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Thread: Why It's Not All That Bad- Aerator Heating Up Water, I Think?

  1. #1
    Oyagoi yerrag's Avatar
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    Post Why It's Not All That Bad- Aerator Heating Up Water, I Think?

    I've been thinking of ways lately to keep my aerator from increasing my water temperature, as my pond is in the tropics and it doesn't need to be warmed up. But yesterday, I was being thankful of how well the circulation of my pond is, and wonder why it is so. Why I focused on circulation was because I've been focusing on solid waste from the koi. If the circulation is excellent, all koi waste would just as soon they're made be sent packing to the sump via the bottom drain. It appears that is the case with my pond, as I don't see waste littered along the bottom floor or across the water column.

    I had my TPR (tangential pond return) plugged up, and all return is coming thru my waterfalls. So I am wholely dependent on my Matala bottom diffuser to provide circulation for the pond. When I first tried this setup, it wasn't to improve circulation. In fact, I thought I would sacrifice circulation. But to my surprise, circulation improved, my gauge being how waste was quickly being cleaned up (By the way, I changed to this setup to increase aeration, but didn't think of it as but a temporary thing, more as an experiment).

    The more I thought about this serendipitous outcome, the more dumbfounded I got since I could not explain the hydrodynamics. I then remembered Disney's Nemo and how he rode the sea current, and how the ocean currents are driven by the thermohaline effect, where temperature gradients and changes is salinity affect the movement of water in the ocean. And it dawned on me why diffusers, driven by warmer air, do as good a job with water circulation.

    It is that the water that is driven upwards get warmed up by the diffuser air. Upon reaching the surface, it stays on the surface as it is lighter, and gets pushed outward toward the pond walls. As the bottom water gets sucked into the bottom drain, a gradual displacement of water occurs with the warmer water gradually sinking down, along the entire expanse of the pond. This allows all the water to be sucked towards the center, where the bottom drain is located, and along with the water solid wastes are sucked in. The direction of flow is radially directed towards the bottom drain, and keeps the solid wastes from being diverted away elsewhere in the water column.

    I've drawn two sketches and perhaps the attached photos of them will explain it better:
    Why It's Not All That Bad- Aerator Heating Up Water, I Think?-image.jpgWhy It's Not All That Bad- Aerator Heating Up Water, I Think?-image.jpg

    This is just my own guess. But my point is perhaps I should just let things be and allow the aerator to slightly heat up the pond.

  2. #2
    Daihonmei MikeM's Avatar
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    I agree with your sketches as to what is occurring with water circulation due to the aeration. I disagree that it is because the air bubbles are warming the water. The same currents are created if the air is colder than the pond water. It is the same effect as occurs when using airlifts in lieu of water pumps.

    The aeration does warm the water by moving water to the surface where it comes into contact with warmer air. In a 4-season climate, aeration will chill the water by increasing contact with cold surface air. In theory, water might be so warmed that the lower oxygen capacity was less than if there was no aeration and the water was cooled by contact with cooler ground temperatures. But, somebody who tried to do the calculations basically concluded that the koi would be dead before the water got that warm. Besides, not many koi ponds in Death Valley or the Sahara. ....So, keep up the aeration even though it has the effect of warming the water some.

  3. #3
    Nisai
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    I`m with Mike here, in the much cooler temperatures of the UK, any heating of the water is a bonus.

    The reason we put our airated bottom drains in the centre of our ponds, is so that the air/water currents can rise in the middle of the pond, spread out to the edges then sink back down to the floor, when it then sweeps its way back to the bottom drain again, taking any wastes it bumps into with it. That is how my drain has worked for the last 25 years or so anyway. Nice clean bottom for all that time.

    Once you put a TPR in to the pond, you destroy the functional circulation and end up with waste all over the place.

    Chris

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    Oyagoi yerrag's Avatar
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    Quote Originally Posted by ageinghippy View Post
    Once you put a TPR in to the pond, you destroy the functional circulation and end up with waste all over the place.

    Chris
    Glad to hear this from you, Chris. Nice to get that confirmation as that is just how I am observing it.

    However, I wish I could be having my cake and eating it too. The warm, or actually hot air from my air pump, doesn't help in keeping my pond temps as cool as I could possibly want, especially during summer where I'm at. Still, I'm still happy I'm getting excellent circulation. Less poop floating around I'll gladly take over a slightly warmer water temperature. I think the koi will agree to that as well.

