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Ken Schifftner July 6, 2000 23:13

swirling two phase flow
 
We are seeking an expert CFD witness in the PA area regarding the differences between plug flow and swirling flow in which a gas passes vertically upward in a cylindrical vessel through a liquid dispersed wall to wall creating an ebulating or "fluidized" turbulent two phase zone. In one case the gas enters the zone axially (upward) only, and in the other the gas enters the zone with axial, and radial components forming a slowly rotating central vortex.

The adversary claims that even in swirling gas flow, the axial components of the gas flow still comprise a parabolic or near parabolic velocity pressure profile. We dispute this. Thank you

Adrin Gharakhani July 7, 2000 13:28

Re: swirling two phase flow
 
> The adversary claims that even in swirling gas flow, the axial components of the gas flow still comprise a parabolic or near parabolic velocity pressure profile.

What is a velocity pressure profile?

Adrin Gharakhani

Ken Schifftner July 7, 2000 16:59

Re: swirling two phase flow
 
In conventional test methods for gas flowing in a conduit, the velocity pressure profile is the graphed depiction of the velocity presures measured at the individual test locations across the conduit. The "X" axis is typically the conduit diameter or cross-section and the "Y" axis is typically the velocity pressure recorded in suitable units of pressure.

In plug or laminar flow, the velocity pressures are all axial and typically range from a maximum in the center of the vessel to a minimum at the wall if the vessel is of uniform cross-section. In swirling flow, the velocity pressures are yawed and are the vector resultant of the x, y, and z components of flow as measured each test point.

The velocity pressure profile is indicative of the kinetic energy the gas posseses.

Adrin Gharakhani July 7, 2000 19:00

Re: swirling two phase flow
 
I have never heard of the term "velocity pressure"!

> In plug or laminar flow, the velocity pressures are all axial and typically range from a maximum in the center of the vessel to a minimum at the wall if the vessel is of uniform cross-section.

Now, I'm completely confused (I'm trying to figure out the physics to understand what you are implying by velocity pressure). If a variable is all axial in its variation, then I can only understand that there is no variation in the radial direction. Therefore, you can't expect a max. or min. anywhere in the radial direction for a purely axial variation of the variable. Also, if you have a laminar pipe flow (assuming it is fully developed) then the pressure _will be_ constant in the radial direction and will have a constant gradient in the axial direction; i.e., the pressure will vary linearly along the pipe. The corresponding velocity will have a max. at the center. (But velocity and pressure are two different things, of course). Lastly, you can't have a plug flow due to boundary layer development. (My understanding of plug flow is one with uniform velocity profile across the radius).

Adrin Gharakhani

John C. Chien July 7, 2000 21:01

Re: swirling two phase flow
 
(1). I must say that the near field of tangential inlet flow will be different from that of the pure axial inlet flow. (2). But the size and extend of the region will depend on the tangential velocity, the mass flow rate (which determine the axial velocity), the viscosity, the size of the pipe. (3). So, without knowing all these factors, all I can say is, the near field will be different, and eventually it will depend on the mass flow rate only, further downstream from the inlet. (4). Don't ask me to do the simulation for you. But you can set up the test with a long pipe and check the flow field. (5). I think, the initial vortex will eventually break down, and the flow will resume the normal axial flow behavior.

Ken Schifftner July 10, 2000 13:43

Re: swirling two phase flow
 
Our studies (and common sense) show that swirling flow will yield an axial velocity pressure profile quite removed from a "plug" or laminar profile.

These devices are patent number 4,432,914 and 6,007,055 if that is of interest. The older one uses a vertical gas flow direction through a curved grid. The later design induces the liquid regime to swirl both by using vanes and by utlizing the Coriolis effect that imparts a slight swirl to the decending liquid.

Note, the "fluidized" zones are truncated. The gas and liquid disengages above the zone. If the vessel above the zone were sufficiently tall (which does not occur in practice), the gas motion would indeed eventually create a purely axial flow pattern.

John C. Chien July 10, 2000 14:19

Re: swirling two phase flow
 
(1). My comment was based on a very simple model. So, it is far from the real device. (2). If the device has finite length and size, the near field of the inlet will dominate the flow processes. This can only be validated based on the real device testing. (3). I am very very busy right now,(working on 3-D analysis) and I will not be able to check out your patent drawings. But if you can describe the device easier to understand, other readers might be able to give you some comments.


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