Finding flow rate with limited knowns

In summary, the conversation revolved around calculating the flow rate of a diaphragm pump through a length of pipe without knowing the velocity. One person suggested using Poiseuille's Law to calculate the flow rate, while another mentioned using a pump curve from the manufacturer. The final calculation estimated a flow rate of 16gpm for a 1hp pump.
  • #1
InsideCenter
3
0
Hello all,

My basic problem is I'm trying to figure out what flow rate a diaphragm pump can provide through a length of pipe. I know the pump's max pressure and all the details of the pipe and the fluid (80w-90 gear oil), but can I solve this without knowing the velocity? Is there a way to solve the velocity through these (or other easily obtained) knowns?

Thanks,
IC
 
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  • #2
yes, what is the rpm and cubic inches/rev of the pump?
 
  • #3
It's a pneumatically powered diaphragm pump, not a gear pump. The cycle rate is not constant as it depends on the media being pumped. The more viscous the media, the slower the cycle time.

Is there not a way to calculate flow rate without velocity?
 
  • #4
Alright, I've think I'm on the right track with Poiseuille's Law. Q=[(p1-p2)(radius^4)]/[(8/pi)(viscosity)(length)]

Change in pressure is 125psi
radius is 0.5 inches
viscosity is 1.4 poise (80w90 at 40 degrees C)
length is 200 ft.

I'm getting in the area of 16gpm. I expected much less. Can anyone double-check this??
 
  • #5
That's about 1hp, sounds about right, not sure of the formula, plenty of pipe flow calculators out there but most of the time manufacturers have a pump curve for different viscosity's.
 

1. How do you calculate flow rate with limited knowns?

To calculate flow rate with limited knowns, you will need to use the equation Q = AV, where Q is the flow rate, A is the cross-sectional area of the pipe or channel, and V is the velocity of the fluid. You will also need to know at least two of these variables to solve for the third.

2. What are the limitations of finding flow rate with limited knowns?

The main limitation of finding flow rate with limited knowns is that the calculated flow rate may not be accurate. This is because the equation assumes that the fluid is flowing at a uniform velocity, which may not always be the case in real-world situations. Additionally, the equation does not take into account factors such as turbulence, viscosity, and friction, which can affect the actual flow rate.

3. What are some common knowns used to calculate flow rate?

Some common knowns used to calculate flow rate include the diameter or cross-sectional area of the pipe or channel, the pressure or head of the fluid, and the density and viscosity of the fluid. Other knowns may include the length of the pipe or channel, the type of fluid being used, and the flow rate at a different point in the system.

4. How can you improve the accuracy of flow rate calculations with limited knowns?

To improve the accuracy of flow rate calculations with limited knowns, you can use more precise measuring tools, take multiple measurements at different points in the system, and account for any factors that may affect the flow rate, such as turbulence or friction. You can also use more advanced equations that take into account these factors.

5. What are some practical applications of finding flow rate with limited knowns?

Finding flow rate with limited knowns is important in many industries, including water treatment, chemical manufacturing, and oil and gas production. It can also be useful in designing and maintaining water supply and drainage systems, as well as in environmental monitoring and research. Additionally, understanding flow rate can help optimize processes and reduce waste and costs.

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