Fill time for a pressurised system

[sph99]

Hi everyone

I have a problem whereby I need to calculate the time to fill and then deflate a catheter balloon. This consists of a hand pump connected to a long tube which then widens out to the balloon vessel. I need to reach a certain pressure in the balloon. The balloon is already expanded and it is assumed no further expansion of the material will occur.

I know the volumetric flow rate (Q) from the hand pump. The length (L) of the tube is 1400mm. I have calculated the pressure drop across the tube (delP).

How to I determine how long it will take to fill both the tube and the balloon from vacuum to a given pressure and then how long to pull a vacuum on the system? Any help appreciated.

I previously used Pressure = mass*Gas Constant*Temperature/Volume. I did this at intervals until the pressure in the vessel equaled the pressure required, giving me the time required. However I found that this did not match my experiment. (The calculated times were much greater than the actual)

note to mod: feel free to move this thread

 

[eljose79]

if it is not in the correct locationHello,

Thank you for sharing your problem with us. I am a scientist and I would be happy to offer some suggestions on how to approach this problem.

Firstly, it is important to understand the underlying principles of fluid dynamics and gas laws to accurately calculate the time to fill and deflate the catheter balloon. The ideal gas law that you have mentioned, PV = nRT, is a good starting point but it may not be sufficient in this case as it assumes constant temperature and does not take into account the fluid flow dynamics.

To accurately calculate the time, you will need to consider the following factors:

1. Flow rate: As you have mentioned, you know the volumetric flow rate from the hand pump. This is an important factor as it determines the rate at which the fluid is moving through the tube and into the balloon.

2. Tube diameter and length: The diameter and length of the tube will also affect the flow rate and the time it takes to fill the balloon. A wider tube will allow for faster flow and a shorter tube will result in a shorter filling time.

3. Pressure drop: The pressure drop across the tube is another important factor to consider. This is affected by the fluid viscosity, tube diameter and length, and the flow rate. A higher pressure drop will result in a faster filling time.

4. Balloon material and volume: The material and volume of the balloon will also play a role in determining the filling time. A more elastic material will expand faster and a larger volume will require more time to fill.

With these factors in mind, you can use the Bernoulli's equation, which relates the pressure, density, and velocity of a fluid, to calculate the time to fill the balloon. This equation takes into account the fluid flow dynamics and can provide a more accurate estimation of the time required.

To determine the time to fill the balloon, you can use the following formula:

t = (V * delP)/(Q * A)

Where:
t = time (s)
V = volume of the balloon (m3)
delP = pressure drop (Pa)
Q = flow rate (m3/s)
A = cross-sectional area of the tube (m2)

Similarly, to determine the time to deflate the balloon, you can use the same formula but with the pressure drop being the difference between the initial pressure and the vacuum pressure.

I hope this helps you in your calculations. Remember, these equations