Ergun Equation reulting to zero pressure ratio


by maistral
Tags: equation, ergun, pressure, ratio, reulting
maistral
maistral is offline
#1
Sep16-13, 12:09 AM
P: 72
I was trying to emulate a packed bed reactor, and apparently the pressure midway at the packed column became zero, until my numerical method failed altogether (as the pressure variable in the Ergun is at the denominator).

I'd like to be enlightened about one thing - does this phenomena (zero pressure midway the packed column) has something to tell me at what will happen at the end? No gas flow or something, perhaps? Thanks.

EDIT: Sorry for the title spelling error, it's 'resulting', not reulting.
Phys.Org News Partner Engineering news on Phys.org
Lifting the brakes on fuel efficiency
PsiKick's batteryless sensors poised for coming 'Internet of things'
Researcher launches successful tech start-up to help the blind
Chestermiller
Chestermiller is offline
#2
Sep16-13, 11:44 AM
Sci Advisor
HW Helper
Thanks
PF Gold
P: 4,435
Quote Quote by maistral View Post
I was trying to emulate a packed bed reactor, and apparently the pressure midway at the packed column became zero, until my numerical method failed altogether (as the pressure variable in the Ergun is at the denominator).

I'd like to be enlightened about one thing - does this phenomena (zero pressure midway the packed column) has something to tell me at what will happen at the end? No gas flow or something, perhaps? Thanks.

EDIT: Sorry for the title spelling error, it's 'resulting', not reulting.
The pressure should not go to zero if you are using the ergun equation. Please write your form of the ergun equation so we can see what you are dealing with.

Chet
maistral
maistral is offline
#3
Sep16-13, 04:11 PM
P: 72
I was toying around the flowrate, Vo. When I assign increasing values for Vo, I found out that the pressure is going down.
Attached Thumbnails
ergun.png  

Chestermiller
Chestermiller is offline
#4
Sep16-13, 06:06 PM
Sci Advisor
HW Helper
Thanks
PF Gold
P: 4,435

Ergun Equation reulting to zero pressure ratio


Quote Quote by maistral View Post
I was toying around the flowrate, Vo. When I assign increasing values for Vo, I found out that the pressure is going down.
What determines the pressure at the inlet and outlet of the bed?
maistral
maistral is offline
#5
Sep17-13, 03:22 AM
P: 72
I'm really sorry, I didn't understand the question :|

Actually what's happening is that, the inlet pressure is at 7.5MPa, and I am using the Ergun equation to find out the outlet pressure. What's happening is that if I toy around the Vo by increasing it (volumetric rate), the pressure decreases rapidly until it approaches a certain high Vo value and the pressure approaches 0.

I was wondering if this is equivalent to a physical phenomenon when the exit pressure becomes zero (ie. the gas won't flow anymore, the packings get destroyed, or something).
Chestermiller
Chestermiller is offline
#6
Sep17-13, 06:50 AM
Sci Advisor
HW Helper
Thanks
PF Gold
P: 4,435
Quote Quote by maistral View Post
I'm really sorry, I didn't understand the question :|

Actually what's happening is that, the inlet pressure is at 7.5MPa, and I am using the Ergun equation to find out the outlet pressure. What's happening is that if I toy around the Vo by increasing it (volumetric rate), the pressure decreases rapidly until it approaches a certain high Vo value and the pressure approaches 0.

I was wondering if this is equivalent to a physical phenomenon when the exit pressure becomes zero (ie. the gas won't flow anymore, the packings get destroyed, or something).
What you are saying is that, as you increase the throughput rate through a packed bed, the pressure drop through the bed increases. Why does this surprise you?
maistral
maistral is offline
#7
Sep17-13, 08:25 AM
P: 72
Uh, I do know that the pressure should go down, but what I mean is that the pressure ratio at the end given a certain high flowrate is zero; does this signify something as a physical phenomenon? No effluent or something?

This is my first time to see a zero pressure ratio in my calculations, I'm sorry. XD
Chestermiller
Chestermiller is offline
#8
Sep17-13, 11:01 AM
Sci Advisor
HW Helper
Thanks
PF Gold
P: 4,435
Quote Quote by maistral View Post
Uh, I do know that the pressure should go down, but what I mean is that the pressure ratio at the end given a certain high flowrate is zero; does this signify something as a physical phenomenon? No effluent or something?

This is my first time to see a zero pressure ratio in my calculations, I'm sorry. XD
I don't know what you mean by the pressure ratio.

Chet
maistral
maistral is offline
#9
Sep18-13, 12:59 AM
P: 72
I mean P/Po is going towards zero. The P there at the denominator is continually decreasing, causing the entire thing to approach zero apparently.

I was wondering what does this have to do as a physical phenomenon, when the exit pressure is zero.
maistral
maistral is offline
#10
Sep18-13, 06:21 AM
P: 72
Arr, nevermind. Fluidization velocity is what I was looking for, apparently. Thanks.


Register to reply

Related Discussions
Derivation of the equilibrium saturation ratio equation? Calculus & Beyond Homework 1
Pressure Ratio Problem Introductory Physics Homework 0
Pressure ratio problem Biology, Chemistry & Other Homework 4
pressure change and area ratio help Engineering Systems & Design 4
Engine experts, how does rod ratio effect how much pressure is applied to cyl. walls? Mechanical Engineering 20