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Water Bath Design

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  • Andrew Forsberg
    Hi there Distillers, I m starting to get back to designing and fabricating a new still and would very much appreciate some advice on water bath design. There
    Message 1 of 13 , May 31, 2005
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      Hi there Distillers,

      I'm starting to get back to designing and fabricating a new still and
      would very much appreciate some advice on water bath design. There might
      be other forums, like miniature railway boards, which I should
      investigate as well, so if anyone has useful links I'd love to see them.

      The plan is -- surround a 70 litre boiler with a cut down 40 gallon drum
      which is half filled with heavily salted water. The surrounding drum
      would be welded to the boiler, and have a pressure release valve, a
      drain tap, and a screw cap fitting for filling the water bath.

      Here are the things I'm not so very certain about:
      1) Is a sight glass a worthwhile investment? Seeing as the jacket will
      be sealed after filling? I'm not quite sure how a sight glass would work
      around the insulation either.
      2) How many atmospheres is considered reasonably safe as far as pressure
      goes? I'm extremely not keen to get coated in superheated liquids AGAIN.
      I know a small amount of pressure for the steam above the water surface
      would be a good thing, but safety comes first!
      3) Is there a rule of thumb when it comes to indirect heating and
      guestimating heat transfer? i.e., if 2 x 1.2kW elements were heating the
      water jacket, and the jacket and boiler were well insulated, could I
      expect the boiler to receive more or less 2kW of heat? Ish? I know...
      terribly scientific...
      4) Are there any rules of thumb when it comes to heat input distribution
      for water jacket? For instance, is it better to have 4 or more small
      equidistant elements heating the jacket, or will 2 opposite elements do?
      5) Will the jacket just continue to build up pressure after the water
      comes to the boil? Or do they tend to transfer heat to the inner vessel
      readily?
      6) Is there a standard ratio of height and/or diameter to thickness for
      water jackets? Too thin would obviously be no good for a boiler, but too
      thick would mean there's a heck of a lot of water to heat up in the
      first place. More to the point, what would be considered 'too thick' or
      'too thin'?

      Sorry -- I'm guessing all of the above could be answered in a hundred
      different ways, and in the end they all boil down to 'what are you
      trying to do?' Some general advice and a shove in the right direction
      would be great. Schematics of working water jackets would be absolutely
      fabulous! Still, I'm happy to do the hard work on my own as well, and
      will report results later.

      Cheers
      Andrew
    • abbababbaccc
      Just an idea, but why don t you use oil in the jacket and a thermostat to keep the temperature reasonable? If you keep the oil at 100-120C temperature it
      Message 2 of 13 , May 31, 2005
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        Just an idea, but why don't you use oil in the jacket and a
        thermostat to keep the temperature reasonable? If you keep the oil at
        100-120C temperature it shouldn't flash very easily and you could
        leave the system open to atmosphere.