  5. #5
    Oyagoi yerrag's Avatar
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    This brings up a side topic: If TPRs counteract the circulation in a pond, is the use of the TPR justified? The main use of a TPR, aside from returning filtered water to the pond, is for a current strong enough to develop the koi's body, right? So is that a good reason to destroy an otherwise good circulation system which provides good aeration throughout the pond as well as reduce the retention time of solid waste in the water column? Should we be thinking of another way then to help develop koi body and structure as we discard the TPR?

  6. #6
    Oyagoi yerrag's Avatar
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    Quote Originally Posted by MikeM View Post
    I disagree that it is because the air bubbles are warming the water. The same currents are created if the air is colder than the pond water.
    Since the air pump is hot, and the air it expels to the diffuser is hot/warm, and this can be confirmed by touching the 3/4" PVC airline, it would heat up the pond water, especially where it is in contact with as air is diffused and rises. I would think that this contributes more to heating the pond than water being brought into contact with warm air as it surfaces along with air from the diffuser. The water surface area in contract with the atmosphere remains more or less unchanged whether or not there is aeration. In summer weather, the effect is insignificant. In winter weather, the effect is significant. Aeration makes the water colder, whereas not aerating causes the surface to freeze, and keeps the bottom water from getting colder and from freezing.

    If the air from the aerator is colder than the water, it makes the water colder and heavier as well. Heavier water tends to sink and thus, not remain on the surface. So the water brought up by aeration will not stay on the surface and be pushed towards the pond walls, and this will not bring about good circulation. It will be like the second illustration, which is inferior to the circulation in the first illustration.

  7. #7
    Daihonmei MikeM's Avatar
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    Quote Originally Posted by yerrag View Post
    Since the air pump is hot, and the air it expels to the diffuser is hot/warm, and this can be confirmed by touching the 3/4" PVC airline, it would heat up the pond water, especially where it is in contact with as air is diffused and rises. I would think that this contributes more to heating the pond than water being brought into contact with warm air as it surfaces along with air from the diffuser. The water surface area in contract with the atmosphere remains more or less unchanged whether or not there is aeration. In summer weather, the effect is insignificant. In winter weather, the effect is significant. Aeration makes the water colder, whereas not aerating causes the surface to freeze, and keeps the bottom water from getting colder and from freezing.

    If the air from the aerator is colder than the water, it makes the water colder and heavier as well. Heavier water tends to sink and thus, not remain on the surface. So the water brought up by aeration will not stay on the surface and be pushed towards the pond walls, and this will not bring about good circulation. It will be like the second illustration, which is inferior to the circulation in the first illustration.
    Yerrag, I acknowledge that the air pump will add some heat to the air being pumped into the pond. I still disagree with you. The water surface area in contact with the atmosphere is not the same with or without aeration, and more importantly, the water molecules in contact with the surface is radically greater with aeration than without. The heat exchange is very much like oxygen exchange. The surface area exposed to the atmosphere increases due to all the ripples created on the water surface. This may be a small percentage increase or double the flat surface, or even more, depending on how vigorously aerated. The big factor is the movement of water from the bottom to the surface, with currents across the surface of the pond continually exposing additional molecules to the surface temperature interface. I agree that contact with the air bubbles within the aeration stream will result in heat exchange, but the quantity of water exposed to the bubbles' surface is minor compared to the revolving mass exposure at the surface.

    Think about your statement: "Aeration makes the water colder, whereas not aerating causes the surface to freeze, and keeps the bottom water from getting colder and from freezing. If the air from the aerator is colder than the water, it makes the water colder and heavier as well. Heavier water tends to sink and thus, not remain on the surface. So the water brought up by aeration will not stay on the surface...." You are correct that aeration in a cold climate winter makes the pond water colder. This will be true even if the aeration uses air drawn from within a heated building. The reason is due to the increased surface interface resulting from aeration bringing bottom water to the surface, which does not stay there (despite being warmer) because currents keep the water moving, continually brushing against the colder atmosphere.

  8. #8
    Oyagoi yerrag's Avatar
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    You're making perfect sense, Mike. So the effect of a diffuser is primarily for creating turbulence at the water surface, which impacts aeration more than the air bubbles created by the diffuser. A more powerful aerator makes for more aeration due to the larger amount of air-water interface exposure created by the surface turbulence, and not as much due to the effect of more air bubbles created.

