dreaminmel
New member
We have now entered the twilight zone... do do do do... :lol:
overskimming ha!!
- Thread starter LFS_worker
- Start date
dreaminmel
New member
Pics on Brian's behalf... :thumbsup:
aerofoamer
acro
zoanthids
xenia
aerofoamer
acro
zoanthids
xenia
dreaminmel
New member
and link for video of skimmer in action... 
kimoyo
Active member
Gary, you are obviously a very knowledgeable reefer with a very nice tank. As I am sure Mr. Marini is also extremely knowledgable and possibly has another explanation for this. But from the way you describe and others have its just doesn't make sense to me.
1) Air bubbles are all over inside the skimmer. The water will be in contact with air bubbles while on the inside of the skimmer.
2) The height of the water determines when the water exits the skimmer.
Using a deltec ap600 as an example, the water enters somewhere towards the upper middle of the skimmer body. The exit begins near the bottom and then has to travel upward a certain amount to exit the skimmer. Different things will determine the operating water level but the water has to rise to exit. Because the water has to rise (go vertical), this will determine how long water stays inside the skimmer. When filling up the skimmer, if you fill it up at a slow rate (gph) the water will rise slowly, if you fill it up at a faster rate the water will rise quickly going towards the exit. Because of this only the vertical component of the velocity will determine how long the water will spend in the bubble filled skimmer (regardless of its horizontal motion) and thus determine the contact time.
1) Air bubbles are all over inside the skimmer. The water will be in contact with air bubbles while on the inside of the skimmer.
2) The height of the water determines when the water exits the skimmer.
Using a deltec ap600 as an example, the water enters somewhere towards the upper middle of the skimmer body. The exit begins near the bottom and then has to travel upward a certain amount to exit the skimmer. Different things will determine the operating water level but the water has to rise to exit. Because the water has to rise (go vertical), this will determine how long water stays inside the skimmer. When filling up the skimmer, if you fill it up at a slow rate (gph) the water will rise slowly, if you fill it up at a faster rate the water will rise quickly going towards the exit. Because of this only the vertical component of the velocity will determine how long the water will spend in the bubble filled skimmer (regardless of its horizontal motion) and thus determine the contact time.
kimoyo
Active member
I'm not sure where this is going but I don't agree that air 'lingers' in the skimmer. Like with all skimmers, air has an in/out rate like water has an in/out rate. If as suggested, the air just stayed in the skimmer and you keep adding more air, wouldn't after a while the skimmer be filled with just air. I don't agree, the way it works is that air enters the skimmer at a certain rate and leaves the skimmer at that rate. And that rate can be different than the water rate, just like with other skimmers.
Its also, depending on the tank, plausibly that bubbles get saturated (filled up) with organics fairly quickly. You want fresh bubbles for the dirty water, not fresh dirty water for dirty bubbles.
Last edited:
Gary Majchrzak
Team RC
Define contact time, Rich.
You already said it- it's the amount of water the air bubbles are exposed to.
A taller or larger diameter skimmer can skim more water at the same GPH as a similar skimmer of smaller volume because greater volume allows more contact time.
The greater volume causes a greater distance the air/water mixture must travel in order to exit the skimmer. A greater distance to travel allows more contact time between the air and water.
Swirling bubbles do not collide and combine in an Aerofoamer except in the riser neck where they form skimmate.
So the diameter of a skimmer has no bearing on contact time, Paul?
Brian- I wouldn't be surprised if your Xenia starts suffering from the cleaner environment. Xenia naturally occur in environments that are higher in organics than do stony corals; that's why some folks use Xenia for nutrient export in reef aquaria.
Last edited:
LFS_worker
'ignoramus maximus'
Gary The xenia Is one of my main concerns in the aquarium ... Im keeping a close eye on this species.. If it stops pulsing I know that It will have to go (not die) ... Im almost counting on it stoping shortly.
Today I have to feed the fish ... They will be fed about 1.5cc of piscine energetics mysis shrimp (very oily).
