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Re: [pop-pop-steamboats] Our new members

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  • Donald Qualls
    ... I ve been interested in Pop-Pop boats for a long time, and always felt there was still a biggish hole in the explanations of how the engine works --
    Message 1 of 17 , Nov 30, 2007
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      Frank McNeill wrote:
      > Hi All,
      >
      > We have four new members who were "tricked" into joining our motley
      > crew by a message that I posted on the Yahoo discussion group,
      > LittleEngines at <http://groups.yahoo.com/group/LittleEngines/>.
      > In the alphabetical order of their Yahoo IDs, our new members are:
      > brian458666, gpomier, rogerkrahl and silntobsvr
      > Thanks. new members for joining us on pop-pop-steamboats, and best
      > wishes to all.
      >
      > old Frank (a great grandfather since 10/01/2007)
      >

      I've been interested in Pop-Pop boats for a long time, and always felt
      there was still a biggish hole in the explanations of how the engine
      works -- specifically, how can the steam in the tube cool enough to get
      water back into the hot section, if the hot section stays hot? That is,
      not a question of the reaction effect (the linear vs. hemispheric
      argument seems valid there), but rather of how the engine continues to
      operate indefinitely (pending fuel supply for the burner)...

      I might have to build one out of Pyrex tube sometime so I can see the
      water movement inside...

      --
      If, through hard work and perseverance, you finally get what you want,
      it's probably a sign you weren't dreaming big enough.

      Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

      Opinions expressed are my own -- take them for what they're worth
      and don't expect them to be perfect.
    • David Halfpenny
      ... From: Donald Qualls ... Well some engines don t run continuously. They may set off fine, and then stutter to a frustrating halt.
      Message 2 of 17 , Nov 30, 2007
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        ----- Original Message -----
        From: "Donald Qualls" <silent1@...>

        > how can the steam in the tube cool enough to get
        > water back into the hot section, if the hot section stays hot? That is,
        > not a question of the reaction effect (the linear vs. hemispheric
        > argument seems valid there), but rather of how the engine continues to
        > operate indefinitely (pending fuel supply for the burner)...

        Well some engines don't run continuously. They may set off fine, and then
        stutter to a frustrating halt.

        One clue is that the engines work better with the right amount of air in
        them. (Quite what the right amount is, and whether it increases or
        decreases during a run is another matter altogether.)

        So the air and the water act as a spring-mass-damper system, with a
        resonant frequency.

        This of course is in addition to all the evaporation and condensation going
        on, but all the same it is a clue.

        The important thing about a resonance is that the Output is out of phase
        with the input: the movement is greatest when the pressure is least. If you
        find this counter-intuitive, I recommend spending a few years pushing kids
        on swings as being a better path to illumination than diving into the
        maths.

        There's an analogy here between a pop-pop and a "displacerless" Stirling
        engine. Resonance causes the air in the sole cylinder to move 90degrees out
        of phase with the piston, just like a crankshaft-driven displacer would.

        David 1/2d
      • Donald Qualls
        ... Aaaah! Key here is that, having never actually operated a pop-pop, I wasn t aware they need some air in the system to operate. This makes perfect sense,
        Message 3 of 17 , Nov 30, 2007
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          David Halfpenny wrote:
          > ----- Original Message -----
          > From: "Donald Qualls" <silent1@...>
          >
          >> how can the steam in the tube cool enough to get
          >> water back into the hot section, if the hot section stays hot? That is,
          >> not a question of the reaction effect (the linear vs. hemispheric
          >> argument seems valid there), but rather of how the engine continues to
          >> operate indefinitely (pending fuel supply for the burner)...
          >
          > Well some engines don't run continuously. They may set off fine, and then
          > stutter to a frustrating halt.
          >
          > One clue is that the engines work better with the right amount of air in
          > them. (Quite what the right amount is, and whether it increases or
          > decreases during a run is another matter altogether.)
          >
          > So the air and the water act as a spring-mass-damper system, with a
          > resonant frequency.
          >
          > This of course is in addition to all the evaporation and condensation going
          > on, but all the same it is a clue.
          >
          > The important thing about a resonance is that the Output is out of phase
          > with the input: the movement is greatest when the pressure is least. If you
          > find this counter-intuitive, I recommend spending a few years pushing kids
          > on swings as being a better path to illumination than diving into the
          > maths.
          >
          > There's an analogy here between a pop-pop and a "displacerless" Stirling
          > engine. Resonance causes the air in the sole cylinder to move 90degrees out
          > of phase with the piston, just like a crankshaft-driven displacer would.
          >
          > David 1/2d

