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  • Mini ducted vacuum coffee extractor concept

    Hi snobs,

    I've been trying to think through a smaller vacuum solution to the humble bean cooler that's been kicking around this thread in various renditions for a number of years.

    The reasons for my re-thinking current solutions:
    1. I want to limit the number of appliances I need to employ in order to get a roast done (think surprise rainfall requiring a rapid collecting up of roasting gear)
    2. I have a less than ideal vacuum-cleaner model that doesn't lend itself to use for coffee transportation (plus, my wife isn't super keen)
    3. Pouring beans from roasting chamber (Soon to be KKTO) is not ideal, especially when dealing with a hot TO.
    4. I like neat tight systems.
    5. I'm a little too keen to build something that vacuums.

    So - having very little knowledge of aero and fluid dynamics, having absolutely no working prototype yet, let alone purchased any of the required goods, here is my present thinking..

    - I'd like to retain the bean cooler in the form of "20L bunnings bucket with the extractor fan" as closely as possible.
    - Install a "vacuum like" fitting to the lid of the bucket to draw the beans (Think pneumatic conveying)

    My hope is to create the required vacuum utilising two fans - the extractor fan in the bucket, and an additional ducted fan attached to the hose.

    A T junction designed for ducted vacuum systems would be fitted to the bucket lid with the curved section routing down into the bucket:
    Click image for larger version

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    Like this, but think the flat part is across the top,

    and a 50mm ducted fan, in the top part of the T junction fitting (perpendicular to the lid) something like this:
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    (Obviously this is image is of a light plastic fan - I'd find something more sturdy)
    The alternative would be to get a centrifugal fan of some sort, but they are more expensive.

    And a strategically inserted filter into the piping, with the resulting set up something like this:

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    So the idea is that the ducted fan is running, and the extractor fan is running, all drawing air through the main (sufficiently heat resistant) tube (while the lid of the bucket is on), creating suction to draw the beans from the roaster, past the ducted fan (due to filter inserted into the tube) and down into the bucket, which will hopefully have more drawing power than the smaller fan.

    So.. What I need to determine is whether:

    A. The large fan is able to generate suction at all while the bucket lid is on and the bottom of the bucket is relatively open
    B: A small fan is powerful enough to assist with the suction process, or would end up being entirely useless
    C. The whole system wont collapse under heat + air pressure

    I'm gonna give it a crack I think - but, am opening up to suggestions/ideas before I venture off and do any of this. If anyone with the current cooling bucket concept can let me know if they can get suction from the large fan with the lid on, that would be especially awesome, and would give me confidence to move forward!

    Thanks in advance.

    readeral
    Attached Files
    Last edited by readeral; 11 August 2015, 06:00 PM. Reason: detail about fans.

  • #2
    I realise this is probably just crazy - but humour me...

    Comment


    • #3
      Edit: I'm not sure I've interpreted your drawing correctly. Is that the roaster or the bucket cooler?

      If it's the bucket cooler, with airflow going downward, I'm not entirely sure you need the small fan at all. Just make sure the vacuum hose is sufficiently narrow to maximize the air velocity (and the shorter the better).

      -----------

      Ok. So, 'suction' isn't really what is important here. That just implies that the pressure is below atmospheric (which means nothing on its own).

      What you need is flow - or more precisely, velocity. The air flowing past the beans is what makes them move.

      You will need the velocity to exceed a certain value (i.e. the critical velocity) to lift them in opposition to gravity. Specifically, you need the drag force to exceed the force due to gravity (the model describing this is known as Stokes' Law).

      I can see a number of potential problems with your design.


      - You will probably not get much airflow drawn through the beans in the roast chamber.
      - The roast chamber is significantly larger in diameter than the outlet duct (which means a much lower velocity where you need it most!)

      I think you need to try to either push, or draw the air directly over the beans. "Pushing" will generally be more effective, unless you can recycle the fan discharge back to the suction side.


      Hope that helps!

      Comment


      • #4
        Awesome! Someone who knows way more than me to get the conversation started. The whole thing is probably untenable, but might be a fun conversation to pursue anyway -

        I'm just gonna ask clarifying questions at this stage

        So, the goal is to still use a hose to "gather" the beans (like you'd use a vacuum cleaner) so the intake diameter would be an inch-ish if I understand you correctly on the needs of the intake?

