheet metal they talk
> > about % open area. Is there a % open area maximum for round tube firebox
> > condensers?
> >
> > i.e. I can get about 31 tubes in a 2" pipe and 73 in a 3" pipe on a
> > .3125 pitch triangular pattern. 0.3125 pitch - 0.25 tube dia = 0.0625
> > between tubes (1/16"). I want my generic, detachable output condenser to
> > handle about 15-20KW and to get a reasonable length that's a lot of
> > parallel tubes.
> >
> > Thanks
> > Daryl
> >
>
>
> 15-20KW ??!!? You looking to produce 5 gallons per hour? Not in the hobby range. You need an engineer consultant.
>
>
> Slainte!
> regards Harry
>
This is an output condenser not reflux. Its a common 60,000 BTU hardware store propane heater (~20KW) which I'm thinking would be good for a stripper. If I want to crank it up and take the output back down to 20C for measuring this is what's needed worst case.

The other aim I'm trying to achieve is to minimize flow restriction or rather conserve the open tube area even though it's going through a condenser which is what led me to the firebox.

The question (tube spacing) is really applicable to *all* firebox condensers though if you want to make them as efficient/small as possible. I searched on tube spacing in both groups and really got nothing on this subject. I'm hoping to get a rule of thumb on open area vs efficiency drop-off which, I think, would be universally useful. Any help/pointers would be appreciated.

Cheers
Daryl
• I have one of those burners, and turned down low it seems to work just fine.... No one says we have to max them out! R daryl_bee wrote: ...
Message 4 of 9 , Jun 2, 2009
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I have one of those burners, and turned down low it seems to work just
fine.... No one says we have to max them out!

R

daryl_bee wrote:
<snip>
> This is an output condenser not reflux. Its a common 60,000 BTU hardware store propane heater (~20KW) which I'm thinking would be good for a stripper.
<snip>
• check the pictures from Whammo57.... there is a diagram of a tube in shell condenser with 21 tubes and the spacing Kim
Message 5 of 9 , Jun 2, 2009
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check the pictures from Whammo57.... there is a diagram of a tube in shell condenser with 21 tubes and the spacing

Kim

--- In new_distillers@yahoogroups.com, "daryl_bee" <darylbender@...> wrote:
>
> --- In new_distillers@yahoogroups.com, "Harry" <gnikomson2000@> wrote:
> >
> > --- In new_distillers@yahoogroups.com, "daryl_bee" <darylbender@> wrote:
> > >
> > > If I'm making a firebox condenser with, say, 1/4" OD tubes what is the
> > > minimum tube-pitch before cooling becomes ineffective? Is there some
> > > theoretical guide for this? Does it matter as long as they don't touch?
> > > I guess another way to look at it is in perforated sheet metal they talk
> > > about % open area. Is there a % open area maximum for round tube firebox
> > > condensers?
> > >
> > > i.e. I can get about 31 tubes in a 2" pipe and 73 in a 3" pipe on a
> > > .3125 pitch triangular pattern. 0.3125 pitch - 0.25 tube dia = 0.0625
> > > between tubes (1/16"). I want my generic, detachable output condenser to
> > > handle about 15-20KW and to get a reasonable length that's a lot of
> > > parallel tubes.
> > >
> > > Thanks
> > > Daryl
> > >
> >
> >
> > 15-20KW ??!!? You looking to produce 5 gallons per hour? Not in the hobby range. You need an engineer consultant.
> >
> >
> > Slainte!
> > regards Harry
> >
> This is an output condenser not reflux. Its a common 60,000 BTU hardware store propane heater (~20KW) which I'm thinking would be good for a stripper. If I want to crank it up and take the output back down to 20C for measuring this is what's needed worst case.
>
> The other aim I'm trying to achieve is to minimize flow restriction or rather conserve the open tube area even though it's going through a condenser which is what led me to the firebox.
>
> The question (tube spacing) is really applicable to *all* firebox condensers though if you want to make them as efficient/small as possible. I searched on tube spacing in both groups and really got nothing on this subject. I'm hoping to get a rule of thumb on open area vs efficiency drop-off which, I think, would be universally useful. Any help/pointers would be appreciated.
>
> Cheers
> Daryl
>
• ... 60,000 BTU isn t nearly the equivalent of 20KW in terms of actual heat transfer when you compare an open flame with an immersion heater. My shell-and-tube
Message 6 of 9 , Jun 2, 2009
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--- In new_distillers@yahoogroups.com, "daryl_bee" <darylbender@...> wrote:
> This is an output condenser not reflux. Its a common 60,000 BTU hardware store propane heater (~20KW) which I'm thinking would be good for a stripper. If I want to crank it up and take the output back down to 20C for measuring this is what's needed worst case.