          Aaaah! Key here is that, having never actually operated a pop-pop, I
          wasn't aware they need some air in the system to operate. This makes
          perfect sense, then; the steam forces water out, but doesn't completely
          clear the tube (so no steam bubbles emitted) and the inertia of the
          water pulls the pressure in the tube well below ambient; this then
          causes water to rush back in and actually compress the remaining air (as
          well as condensing some of the steam), and if things are all well, the
          inertia of the inflowing water will be sufficient to bring enough into
          the hot zone of the boiler to power another cycle.

          As you say, the water remaining in the pipe is acting as the piston in a
          hybrid of a Stirling cycle and a phase-change system similar to the
          Rankine steam cycle.

          BTW, I've seen photos and drawings of very large steam pumping engines
          that used only the water as their pistons, but (of course) they used a
          separate boiler and a valving system of some sort to control the steam.
          The pop-pop sounds like it uses a similar cycle, but with steam
          controlled by access of water to the hot section.
          --
          If, through hard work and perseverance, you finally get what you want,
          it's probably a sign you weren't dreaming big enough.

          Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

          Opinions expressed are my own -- take them for what they're worth
          and don't expect them to be perfect.
        • David Halfpenny
          ... From: Donald Qualls ... Yes. However few owners give any thought to air: it just happens, or not. With the diaphragm type motor,
          Message 4 of 17 , Nov 30, 2007
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            ----- Original Message -----
            From: "Donald Qualls" <silent1@...>

            > This makes perfect sense, then;

            Yes.

            However few owners give any thought to air: it just happens, or not.

            With the diaphragm type motor, it would be hard to exclude all air as it
            will lurk in the recesses when the motor is first filled.

            However with the coil type it would be difficult to include any, but some
            will come out of solution as soon as the water is heated.

            It is possible that there are several different types of successful
            configuration - long tubes, short tubes, immersed tubes, inboard tubes etc
            and I can't get my head round it all. But as you say, folk who have made
            transparent motors have found them instructive.

            David 1/2d

            Jargon:

            A Stirling engine:
            - compresses a load of gas (usually air),
            - heats it up while compacted
            - lets it expand (providing a power stroke)
            - cools it down while expanded.
            Repeat.

            A Rankine engine:
            - boils a load of liquid (usually water),
            - lets the steam expand (providing a power stroke)
            - condenses it back into water
            - pumps it back into the boiler.
            Repeat.

            Either can be used either as a motor or be motor-driven to act as a heat
            pump shifting heat from a colder zone to a warmer one. For example a
            Rankine engine can be made either as a steam power plant or as a
            motor-driven refrigerator.

            There have been a lot more Rankine engines built than Stirling engines
            because it's a heck of a lot easier to pump liquid than to compress gas,
            and because a lump of steam holds a lot more heat than a lump of air at the
            same temperature.