        Also - what do you mean not much airflow drawn through the beans in the roast chamber? I wonder if you are envisioning a closed system (eg a pipe entering the side of a KKTO, lid on, to draw out beans - rather than opening the lid right up and directing a tube to the beans)

        In realising suction is not so much the goal - if my roast chamber is perforated (allowing air to move between beans and hose) - I still might need a much more powerful fan to achieve enough airflow (velocity) for what I want to do, yes?

        And I'm not sure I understand what you mean in the final paragraph.

        Would it be helpful to my cause if the bottom of the cooling chamber was not opened wide up, but just had one exit hole (like the smaller fan would?)

        Comment


        • #5
          (Thanks for engaging!)

          Comment


          • #6
            Originally posted by readeral View Post
            Awesome! Someone who knows way more than me to get the conversation started. The whole thing is probably untenable, but might be a fun conversation to pursue anyway -

            I'm just gonna ask clarifying questions at this stage

            So, the goal is to still use a hose to "gather" the beans (like you'd use a vacuum cleaner) so the intake diameter would be an inch-ish if I understand you correctly on the needs of the intake?

            Also - what do you mean not much airflow drawn through the beans in the roast chamber? I wonder if you are envisioning a closed system (eg a pipe entering the side of a KKTO, lid on, to draw out beans - rather than opening the lid right up and directing a tube to the beans)

            In realising suction is not so much the goal - if my roast chamber is perforated (allowing air to move between beans and hose) - I still might need a much more powerful fan to achieve enough airflow (velocity) for what I want to do, yes?

            And I'm not sure I understand what you mean in the final paragraph.

            Would it be helpful to my cause if the bottom of the cooling chamber was not opened wide up, but just had one exit hole (like the smaller fan would?)
            Apologies, the first time I read your post, I thought the image was of the roaster, with an extraction device mounted on top. I now realise it is the bean cooler.

            I would think an extraction fan would move enough air to be able to 'suck' the beans through, given a small enough inlet nozzle. You could also try angling the nozzle at 45° (from memory this reduces the required velocity), and having the bean cooler lower than the roaster (to aid transfer of the beans through the tube).

            Comment


            • #7
              The ducted fan will draw air from the path of least resistance. Even with the bucket fan running (they're really weak), the ducted fan will likely take air from the bucket and won't create the negative pressure you require through the hose. The longer your hose, the more pressure drop you will have, exacerbating the problem.

              If you could make some sort of flap at the lid/outlet which will close while the ducted fan is on, it might create enough suction through the hose. Like a check valve. There would need to be enough space between the flap and the ducted fan for the whole quantity of beans to sit before the fan is turned off and the flap allowed to open to drop the beans. This could be tricky to make properly, not to mention finding a material suitable for 200 degree beans to sit on.

              You will most likely use a radio controlled plane EDF (electric ducted fan). If anything is going to be capable in the size you want, they will be. I can't seem to find any data in the specs about blade pitch, so I don't know if we can determine velocity (it would be difficult do calculate with the resistance of the hose, too), but some of them pull up to 1.7kg's of thrust and I'm sure that'd do it. It just depends how much you want to spend on this project. The most thrust that the 50mm fans pull is 550g. You might need to go for a larger unit and use PVC reducers for your Y-junction. I also don't know how some of those motors would go with 200 degree heat hitting them while they're spinning at max RPM.

              Hardware & Accessories>EDF Systems & Parts>EDF Units - With Motor

              It's definitely an interesting idea...but it might prove to be fairly difficult to get a working model in the DIY scheme of things.

              Comment


              • #8
                Or.... Just buy four of the largest, most powerful EDF's and place like so....

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                Just be sure to have a tight seal and wear some ear muffs!

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                • #9
                  Seems like you are overcomplicating it a bit. If the extractor fan isn't enough, you could try two in series. Otherwise, maybe make use of a vacuum cleaner. Source a spare hose, chop it in half. Attach both halves (at the cut end) to a bucket lid. Seal all the holes in the bucket (try gladwrap).
                  Attach to vacuum as normal, poke the other end (with a narrow nozzle) into the roaster. Turn on. Bingo.

