# Constant water drop rate (via diffusion)?

1. Apr 26, 2007

### leoflc

Hi,

I need to make a simple and cheap device that I can water droplet at a constant rate (from a bucket of water).
The size of the droplet doesn't matter, it just needs to be dropping at a constant rate (at least for a day).

So I was thinking, can I acheive that by putting half of a cloth in the bucket, and the other half on the outside of the bucket. By doing that, the water should be sucked out of water because of diffusion, and the outside half of the cloth will be dropping water droplet at a constant rate.

Will this work?
Is ther any other way I can make a device that can drop water droplet at a constant rate (at least for a day)?
Is is there data out there that can help me with the diffusion rate for certain type of material?

Thank you very much!

2. Apr 28, 2007

### lpfr

It can work, but this has nothing to do with diffusion. It is just capillarity that "sucks" the water and prime de siphon. But the rate will not be really constant. It will depend on the difference of height between the surface of the water in the bucket and the extremity of the rope (better than a cloth).
If you need a really constant rate, you must use a trick. Take a tight container (a big one) and a stopper. Put a pipe trough the stopper and adjust the pipe in order that its low opening is almost at the bottom of the water. Insert the rope through the pipe. It must not be tight. Air must pass freely between the rope and the inner wall of the pipe.
As the water is sucked, the level in the pipe will descent until it arrives at the lower extremity of the pipe. Then air bubbles will enter the container as the water is slowly sucked.
Now the distance which determines the drops rate is the height between the bottom of the pipe and the lower extremity of the rope.

3. Apr 29, 2007

### cesiumfrog

Basically idea is to have a vessel with constant fluid level (hence constant pressure despite that the reservoir empties).

lpfr's idea is equivalent to using the base of a bird-feeder as that vessel.

Another version (I think I got this one from Hero of Alexandria) is to have a large reservoir drip into a smaller container (quickly, so that the smaller container is constantly overflowing, and let the overflow be discarded down some other hose). Now, since the pressure (ie. level) in the smaller container remains constant, a tap at its bottom will drip at a constant rate.

Last edited: Apr 29, 2007
4. Apr 29, 2007

### leoflc

Thanks for the helps!
I don't really need the rate to be that consistence, just need to be accurate enough for a day.
I was thinking about suing the capillarity idea to make a water clock.

5. Apr 29, 2007

### leoflc

Thanks a lot for the tip.
But I'm not so sure what is the stopper, can I get that from places like homedepot?
Thanks a lot!

6. Apr 30, 2007

### lpfr

The stopper is just the cap of the container or the cork of a bottle. It is what renders the container thigh. It comes with the container.

You can do a capillary clock, it can work. You can even consider entering the records book with the most imprecise clock in the world. The reason is that drop rate and drop size depend on viscosity of the water, surface tension of the water and evaporation rate. All this depend on the temperature. The evaporation rate depends also on air humidity and air circulation.