Finding mass, knowing velocity but not momentum.

[caitlin t]

Hi there,

I am trying to find m=p/v. I found the velocity through knowing the gas flow-rate and cross sectional area of the cylinder. However, I am stuck with finding the mass without knowing how to calculate the momentum. Can anyone suggest some more equations to lead to the answer? Help on this matter would be much appreciated!

Caitlin t

 

[bp_psy]

Since you give almost no info of what the problem actually is then You shouldn't expect a clear answer.Anyway if you have the density of the gas you could determine the mass of some volume element of the gas using the cross sectional area.

 

[caitlin t]

I am trying to calculate the Force that the gas flow rate is inflicting on the top surface of a packed bed in a cylindrical vessel. Since F=ma, I am trying to determine the mass. I know the cross sectional area from the diameter but I don't know the height of the top section of the vessel (height from the top of vessel to packed bed) to find the volume. I have assumed a reasonable height but this has given me a very high mass result which looks incorrect. Is there another way I can find the mass using the known velocity or mass flow rate? Thank you for replying.

 

[K^2]

Shouldn't the force be on the packing rather than the wall? I'm still not quite sure what the setup is like. If you have a flow in and flow out, with the difference in flow velocity, you can use Bernoulli equation to obtain pressure differential and use that to compute the force.

 

[PJC01]

Hello Caitlin,

Thank you for reaching out for help with your calculations. To find the mass, you will need to use the equation m = p/v, as you have correctly identified. However, to calculate the momentum (p), you will need to use the equation p = mv, where m is the mass and v is the velocity. Since you already have the velocity, you can use this equation to find the momentum, and then plug that value into the equation for mass. Additionally, you can also use the equation p = FΔt, where F is the force and Δt is the change in time. If you have any further questions or need more assistance, please don't hesitate to ask. Good luck with your calculations!

Best,