B Liquid Flow Calculation out of a pressurized tank

AI Thread Summary
The discussion centers on calculating liquid discharge times from a pressurized tank, specifically for a cylindrical tanker used for transporting chemicals. The engineer seeks to understand how to factor in the overpressure from air during the discharge process, alongside the force of gravity. Clarification is requested on using Bernoulli's equation, particularly regarding unit cancellation when calculating exit velocity. The key point highlighted is the necessity of multiplying by the gravitational conversion factor (g_c) to ensure proper unit alignment. Understanding these principles is crucial for accurate flow rate calculations in pressurized systems.
Evan Jones
I am an engineer who needs to help my chemical transport girl friend with a little basic physics. It has been about 35 years since basic physics for me so I am rusty. She wants to understand how to calculate the following:

She drives a large tanker (cylindrical) which carries a variety of liquid chemicals and wants to understand how to calculate the discharge times. When they discharge the chemicals at the destination, they pump (and maintain) an over pressure of air in the tank during the discharge process. The fluid drains through a hose into an open (non-pressurized) tank. I know the fluid properties of the various chemicals, I just need to see if anyone can assist with the calculation. Am I just adding the force of the over pressure to the force due to gravity? If this were an open tank, I know how to make that calculation from the tank, through the hoses, and into the destination tank. I just don't understand how to account for the over pressure.
 
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The answer to your question is Yes.
 
Chestermiller said:
The answer to your question is Yes.
Can I ask you @Chestermiller to please expand on your answer. I am working on a similar problem whereby I need to determine the flow rate out of a tank that is under constant pressure from a hydraulic ram plate. I have looked at Bernoulli's equation but, I cannot make the units cancel out when calculating the exit velocity. Specifically, the term (P_tank - P_atm)/ density. The units for Pressure are in pounds-force per ft^2 while the units for density are in pounds-mass per ft^3. What am I missing for the equation v = (2*(P_tank - P_atm) / d)^1/2. Any assistance is much appreciated.
 
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fcroma said:
Can I ask you @Chestermiller to please expand on your answer. I am working on a similar problem whereby I need to determine the flow rate out of a tank that is under constant pressure from a hydraulic ram plate. I have looked at Bernoulli's equation but, I cannot make the units cancel out when calculating the exit velocity. Specifically, the term (P_tank - P_atm)/ density. The units for Pressure are in pounds-force per ft^2 while the units for density are in pounds-mass per ft^3. What am I missing for the equation v = (2*(P_tank - P_atm) / d)^1/2. Any assistance is much appreciated.
You need to multiply by g_c.
 

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