Basic Fluid Dynamics: Calculating Exit Velocity & Mass Flow Rate

In summary, the conversation discusses calculating exit velocity and mass flow rate for a vessel holding a liquid at a given pressure and a given opening. The engineer is looking for a basic understanding and mentions ignoring internal friction and assuming constant pressure. Another participant suggests that, without friction, the exit velocity would be enough to squirt a stream back up to the height of the fluid's surface, which is about 30 feet for water at one atmosphere. They also mention that doubling the pressure would result in a multiplied stream velocity.
  • #1
bootsnbraces
13
0
Hi guys and girls,

I hope you can help an electronics engineer out of his place in the mechanical world:rolleyes:

My very basic question is for a vessel holding a liquid at a given pressure and a given opening in the vessel how can i calculate exit velocity and mass flow rate? Like if i blow a balloon up to say 1 bar (good balloon huh:)) and then put a 1mm hole inside it how fast will the air be traveling as it leaves the balloon?


I don't need anything to detailed ( not worried about internal friction losses etc) and for now i can assume the vessel is fed by constant pressure mechanism i.e it won't drop pressure as it empties!

Any help gratefully recieved
 
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  • #2
Ignoring friction, the exit velocity should be just enough to squirt a stream back up to the height of the surface of the fluid.

That's about 30 feet for water at one atmosphere. 30 feet at one g is about 45 feet per second. Double the pressure and you multiply the stream velocity by sqrt(2).
 

FAQ: Basic Fluid Dynamics: Calculating Exit Velocity & Mass Flow Rate

1. What is fluid dynamics?

Fluid dynamics is the study of how fluids (liquids and gases) behave under various conditions, such as when they are in motion or when they interact with solid surfaces.

2. How do you calculate exit velocity?

Exit velocity can be calculated using the Bernoulli's equation, which states that the total energy of a fluid remains constant. The equation includes variables such as pressure, density, and velocity, which can be measured or calculated based on the specific situation.

3. What is mass flow rate?

Mass flow rate is the amount of mass that passes through a given area per unit of time. It is often expressed in units of kilograms per second and is an important factor in fluid dynamics calculations.

4. What is the relationship between exit velocity and mass flow rate?

Exit velocity and mass flow rate are directly related. As the exit velocity increases, the mass flow rate also increases. This is because the faster the fluid is moving, the more mass it can carry per unit of time. However, the relationship is not linear and depends on other factors such as the size and shape of the exit opening.

5. How is fluid dynamics used in real-world applications?

Fluid dynamics has many practical applications, such as in designing aircrafts and automobiles, predicting weather patterns, studying ocean currents, and optimizing industrial processes. It is also used in medical fields to understand blood flow and in environmental engineering to analyze water and air pollution.

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