            There: the fundamentals of Mechanical Engineering on a postcard!
          • Donald Qualls
            ... Well, at least as it stood ca. 1900, when internal combustion wasn t yet a major player in the prime mover game. In fact, most steam engines made over the
            Message 5 of 17 , Nov 30, 2007
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              David Halfpenny wrote:
              > Jargon:
              >
              > A Stirling engine:
              > - compresses a load of gas (usually air),
              > - heats it up while compacted
              > - lets it expand (providing a power stroke)
              > - cools it down while expanded.
              > Repeat.
              >
              > A Rankine engine:
              > - boils a load of liquid (usually water),
              > - lets the steam expand (providing a power stroke)
              > - condenses it back into water
              > - pumps it back into the boiler.
              > Repeat.
              >
              > Either can be used either as a motor or be motor-driven to act as a heat
              > pump shifting heat from a colder zone to a warmer one. For example a
              > Rankine engine can be made either as a steam power plant or as a
              > motor-driven refrigerator.
              >
              > There have been a lot more Rankine engines built than Stirling engines
              > because it's a heck of a lot easier to pump liquid than to compress gas,
              > and because a lump of steam holds a lot more heat than a lump of air at the
              > same temperature.
              >
              > There: the fundamentals of Mechanical Engineering on a postcard!

              Well, at least as it stood ca. 1900, when internal combustion wasn't yet
              a major player in the prime mover game. In fact, most steam engines
              made over the past four hundred years have been an "open" version of the
              Rankine cycle, with the pump back to the boiler and often the condenser
              omitted in the interest of mechanical simplicity and/or reliability
              and/or lightness. I'm sure that's the case, because there have almost
              certainly been more steam engines built as locomotives and tractors than
              all other applications together, and virtually all of those are open cycle.

              Which, of course, doesn't change the elegance of an engine that can
              drive a tiny watercraft with no moving parts other than the working fluid...

              Worth noting relative to Stirling that the compression and expansion is
              typically a pretty small percentage of the volume; most of the designs
              I've looked at seem to run 3-5% volume change over the full stroke of
              the power piston. Steam, by comparison, has an expansion (if I recall
              correctly) of about 260:1 over the liquid phase; that makes steam
              engines capable of immense effort at very low speed (at least those that
              are designed for that kind of thing, minimum feature set including a
              variable cutoff valve gear) while Stirling is closer to an internal
              combustion engine in the way it runs -- that is, must keep up a pretty
              good rotational clip to run at all, because each power stroke produces
              relatively little energy.
              --
              If, through hard work and perseverance, you finally get what you want,
              it's probably a sign you weren't dreaming big enough.

              Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

              Opinions expressed are my own -- take them for what they're worth
              and don't expect them to be perfect.
            • David Halfpenny
              ... From: Donald Qualls ... Yes indeed - letting the condensing happen in the atmosphere and substituting alternative Working Fluid
              Message 6 of 17 , Nov 30, 2007
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                ----- Original Message -----
                From: "Donald Qualls" <silent1@...>


                > most steam engines
                > made over the past four hundred years have been an "open" version of the
                > Rankine cycle, with the pump back to the boiler and often the condenser
                > omitted in the interest of mechanical simplicity and/or reliability
                > and/or lightness.

                Yes indeed - letting the condensing happen in the atmosphere and
                substituting alternative Working Fluid is technically cheating, just as
                leaving a turbine wake behind and ingesting substitute air is.

                > there have almost
                > certainly been more steam engines built as locomotives and tractors than
                > all other applications together, and virtually all of those are open
                > cycle.

                I'm sure you are right, but for such an influential piece of kit the number
                of steam locomotives built has been surprisingly few. I've not seen any
                estimate that exceeds a million. The humble pop-pop may well be (or soon
                become) more numerous!
                >
                > Which, of course, doesn't change the elegance of an engine that can
                > drive a tiny watercraft with no moving parts other than the working
                > fluid...
                >
                Absolutely! D
              • Donald Qualls
                ... Well, don t forget that most of steam s influence was in the days when a few dozen of something important could change the world. But look at what else
                Message 7 of 17 , Dec 1, 2007
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                  David Halfpenny wrote:
                  > ----- Original Message -----
                  > From: "Donald Qualls" <silent1@...>
                  >
                  >
                  >> there have almost
                  >> certainly been more steam engines built as locomotives and tractors than
                  >> all other applications together, and virtually all of those are open
                  >> cycle.
                  >
                  > I'm sure you are right, but for such an influential piece of kit the number
                  > of steam locomotives built has been surprisingly few. I've not seen any
                  > estimate that exceeds a million. The humble pop-pop may well be (or soon
                  > become) more numerous!

