Flow on sloped floor of tank - Bernoulli

[blitz97]

All. I am wondering if anyone had input on this subject. I have a rectangular tank where I am pumping water down the sides onto a sloped bottom that is draining off into a side reservoir. Simple Bernoulli equation anaylsis can guide me to what flow down the walls I need to keep a certain dpeth on the floor based on the drain size. However, I am not clear how the slope of the floor comes into play when determining what depth I can maintain. Can anyone provide any guidance?
Thanks

 

[BigInch]

You need to study up on "open channel flow".


Independent events are seldomly independent.

 

[racookpe1978]

You will have one of four things occur, depending on drain size (and total resistance to flow of the drain and its pipe) and whether or not the drain is gravity-only, or goes to the suction of a pump.

1) Gravity flow, flow into tank (down the walls) is less than resistance of the drain cover and pipe: The tank will never fill up. All fluid going into the tank will flow down into the sump and out the pipe. The pipe will never "fill" and in horizontal runs, will approximate an open channel or half-filled round pipe.

2) Gravity flow, flow into tank is more than what the pipe can transmit: The pipe will try to empty the tank, but there is too much resistance. The pipe will fill, the tank will fill up the sloped bottom until the gravity head between the lowest point of the pipe and top of fluid created exceeds the resistance to flow of the pipe and drain cover and whatever is plugging the pipe (algae, debris, throttled valve, pump impeller, slug, waste, whatever.

3) induced flow (pipe goes to a running pump, but input to the tank is less than pump's suction pressure. Pump will run, flow will go into the impeller but will it will sooner or later suck out the fluid in the pipe and the tank and the pump will cavitate. Tank will never fill up until the pump breaks.

4) induced flow, but flow into tank is greater than maximum possible pump induced suction pressure: Tank will again fill up until the gravity head exceeds the suction NPSH and some balance will settle out. Note: If there is too little gravity head for equilibrium (or if the pump is less than inlet flow, the tank will still overflow eventually.)

 

[darai]

why don't you go "brute force" route?
get you a dip stick, vary flow-in rates, measure corresponding heights maintained.
That's how flow curves are validate.

 

[blitz97]

Thanks all! Open channel flow theory is just what was I needing.