Welcome to Koi Forum. Is this your first visit? Register
Results 1 to 8 of 8
  1. #1
    Extreme Koi Member Rank = Adult Champion NickK-UK's Avatar
    Join Date
    May 2015
    Posts
    1,539
    Thanks / Likes
    1746

    Gravity fed protein skimmer.

    So.. been thinking again

    Most protein skimmers use small bubbles of air to attach to small solids or dissolved solids to separate from the water. The importance here is small bubbles. To make these people use air stones and pin wheel impellers to break bubbles into small bubbles (I'm ignoring an issue of over saturating the oxygen content), or cascading the flow down through media. All of these seem to use a water pump of some description.

    However gas within a liquid held under pressure, when expanded also creates very small bubbles.

    My thinking here is to use the natural pressure depth of water to improve the efficiency of creating the bubbles. Same as when people get the bends diving..

    1. Water from the filter return enters the sump through a U bend. Just before it enters a small stream of air is injected using an ayirstone. Not powerful enough to cause an airlock or to resist the airlock.
    2. As the water + air goes down it's applied to atmospheric+0.175bar of pressure (1.75m depth of the sump) causing the air to be compressed and some to be absorbed into the water itself
    3. The water then rises reducing the pressure from atmospheric+0.175 bar back to the atmosphere - this causes the air bubbles to expand but also there's no pressure to hold the gas in the water and the gas forms very fine bubbles as it moves up the column.
    4. At the top there's two open Ts which catch the foam produced - two are used to that if the first misses, the second catches it.
    5. The water then enters the sump.
    6. The airlift then pulls the water from the sump - causing the water to be pulled into the sump through the protein skimmer.

    IMG_7922.jpg

    Just an idea at the moment. The idea is that I'd use one of the 4" returns and sit this on it, the other providing a standard diffuser.


    14000l, my mutts: Chargoi (2010), Doitsu (2022), Tancho (2022), Kujaku (2022), Hi Utusri (2022)

  2. #2
    Extreme Koi Member Rank = Adult Champion NickK-UK's Avatar
    Join Date
    May 2015
    Posts
    1,539
    Thanks / Likes
    1746
    Just extending the thinking: https://www.engineeringtoolbox.com/a...ter-d_639.html

    So I need to calculate the standard atmospheric then atmosphere+0.175 bar (17.5kpa). Then we can see the volume of air that would be absorbed and reappear. A slightly cruder mechanism is to use a pinwheel spinning in the flow. Only issue is it uses electrical power which I'm trying to avoid.

    So using the engineering toolbox they give desolved air at 1 and 2 atmospheres in g/kg.

    at 25degC g/kg
    Dissolved air at 1 atm (1.0135bar) 0.023
    Scaled at 1.01325 bar + 0.175 bar (at 1.75m)
    0.023 + 0.175 *(0.045-0.023) = 0.023 + 0.00385
    0.02685
    Compression difference 0.00385

    So we know how many grams of air per kg of water (ie in 1m3). However I want to know how many litres of air this is - as it basically says if this is worth attempting or not.

    So if 1 litre of air is 1.225g at sea level (ie 1atm - but assume same temp). That's 1.225*0.00385 = 0.0047 litres or 4.7ml of nano/micro bubbles (small) per 1m3 of flow in addition to the visible bubbles.

    A coke bottle (carbon dioxide rather than nitrogen) ranges between 276 and 379 kilopascals. One atmosphere is 101kpa so that's 2.5-3.8 atmospheres, so opening a bottle is between 1-3 atmosphere change. So this isn't going create bubbles like opening a pop bottle, also given the flow rates and the time to dissolve rate, it would add some micro bubbles but still needs a bubble generating mechanism. For this to work passively- it would require 10 meters of water depth per atmosphere, so it would require a U bend 20-30 meter straight down.