        - Riku

        --- In Distillers@yahoogroups.com, Andrew Forsberg <andrew@u...>
        wrote:
        > Hi there Distillers,
        >
        > I'm starting to get back to designing and fabricating a new still
        and
        > would very much appreciate some advice on water bath design. There
        might
        > be other forums, like miniature railway boards, which I should
        > investigate as well, so if anyone has useful links I'd love to see
        them.
        >
        > The plan is -- surround a 70 litre boiler with a cut down 40 gallon
        drum
        > which is half filled with heavily salted water. The surrounding drum
        > would be welded to the boiler, and have a pressure release valve, a
        > drain tap, and a screw cap fitting for filling the water bath.
        >
        > Here are the things I'm not so very certain about:
        > 1) Is a sight glass a worthwhile investment? Seeing as the jacket
        will
        > be sealed after filling? I'm not quite sure how a sight glass would
        work
        > around the insulation either.
        > 2) How many atmospheres is considered reasonably safe as far as
        pressure
        > goes? I'm extremely not keen to get coated in superheated liquids
        AGAIN.
        > I know a small amount of pressure for the steam above the water
        surface
        > would be a good thing, but safety comes first!
        > 3) Is there a rule of thumb when it comes to indirect heating and
        > guestimating heat transfer? i.e., if 2 x 1.2kW elements were
        heating the
        > water jacket, and the jacket and boiler were well insulated, could I
        > expect the boiler to receive more or less 2kW of heat? Ish? I
        know...
        > terribly scientific...
        > 4) Are there any rules of thumb when it comes to heat input
        distribution
        > for water jacket? For instance, is it better to have 4 or more small
        > equidistant elements heating the jacket, or will 2 opposite
        elements do?
        > 5) Will the jacket just continue to build up pressure after the
        water
        > comes to the boil? Or do they tend to transfer heat to the inner
        vessel
        > readily?
        > 6) Is there a standard ratio of height and/or diameter to thickness
        for
        > water jackets? Too thin would obviously be no good for a boiler,
        but too
        > thick would mean there's a heck of a lot of water to heat up in the
        > first place. More to the point, what would be considered 'too
        thick' or
        > 'too thin'?
        >
        > Sorry -- I'm guessing all of the above could be answered in a
        hundred
        > different ways, and in the end they all boil down to 'what are you
        > trying to do?' Some general advice and a shove in the right
        direction
        > would be great. Schematics of working water jackets would be
        absolutely
        > fabulous! Still, I'm happy to do the hard work on my own as well,
        and
        > will report results later.
        >
        > Cheers
        > Andrew
      • Robert Lemmen
        ... this is how it is done quite often in labs. you can heat the oil up to much higher temperatures, and the difference between the temperature inside the
        Message 3 of 13 , May 31, 2005
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          On Tue, May 31, 2005 at 10:35:03AM -0000, abbababbaccc wrote:
          > Just an idea, but why don't you use oil in the jacket and a
          > thermostat to keep the temperature reasonable? If you keep the oil at
          > 100-120C temperature it shouldn't flash very easily and you could
          > leave the system open to atmosphere.

          this is how it is done quite often in labs. you can heat the oil up to
          much higher temperatures, and the difference between the temperature
          inside the boiler and the oil will determine the input power. if you
          want to do it really well, don't just turn your power ona nd off, but
          make it adjustable and control that with a thermometer. this way you
          will avoid temperature fluctuations.

          cu robert

          --
          Robert Lemmen http://www.semistable.com
        • abbababbaccc
          Actually, I think it wouldn t hurt too much if the temperature fluctuates few degrees due to thermostat. If the oiltemperature varies from 120-124C it s still
          Message 4 of 13 , May 31, 2005
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            Actually, I think it wouldn't hurt too much if the temperature
            fluctuates few degrees due to thermostat. If the oiltemperature varies
            from 120-124C it's still always above the boiling point of the mash and
            the effect on heat transfer to the boiler should be quite small. You
            can of course heat the oil even more and lessen the effect of variance.

            - Riku

            --- In Distillers@yahoogroups.com, Robert Lemmen <robertle@s...> wrote:
            > On Tue, May 31, 2005 at 10:35:03AM -0000, abbababbaccc wrote:
            > > Just an idea, but why don't you use oil in the jacket and a
            > > thermostat to keep the temperature reasonable? If you keep the oil
            at
            > > 100-120C temperature it shouldn't flash very easily and you could
            > > leave the system open to atmosphere.
            >
            > this is how it is done quite often in labs. you can heat the oil up to
            > much higher temperatures, and the difference between the temperature
            > inside the boiler and the oil will determine the input power. if you
            > want to do it really well, don't just turn your power ona nd off, but
            > make it adjustable and control that with a thermometer. this way you
            > will avoid temperature fluctuations.
            >
            > cu robert
            >
            > --
            > Robert Lemmen http://www.semistable.com
          • Robert Lemmen
            ... well, it s almost 10% more in heat transfer at 78°C mash temperature... cu robert -- Robert Lemmen
            Message 5 of 13 , May 31, 2005
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              On Tue, May 31, 2005 at 01:09:39PM -0000, abbababbaccc wrote:
              > Actually, I think it wouldn't hurt too much if the temperature
              > fluctuates few degrees due to thermostat. If the oiltemperature varies
              > from 120-124C it's still always above the boiling point of the mash and
              > the effect on heat transfer to the boiler should be quite small. You
              > can of course heat the oil even more and lessen the effect of variance.

              well, it's almost 10% more in heat transfer at 78°C mash temperature...

              cu robert

              --
              Robert Lemmen http://www.semistable.com
            • don1lia2joe3
              If you read the previous post where I replied to using the old still for a beer striper you will notice that this still uses an oil bath for heat, the problem
              Message 6 of 13 , May 31, 2005
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                If you read the previous post where I replied to using the old still
                for a beer striper you will notice that this still uses an oil bath
                for heat, the problem with the one I have is that it gets to hot for
                use as a pot still and I do not want to convert that one to a reflux
                colum.