60,000 BTU isn't nearly the equivalent of 20KW in terms of actual heat transfer when you compare an open flame with an immersion heater.

My shell-and-tube condenser (14 X 3/8"OD tubes soldered in rows of 3-4-4-3 into a 2" cap) will handle a 100K+ BTU burner at full blast.

> The other aim I'm trying to achieve is to minimize flow restriction or rather conserve the open tube area even though it's going through a condenser which is what led me to the firebox.

I would use a rough "1/2 of your tube OD" spacing between tubes. Remember also, your shell has a lot to do with it also. I used a 2" (trade size, not actual OD) cap as my tube bundle, but accidentally went overkill with a 4" ABS shell. The problem I foresaw was the lack of flow along the surface of the tubes. I put baffles inside the shell to constrict flow to the space immediately adjacent to the tubes.

> The question (tube spacing) is really applicable to *all* firebox condensers though if you want to make them as efficient/small as possible. I searched on tube spacing in both groups and really got nothing on this subject. I'm hoping to get a rule of thumb on open area vs efficiency drop-off which, I think, would be universally useful. Any help/pointers would be appreciated.

Some variables to take into consideration:
- The temperature of your coolant. Obviously, if your water is 25C, you're never going to get your condensate down to 20C.
- The difference in temperature between the coolant (variable) and the temperature of the vapor (relatively constant) affects your efficiency.
- The capacity of your coolant pump. The higher the capacity, the faster the flow of coolant along your tubes and therefore more efficient heat transfer. Also, as the spaces between tubes is reduced, the more drag is placed on the coolant and therefore the inclination to bypass the constriction at other locations.

It's a start...I can fill in any (of the many) gaps as needed, but hopefully this is something to chew on.

Trid
-will be building another sooner or later
• Hi, I m no expert on shell and tube condensor design but I ll through in my 2 cents. (BTW Iid never heard of them being called firebox or shotgun condensors
Message 7 of 9 , Jun 3, 2009
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Hi,
I'm no expert on shell and tube condensor design but I'll through in my 2 cents. (BTW Iid never heard of them being called firebox or shotgun condensors until I joined here)
Designing shell and tube condensor can be a complex business but at small scale (<2-3kw) a lot of this can be factored out by over design without much risk. As things get bigger the design get more involved so be warned, there is a heap of information out there as these thing have been used since the dawn of time (well at leat since the industrial revolution :)

My gut tells me that you won't get away with placing your tubes that close together as the condensate could (will?) hold up in the condenser (and basiclly block it). FYI, I've spaced mine 6mm betwen tube surfaces and fitted 37x1/4 inch tubes in a 4 inch shell nicely. Based on my rough calculations my design at 20kW would need to be about 2 to 3 foot long. I post data once I get it steamed up.

It might pay do as much research as you can before you start cutting copper, so here are a couple of links that might help get you started...
http://www.cheresources.com/designexzz.shtml
http://www.engineeringpage.com/technology/thermal/pitch.html

I've put together a small spreadsheet model that could help you get started. I'll tidy it up and post it over the weekend but you will still need to make some big assumptions. By big I mean it would be easy to build a unit that was either far too big (i.e. wasted copper, my guess is you'll need about 20m of 1/4 inch tube) or too small (and you'll have to throw a power of cooling water throught it).
It would still be a good idea to talk to an expert and try to bribe him with some product ;)

Good luck.
Sid.
• ... Very good contribution Sid. Probably should be in the Advanced Distillers group. This is the group for new starters. Jim can probably relocate it. Your
Message 8 of 9 , Jun 3, 2009
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--- In new_distillers@yahoogroups.com, "landrover_ffr" <sid.rains@...> wrote:
>
> Hi,
> I'm no expert on shell and tube condensor design but I'll through in my 2 cents. (BTW Iid never heard of them being called firebox or shotgun condensors until I joined here)
> Designing shell and tube condensor can be a complex business but at small scale (<2-3kw) a lot of this can be factored out by over design without much risk. As things get bigger the design get more involved so be warned, there is a heap of information out there as these thing have been used since the dawn of time (well at leat since the industrial revolution :)
>
> My gut tells me that you won't get away with placing your tubes that close together as the condensate could (will?) hold up in the condenser (and basiclly block it). FYI, I've spaced mine 6mm betwen tube surfaces and fitted 37x1/4 inch tubes in a 4 inch shell nicely. Based on my rough calculations my design at 20kW would need to be about 2 to 3 foot long. I post data once I get it steamed up.
>
> It might pay do as much research as you can before you start cutting copper, so here are a couple of links that might help get you started...
> http://www.cheresources.com/designexzz.shtml
> http://www.engineeringpage.com/technology/thermal/pitch.html
>
> I've put together a small spreadsheet model that could help you get started. I'll tidy it up and post it over the weekend but you will still need to make some big assumptions. By big I mean it would be easy to build a unit that was either far too big (i.e. wasted copper, my guess is you'll need about 20m of 1/4 inch tube) or too small (and you'll have to throw a power of cooling water throught it).
> It would still be a good idea to talk to an expert and try to bribe him with some product ;)
>
> Good luck.
> Sid.
>