Mel thanks for posting that for me
kimoyo - there appears to be the same ammount of bubbles in the reaction chamber at any given time ... when I started the skimmer it took about 35 seconds for there to be any "skimmer head" . At any given Time if I plug the air intake I will stop the air then re-introduce air It will take about 15 seconds before I get any "skimmer head" by shimmer head I mean where the airbubbles condence in the collar and make foam.
Brian
Today I have to feed the fish ... They will be fed about 1.5cc of piscine energetics mysis shrimp (very oily).
Mel thanks for posting that for me
kimoyo - there appears to be the same ammount of bubbles in the reaction chamber at any given time ... when I started the skimmer it took about 35 seconds for there to be any "skimmer head" . At any given Time if I plug the air intake I will stop the air then re-introduce air It will take about 15 seconds before I get any "skimmer head" by shimmer head I mean where the airbubbles condence in the collar and make foam.
Brian
manderx
New member
yes, air out = air in, after it takes some time to hit equalibrium. there is this lag between the time the first bubble is injected till the first bubble exits. when you swirl the water, you extend this lag. forget about vector components, they don't apply here since the bubbles are so heavily influenced by the water around them. for example, if you have 2 skimmers with the same airflow going into it. in one skimmer the bubbles linger 20 seconds. in the other, they linger 30 seconds. that direclty means that 50% (minus loss from bubbles merging though this doesn't happen too much since the bubbles are not colliding) more surface area of bubbles within roughly the same amount of water (so doing that much more work) at any given snapshot in time. the more bubbles there are, the thinner the film of water between bubbles, so that more proteins within the water are actively touching and air/water interface.
who says bubbles lose their stickiness when they get dirty? i can easily envision them getting even stickier when they are dirty, as the proteins entangle each other. but i can also envision proteins dropping off the bubble easier as they get dirtier just beacuse there are more on it to drop off (i haven't read anything conclusive either way), which is why i think the more important aspect of swirling is the bubbles never descend in the body/riser. it's ok for a protein to drop off as long as the bubble is higher in the chamber than they were before, since it'll probably get picked up by another bubble and moved up the body a little farther before it drops off again. baby steps. what you don't want is for a bubble to take a load of proteins down the column and have some drop off near the outlet. when i had a myreef beckett (which doesn't swirl) i saw bubbles upwelling and downwelling through the entire height of the bottom riser several times before finally making it up to the neck.
kimoyo
Active member
Contact time is the amount of time the water is exposed to the air bubbles.
I agree with what you are said here. But what your missing is that for a given volume its the greater distance in the vertical direction because only the vertical direction determines when the water exits the skimmer (i.e. how long the water stays inside the skimmer in contact with the air bubbles).
Yes, of course it has a bearing, but you decide on the diameter when its being made and after that its fixed. So once the skimmer is made, for that specific volume (diameter), only the water height, how fast the water rises, will affect the contact time.
Please keep in mind, that we are talking about one skimmer, same diameter, same volume, only difference is the 45 elbow for it to swirl on not. And asking if the swirling increases contact time, which it can't because contact time is a function of the vertical velocity.
Thank you for the observation.
If this were true, that the swirling increases the dwell time of the air bubbles, then I would agree that contact time is increased by swirling the water. But, unless I'm misunderstanding this, to do that the swirling motion would have to reduce the upward buoyancy force of the air bubble. That would be an interesting discussion.
Here is a passage from an article by Randy Holmes-Farley.