    The advantage of having a diffuser, over a surface aerator though, is the ability of the diffuser to induce better circulation in the pond by causing more bottom water to rise to surface and push surface water towards the pond walls. In a warm summer weather, the resulting higher surface water temperature allows the surface water to stay on the surface longer and be pushed further towards the pond wall. The more of the previously bottom water becoming surface water is pushed towards the walls, the better the circulation is. As the bottom drain sucks in water, the surface water fills in the lower layers of the water strata throughout the pond.

    The implication here then is that the more turbulence the better. This makes the waterfall and other surface aeration inferior at aeration. I now wonder whether it is better to have just one diffuser attached to one air pump to have higher turbulence (assuming the diffuser is matched to the air pump in capacity) than multiple diffusers attached to the same air pump. Is there more turbulence one way or the other, or is it the same?

  9. #9
    Jumbo sacicu's Avatar
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    Quote Originally Posted by MikeM View Post
    Yerrag, I acknowledge that the air pump will add some heat to the air being pumped into the pond. I still disagree with you. The water surface area in contact with the atmosphere is not the same with or without aeration, and more importantly, the water molecules in contact with the surface is radically greater with aeration than without. The heat exchange is very much like oxygen exchange. The surface area exposed to the atmosphere increases due to all the ripples created on the water surface. This may be a small percentage increase or double the flat surface, or even more, depending on how vigorously aerated. The big factor is the movement of water from the bottom to the surface, with currents across the surface of the pond continually exposing additional molecules to the surface temperature interface. I agree that contact with the air bubbles within the aeration stream will result in heat exchange, but the quantity of water exposed to the bubbles' surface is minor compared to the revolving mass exposure at the surface.

    Think about your statement: "Aeration makes the water colder, whereas not aerating causes the surface to freeze, and keeps the bottom water from getting colder and from freezing. If the air from the aerator is colder than the water, it makes the water colder and heavier as well. Heavier water tends to sink and thus, not remain on the surface. So the water brought up by aeration will not stay on the surface...." You are correct that aeration in a cold climate winter makes the pond water colder. This will be true even if the aeration uses air drawn from within a heated building. The reason is due to the increased surface interface resulting from aeration bringing bottom water to the surface, which does not stay there (despite being warmer) because currents keep the water moving, continually brushing against the colder atmosphere.
    Hi Mike,

    It all boils down to surface area in contact with air molecules and not necessarily because the surface of the pond is the major contributor. Take for example a small bubble but more bubble diffuser placed in a deeper pond as opposed to a course bubble but considerably less bubble air diffuser placed in a shallower pond. Since there will be more surface area of air in contact with more smaller bubbles in the water as compared to using a course diffuser regardless how it creates more ripples or displacement, that means better oxygen transfer efficiency is produced. However, in a very large surface area pond with a shallower setup, it could be possible that using a course air bubble diffuser creates better oxygen transfer and displacement in water surface is optimized better in a larger surface area. IMO, a pond that is deeper with a smaller footprint would be better with a finer airdiffuser while a shallow pond but very big surface area would be better off with a courses airdiffuser. Very deep and very large ponds would be a challenge to aerate IMO. This also covers in the laws of thermodynamics. The finer and more droplets of water in shower exposed to cooler air, the faster the pond water can cool or can maintain a cooler temperature. On the other side, I maintain a total of six airpumps pumping out a total of 460lpm in several japanese airhose that deliver fine air bubbles. I do not choose airpumps that produces heat(usually those that churn out 100lpm heats up). In fact I have returned twice Resun 100LPM because the air it was blowing out was much hotter compared to ambient air. Once I used it in a 3 ton setup and overnight water temperature increase from 26 to 30C despite ambient air of just 26C. Presently all my airpump are aircooled to prevent it not only from releasing heat to the pond but also to protect its components longer.

  10. #10
    Daihonmei MikeM's Avatar
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    Quote Originally Posted by yerrag View Post
    The implication here then is that the more turbulence the better. This makes the waterfall and other surface aeration inferior at aeration. I now wonder whether it is better to have just one diffuser attached to one air pump to have higher turbulence (assuming the diffuser is matched to the air pump in capacity) than multiple diffusers attached to the same air pump. Is there more turbulence one way or the other, or is it the same?
    Yes, the more turbulence the higher the oxygenation/heat exchange impact. The growing practice at shows is to use two airstones in each show tank. Oxygenation is greatly increased mainly due to the surface conflict of ripples from two sources. Of course, more is better only if done within reason. Koi still need their quiet zones in the pond.

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