                  Did try to post a sketch, but tapatalk keeps crashing when I do.

                  Comment


                  • #10
                    Originally posted by MrJack View Post
                    Seems like you are overcomplicating it a bit.
                    What part? The flap/check-valve part? Yeah...I don't see it being easily do-able at a DIY scale. It was merely a suggestion to overcome the issue of the fan drawing most of the air from the bucket rather than through the hose.

                    I'm just doubtful that you'd be getting enough flow through the hose when you have an unrestricted hole so close to the ducted fan. I don't know if adding a second fan would make the hose have that much more flow. It will probably draw even more air from the bucket.

                    I think the wet/dry bucket style vacuum is probably the best option. Possibly work the bean cooler into the vacuum rather than trying to work the vacuum into a bucket-bean-cooler.

                    Comment


                    • #11
                      Originally posted by dan110024 View Post
                      The ducted fan will draw air from the path of least resistance. Even with the bucket fan running (they're really weak), the ducted fan will likely take air from the bucket and won't create the negative pressure you require through the hose. The longer your hose, the more pressure drop you will have, exacerbating the problem.

                      If you could make some sort of flap at the lid/outlet which will close while the ducted fan is on, it might create enough suction through the hose. Like a check valve. There would need to be enough space between the flap and the ducted fan for the whole quantity of beans to sit before the fan is turned off and the flap allowed to open to drop the beans. This could be tricky to make properly, not to mention finding a material suitable for 200 degree beans to sit on.

                      You will most likely use a radio controlled plane EDF (electric ducted fan). If anything is going to be capable in the size you want, they will be. I can't seem to find any data in the specs about blade pitch, so I don't know if we can determine velocity (it would be difficult do calculate with the resistance of the hose, too), but some of them pull up to 1.7kg's of thrust and I'm sure that'd do it. It just depends how much you want to spend on this project. The most thrust that the 50mm fans pull is 550g. You might need to go for a larger unit and use PVC reducers for your Y-junction. I also don't know how some of those motors would go with 200 degree heat hitting them while they're spinning at max RPM.

                      Hardware & Accessories>EDF Systems & Parts>EDF Units - With Motor

                      It's definitely an interesting idea...but it might prove to be fairly difficult to get a working model in the DIY scheme of things.
                      All of this quite helpful - I'm aware that the amount of air in the bucket will be a problem - I just wondered whether the work of the extractor would be sufficient to reduce that problem. Granted you suggest it's too weak (probably highly likely!) it still would vary model to model I suppose. Furthermore, how the unit is built, whether air can flow back through the unit (through it's housing) etc. is something to suss out. Still - I'm not sure this project is unviable.

                      I think the plastic EDF units would struggle quite a bit, I don't think I'd be willing to try with a plastic fan - well, not without considering what type of plastic more carefully... But maybe the motor itself is something I need to think more carefully about too.

                      Originally posted by MrJack View Post
                      Seems like you are overcomplicating it a bit. If the extractor fan isn't enough, you could try two in series. Otherwise, maybe make use of a vacuum cleaner. Source a spare hose, chop it in half. Attach both halves (at the cut end) to a bucket lid. Seal all the holes in the bucket (try gladwrap).
                      Attach to vacuum as normal, poke the other end (with a narrow nozzle) into the roaster. Turn on. Bingo.

                      Did try to post a sketch, but tapatalk keeps crashing when I do.
                      The series idea is probably necessary - are you suggesting two extractors in series?

                      The goal was to explore an alternative to using vacuum. That's well documented elsewhere on this site and others - so I'd have no issues putting one together if my vacuum was not an overly electronic PITA.

                      Originally posted by dan110024 View Post
                      What part? The flap/check-valve part? Yeah...I don't see it being easily do-able at a DIY scale. It was merely a suggestion to overcome the issue of the fan drawing most of the air from the bucket rather than through the hose.

