Surface skimming calculation

[guserto4]

I know I've read opinions on the length of an overflow box based on x. I don't remember if x is surface area of tank, tank volume, flow volume, etc. and can't seem to search out a thread that discusses it. Can somebody remind me what the suggested length of overflow is per x?

I'm going for ultra quiet, and I'm sure that plays a factor.

Thanks

 

[Gorgok]

You don't need a calculator for that. You want the longest edge possible for best results. Can't get much longer than the entire length of the tank without it becoming silly though.

 

[guserto4]

C2C all the way around!!!
Yes, that would be silly.

I swear I've read there was some go by... Hmmm.

 

[uncleof6]

You can use weir calculations to determine the thickness of the layer of water going over a weir (head height behind the weir.) By measuring the head height behind the weir along with the width of the tank and width of the weir, the exact flow rate over the weir (through the system) can be calculated.

The basic concept is the longer the weir at given flow rate, the thinner the layer of water (lower head height,) and the better the surface skimming/surface renewal. As was pointed out already, you cannot get better than the full width of the tank. (what would be considered the width of the river or 'channel' for weir calculations,) so actually going through the math is rather pointless. Since the equation is not 'linear' rather exponential (velocity increases as you get closer to the weir) it would not be x per y rather x^3/2 .... per y (not related to the weir calculations just made up, although the exponent at the end of the Kindsvater-Carter equation is 3/2... sqroot of (h+K_h)³ where h+K_his the effective head height)

What you are searching for are the weir calculations. By manipulating the equation, you can build a model that will predict performace at various flow rates/lengths of weirs. (There is one on th RC home page, how accurate it is I don't know, the pipe sizes are way off...) Remember the lengths used are effective lengths, not total lengths. E.G when teeth are present, the effective length is the sum of the spaces between the teeth. These equations are posted all over the internet. A word of caution however, they are not for those without a scientific mindset...