                My suggestions would include using a proper thermal transfer oil
                because it does not boil and the flash point is around 600F there is
                also very little expantion when it heats up like there is with salt
                water (also not corrosive)

                Another thing to consider is the heating, Oil holds heat a looooong
                time and cools down slooooly!! if you over heat your boiler your
                alcohol could be gone before you can cool it down. This is the
                problem with my still, the low end of my thermostat is 170F and runs
                up to 190F before automatic shutdown.

                My setup uses only one 220 V water tank heating element and works
                quite well at giving even heat.

                Please do not suggest that I change this still, it will not be used
                for Alcohol use but makes a good learning tool.

                As an added note:

                I already have my license to distill up to 10,000 gallons per year
                of alcohol in the United States for use as fuel, and I am designing
                and building a "small" continous run colum still with drying colums
                so that I can distill 5 to 10 gallons a day of 200 proof to mix with
                gasoline.

                Still is in planning stages but making and learning on smaller
                boilers and colums as I go, without this site it would not be
                possable to have this much fun learning.

                Thanks to all.



                --- In Distillers@yahoogroups.com, "abbababbaccc"
                <abbababbaccc@y...> wrote:
                > Actually, I think it wouldn't hurt too much if the temperature
                > fluctuates few degrees due to thermostat. If the oiltemperature
                varies
                > from 120-124C it's still always above the boiling point of the
                mash and
                > the effect on heat transfer to the boiler should be quite small.
                You
                > can of course heat the oil even more and lessen the effect of
                variance.
                >
                > - Riku
                >
                > --- In Distillers@yahoogroups.com, Robert Lemmen <robertle@s...>
                wrote:
                > > On Tue, May 31, 2005 at 10:35:03AM -0000, abbababbaccc wrote:
                > > > Just an idea, but why don't you use oil in the jacket and a
                > > > thermostat to keep the temperature reasonable? If you keep the
                oil
                > at
                > > > 100-120C temperature it shouldn't flash very easily and you
                could
                > > > leave the system open to atmosphere.
                > >
                > > this is how it is done quite often in labs. you can heat the oil
                up to
                > > much higher temperatures, and the difference between the
                temperature
                > > inside the boiler and the oil will determine the input power. if
                you
                > > want to do it really well, don't just turn your power ona nd
                off, but
                > > make it adjustable and control that with a thermometer. this way
                you
                > > will avoid temperature fluctuations.
                > >
                > > cu robert
                > >
                > > --
                > > Robert Lemmen
                http://www.semistable.com
              • toddk63
                What boiler codes will you be building this to and what class of boiler operating license do you have? Seriously, any vessel over 1 atm. requires a pressure
                Message 7 of 13 , May 31, 2005
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                  What boiler codes will you be building this to and what class of
                  boiler operating license do you have? Seriously, any vessel over 1
                  atm. requires a pressure vessel code stamp and there is a reason that
                  operators of power boilers require licensing. This shit can be
                  dangerously fatal if not done right.

                  Todd K.


                  > 2) How many atmospheres is considered reasonably safe as far as pressure
                  > goes? I'm extremely not keen to get coated in superheated liquids AGAIN.
                  > I know a small amount of pressure for the steam above the water surface
                  > would be a good thing, but safety comes first!
                • Andrew Forsberg
                  Righto, so the answers so far suggest: 1) Pressure release at 1 atm would be a very good thing. 2) Probably best to stick to water + salt. It will be quicker
                  Message 8 of 13 , May 31, 2005
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                    Righto, so the answers so far suggest:

                    1) Pressure release at 1 atm would be a very good thing.
                    2) Probably best to stick to water + salt. It will be quicker to adjust
                    than oil, and since the entire boiler system is stainless there's no
                    issue with corrosion. 104 / 105 degC should be fine for a maximum heat.
                    3) Invest in a decent thermostat for a single heavy duty element.

                    Great. Thank you all very much for your help!