Once the skimmer has generated a large amount of surface area, the next issue involves allowing enough time for organics to actually diffuse to the interface. How long does this take? That's an important question without a perfect answer. Diffusion of molecules in water can be slow. For very large molecules, like proteins and carbohydrates, it can be very slow. It might take hours for a protein to diffuse a few inches in water. Fortunately, we do not need to rely on pure random diffusion to carry organics to the surface. Nearly all skimmers have bubbles in a turbulent environment, where they can be carried around by water flow as well as by diffusion. As they approach the bubble surface, however, movement of water relative to the bubble will be greatly reduced, and diffusion will be necessary for the final travel to the interface. The amount of time necessary for complete accumulation of organics at the surface will also depend upon the concentrations of organics in the water, and even on the chemical nature of the organics present. It makes perfect sense that in water with high levels of organics, the interfacial area will be rapidly occupied by organics. That is because there are enough in the local area around the bubble to saturate the interface. When the concentrations are lower, organics have to diffuse from farther and farther away from the bubble to saturate it. Additionally, different organics have different strengths of binding to the air/water interface. Things which have a strong preference will slowly replace those already at the interface which have a lower binding strength. Thus, a bubble which is completely occupied with organics might still be changing with time on exposure to tank water. It will not, however, go on increasing its organic load indefinitely. For these reasons, one cannot readily state that a certain amount of time is necessary for organics to fully saturate bubbles. Further, it is incorrect to claim that it is always better to increase the contact time between bubbles and the tank water. Likewise, the way in which the bubbles move relative to the water is important. If the bubbles are moving against the water flow, or are in a turbulent environment, the required absorption time will be lower (because the water flow helps bring organics to the interface) than if the bubbles are moving with the water flow.
I think many of our tanks have a lot of organics and the bubbles become saturated quickly. Thats why you can take an ap600 on a 120G and replace it with an ap702 and get more skimmate per hour, regardless of flow thru gph.
Gary Majchrzak
Team RC
Why are skimmers of the same height yet different diameter rated differently at the same GPH?
Contact time is the answer.
This is the truth. We must move on. This debate has sidetracked the original thread.
Last edited:
LBCBJ
New member
This discussion is way to damn complicated. A simple mind should understand that a given volume of water that is forced up, back down, and then back up (hence "swirling") will have greater contact time than a stream of water that flows only upward.
All of the water in my Deltec does not move vertically at the same rate, some pockets of water are "swirled" and therefore held in the reaction chamber for a slightly longer amount of time.
All of the water in my Deltec does not move vertically at the same rate, some pockets of water are "swirled" and therefore held in the reaction chamber for a slightly longer amount of time.
manderx
New member
like i said before, it's easy to test with a bucket. knock yourself out.
yeah, i've read that, and that's why i said what i did in the second part of of my text you quoted. but i'm not entirely conviced of randy's version. if they did get saturated like that we wouldn't see a stiff foam head at the top of the riser.
that is exatly what we are trying to avoid with swirling. we want bubbles to corkscrew around the body from the bottom up to the top, with no downwards movement. my deltec (902) does swirl somewhat, but nowhere near as forcefully as a aerofoamer does with the appropriate pump. the aerofoamer my buddy had looked like a flushing toilet it was swirling so fast with his GRI520 and was the most amazing skimming i've ever seen (and i've seen all the current 'hot' skimmers). i would probably have one if i wanted to pay the power for it.
BeanAnimal
Premium Member
A lot of good information... but a lot of bad assumptions here.
Firstly, yes the qty of water in = the qty water out. The qty air in= the qty air out.
However we can not assume that the air and the water are bound together as the sole component of contact time, nor can we assume that every molecule of water (or air) leaves the skimmer at the same rate. It is certainly not an ordered chain, pressurized pipe or free flow channel with laminar (or low reynolds) flow. Some molecules may remain for minutes or hours, while others enter and leave at the rate of flow.
Remember the air is not attached to the water. The turnover rate of the skimmer therefore is only one facter with regards to contact time. There are MANY other factors that come into play.
A "calm" skimmer may have a low reynolds number and the bubble buoyancy will be the major component of the rise time and hence contact time. The deeper the skimmer the more buoancy and the higher the velocity and the faster the water movement.. (think airlift). In this case the turbulance is mostly due to the bubbles themselves (and the water they drag along with them).
However when you add a swirling component to the body, the bubbles take a much longer path to the surface. By all means the angular path and viscocity of the water have an effect on the rate of rise. Rich (not to pick on you... I just know your position on this matter), you keep saying that this causes turbulance and the combination of bubbles. Actually the opposite could be demonstrated. The swirling of the water is much more orderly than the random turbulance of the bubbles rising on their own. Read on...