    So I think one option for making a passive pin wheel - the 4" flow driving a 1" bubble generator. The 4" flow turbine drives a shaft that drives a gearbox and a 1" pinwheel on 1" flow. The air is then foamed up by the 1" path that rejoins the 4" flow on the way down.
    14000l, my mutts: Chargoi (2010), Doitsu (2022), Tancho (2022), Kujaku (2022), Hi Utusri (2022)

  3. #3
    Nick... have a look at this guy... quite simple but effective

    [https://youtu.be/CTDeg5xv_mI


    Sent from my iPhone using Tapatalk

  4. #4
    Extreme Koi Member Rank = Adult Champion NickK-UK's Avatar
    Join Date
    May 2015
    Posts
    1,539
    Thanks / Likes
    1746
    Quote Originally Posted by Ricey74 View Post
    Nick... have a look at this guy... quite simple but effective
    [https://youtu.be/CTDeg5xv_mI
    Pump fed I'm afraid There's a good example of a media based contra-flow shower pump fed here: https://www.youtube.com/watch?v=-Ci-2Gd8dWM the only issue I have with his design is the output - you want the returning water level to be high enough to prevent the foam from returning to the pond.

    A good summary on skimmer designs: https://www.youtube.com/watch?v=t7jzFudfgZw

    What I'm looking todo is not have a pumped skimmer if possible but use in an existing gravity feed with airlifts. The airlift will have some skimming but it's purpose is to lift so you don't want to mess with water flow within the lift tube. In the airlift isn't the best location either as a skimmer, you want dwell time for the DOC to attach to the bubbles.

    The pond design has twin 110mm incoming from the RDF/BIO into the sump/anoxic chamber. Then twin 110mm airlifts out. The inlets need to be diffused - so there is pipework and I was thinking if it would work, to swap one of the diffusers with a protein skimmer attachment. I'm just trying to design something with a pin wheel and small air feed with enough dwell time.

    I could run a pinwheel into the return of the BIO.. the flow has then got 4m of dwell time and then simply put a T on the returns so that they collect the foam the only issue is that the pipe drops down underground so there's an airlock potential unless the flow is fast enough vs foam.
    14000l, my mutts: Chargoi (2010), Doitsu (2022), Tancho (2022), Kujaku (2022), Hi Utusri (2022)

  5. Thanks Ricey74 Thanked / Liked this Post
  6. #5
    Extreme Koi Member Rank = Adult Champion NickK-UK's Avatar
    Join Date
    May 2015
    Posts
    1,539
    Thanks / Likes
    1746
    This Princeston paper is interesting: https://www.princeton.edu/news/2017/...-and-no-filter

    edit: they use polydimethylsiloxane - a silicon with a permeability with CO2. So that is specifically CO2. However..

    Perhaps having a long trough with lots of bubbles to cause the particles to be lifted and then separated may be a combination of the skimmer and have a membrane less filter for fines.

    What you could do is use the clean side water, add air then fed back through a pinwheel. The foam bubbles then are injected through a mesh at the base of the trough. Creating fine bubbles without needing lots of small holes.

    A variable blade then separates the water flow. This could be adjusted by water level or by physically changing the blade depth (even using a float to cope with changing lengths). A closed tube and a couple of T junctions rotated allowing overspill of the top later would work too without needing a blade.

    So my thinking is something like this:

    IMG_8051.jpg

    You could use a full 4" pipe with holes but then use a gutter 1/2 pipe welded to the underside covering the holes (the pipe holes act as the mesh, the gutter side acts to distribute the air/foam mixture) to leave a full 4" bore clear.

    If you use ozone in the air.. it also acts like a clarifier and steriliser (no bio filter build up and no UVC needed). Just need to have the output into a pipe and the ozone vented to the outside (very bad for your health).

    The reason I like this design is that I can fit this as part of the return from the BIO before it goes back underground - the pipe would be about 2m long and 60cm under water level but it's possible to make the "splitter" a couple of long tubes from the T back up toward wards water level where it could overflow into a trough. The maximised dirty water then can be filtered and the clean back to the pond.
    14000l, my mutts: Chargoi (2010), Doitsu (2022), Tancho (2022), Kujaku (2022), Hi Utusri (2022)

  7. Thanks Ricey74 Thanked / Liked this Post
  8. #6
    Extreme Koi Member Rank = Adult Champion NickK-UK's Avatar
    Join Date
    May 2015
    Posts
    1,539
    Thanks / Likes
    1746
    I've been reading up a little on precisely how a DOC skimmer works. It's the electrical charge between the inside surface of the bubble and the water boundary. The molecules of the DOC have a charge that then simply sticks - one end of the DOC pointing to the bubble and one end to the water. This also works at a larger scale - the bubbles lift the larger particles in the water flow to the top too. In the Princeton design the CO2 permeates the silicon and the CO2 has a charge that attracts the particles. As the mix flows horizontally the CO2 rises and permeates out of the other side of the silicon membrane at the top of each channel. This causes the particles to rise and allows the particle rich fraction to be skimmed off.

