Fluid Dynamics of helium gas

In summary: Basically, you are correct in that using only the inlet and outlet would be incorrect. However, if we assume that the pressure between sections is constant, then we can use Bernoulli's equation between sections.
  • #1

ilc

3
0
Hello

here is a schematic of the problem: http://imgur.com/CgcybVT

A stream of helium gas will be used to carry aerosolized particles.

I am assuming conservation of mass (and mass flow)

The mission is to find the exit stream velocity of the gas
. For the time being, i am assuming the weight of particle is negligible and doesn't reduce helium velocity.

I am using Bernoulli's equation... would it be correct to only focus on the inlet and exit ?

I feel the changes in area matter because as area increases, velocity decreases to maintain constant mass flow.

Advice?

Thanks!
EDIT: I forgot to mention the system is under vacuum, and he outlet pressure of 0.065 psi is that of the vacuum chamber

here is a better diagram: http://imgur.com/64b7WLT
 
Last edited:
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  • #2
1) You can't use only the inlet and outlet since there are a lot of things in between there that are "lossy" in terms of pressure. In other words, not all of that pressure is going to be converted to velocity.

2) It appears that what you are reporting here is gauge pressure. If so, that strongly implies to me that this flow is likely compressible and you can't use Bernoulli's equation at all.
 
  • #3
boneh3ad said:
1) You can't use only the inlet and outlet since there are a lot of things in between there that are "lossy" in terms of pressure. In other words, not all of that pressure is going to be converted to velocity.

2) It appears that what you are reporting here is gauge pressure. If so, that strongly implies to me that this flow is likely compressible and you can't use Bernoulli's equation at all.
There's a compressible form of Bernoulli equation, right?
 
  • #4
Chestermiller said:
There's a compressible form of Bernoulli equation, right?

More of a "compressible generalization", but yes. Unfortunately, it is not very simple to use.
 
  • #5
boneh3ad said:
1) You can't use only the inlet and outlet since there are a lot of things in between there that are "lossy" in terms of pressure. In other words, not all of that pressure is going to be converted to velocity.

2) It appears that what you are reporting here is gauge pressure. If so, that strongly implies to me that this flow is likely compressible and you can't use Bernoulli's equation at all.
Hi:
boneh3ad said:
1) You can't use only the inlet and outlet since there are a lot of things in between there that are "lossy" in terms of pressure. In other words, not all of that pressure is going to be converted to velocity.

2) It appears that what you are reporting here is gauge pressure. If so, that strongly implies to me that this flow is likely compressible and you can't use Bernoulli's equation at all.

Hi there,

it appears I forgot to mention the system is under vacuum... and the outlet pressure of 0.065 psi is that of the vacuum chamber

here is a better diagram: http://imgur.com/64b7WLT

We can assume vacuum extends upto the inlet Helium stream. This means density of Helium will change once it leaves the gas tank and that its compressible. As such, it makes calculate the density (rho = P*MW/(RT)) at vacuum pressure, right ?

With regards to your comment in 1): since i am assuming constant mass flow, couldn't i use rho*V*A between sections and work my way up to calculate the outlet velocity?
 

1. What is the density of helium gas?

The density of helium gas varies depending on temperature and pressure, but at standard conditions (0°C and 1 atm), it is approximately 0.1785 g/L.

2. How does helium gas behave differently from other gases?

Helium gas is much lighter than other gases, which means it has a lower density and viscosity. It also has a higher thermal conductivity and diffusivity, making it easier to diffuse and transfer heat.

3. What is the effect of temperature on the fluid dynamics of helium gas?

As with most gases, the viscosity and density of helium gas decrease with increasing temperature. This leads to lower friction and easier flow, making it a good choice for applications that require low resistance.

4. How does helium gas behave when compressed?

Unlike most gases, helium gas does not condense when compressed at standard temperatures and pressures. Instead, it remains in a gaseous state and becomes more dense, increasing its viscosity and thermal conductivity.

5. What are some practical applications of the fluid dynamics of helium gas?

Helium gas has many industrial and scientific applications, such as in cryogenics, gas chromatography, and as a coolant in nuclear reactors. It is also commonly used in balloons and airships due to its low density and high buoyancy.

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