                      I'm just doubtful that you'd be getting enough flow through the hose when you have an unrestricted hole so close to the ducted fan. I don't know if adding a second fan would make the hose have that much more flow. It will probably draw even more air from the bucket.

                      I think the wet/dry bucket style vacuum is probably the best option. Possibly work the bean cooler into the vacuum rather than trying to work the vacuum into a bucket-bean-cooler.
                      Yeah so vacuum isn't what this thread is about - even if it is the best option, this thread is more about stretching the cooler concept further and continuing to innovate. I'm sure there is some sort of solution that'd be doable at DIY level! But, even if there isn't... people can read about vacuum elsewhere

                      With careful consideration to the diameter of the air passages - it might be possible. I'll begin experimenting next week.

                      Comment


                      • #12
                        Surely 'innovation' requires some kind of improvement?

                        A vacuum works on a simple principle:
                        - A blower pushes air out of a chamber, reducing the pressure.
                        - At the other end of a chamber, there is a hose connected.
                        - The air in the hose is at a higher pressure than the chamber, and thus flows towards the blower.
                        - If the blower is powerful enough, the velocity of the air coming in the other end is enough to drag particles with it.

                        So, basically you want to do exactly what a vacuum does, with a less effective blower (i.e. a fan)...

                        Comment


                        • #13
                          I may have to eat my own words (or do we drink them, here?).

                          I've run your basic design through a fluid dynamics simulation. I still need to determine the negative pressure which the exhaust/bucket fan can create (I may have time over the weekend to make a DIY water manometer which will allow me to work it out), but even with only 10 pascals of negative pressure on the outlet where your beans will drop, it's getting a decent amount of velocity through the hose section. I estimated that your air velocity through the fan would be 2 meters per second. It's a pretty rough guesstimate and could very well be wrong. I also kept the all of the pipe at a diameter of 50mm. It's also assuming the pipe is completely smooth (which it won't be if it's flexible). We could look at introducing some sort of restriction/smaller pipe where the beans exit to counteract any velocity drops that a corrugated hose makes.

                          Anyway, after a quick mock up, this is what the CFD sim spat out. I'm wondering how accurate the 4m/s calculation is when I gave it a 2m/s velocity at the outlet. Air velocity is higher at the centre of pipework due to static pressure towards the edges, but a 100% increase seems a lot.

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                          If I'm not too bogged down with actual study over the weekend, I'll see if I can rig up a manometer and see what negative pressure the bucket fan pulls. Also, have you got any idea on what you want to use as the hose? Keeping in mind that it's going to have to withstand 220 degree beans.


                          I've also re-read some of MrJacks posts that I was going against. I think I was misreading a couple of them on the tapatalk app
                          Apologies for disputing them. Haha.
                          Last edited by dan110024; 21 August 2015, 10:17 PM.

                          Comment


                          • #14
                            Originally posted by MrJack View Post
                            Surely 'innovation' requires some kind of improvement?

                            So, basically you want to do exactly what a vacuum does, with a less effective blower (i.e. a fan)...
                            Yep. Probably. Less effective if still sufficient is fine in my book.. The innovation would be convenience of not needing to lug a vacuum around I guess. Each to their own. To me that's worth investigating. I appreciated the suggestion that the extractor fan might have been enough. Consequently I went and gave that a crack. Here are my initial thoughts - many mistakes made, but good to learn some things.

                            I got from Bunnings an HPM exhaust fan, because it offered 350m3/h which was the highest amount of air movement I could purchase under $30 [Apparently that's 12m/s at 50mm Dan?] - maybe if my system was perfectly sealed and air could only come through the host I'd get that 12m/s, but it's probably more likely something like 8m/s.

                            Unfortunately for me, the fan didn't lodge in the buckets Bunnings sold like previous threads suggested Arlec fans might. But I think the buckets have changed anyway, so just going with an Arlec wasn't going to guarantee that experience. What I did do was utilise some of the silicone hose that I had left over from my slowly-coming-together KKTO build which has held it in place nicely and has the benefit of a tighter air seal as well.