                    Cheers
                    Andrew

                    don1lia2joe3 wrote:

                    >If you read the previous post where I replied to using the old still
                    >for a beer striper you will notice that this still uses an oil bath
                    >for heat, the problem with the one I have is that it gets to hot for
                    >use as a pot still and I do not want to convert that one to a reflux
                    >colum.
                    >
                    >My suggestions would include using a proper thermal transfer oil
                    >because it does not boil and the flash point is around 600F there is
                    >also very little expantion when it heats up like there is with salt
                    >water (also not corrosive)
                    >
                    >Another thing to consider is the heating, Oil holds heat a looooong
                    >time and cools down slooooly!! if you over heat your boiler your
                    >alcohol could be gone before you can cool it down. This is the
                    >problem with my still, the low end of my thermostat is 170F and runs
                    >up to 190F before automatic shutdown.
                    >
                    >My setup uses only one 220 V water tank heating element and works
                    >quite well at giving even heat.
                    >
                    >Please do not suggest that I change this still, it will not be used
                    >for Alcohol use but makes a good learning tool.
                    >
                    >As an added note:
                    >
                    >I already have my license to distill up to 10,000 gallons per year
                    >of alcohol in the United States for use as fuel, and I am designing
                    >and building a "small" continous run colum still with drying colums
                    >so that I can distill 5 to 10 gallons a day of 200 proof to mix with
                    >gasoline.
                    >
                    >Still is in planning stages but making and learning on smaller
                    >boilers and colums as I go, without this site it would not be
                    >possable to have this much fun learning.
                    >
                    >Thanks to all.
                    >
                    >
                    >
                    >--- In Distillers@yahoogroups.com, "abbababbaccc"
                    ><abbababbaccc@y...> wrote:
                    >
                    >
                    >>Actually, I think it wouldn't hurt too much if the temperature
                    >>fluctuates few degrees due to thermostat. If the oiltemperature
                    >>
                    >>
                    >varies
                    >
                    >
                    >>from 120-124C it's still always above the boiling point of the
                    >>
                    >>
                    >mash and
                    >
                    >
                    >>the effect on heat transfer to the boiler should be quite small.
                    >>
                    >>
                    >You
                    >
                    >
                    >>can of course heat the oil even more and lessen the effect of
                    >>
                    >>
                    >variance.
                    >
                    >
                    >>- Riku
                    >>
                    >>--- In Distillers@yahoogroups.com, Robert Lemmen <robertle@s...>
                    >>
                    >>
                    >wrote:
                    >
                    >
                    >>>On Tue, May 31, 2005 at 10:35:03AM -0000, abbababbaccc wrote:
                    >>>
                    >>>
                    >>>>Just an idea, but why don't you use oil in the jacket and a
                    >>>>thermostat to keep the temperature reasonable? If you keep the
                    >>>>
                    >>>>
                    >oil
                    >
                    >
                    >>at
                    >>
                    >>
                    >>>>100-120C temperature it shouldn't flash very easily and you
                    >>>>
                    >>>>
                    >could
                    >
                    >
                    >>>>leave the system open to atmosphere.
                    >>>>
                    >>>>
                    >>>this is how it is done quite often in labs. you can heat the oil
                    >>>
                    >>>
                    >up to
                    >
                    >
                    >>>much higher temperatures, and the difference between the
                    >>>
                    >>>
                    >temperature
                    >
                    >
                    >>>inside the boiler and the oil will determine the input power. if
                    >>>
                    >>>
                    >you
                    >
                    >
                    >>>want to do it really well, don't just turn your power ona nd
                    >>>
                    >>>
                    >off, but
                    >
                    >
                    >>>make it adjustable and control that with a thermometer. this way
                    >>>
                    >>>
                    >you
                    >
                    >
                    >>>will avoid temperature fluctuations.
                    >>>
                    >>>cu robert
                    >>>
                    >>>--
                    >>>Robert Lemmen
                    >>>
                    >>>
                    >http://www.semistable.com
                    >
                    >
                    >
                    >
                    >
                    > Distillers list archives : http://archive.nnytech.net/
                    > FAQ and other information at http://homedistiller.org
                    >Yahoo! Groups Links
                    >
                    >
                    >
                    >
                    >
                    >
                    >
                    >
                    >
                    >
                    >
                    >
                  • Andrew Forsberg
                    Hi all, The internet has provided me with far too many conflicting rates and formulae for calculating whether an external water bath for a stainless steel
                    Message 9 of 13 , Jun 1, 2005
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                      Hi all,

                      The internet has provided me with far too many conflicting rates and
                      formulae for calculating whether an external water bath for a stainless
                      steel boiler will or will not provide sufficient heat.