                  Well, don't forget that most of steam's influence was in the days when a
                  few dozen of something important could change the world. But look at
                  what else steam has done -- powered ships (the bulk of which after about
                  WWII ran turbines instead of steam expanders) and operated stationary
                  power installations (either electric generation -- again, virtually
                  always turbine -- or things like mine engines); both of those are surely
                  fewer in number than even locomotives. One could make a case that there
                  have been more model steam engines built than there ever were full size
                  ones, though I don't know where you'd get the figures to back it up...

                  --
                  If, through hard work and perseverance, you finally get what you want,
                  it's probably a sign you weren't dreaming big enough.

                  Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

                  Opinions expressed are my own -- take them for what they're worth
                  and don't expect them to be perfect.
                • David Halfpenny
                  ... From: Donald Qualls ... OK then: An Infernal Confusion engine: - compresses a lump of air, - heats it up a lot - expands it
                  Message 8 of 17 , Dec 1, 2007
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                    ----- Original Message -----
                    From: "Donald Qualls" <silent1@...>

                    >> There: the fundamentals of Mechanical Engineering on a postcard!
                    >
                    > Well, at least as it stood ca. 1900, when internal combustion wasn't yet
                    > a major player in the prime mover game.

                    OK then: An Infernal Confusion engine:
                    - compresses a lump of air,
                    - heats it up a lot
                    - expands it (providing a power stroke)
                    - lets it escape along with the products of combusion (which may also
                    provide a reaction thrust)

                    The one closest to the pop-pop is the pulse-jet or doodelbug engine, which
                    also uses an oscillating column of fluid in a backwards-pointing tube. (My
                    parents weren't very fond of these as they were married in London in August
                    1944.) In this case, the resonant pressure wave opens and closes the air
                    inlet valve, sucks in and atomises the liquid fuel and compresses the
                    ingested air. Ignition is usually by contact between the explosive mixture
                    and the hot walls of the combustion chamber.
                    The result is very simple and powerful model boat engine that is several
                    decibels noisier than a pop-pop

                    David 1/2d

                    There are one or two additional details, but the core science behind post
                    mediaeval Mechanical Engineering isn't mechanics, or mechanisms, or
                    materials, important as they all are: it's thermodynamics.
                  • Donald Qualls
                    ... Of course, this cycle, like the Rankine, can be used either in batch mode or in continuous mode. Common piston, rotary, and pulse-jet engines operate
                    Message 9 of 17 , Dec 1, 2007
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                      David Halfpenny wrote:
                      > ----- Original Message -----
                      > From: "Donald Qualls" <silent1@...>
                      >
                      >>> There: the fundamentals of Mechanical Engineering on a postcard!
                      >> Well, at least as it stood ca. 1900, when internal combustion wasn't yet
                      >> a major player in the prime mover game.
                      >
                      > OK then: An Infernal Confusion engine:
                      > - compresses a lump of air,
                      > - heats it up a lot
                      > - expands it (providing a power stroke)
                      > - lets it escape along with the products of combusion (which may also
                      > provide a reaction thrust)

                      Of course, this cycle, like the Rankine, can be used either in "batch"
                      mode or in "continuous" mode. Common piston, rotary, and pulse-jet
                      engines operate in pulsed or "batch" mode, where a discrete "lump" of
                      working fluid goes through the entire cycle independent of other
                      charges, while ramjets, turbojets and turbofans and at least one variant
                      piston engine (an internal combustion version of an elbow engine)
                      operate in continuous mode, where all parts of the cycle operate on a
                      flowing stream of working fluid (rather like the difference between pot
                      distillation and a distillation column, or lab synthesis vs. an
                      industrial process).

