Mass flow calculation

[tomol]

Hi,

If you have following information; the fluid is water, pressure 4,5 bar, pipe dimension 2", cooling water temp. 6,7°C. Is it possible to calcutate how much water there will be in the tank in 1 hour? Or am I missing information? The only way I have found to make this calculation requires speed, which I can't figure out how to calculate.

All help appreciated,

Tom

 

[poetix99]

Yes you need the fluid (water) velocity.

The pressure you've given; what does that actually designate? Some sort of supply pressure from the water source, we might suppose...

You must know the total resistance to flow: from the water "source" to the tank. This resistance is from pipe wall friction, fittings, valves and any other features in the fluid system.

The calculation of liquid (i.e. incompressible fluid) is generically of the form:

FLOW = CONST * AREA * (1/RESISTANCE) * (PRESS. DROP)^0.5

I suggest that you consult a reference such as Crane Technical Paper #410, or a text on flow metering such as the one by "Miller" (out of print).

Undergraduate fluid mechanics texts could also be useful, especially in getting some of the theoretical basics of fluid flow. (I see that you're "Electrical"; I daresay from your question - and what is missing - that you might need to get a grounding in some of the basics.) Electrical analogies are quite helpful in understanding some of the basics (pressure - voltage, tanks - capacitors, flow - current, resistance - resistance, etc.), but with caution.

Depending upon what is actually supplying the water, you might also need to know more about the characteristic of the source (whether it is a pump, a large elevated tank, etc.). It is quite possible that the pressure (4.5 bar in your case) might actually vary as a function of the rest of the system.

Have fun!

 

[tomol]

Hi there,

Thanks for answering me. As you said, I am electrical (and I am stuck). What we are dealing with here is an customer which on his site has a cooling water line which has design data as previously mentioned. This means that I will not try to calculate any losses or anything. I guess to avoid having to many questions on exact pressure and so on they have given us 4,5 bar normal and 10 bar max etc. This gives us huge tolerances for our calculations and they won't be "exact science". What I am trying to do is to get an indication on how much cooling water we can expect to receive from our customer.
My guess was that I should been able to use an equation (which I don't know) to calculate the speed from pressure, area and density (taken that I'm not including friction and loss from valves and bends).
Anyway, thanks for your help, I follow your advice and do some investigating.

Tom

 

[TD2K]

If you can find a copy of Crane's technical paper 410, it has the information you will need. If you have an email address, I can send you some of the key pages.

Basically, you'll need to know the inlet pressure (or pressures), the length and size of the piping and number of fittings/valves, etc to estimate the resistance to flow. Depending on the tank's elevation and water level, you'll need to also include the head of the water in the tank.

 

[tomol]

Hi,

Thanks for offering, my email address is tom@olsen.as