First Mistakes

[Geo]

There's definitely a mechanical reason for it. Perhaps the movement up creates a vacuum or an area of low pressure just under the filter holding the next drop suspended or at least held against the bottom. Perhaps the upward motion suspends the liquid inside the filter and the downward movement creates a vacuum inside the filter, stopping the liquid from passing through. Maybe its a little of each creating that two tenths of a second delay in the next drip.

 

[solar_plasma]

Maybe one of our physicists likes to join in: zero gravity maneuver or vacuum or both?

 

[lysdexic]

The math is beyond me but my limited understanding of the concept suggests it's not a "zero g" situation. Accelerating an object straight up (perpendicular to the earth's surface) or "up" in general generates a >1G force. On the downward "stroke" the object would experience a <1G force. If "0G" were achieved on the downward motion the funnel, filter and contents would be in free fall and the switch to upward motion (>1G) would probably be messy. It always seemed counter intuitive to me (as with moving a colander of dripping pasta), but it does work... I'm kind of curious as well. If you're good with the math, here's one of many places that discusses how free fall is achieved with parabolic flight:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598414/

 

[jason_recliner]

For siphoning, I used a 5/16" ID clear plastic tubing for 5 gallon buckets and about 3/16" ID tubing for 4 liter beakers. The undesirable curl (from being wrapped around a reel at the store) makes siphoning difficult, but the curl can be permanently removed from the tubing by soaking it in a pot of hot water on the stove for a few minutes, until the tubing becomes cloudy, and then quickly hanging it up for an hour or so with a weight attached to the bottom.

A little trick I used to use in winemaking, is to insert a wooden skewer into the low end of the tubing to stiffen it. Leave the pointy end hanging out about 1/2", or whatever is applicable to you. This helps keep the tube off the bottom, and easy to remove the skewer. If you have something plastic, it might be better than wood here.

 

[lazersteve]

I lost over a half ounce of gold due to steam explosions while force drying gold powder. I set up my hotplate on my work table and set up a visionware casserole to dry powder and placed the wet powder in it and turn on the heat and left. I obviously set the heat too high because when I got back there were craters in the now dry powder and wet powder all over the place. I remember finding some on an old satellite dish about fifteen feet from the table. At least it was my gold but it was a horrible mistake for me and about made me sick.

Always increase heat gently over time. It may not be the fastest way, but it is the safest. Steam explosions are extremely dangerous and costly to boot.

Breaking up the surface of the material to allow the trapped moisture to escape is also a good idea when heating powders that contain a lot of moisture. Never pack wet material into a container then heat rapidly, you are basically forming a mini cannon of sorts. If the pressure of the expanding steam has somewhere to go, chances are it will not launch the powder into space.

Steve

 

[g_axelsson]

Maybe one of our physicists likes to join in: zero gravity maneuver or vacuum or both?

The speed needed to create a vacuum behind the funnel is so high so the last drip would be the least of your problems. I think we can disregard of any vacuum effects.

Let's study the forces acting on the last drop. Something is holding it back or it would drip down immediately. That force is surface tension, it holds the drop at the end of the funnel.
When the gravitational pull becomes stronger than the surface tension a drop starts to fall. Immediately after it has fallen the amount of liquid left isn't enough to form another drop from gravity alone.
If you try to bob the filter up and down the filter will see more or less acceleration or gravitational pull (it's impossible to determine if you are accelerating in space or sitting still in a gravitational field, gravitation and acceleration is the same thing physically).
When increasing speed downwards the force is lower than 1g, when decreasing speed downwards the force is higher than 1g. When increasing speed upwards the force is higher than 1g, when decreasing speed upwards the force is lower than 1g.
In other words, the drop sees a higher force during the lower part of the up-down bobbing and a lower force at the upper part. If you time it and makes a parabolic path between your buckets then the filter sees a low force during the upper part of the move, could even be zero g. A low force means no drops are forming.
The higher forces acting on the liquid at the bottom of the bobbing movement creates drops with less liquid than needed if it was only sitting still, so when a drop has formed during the bobbing it takes longer for the liquid to add enough mass for a drop to form when sitting still.

Okay, the reason no drop are formed during the top movement is that the filter effectively feels zero or low gravitational pull during the move. the reason it takes longer for next drop to form after the move is that it needs to fill up the extra fluid needed to create a drop at 1g only.

I hope I was clear with my explanation. :mrgreen:

Göran, your local physicist.