                            I also found a ShopVac hose sitting on clearance at Masters for $10, so nabbed that as my test hose. Figured I could use it till it died, then find something a little more suitable (open to suggestions! Doesn't really seem to be many good options out there). I cut a hole in the lid of the bucket and fed it in using the bits and pieces that came with the hose. In order to cut the hole as small as possible, I taped one attachment to another, which resulted in a bulging shape before the hose entered the bucket like this

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                            That was a mistake (Again according to your post Dan, that'd have the effect of increasing the drop in velocity [decreasing the velocity!!] of the beans? - probably not ideal) - so I'll untape the attachment, and pull off the one attached to the hose and see what I can do to narrow it. I might even turn the whole hose around and use the normal sucking end as the end that deposits instead.

                            I cut a hole in the bottom of the bucket with just enough room to squeeze through the power cord - unsure about what effect the amount of exhaust room would have on the whole suction effort.

                            After putting all this together (without a sieve in the bucket unfortunately - I didn't have a suitably sized one) I tested it out with the lid off. What I found was that the fan was pulling air in through the centre of the fan - but was also blowing air out near the perimeter. I stupidly thought that it was the design of the fan at fault, so pulled out the fan to attach some black plastic to the back of it to try to reduce the backflow... not realising that in fact the air that was being drawn through the fan didn't have enough room to escape through the tiny hole that I had made for the power cable.. duh.

                            What tipped this off for me was that once it was all put together with the lid on, I could feel a tiny bit of suction through the hose (with my hand over it) but when I plugged the hole at the bottom with my foot, the suction stopped all together. All that was happening was recirculation of the air within the bucket, a struggling fan, and maybe a bit pushed and pulled through the hose. Again Duh.

                            So - my next steps:
                            1. Remove my crappy plastic mods to the fan
                            2. remove the hose attachments and turn the hose around
                            3. put in a sieve - picked one up from IKEA that will hopefully do the job.

                            What I _think_ I need to do (some advice if anyone knows!):
                            1. Increase the amount of air that can be expelled from the bucket by putting in some more holes.
                            2. Maybe shorten my hose? [@MrJack you suggested this?]

                            In order to get the most efficiency out of the fan and avoid the backflow, I guess the holes need to allow the whole 12 m/s of air to escape, but no more. I'm not entirely sure how to measure that to avoid cutting too many holes. I guess it'll be a bit of trial and error. Even if the system isn't closed and I'm not drawing 12 m/s directly through the hose, the fan still will still want to push that amount out (irrespective of where it finds that air)

                            Anyway - that's where I am at right now. I'm hopeful it'll work!

                            Comment


                            • #15
                              Sounds like you're making progress!

                              With fans/pumps/compressors, there is typically a relationshio (shall we say trade-off) between the pressure increase (between suction and discharge side) and the flowrate achieved. Your fan won't always flow 12 m3/s (as you have discovered) - only in free air.

                              In your design, the driving force for the beans isn't really the fan at all. It's the atmosphere "pushing" it's way into the duct, flowing towards the low pressure area at the fan suction. The job of the fan is to remove that air as efficently as possible.

                              You want as little restriction on the discharge (exhaust) side of the fan as possible, to ensure that all of the "available pressure drop" is on the suction side of the fan.

                              The amount air which will flow through the system will be largely defined by the route between atmosphere and fan suction. You have at best maybe 50kPaa at the fan suction (before the fan will no longer be capable of moving more air).

                              Which means that the flow you will achieve will be whatever flow results in 50kPa of frictional pressure losses. Frictional losses increase with velocity and "add up" along the length of a flow path.

                              Narrower, longer passages therefore result in more frictional pressure losses for an equivalent volumetric flowrate. However, you have an additional constraint - mainataining sufficient velocity to move the beans. So you want a duct which is only just narrow enough to ensure there is sufficient velocity to move the beans, and as short as practical from a use perspective.

                              In analogy, imagine bailing out a leaky boat with bucket. If you bail faster than the leaks you start to empty the boat. If you slow down, it fills with water. But, if if you bail too fast, you spill water back into the boat. In addition, you will never be able to make the boat floor completely dry with a bucket...

                              Hope this is of some help. Also consider that all of the above (and all explanations of fluid flow) are just models - simplified ways of understanding reality - they are all wrong to some extent.

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