                      I'd very much appreciate it if an engineer on the list would give this a
                      once over:

                      T1 = 105 degC (water + table salt jacket)
                      T2 = 78 degC (mash)
                      Heat transfer coefficient = no idea... Ignoring it for the moment.
                      K = approx 14 W(m2 . K) (I have seen more figures for SS than I care to
                      poke sticks at. This is the most conservative, and is for 270K, so
                      anything better would be super).
                      Q = Watts
                      A = Area = .64m2
                      D = thickness of the SS wall = approx 2 mms

                      Q/A = (T1 - T2) / (D . 1/K)

                      Q/A = (27) / (.002 / 14)
                      = 27 . 7000
                      = 189,000

                      Q = 189,000 . 0.64
                      = 120.96 kW

                      So, what I'd like to know is -- will a 2mm stainless steel wall for an
                      area of .64m2 allow heat to pass through at a rate of up 120kW for that
                      temperature differential? Even approximately? As long as it's higher
                      than 3 or 4kW I'm happy. Unfortunately some formulae I've found
                      suggested the figure would be closer to 800W...

                      Cheers and thanks,
                      Andrew
                    • abbababbaccc
                      Andrew, a mash temperature will typically vary inbetween 90C (~17%) - 99C (~1%) during operation. IMO you ll get missleading results by using 78C for mash
                      Message 10 of 13 , Jun 1, 2005
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                        Andrew, a mash temperature will typically vary inbetween 90C (~17%) -
                        99C (~1%) during operation. IMO you'll get missleading results by
                        using 78C for mash temperature.

                        - Riku

                        --- In Distillers@yahoogroups.com, Andrew Forsberg <andrew@u...>
                        wrote:
                        > Hi all,
                        >
                        > The internet has provided me with far too many conflicting rates and
                        > formulae for calculating whether an external water bath for a
                        stainless
                        > steel boiler will or will not provide sufficient heat.
                        >
                        > I'd very much appreciate it if an engineer on the list would give
                        this a
                        > once over:
                        >
                        > T1 = 105 degC (water + table salt jacket)
                        > T2 = 78 degC (mash)
                        > Heat transfer coefficient = no idea... Ignoring it for the moment.
                        > K = approx 14 W(m2 . K) (I have seen more figures for SS than I
                        care to
                        > poke sticks at. This is the most conservative, and is for 270K, so
                        > anything better would be super).
                        > Q = Watts
                        > A = Area = .64m2
                        > D = thickness of the SS wall = approx 2 mms
                        >
                        > Q/A = (T1 - T2) / (D . 1/K)
                        >
                        > Q/A = (27) / (.002 / 14)
                        > = 27 . 7000
                        > = 189,000
                        >
                        > Q = 189,000 . 0.64
                        > = 120.96 kW
                        >
                        > So, what I'd like to know is -- will a 2mm stainless steel wall for
                        an
                        > area of .64m2 allow heat to pass through at a rate of up 120kW for
                        that
                        > temperature differential? Even approximately? As long as it's higher
                        > than 3 or 4kW I'm happy. Unfortunately some formulae I've found
                        > suggested the figure would be closer to 800W...
                        >
                        > Cheers and thanks,
                        > Andrew
                      • Andrew Forsberg
                        That s a very good point. Well, even at only 1 deg C difference the rate is 4.4kW for that area of 2mm SS wall. The other problem will have to be how to
                        Message 11 of 13 , Jun 1, 2005
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                          That's a very good point. Well, even at only 1 deg C difference the rate
                          is 4.4kW for that area of 2mm SS wall. The other problem will have to be
                          how to insulate the jacket optimally. One thing at a time.

                          So, do those calculations look even roughly correct to you?

