Chart: Contact Time from Volume and Flow Rate

[Jgray152]

I finally put together a chart and a graph which tells you the amount of contact time there is between the water and media when using the flow rate and volume of media.

Notice how the contact time drops drastically from 100-700 GPH compaired to higher flow rates? I am not sure why this is but I have used two different fluid velocity calculators and both come up with the same velocities. I have also calculated the volume differently and the flow rate differently and always come up with the same answers. So, it must be correct. Its very interesting.

Here is how I initially calculated the figures

It doesn't really matter what the dimentions are as long as it equals the right volume. It also doesn't matter if its a tube or a sqaure box.

So I used "6 inch diameter pipe" as my base value to figure out the volume.
6" diameter has an area of 28.25 cu/in. A Box 3.02 x 3.02 x 3.02 has about the same volume.

1 liter = 61.02 cubic inches

6" x 10.80" = 5 liters.

61.02 * 5 = 305.1 cu/in.
305.1 / 28.25 = 10.8"

100 GPH = 0.22694 inches per second through a 6" diameter tube.

10.8 / 0.22694 = 47.59 seconds of contact time.

This is what I did throughout the board. I actuall used Excel to calculate all the values.

 

[hybridtheoryd16]

i have no idea what you are trying to accomplish here but good job on the work. ------------It has long been known that just because a high flow rate has a lower contact time does not mean that it does not work as well. As long as you acheive a flow rate that enables the bacteria to comsume enough ammonia for a given bio load then you are good. And a larger flow rate will actually balance out in a sealed system because for example you only have 300 gallons of water to flow. So a lower flow rate has more contact time on one pass ,but a higher flow rate will get more passes thru the media in any given time period compared to the lower flow rate. That is why it is said that more filtration and turn over rate is never a bad idea. You only get into trouble with to little.-------------------So a good experiment would be to figure out how much conatct time is needed to convert the most ammonia and then nitrite. And that would be worth its wieght in gold.

 

[Jgray152]

Its also known that a contact time which is to short will not work either.

Example, THe Eheim 2080 cycling faster than the Fx5.

2080 has about 36 seconds of contact time where the Fx5 has 10 seconds. The Fx5 also has a much higher velocity too than the Eheim.

This is also to show you that you don't need 60-80-150 liters of bio media that some people put in the huge wet/dry system just because they have a 400 Gal. aquarium.

Many don't know the contact time. I have had people say, "its all about contact time". When they don't even know how much contact time they are getting. They could be getting 50 seconds which is a lot, when they could use a canister with 20 seconds of time.

 

[hybridtheoryd16]

Yea I have went back and forth with people over the contact time thing myself. And for me it is blindingly simple. With a higher flow/turn over you will get a lower contact time per pass but more passes thru the media in a given amount of time. And people just can't get that. It is a sealed system here and as long as you make it to the bottom of the thresh hold for conatct time you are good and any more flow just gets better.

 

[Jgray152]

I believe there is a point though.

I understand what you are saying and I agree.

But lets just say we had a filter running 1800 GPH with 5 liters of media on a 240 Gal tank and a filter running at 1000 GPH with 20 liters of media on a 240 Gal tank. This is where it starts to get tricky, this is where you start to scratch your head. The question is, which will perform better? I think its obveous in my example, atleast I hope, but there is a lot about nitrification times we just don't know.

The point is, if you wan't a high flow rate, you wan't a lot of media so that more toxins can be removed through one pass instead of multiple.

 

[CHOMPERS]

...but there is a lot about nitrification times we just don't know.

Yep. Nice job though, but all that work was for naught.

It isn't realistic to design for single pass efficiency in a bio-filter because the bacteria population varies widely with the available food. The ammonia source is not constant, especially if the fish are not fed daily. The bacteria population growth/reduction lags behind the change in the food level.

 

[CHOMPERS]

...I am not sure why this is but I have used two different fluid velocity calculators and both come up with the same velocities.

It's because the calculators used an exponential function to produce those results. Which calculators did you use?

 

[Dr Joe]

I with CHOMPERS and I think your looking at contact time as a function of erosion in this case, which it isn't since bacteria aren't treated this way.

I think we went over some of this when johnptc was working on his setup, it may still be in the back threads.

Dr Joe

.

 

[Jgray152]

It's because the calculators used an exponential function to produce those results. Which calculators did you use?

If you could explain deeper, that would be excellent, because this bugs me and does not seem to be producing the results I expected to see.

This is the second calculator that I used. This first time I used this calculator was when I built the table.
http://www.eesiflo.com/flow_calculator_01.html

This is the other one I have used for a long time.
http://www.1728.com/flowrate.htm

It really bugs me because I was expecting more linear results instead of what I got.

I think we went over some of this when johnptc was working on his setup, it may still be in the back threads.
p.q

Do you remember what thread that was? I am interested.

 

[CHOMPERS]

It stems from the formula for the area of a circle,

A=(pi) r^2

or

A=(pi/4) D^2

The exponent is the r or D squared. When you double the diameter of a circle (or pipe), the area quadruples.

How did you go from the calculators to deriving your charts?