                      > The one closest to the pop-pop is the pulse-jet or doodelbug engine, which
                      > also uses an oscillating column of fluid in a backwards-pointing tube. (My
                      > parents weren't very fond of these as they were married in London in August
                      > 1944.) In this case, the resonant pressure wave opens and closes the air
                      > inlet valve, sucks in and atomises the liquid fuel and compresses the
                      > ingested air. Ignition is usually by contact between the explosive mixture
                      > and the hot walls of the combustion chamber.
                      > The result is very simple and powerful model boat engine that is several
                      > decibels noisier than a pop-pop

                      The classic valved pulsejet actually has a front intake and almost
                      entirely one-way flow, and model airplane versions have a venturi
                      carburetor built into the intake at the forward end (the German design,
                      too large to work well with a flat reed valve, incorporated the fuel
                      delivery into the grid that held the valves, so didn't as much resemble
                      a simple venturi carburetor).

                      There are actually a couple valveless pulse jets that are even closer to
                      a pop-pop in operation; all compression and flow control is due to
                      pressure pulses in resonance with the pipe, and both pipe openings face
                      backward and produce thrust (though the designs I've seen have them
                      different lengths and the overall flow is from the shorter pipe to the
                      longer; there has to be some directional flow to keep drawing in fresh
                      air and fuel and removing combustion products, of course, but it could
                      be worth testing to see if this would be the case with our kind of
                      pop-pop, since tuning the tubes to product directional flow has the
                      potential to greatly increase the efficiency of the engine). The
                      resonance frequency in these, in hobbyist scales, tends to be in the
                      mid-upper audible range, leading them to produce a very distinctive
                      screaming sound in addition to the usual loud roar of any jet exhaust.

                      > David 1/2d
                      >
                      > There are one or two additional details, but the core science behind post
                      > mediaeval Mechanical Engineering isn't mechanics, or mechanisms, or
                      > materials, important as they all are: it's thermodynamics.

                      Yep, pretty much anything invented since James Watt improved the pumping
                      engine at the mine where he worked (by inventing, out of laziness, an
                      automatic valve gear to replace the continuous attention of a boy)
                      depends on thermodynamics, at least until you start getting into
                      practical electricity in the late 19th century. At that point,
                      Maxwell's laws of electromagnetism become the important ones...

                      --
                      If, through hard work and perseverance, you finally get what you want,
                      it's probably a sign you weren't dreaming big enough.

                      Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

                      Opinions expressed are my own -- take them for what they're worth
                      and don't expect them to be perfect.
                    • David Halfpenny
                      ... From: Donald Qualls ... All good stuff, and worth remarking - for the benefit of Our new members in the subject line - that
                      Message 10 of 17 , Dec 1, 2007
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                        ----- Original Message -----
                        From: "Donald Qualls" <silent1@...>

                        >>>> the fundamentals of Mechanical Engineering on a postcard!

                        All good stuff, and worth remarking - for the benefit of "Our new members"
                        in the subject line - that very little of our traffic is this
                        philosophical.

                        We major in the sheer delight of simple little boats, whether mass produced
                        from printed tinplate or cunningly homemade out of cardboard or balsa wood.


                        My 'Rattanndeep Enterprise' tinplate Titanic fell out of the cupboard today
                        (I caught her before she hit the deck).
                        http://www.angelfire.com/extreme2/rattandeepenterprise/

                        I took a look at her workings. The burner is a 7/8" diameter tinplate tray
                        balanced precariously on the outlet pipes out of reach and out of sight,
                        and very close to the underside of the pop-chamber. So I think it's fair to
                        say that the chances of a successful run As Supplied are vanishingly
                        small - par for the course I suppose ;-)

                        I shall try to sail her in the kiddies' paddling pool in the park while
                        it's too cold for kiddies to paddle, but not cold enough to be drained for
                        the winter. I've got some brand new Wellies (gumboots) in case of
                        emergency!

