h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Can anyone give me a calculation for how long it would take a container of a certain size to empty of a liquid through a hose of a certain size?

Eg a 100L barrel of water through a 30ml (inside diameter) hose.

Does it matter how long the hose is?

I need to know how to do the calculation for different sizes.

You've been neglected, kea. No longer.

Can't help with a formula, just a comment or so.

. Narrower pipe, slower flow of course.

. I think it will matter how long the hose is - but for anything less than several metres of your 30mm pipe it may not be very much at all, possibly even ignorable.

. The important thing (until I'm corrected, that is,) is the head of water (the height of the surface above the release point).

That head of water will reduce as the barrel empties so the flow will slow down.
Further, if it's emptying into a narrower container (say, a watering can) then the head of water is being reduced at both ends - barrel falling, can rising - that's assuming that the hose low end is below the surface in the can (phew! nearly missed that last bit - thanks, preview)

My friend has such an arrangement (ie water stored in a large tub) to water plants when he is away. He has a small, battery operated timer valve - so that [x] litres of water are released twice a day. He had to stand and measure the amount released against the time it took, and then adjust the timer.

Interesting query. I have no answer, of course, but I think that length of hosepipe would matter as there would be some 'friction' of the water as it runs through the pipe. Probably neglible if the length is under a metre, but quite visible if the tubing ran from a house to a garden some distance away.

Another factor, is the top of the barrel open in any fashion? If not, as water leaves there might be a vacuum that develops in the top of the barrel, pulling back on the water. Relieved only by any air that might come back up the tube.

Ah, we do need someone knowledgeable - to views on friction within the pipe.

Open barrel - good point, I assumed... (Never assume anything unless Sir has forgotten to mention it)

- TWO views on friction within the pipe. (preview was my friend)

A "for instance", ... I have a 45 Imperial gallon plastic barrel that was used to convey fruit juices from manufacturing to packaging. A 3" fill hole is now attached to the down-spout of my rain gutters. A 1" relief cap? allows air to move as needed. I fitted a common outdoor water faucet at the bottom. It flows much faster when the barrel is near full than it does when it is down to 30% volume. Mass of the water and gravity assistance becomes a big factor

Looking at Lanza's example above, a timed valve would not be effective for my rain-barrel unless it was assured of being well filled often. An amount of water that leaves when the barrel is full, in say 2 minutes, is much more than what will evacuate once the barrel is at half or less capacity. In her example, I will guess the reservoir is much larger than 40-some gallons and replinished reasonably regularly

I forgot about the drop. There isn't any to speak of - well, less than a metre.

Yes the barrel won't be a closed unit (there will be an air gap that will stop the vacuum).

http://www.lmnoeng.com/Tank/TankTime.htm

It does matter, a bit, how long the hose is. But only a bit.

Dang! Thanks for that Twigster, it is something that I will print (as sites move along)

The H vs Hi are the variable here ...

You might also be interested in...

http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm

Pipe friction loss calculations. I knew that degree in chemical engineering had to be some use to me some day...

The tank time site is pay only. I'm looking for a formula online. What does a little inverted v mean in a calculation?

eg http://www.vbforums.com/showpost.php?s=fbd349a1e5b3c45a0e62f6ffa51b8db1&p=3094674&postcount=5

raised to the power

so, dia^2

is diameter squared.

How do I do to the power of .5? ^0.5

You operate with a Mac computer, right? Check to see if it has a built-in calculator program as Windoze does, that can be switched to 'scientific' mode. And then has the squares, cubes and lots of trigonometry things

Note: ^0.5 same as square root.

Built in Mac calculator = crap. No scientific mode - still.

>>> How do I do to the power of .5? ^0.5

Either ^0.5 or use the square root button on your calculator.

"Built in Mac calculator = crap. No scientific mode - still. "

Which Mac OS are you using???

The Mac Calculator has had a scientific mode via the View menu since OSX 10.1 AFAIK

Mine (OSX 10.6.8) has Basic, Scientific and Programmer. This has been the case since at least 10.2

t.