Fluid Flow calculations
Fluid Flow calculations
(OP)
I' looking at calculating the theoretical flow rate of water through a vertical pipe. This pipe is modeling the suction pipe of a vacuum truck. I'm doing this in an attempt to prove a higher vacuum in the tank is better than a higher flow rate of air being removed from the tank to create the vacuum.
I've attached a diagram with a simplified expectation of what I am expecting to find. Pump A cannot reach a high vacuum, but has a higher flow rate at free air, pump can achieve a higher vacuum but a lower flow rate at free air.
So I am using Bernoulli equation using the pressure difference as 1 Bar at the bottom of the pipe, and 100 mBar at the top, where the pipe enters the vacuum tank. This assumes that the pipe is totally filled with water. I'm trying to remember from uni what the effects of friction loss from the pipe walls will be. Is this the only other thing I need to take into account when finding the theoretical flow rate at the tank inlet? Does anyone know the formula for friction loss? Cheers
I've attached a diagram with a simplified expectation of what I am expecting to find. Pump A cannot reach a high vacuum, but has a higher flow rate at free air, pump can achieve a higher vacuum but a lower flow rate at free air.
So I am using Bernoulli equation using the pressure difference as 1 Bar at the bottom of the pipe, and 100 mBar at the top, where the pipe enters the vacuum tank. This assumes that the pipe is totally filled with water. I'm trying to remember from uni what the effects of friction loss from the pipe walls will be. Is this the only other thing I need to take into account when finding the theoretical flow rate at the tank inlet? Does anyone know the formula for friction loss? Cheers





RE: Fluid Flow calculations
Phil,
You have the head loss at the suction hose inlet and the friction loss in the hose. Since the vacuum tank isn't full of water, there is no velocity related losses at the exit of the hose (it exits into the gas headspace).
Use darcy-weisbach to calculate the friction losses:
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RE: Fluid Flow calculations
RE: Fluid Flow calculations
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RE: Fluid Flow calculations
This type of application is known as an "air lift pump". Unfortunately it is empirical knowledge and it is hard to design an installation without having hands on experience of a very similar installation. Googling will find you a few references, and even some YouTube videos of air lift pumps in action.
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