                        David 1/2d
                        Chartered Mechanical Engineer
                      • brian458666@550access.com
                        ... Yes, and I had a moment of illumination just now as I was loading up my coffee maker...although it does use a check valve, and the older style percolators
                        Message 11 of 17 , Dec 1, 2007
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                          >
                          > There are actually a couple valveless pulse jets that are even closer to
                          > a pop-pop in operation;

                          Yes, and I had a moment of illumination just now as I was loading up my
                          coffee maker...although it does use a check valve, and the older style
                          percolators used a restricted inlet to work.
                          Brian
                        • Donald Qualls
                          ... I ve got a stovetop type percolator that has a very broad, flat funnel covering the base and feeding into the vertical pipe, with liquid flow under the
                          Message 12 of 17 , Dec 1, 2007
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                            brian458666@... wrote:
                            >
                            >> There are actually a couple valveless pulse jets that are even closer to
                            >> a pop-pop in operation;
                            >
                            > Yes, and I had a moment of illumination just now as I was loading up my
                            > coffee maker...although it does use a check valve, and the older style
                            > percolators used a restricted inlet to work.
                            > Brian

                            I've got a stovetop type percolator that has a very broad, flat funnel
                            covering the base and feeding into the vertical pipe, with liquid flow
                            under the funnel permitted only through a couple tiny openings or under
                            the edge if a pressure pulse should lift the pipe and basket clear of
                            the pot base. The electric percolator I used to own had a rather tiny
                            boiler chamber, roughly hemispherical, under the base of the pipe, and
                            again a couple small openings to admit liquid. To my eye, they depend
                            on the bulk of liquid in the pot being fairly well below boiling, so it
                            takes a few seconds (even when the pot has begun to perk) for inflowing
                            liquid to boil, after which rising bubbles push liquid out the top of
                            the pipe; as the coffee heats, bubbles push smaller and more frequent
                            slugs of liquid into the dome to drip through the grounds until the pot
                            stops working at all when the liquid is very close to boiling -- just
                            steam comes up the pipe, because the liquid can't fill the working
                            chamber, much less the pipe, before it boils.

                            An automatic drip coffee machine (a la Mr. Coffee) works similarly but
                            with a limited supply of water; mine seems to have an unrestricted
                            intake from the tank, and depends on the temperature of the water supply
                            to regulate the rate of boiling, which in turn regulates the temperature
                            of the water that gets poured into the grounds basket. It's a little
                            topsy-turvy, though; start with water that's too warm and you'll get
                            mostly steam and poor flow through the pipe, while starting with icy
                            cold water gives the best coffee because you get good slugs of water and
                            they heat up just right before the hot spot boils and pushes them
                            through. This pot, however (mine's a Melitta), seems to depend strongly
                            on the inertia of water in the tank as well as on heating most strongly
                            near the intake to produce a useful pumping action. I didn't see
                            anything I could identify as a check valve when I had it apart for
                            cleaning after a period of disuse...

                            --
                            If, through hard work and perseverance, you finally get what you want,
                            it's probably a sign you weren't dreaming big enough.

                            Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

                            Opinions expressed are my own -- take them for what they're worth
                            and don't expect them to be perfect.
                          • brian458666@550access.com
                            ... Yes, I had completely forgotten about the stovetop variety and was going with the electric ones only. Most of the electric percolators used a small boiler
                            Message 13 of 17 , Dec 1, 2007
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                              Quoting Donald Qualls <silent1@...>:

