CO2 flow meter – concept to be verified.

[Yugang]

The most common method for measuring CO2 flow in our hobby is the CO2 bubble counter. It is cheap and reliable but has a few disadvantages. We can count the bubbles, but the size of the bubble may vary from one product to another, so we don’t really have an accurate measure of the CO2 volume per minute. Furthermore, for larger aquariums the number of bubbles may exceed 5-10 per second and may be hard to measure without taking videos that can be replayed slow motion.

An alternative would be a professional gas flow meter. Not cheap, needs some corrections for a.o. gas pressures, and user experience for correct use.

I have been thinking some time ago how we could simplify flow measurement for CO2 in our tank, but lost interest as I am using a reactor in overflow mode and therefore do not care anymore about stabilizing my CO2 flow. My reactor stabilizes CO2 injection, irrespective of CO2 flow.

I’d like to share here a concept that I came up with, that may be interesting for a hobbyist or manufacturer to test and develop into a product. I have no plan to take it further but will be happy to put it here in public domain for anyone who sees an opportunity.




The working principle would be in the above graph. We start on the left, where an inverted cup collects injected bubbles in our flow meter. This cup may have a scale printed on it, so that we can read the volume of the gas bubble. Going from 1 to 2, we see that the cup fills, while also the ‘syphon’ fills as pressures equilibrate. When we continue to fill the inverted cup, the ‘syphon’ will start to release gas to the gas pocket in the top of the device, 3, until the cup is empty, 4, and the process repeats itself starting with 1.

The user now times the cycles from 1 to 4, while noting the gas volume when the cup starts releasing.

This will give an accurate volume per minute, in a product that can be really cheap, has no moving parts or complicated technology and should be very reliable for the mainstream hobbyist.

This is a basic working principle but needs further optimization and testing as a proof of concept and development into a product. There will be some challenges in the practical implementation but am quite confident it can be made to work.

Anyone who is interested to run with it and bring something new (as far as I know) to the hobby, feel free.

P.S. I do also have a more radical idea that may be even cheaper, but has probably a few more challenges and risks with proof of concept. I may post that later.

 

[Anonymous_One]

... when the cup starts releasing

I have a question: Do I understand correctly that the siphon activate when (and only when) the amount of gas in the cup reaches the rim (= the siphon's overflow)? And at that point the siphon will pump (suck) all the gas from the cup into the gas pocket?

PS: I will definitely try it at the earliest opportunity, but for now probably only in a bucket or some larger glass container.

 

[Yugang]

I have a question: Do I understand correctly that the siphon activate when (and only when) the amount of gas in the cup reaches the rim (= the siphon's overflow)? And at that point the siphon will pump (suck) all the gas from the cup into the gas pocket?

PS: I will definitely try it at the earliest opportunity, but for now probably only in a bucket or some larger glass container.

It will start releasing when the level approaches as in picture "2". The gas will then start to enter the upward siphon tube on the right, and as gas is lighter than water it will start to move up. The cup will release in a rather short time, until picture "4" and the left siphon part starts to suck water instead of CO2.

It is like siphoning water out of your tank, but then in the inverse using gas that wants to go up rather than water that wants to go down.

I also like to see it work, as it is always possible that I am wrong with my assumptions. It would not be the first time . But then, I have another more radical idea is a backup.

 

[Art]

As always @Yugang, thanks for continually thinking of ways to improve our hobby through innovation.

I think this is a variation on a bell siphon that is in common use. I have used it to make wet dry emersed growing containers for plants. It works very well over the long term as it has no moving parts.

Assuming a steady flow of gas, I think that you would be able to determine the amount you are putting into the aquarium on a per (insert time frame).

Without trying to put down the idea, or the use of flowmeters etc., why is this important to know?

 

[Yugang]

I think this is a variation on a bell siphon that is in common use.

The bell siphon works with water, if I understand correctly, but the above concept uses it to 'siphon' CO2 gas in stead of water. The physics is indeed similar, applying the principle that pressures equalise if that makes sense.

 

[Yugang]

PS: I will definitely try it at the earliest opportunity, but for now probably only in a bucket or some larger glass container.

I am quite confident that the principle will work at first try, as long as we don't minituarize it into a too small assembly. Assume we use water as the fluid, and the assembly built from glas, there will be adhesive attraction between the two, including a capillary action in the syphon. Designing it in a small package should be done while carefully considering dimensions of the syphon, and perhaps using an oil instead of water.

Without trying to put down the idea, or the use of flowmeters etc., why is this important to know?

You're asking here why so many use drop checkers or flow meter for CO2 flow measurement?
I guess because when using conventional reactors, or diffuser, you want to have a measure of the CO2 injection rate, which is driven by CO2 flow. I lost interest in my initial idea, as for the horizontal reactor I don't care too much about the flow, but it may take time for mainstream hobbyists to follow overflow method.

 

[Yugang]

Further explanation, slightly simplified.

Note that we assume a semi stationary situation, no significant accelerations or velocities in gas or fluid, and that we ignore capillary effects in the siphon tube.

• The pressure in water is proportional to the weight of the water column above it.
• The pressure in a pocket of gas can be assumed constant anywhere, assuming that the gas is not flowing, not accelerating and has negligible weight.

Let’s start the analysis here:



The gas pocket in the inverted cup has reached a depth D1, which is slightly deeper than the depth DSiphon. The gas water/interface underneath the cup is not moving, so we can assume that the gas pressure in the cup, including the part of gas in the siphon is proportional to D1. If we now look at the gas/water interface in the siphon, then the water pressure is proportional to DSiphon, and therefore less than the gas pressure at same position. The gas pressure in the siphon is higher than the water pressure and therefore the gas starts to flow out.



Continuing to release gas from the inverted cup, we’ll get in the situation as above. The pressure in the gas pocket is still proportional to D1, and the water pressure at the outflow is proportional to DOutflow. As DOutflow < D1, gas pressure at the siphon outlet continues to be higher than the water pressure and therefore the cup continues to release gas via the siphon.

The process stops when the siphon starts to suck water, and is no longer filled with gas. The cup can now start filling again, until the siphon starts all over again.



I hope this helps.