Very good contribution Sid. Probably should be in the Advanced Distillers group. This is the group for new starters. Jim can probably relocate it.

Your comment on "firebox" & "shotgun". This refers to a design that's an overhead total reflux condenser, not a final product cooler. The shell carries the coolant and the tubes are fed vapor from directly below, being open to the column top and packing.

As you no doubt know, the more usual shell & tube layout normally requires the fluid of higher density (water coolant) to occupy the tubes through waterboxes, and the fluid undergoing phase change (the ethanol vapor) to run in the shell-side.

The "firebox" is the opposite configuration, and it also allows ascending vapor and descending liquid to interfere with each other. Thus purity is affected through contamination.

For this reason I don't recommend the firebox design, although it is easy to fabricate and does work (albeit inefficiently for the materials used). There's just too much chance of liquid holdup in small bore tubing.

Compare the firebox/shotgun to the crossflow I designed, which will outperform a similar sized firebox and/or a coil by orders of magnitude.

Slainte!
regards Harry
• Hi Thanks so much for the excellent info sources. Based on the table in your second link I hit the nail on the head (.312 pitch with .250 tubes) with my
Message 9 of 9 , Jun 5, 2009
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Hi

Thanks so much for the excellent info sources. Based on the table in your second link I hit the nail on the head (.312 pitch with .250 tubes) with my initial sketch. I include a link below so you can see my initial ideas.

http://surfin_dude.tripod.com/20kw_condenser.pdf

I'd be very interested to see your spreadsheet. I'll be off-line for the weekend but will be back on Monday.

The .250 tubes (water in shell/vapour in tubes) seem OK for a condensate condenser but from what I'm reading, and what you say, could suffer from "choking" as a reflux. I'll likely redesign in 3/8" tubing. The idea is to make it as a screw-on component unit that can be used in a variety of applications.

This may be a bit overkill but 60,000 BTU *is* approx 20kW (~17.5). Efficiency of transfer into the still will reduce that but the online condenser calculations tend to bear out it's pretty efficient based on theoretical vs actual heat-up times. I had radial copper support channels (essentially fins) on the bottom of a copper tank over the flame.

Trid got me wondering so I did a test on the water supply and I can get 5.55 l/min @ 11C. So I think a 15"- 18" length is reasonable.

BTW, to Whammo57, nice work!

Cheers
Daryl

--- In new_distillers@yahoogroups.com, "landrover_ffr" <sid.rains@...> wrote:
>
> Hi,
> I'm no expert on shell and tube condensor design but I'll through in my 2 cents. (BTW Iid never heard of them being called firebox or shotgun condensors until I joined here)
> Designing shell and tube condensor can be a complex business but at small scale (<2-3kw) a lot of this can be factored out by over design without much risk. As things get bigger the design get more involved so be warned, there is a heap of information out there as these thing have been used since the dawn of time (well at leat since the industrial revolution :)
>
> My gut tells me that you won't get away with placing your tubes that close together as the condensate could (will?) hold up in the condenser (and basiclly block it). FYI, I've spaced mine 6mm betwen tube surfaces and fitted 37x1/4 inch tubes in a 4 inch shell nicely. Based on my rough calculations my design at 20kW would need to be about 2 to 3 foot long. I post data once I get it steamed up.
>
> It might pay do as much research as you can before you start cutting copper, so here are a couple of links that might help get you started...
> http://www.cheresources.com/designexzz.shtml
> http://www.engineeringpage.com/technology/thermal/pitch.html
>
> I've put together a small spreadsheet model that could help you get started. I'll tidy it up and post it over the weekend but you will still need to make some big assumptions. By big I mean it would be easy to build a unit that was either far too big (i.e. wasted copper, my guess is you'll need about 20m of 1/4 inch tube) or too small (and you'll have to throw a power of cooling water throught it).
> It would still be a good idea to talk to an expert and try to bribe him with some product ;)
>
> Good luck.
> Sid.
>
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