Does the water drag the air, or the air drag the water along? Well the air wants to rise and the water wants to stop moving (friction and equillibrium). So the water tends to drag the air along with it on it's swirling path. However due to friction the water wants to slow down. The air tries to move upwards and in turn drags water with it, as well as further slows the angular velocity. All of this works against the swirl as the bubbles want to go straight up (insert basic newtonian mumbo jumbo here) There is certainly some tubulance and shear involved, but all in all it is still rather orderly compared to just bubbling water in a tube.
Some of the water will rise (or fall) with the eddie currents produced by the shear and turbulance and some of the water will continue along the ever slowing angular path... dragging a large portion of the air along with it.
Read those paragraphs again! That tubulance is why the contact time is longer... say what? Yes the turbulance causes some water to never contact the bubbles and instead go about it's business in another direction.
Before you say it....
Because all bubbles are not uniform, some will break free and add further turbulance by rising MUCH faster. However this happens in a calm skimmer as well. I urge some of you to go look at a "bubble wall" sometime and watch the bubble rise in the narrow columns. The fatter faster bubbles create one hell of a lot of tubulance as the ascend quickly between the smaller bubbles. The surface tension of the bubbles keeps many from combining, but the big crashers do the most damage in the bottom 1/3 of the track.
Trapping these bubbles in a swirling vortex will tame some of this rise (at least until the water slows near the top of the chamber). But at that point (when the grip of the water on the angular path can no longer keep the bubble) the bubbles buoyancy is much less than it would have been deeper in the skimmer and the fat bubbles are much less prone to cuasing damage to the smaller bubbles.
What does this all mean? There will be many molecules of water that have a MUCH longer contact time, rememer the surface tension attraction of the air water interface.
What else does this mean? Well the same QTY of air and water go in and come out. So for every extended contact time unit of air/water, another water molecule gets little or no contact! Simple math folks.
SO what does THAT MEAN? Well we can surely say that Escobal and others have noted that the longer the contact between a bubble and a protien (attached to the water molecule) the more chance it will be bound to the the air instead of the water.
Putting it together? Well we all know a short skimmer and short contact time work on some protiens, but according to Escobal and others, there are other protiens that need much longer contacts to be stripped. Given the same flow and air rate, the longer contact time would be a gift. If the skimming still lacks, then the skimmer needs to be bigger to get the "short contact" protiens as well.
In other words given the same amount of gunk (assuming it is a homegenous mixture of all kinds of protiens) the longer contact skimmer will get both "short" and "long" contact protiens but the shorter contact skimmer will not. Making the "shorter" skimmer "bigger" but not increasing contact time will certainly remove more material, but still not the "long contact" protiens... so one would strive to make the contact LONG and the skimmer LARGER for a given situation.
Phhewwwww.
Firstly, yes the qty of water in = the qty water out. The qty air in= the qty air out.
However we can not assume that the air and the water are bound together as the sole component of contact time, nor can we assume that every molecule of water (or air) leaves the skimmer at the same rate. It is certainly not an ordered chain, pressurized pipe or free flow channel with laminar (or low reynolds) flow. Some molecules may remain for minutes or hours, while others enter and leave at the rate of flow.
Remember the air is not attached to the water. The turnover rate of the skimmer therefore is only one facter with regards to contact time. There are MANY other factors that come into play.
A "calm" skimmer may have a low reynolds number and the bubble buoyancy will be the major component of the rise time and hence contact time. The deeper the skimmer the more buoancy and the higher the velocity and the faster the water movement.. (think airlift). In this case the turbulance is mostly due to the bubbles themselves (and the water they drag along with them).
However when you add a swirling component to the body, the bubbles take a much longer path to the surface. By all means the angular path and viscocity of the water have an effect on the rate of rise. Rich (not to pick on you... I just know your position on this matter), you keep saying that this causes turbulance and the combination of bubbles. Actually the opposite could be demonstrated. The swirling of the water is much more orderly than the random turbulance of the bubbles rising on their own. Read on...