                              > brian458666@... wrote:
                              > >
                              > >> There are actually a couple valveless pulse jets that are even closer to
                              > >> a pop-pop in operation;
                              > >
                              > > Yes, and I had a moment of illumination just now as I was loading up
                              > my
                              > > coffee maker...although it does use a check valve, and the older style
                              > > percolators used a restricted inlet to work.
                              > > Brian
                              >
                              > I've got a stovetop type percolator that has a very broad, flat funnel
                              > covering the base and feeding into the vertical pipe, with liquid flow
                              > under the funnel permitted only through a couple tiny openings or under
                              > the edge if a pressure pulse should lift the pipe and basket clear of
                              > the pot base. The electric percolator I used to own had a rather tiny
                              > boiler chamber, roughly hemispherical, under the base of the pipe, and
                              > again a couple small openings to admit liquid. To my eye, they depend
                              > on the bulk of liquid in the pot being fairly well below boiling, so it
                              > takes a few seconds (even when the pot has begun to perk) for inflowing
                              > liquid to boil, after which rising bubbles push liquid out the top of
                              > the pipe; as the coffee heats, bubbles push smaller and more frequent
                              > slugs of liquid into the dome to drip through the grounds until the pot
                              > stops working at all when the liquid is very close to boiling -- just
                              > steam comes up the pipe, because the liquid can't fill the working
                              > chamber, much less the pipe, before it boils.
                              >
                              > An automatic drip coffee machine (a la Mr. Coffee) works similarly but
                              > with a limited supply of water; mine seems to have an unrestricted
                              > intake from the tank, and depends on the temperature of the water supply
                              > to regulate the rate of boiling, which in turn regulates the temperature
                              > of the water that gets poured into the grounds basket. It's a little
                              > topsy-turvy, though; start with water that's too warm and you'll get
                              > mostly steam and poor flow through the pipe, while starting with icy
                              > cold water gives the best coffee because you get good slugs of water and
                              > they heat up just right before the hot spot boils and pushes them
                              > through. This pot, however (mine's a Melitta), seems to depend strongly
                              > on the inertia of water in the tank as well as on heating most strongly
                              > near the intake to produce a useful pumping action. I didn't see
                              > anything I could identify as a check valve when I had it apart for
                              > cleaning after a period of disuse...

                              Yes, I had completely forgotten about the stovetop variety and was going
                              with the electric ones only. Most of the electric percolators used a small
                              boiler of under an inch in diameter that was at the very bottom of the pot. I
                              haven't seen or used one of those in many years and further details are elusive
                              now, and my Mr. Coffee type devices get a lot of use. It seems that each
                              manufacturer incorporates their own flaws so my standard backup is a french
                              press. But all of mine have check valves molded into the bottom of the
                              reservoir.
                              Brian
                            • Donald Qualls
                              ... I ll have to go look at mine; I couldn t get some pieces apart (they seem to be assembled with one-time latch-in parts, you d break them before they d
                              Message 14 of 17 , Dec 1, 2007
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                                brian458666@... wrote:

                                > It seems that each
                                > manufacturer incorporates their own flaws so my standard backup is a french
                                > press. But all of mine have check valves molded into the bottom of the
                                > reservoir.

                                I'll have to go look at mine; I couldn't get some pieces apart (they
                                seem to be assembled with one-time latch-in parts, you'd break them
                                before they'd fully disassemble), so it's very possible it has a check
                                valve I missed. That would make a lot more sense in terms of avoiding
                                bubbling back up through the tank, and it would only need a small
                                plastic ball trapped in the joint between two pieces.

                                --
                                If, through hard work and perseverance, you finally get what you want,
                                it's probably a sign you weren't dreaming big enough.

                                Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

                                Opinions expressed are my own -- take them for what they're worth
                                and don't expect them to be perfect.
                              • Double Diamonds
                                i was also looking into the possibility of using pulse-jet designs to improve on putt-putt engine work and was considering that it might allow for a faster
                                Message 15 of 17 , Jul 26, 2013
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                                  i was also looking into the possibility of using pulse-jet designs to improve on putt-putt engine work and was considering that it might allow for a faster engine cycle and quiet running from the lack of a diafram might allow more speed

