# Ergun Equation reulting to zero pressure ratio

1. Sep 16, 2013

### maistral

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.

Last edited: Sep 16, 2013
2. Sep 16, 2013

### Staff: Mentor

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

3. Sep 16, 2013

### maistral

I was toying around the flowrate, Vo. When I assign increasing values for Vo, I found out that the pressure is going down.

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4. Sep 16, 2013

### Staff: Mentor

What determines the pressure at the inlet and outlet of the bed?

5. Sep 17, 2013

### maistral

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).

Last edited: Sep 17, 2013
6. Sep 17, 2013

### Staff: Mentor

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?

7. Sep 17, 2013

### maistral

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

8. Sep 17, 2013

### Staff: Mentor

I don't know what you mean by the pressure ratio.

Chet

9. Sep 18, 2013

### maistral

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.

10. Sep 18, 2013

### maistral

Arr, nevermind. Fluidization velocity is what I was looking for, apparently. Thanks.