Does the water drag the air, or the air drag the water along? Well the air wants to rise and the water wants to stop moving (friction and equillibrium). So the water tends to drag the air along with it on it's swirling path. However due to friction the water wants to slow down. The air tries to move upwards and in turn drags water with it, as well as further slows the angular velocity. All of this works against the swirl as the bubbles want to go straight up (insert basic newtonian mumbo jumbo here) There is certainly some tubulance and shear involved, but all in all it is still rather orderly compared to just bubbling water in a tube.
Some of the water will rise (or fall) with the eddie currents produced by the shear and turbulance and some of the water will continue along the ever slowing angular path... dragging a large portion of the air along with it.
Read those paragraphs again! That tubulance is why the contact time is longer... say what? Yes the turbulance causes some water to never contact the bubbles and instead go about it's business in another direction.
Before you say it....
Because all bubbles are not uniform, some will break free and add further turbulance by rising MUCH faster. However this happens in a calm skimmer as well. I urge some of you to go look at a "bubble wall" sometime and watch the bubble rise in the narrow columns. The fatter faster bubbles create one hell of a lot of tubulance as the ascend quickly between the smaller bubbles. The surface tension of the bubbles keeps many from combining, but the big crashers do the most damage in the bottom 1/3 of the track.
Trapping these bubbles in a swirling vortex will tame some of this rise (at least until the water slows near the top of the chamber). But at that point (when the grip of the water on the angular path can no longer keep the bubble) the bubbles buoyancy is much less than it would have been deeper in the skimmer and the fat bubbles are much less prone to cuasing damage to the smaller bubbles.
What does this all mean? There will be many molecules of water that have a MUCH longer contact time, rememer the surface tension attraction of the air water interface.
What else does this mean? Well the same QTY of air and water go in and come out. So for every extended contact time unit of air/water, another water molecule gets little or no contact! Simple math folks.
SO what does THAT MEAN? Well we can surely say that Escobal and others have noted that the longer the contact between a bubble and a protien (attached to the water molecule) the more chance it will be bound to the the air instead of the water.
Putting it together? Well we all know a short skimmer and short contact time work on some protiens, but according to Escobal and others, there are other protiens that need much longer contacts to be stripped. Given the same flow and air rate, the longer contact time would be a gift. If the skimming still lacks, then the skimmer needs to be bigger to get the "short contact" protiens as well.
In other words given the same amount of gunk (assuming it is a homegenous mixture of all kinds of protiens) the longer contact skimmer will get both "short" and "long" contact protiens but the shorter contact skimmer will not. Making the "shorter" skimmer "bigger" but not increasing contact time will certainly remove more material, but still not the "long contact" protiens... so one would strive to make the contact LONG and the skimmer LARGER for a given situation.
Phhewwwww.
BeanAnimal
Premium Member
BTW if my new skimmer kills all of my xenia... I may have a party!
RichConley
New member
Gary, theres a simple answer to that: Higher volume. Because the skimmers contain a larger volume of water, with the same in/out, the column moves slower on the vertical axis.
RichConley
New member
Right, but for every pocket that swirls down with increased contact time, one gets swirled up, and has decreased contact time.
Edit: Just read Beans post.
"
What else does this mean? Well the same QTY of air and water go in and come out. So for every extended contact time unit of air/water, another water molecule gets little or no contact! Simple math folks."
We're saying the same thing here bean.
BeanAnimal
Premium Member
Rich it's not the speed of the water column on the vertical axis, the bubbles pretty much dictate the bulk of that. It's the fact that the larger volume (with the same I/O) will tend to have a higher mix ratio. (back to what I said above, but due to volume not sideways velocity). Some water will tend to stay a LOT longer than it would in the smaller volume chamber.
However, we again are talking "dwell time" vs "contact time" and according to Escobal, the contact time between a protien and the surface tension of a bubble is the key component.
Enjoy.
However, we again are talking "dwell time" vs "contact time" and according to Escobal, the contact time between a protien and the surface tension of a bubble is the key component.
Enjoy.