    Skimmers already do this in that they use a T piece to skim off the DOC rich fraction of foam rather than the water fraction.

    My thinking is that with enough length, that particles of 20 microns could be lifted up the water flow by the air/foam mixture, then as the mass of foam rises up the foam capture tube it makes an airlift to lift the particle rich water column before it overflows (note this is skimming the foam AND the water level just under it) to remove the particles.

    The flow rate would be slightly impacted due to the additional turbulence but the mass of water would still be moving at a decent rate so the length ot pipe is important to get the dwell time required - or have the pipe feed into a chamber where the foam can be captured. Ideally you want 2 minutes of agitated foaming.. two minutes means a large volume - so you could use a 55g 220l drum and have the feed in causing a vortex and bubbles.. but this is by design a counterflow which will slow a gravity fed skimmer's flow rate potential.


    I did think about adding a pin wheel pump to the bio chamber - 185l of water has a high dwell time by design - the pinwheel system could sit in the initial inlet chamber of the Draco bio chamber. The rolling of the bio would then provide the dwell time and the media breaks up the forming larger bubbles. If the rolling movement wasn't so severe then you could put a pond skimmer into the chamber and use that to collect any foam.. The exit of the bio is at the bottom so in a system with a rapid rolling (and the foaming doesn't stop the rolling) then the output will contain a mix of foam and water. If that lead into a 55g 220l blue drum then it would provide the space and dwell time to reduce the flow velocity (the drum being wider) and allow the foam to rise to the top (like a large T bend on a skimmer) and have lower potential to airlock in the system.
    This method, if it works, is more passive and doesn't slow the rate more than is needed and it can have a skimmer setup floating on the water level to skim off the foam - a 2" valve can then be used to tune the flow. At the base of the chamber a 20 micron screen with back wash could be installed on the exit pipe making it a settling chamber.


    I have some pond soil moving todo today so I have plenty of time to think whilst shovelling!
    14000l, my mutts: Chargoi (2010), Doitsu (2022), Tancho (2022), Kujaku (2022), Hi Utusri (2022)

  9. #7
    Extreme Koi Member Rank = Adult Champion NickK-UK's Avatar
    Join Date
    May 2015
    Posts
    1,539
    Thanks / Likes
    1746
    With the completion of the pond and the maths I've used to work out the flow rate in the airlifts. I thought the same concepts could be used to 'small flow analysis' a potential in-pond air powered protein skimmer.

    IMG_9935.jpg

    Previously I worked out my flow rates (air and water) for the system as:
    IMG_9664.jpg

    IMG_9666.jpeg

    IMG_9665.jpeg

    IMG_9667.jpeg

    IMG_9668 2.jpg
    14000l, my mutts: Chargoi (2010), Doitsu (2022), Tancho (2022), Kujaku (2022), Hi Utusri (2022)

  10. #8
    Senior Member Rank = Supreme Champion Ajm's Avatar
    Join Date
    Mar 2018
    Location
    Durham
    Posts
    11,220
    Thanks / Likes
    21135
    Gotta say I love the work you put in to these things nick it always amazes ( and confuses the hell out of me ) never know what am reading but looks the dogs

    Sent from my SM-G973F using Tapatalk
    Freddyboy the legend

    "we are water keepers first"

    Johnathan

  11. Thanks Maddog1 Thanked / Liked this Post
 

 

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
All times are GMT +1. The time now is 01:26 PM. Online Koi Mag Forum
Powered by vBulletin® Version 4.2.3
Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.

vBulletin Improved By vBFoster® (Lite Version), © UltimateScheme, Ltd.