Flux and Flow rate conversion

In summary, Alex is performing a helium leak experiment to calculate the permeability coefficient (K) of a specimen. He is having trouble converting the leak rate (mbar.L/s) to a flux (mol/m^2.s) for his equation. To solve this, the ideal gas law can be used to calculate the number of moles of helium, which can then be used to calculate the flux. This value can then be used in the equation -K = J . delta x / delta P (rearranged Fick's 1st law) to determine the permeability coefficient.
  • #1
AlexN07
1
0
Hi,

I am performing a helium leak experiment in which the detector outputs a number in mbar.L/s which is the amount of helium permeating through a specimen at a given pressure per unit of time.

I am interested in obtaining a permeability coefficient (K) for this specimen for the given pressure with helium as the working fluid.

My equation is: -K = J . delta x / delta P (rearrange Fick's 1st Law)

I know delta x (thickness) and delta P (pressure), however I am having trouble converting the mbar.L/s (leak rate) to a flux J (which I believe is in (mol /m^2 . s) for the equation.

Can somebody please help.

Alex
 
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  • #2
,

I am happy to assist you with your experiment and the calculation of the permeability coefficient (K).

Firstly, let's define the terms in your equation. The flux J represents the amount of substance that passes through a unit area per unit time, and it is usually expressed in units of mol/m^2.s. The delta x is the thickness of the specimen, and the delta P is the pressure difference across the specimen.

To convert the leak rate from mbar.L/s to mol/m^2.s, we need to use the ideal gas law. The ideal gas law states that PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature. Rearranging this equation to solve for n, we get n = PV/RT.

In your experiment, the volume (V) is constant, so we can rewrite the equation as n = P/RT. Since you are using helium as the working fluid, we can assume that the gas constant (R) is 8.314 J/mol.K. The temperature (T) should also be constant throughout your experiment.

Now, we can calculate the number of moles of helium using the leak rate (mbar.L/s) and the pressure (mbar) at a given time. Let's say the pressure is 100 mbar and the leak rate is 10 mbar.L/s. We can convert the pressure to Pa (1 mbar = 100 Pa) and the volume to m^3 (1 L = 0.001 m^3), and then use these values to calculate the number of moles of helium.

n = (100 Pa)(0.001 m^3) / (8.314 J/mol.K)(constant temperature)

Once we have the number of moles, we can use this value to calculate the flux J using the equation J = n/A, where A is the area of your specimen.

Now, you can plug in the values for J, delta x, and delta P into your equation -K = J . delta x / delta P (rearranged Fick's 1st law) to calculate the permeability coefficient (K) for your specimen at the given pressure.

I hope this helps you in your experiment. If you have any further questions or need clarification, please feel free to reach out. Good luck
 

What is flux and flow rate?

Flux is the rate of flow of a physical quantity through a surface. It is usually measured in units of volume per time, such as liters per minute or cubic feet per second. Flow rate, on the other hand, is the volume of fluid that passes through a given surface per unit time. It is typically measured in units of volume per time, such as gallons per minute or cubic meters per hour.

How do you convert flux to flow rate?

To convert flux to flow rate, you need to know the area of the surface through which the fluid is flowing. You can then multiply the flux by the surface area to get the flow rate. For example, if the flux is 5 liters per minute and the surface area is 2 square meters, the flow rate would be 10 liters per minute.

How do you convert flow rate to flux?

To convert flow rate to flux, you need to know the surface area through which the fluid is flowing. You can then divide the flow rate by the surface area to get the flux. For example, if the flow rate is 10 cubic feet per second and the surface area is 5 square feet, the flux would be 2 cubic feet per second per square foot.

What are some common units used for flux and flow rate?

Some common units used for flux include liters per minute, cubic meters per hour, and gallons per minute. For flow rate, common units include cubic feet per second, cubic meters per hour, and gallons per minute. It is important to ensure that the units for flux and flow rate are consistent when performing conversions.

Why is it important to convert between flux and flow rate?

Converting between flux and flow rate is important in many scientific fields, such as fluid dynamics, environmental science, and engineering. It allows us to understand and compare the rate at which fluids are moving through different surfaces, and to accurately measure and predict the behavior of fluids in various systems. It also helps in designing and optimizing systems that involve fluid flow, such as pipelines and pumps.

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