                                  --- In pop-pop-steamboats@yahoogroups.com, Donald Qualls <silent1@...> wrote:
                                  >
                                  > David Halfpenny wrote:
                                  > > ----- Original Message -----
                                  > > From: "Donald Qualls" <silent1@...>
                                  > >
                                  > >>> There: the fundamentals of Mechanical Engineering on a postcard!
                                  > >> Well, at least as it stood ca. 1900, when internal combustion wasn't yet
                                  > >> a major player in the prime mover game.
                                  > >
                                  > > OK then: An Infernal Confusion engine:
                                  > > - compresses a lump of air,
                                  > > - heats it up a lot
                                  > > - expands it (providing a power stroke)
                                  > > - lets it escape along with the products of combusion (which may also
                                  > > provide a reaction thrust)
                                  >
                                  > Of course, this cycle, like the Rankine, can be used either in "batch"
                                  > mode or in "continuous" mode. Common piston, rotary, and pulse-jet
                                  > engines operate in pulsed or "batch" mode, where a discrete "lump" of
                                  > working fluid goes through the entire cycle independent of other
                                  > charges, while ramjets, turbojets and turbofans and at least one variant
                                  > piston engine (an internal combustion version of an elbow engine)
                                  > operate in continuous mode, where all parts of the cycle operate on a
                                  > flowing stream of working fluid (rather like the difference between pot
                                  > distillation and a distillation column, or lab synthesis vs. an
                                  > industrial process).
                                  >
                                  > > The one closest to the pop-pop is the pulse-jet or doodelbug engine, which
                                  > > also uses an oscillating column of fluid in a backwards-pointing tube. (My
                                  > > parents weren't very fond of these as they were married in London in August
                                  > > 1944.) In this case, the resonant pressure wave opens and closes the air
                                  > > inlet valve, sucks in and atomises the liquid fuel and compresses the
                                  > > ingested air. Ignition is usually by contact between the explosive mixture
                                  > > and the hot walls of the combustion chamber.
                                  > > The result is very simple and powerful model boat engine that is several
                                  > > decibels noisier than a pop-pop
                                  >
                                  > The classic valved pulsejet actually has a front intake and almost
                                  > entirely one-way flow, and model airplane versions have a venturi
                                  > carburetor built into the intake at the forward end (the German design,
                                  > too large to work well with a flat reed valve, incorporated the fuel
                                  > delivery into the grid that held the valves, so didn't as much resemble
                                  > a simple venturi carburetor).
                                  >
                                  > There are actually a couple valveless pulse jets that are even closer to
                                  > a pop-pop in operation; all compression and flow control is due to
                                  > pressure pulses in resonance with the pipe, and both pipe openings face
                                  > backward and produce thrust (though the designs I've seen have them
                                  > different lengths and the overall flow is from the shorter pipe to the
                                  > longer; there has to be some directional flow to keep drawing in fresh
                                  > air and fuel and removing combustion products, of course, but it could
                                  > be worth testing to see if this would be the case with our kind of
                                  > pop-pop, since tuning the tubes to product directional flow has the
                                  > potential to greatly increase the efficiency of the engine). The
                                  > resonance frequency in these, in hobbyist scales, tends to be in the
                                  > mid-upper audible range, leading them to produce a very distinctive
                                  > screaming sound in addition to the usual loud roar of any jet exhaust.
                                  >
                                  > > David 1/2d
                                  > >
                                  > > There are one or two additional details, but the core science behind post
                                  > > mediaeval Mechanical Engineering isn't mechanics, or mechanisms, or
                                  > > materials, important as they all are: it's thermodynamics.
                                  >
                                  > Yep, pretty much anything invented since James Watt improved the pumping
                                  > engine at the mine where he worked (by inventing, out of laziness, an
                                  > automatic valve gear to replace the continuous attention of a boy)
                                  > depends on thermodynamics, at least until you start getting into
                                  > practical electricity in the late 19th century. At that point,
                                  > Maxwell's laws of electromagnetism become the important ones...
                                  >
                                  > --
                                  > If, through hard work and perseverance, you finally get what you want,
                                  > it's probably a sign you weren't dreaming big enough.
                                  >
                                  > Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com
                                  >
                                  > Opinions expressed are my own -- take them for what they're worth
                                  > and don't expect them to be perfect.
                                  >
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