                          Cheers
                          Andrew


                          abbababbaccc wrote:

                          >Andrew, a mash temperature will typically vary inbetween 90C (~17%) -
                          >99C (~1%) during operation. IMO you'll get missleading results by
                          >using 78C for mash temperature.
                          >
                          >- Riku
                          >
                          >
                          >
                        • dearknarl
                          Hate to bring bad news, but I m guessing the conduction of heat through the steel will not be your limiting factor, and your 120kW sounds about right. It will
                          Message 12 of 13 , Jun 1, 2005
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                            Hate to bring bad news, but I'm guessing the conduction of heat
                            through the steel will not be your limiting factor, and your 120kW
                            sounds about right.

                            It will more likely be the convection of the water bath and the wash
                            inside the boiler, more so the water bath once it is boiling, that
                            will limit heat transfer.

                            Agitation of both will provide better heat transfer. Trying to
                            calculate heat transfer for such a system would be a nightmare.

                            I'd say your best bet is an experiment, unless you're a hardcore nerd
                            that wants to create a computer model, or a hardcore physicist/maths
                            guru who has way too much spare time =). Let us know how you get on.

                            knarl.

                            --- In Distillers@yahoogroups.com, Andrew Forsberg <andrew@u...>
                            wrote:
                            > Hi all,
                            >
                            > The internet has provided me with far too many conflicting rates and
                            > formulae for calculating whether an external water bath for a
                            stainless
                            > steel boiler will or will not provide sufficient heat.
                            >
                            > I'd very much appreciate it if an engineer on the list would give
                            this a
                            > once over:
                            >
                            > T1 = 105 degC (water + table salt jacket)
                            > T2 = 78 degC (mash)
                            > Heat transfer coefficient = no idea... Ignoring it for the moment.
                            > K = approx 14 W(m2 . K) (I have seen more figures for SS than I
                            care to
                            > poke sticks at. This is the most conservative, and is for 270K, so
                            > anything better would be super).
                            > Q = Watts
                            > A = Area = .64m2
                            > D = thickness of the SS wall = approx 2 mms
                            >
                            > Q/A = (T1 - T2) / (D . 1/K)
                            >
                            > Q/A = (27) / (.002 / 14)
                            > = 27 . 7000
                            > = 189,000
                            >
                            > Q = 189,000 . 0.64
                            > = 120.96 kW
                            >
                            > So, what I'd like to know is -- will a 2mm stainless steel wall for
                            an
                            > area of .64m2 allow heat to pass through at a rate of up 120kW for
                            that
                            > temperature differential? Even approximately? As long as it's higher
                            > than 3 or 4kW I'm happy. Unfortunately some formulae I've found
                            > suggested the figure would be closer to 800W...
                            >
                            > Cheers and thanks,
                            > Andrew
                          • Andrew Forsberg
                            ... Hey Knarl, Bad news is still news, and it s far better to be brought it in the form of advance notice than to jump in first, only to swear and curse later.
                            Message 13 of 13 , Jun 2, 2005
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                              On Wed, 2005-06-01 at 22:52 +0000, dearknarl wrote:
                              > Hate to bring bad news, but I'm guessing the conduction of heat
                              > through the steel will not be your limiting factor, and your 120kW
                              > sounds about right.
                              >
                              > It will more likely be the convection of the water bath and the wash
                              > inside the boiler, more so the water bath once it is boiling, that
                              > will limit heat transfer.
                              >
                              > Agitation of both will provide better heat transfer. Trying to
                              > calculate heat transfer for such a system would be a nightmare.
                              >
                              > I'd say your best bet is an experiment, unless you're a hardcore nerd
                              > that wants to create a computer model, or a hardcore physicist/maths
                              > guru who has way too much spare time =). Let us know how you get on.
                              >
                              > knarl.

                              Hey Knarl,

                              Bad news is still news, and it's far better to be brought it in the form
                              of advance notice than to jump in first, only to swear and curse later.

                              The other problem with the jacket proposal was the thought that it will
                              need to be a stainless steel jacket that's welded to the stainless steel
                              tank. Through tubes might improve the situation, as might encroaching
                              further under the tank... But, tbh, the last thing I want after all that
                              is to need to build an automated stirring paddle mechanism.

                              On a brighter note: the L-bend at the bottom of the tank, before the
                              gate valve, has a couple of small 3/4"-ish OD screw fittings with caps.
                              They look decidedly like they were designed for a steam mixer... :->
                              Hmmmmmmmm.

                              Cheers & thanks,
                              Andrew
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