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-   -   Purging air from system (http://www.physicsforums.com/showthread.php?t=331427)

ChaoticLlama Aug18-09 09:13 PM

Purging air from system
 
Here is the situation:

We are building a small model car (roughly 8 in wide by 18 in long) whereby hydrogen is produced in a chemical reaction, travels through some tubing to our fuel cells, which in turn powers the motor.

The issue lies in the start-up procedure; it is required to purge air from the tubing system so as to not dilute the hydrogen within the system.

Here is how we are purging the system currently:

We begin the reaction, producing hydrogen gas which removes any air present in the tubing, venting to the environment. After the short purge period, the outlets are closed off, and the car proceeds.

The problem is, we require no hydrogen emissions to the environment during the purge.

Is there any way to accomplish this?

Thank you.

P.S., please let me know if this description is unclear, I can provide diagrams and/or pictures as required.

Q_Goest Aug18-09 09:28 PM

Re: Purging air from system
 
Hi Chaotic. Normally such systems are purged with nitrogen or helium prior to initiating hydrogen flow. That way there's no oxygen. It also eliminates the possibility of hydrogen being vented to atmosphere, but here's the catch. Now there's nitrogen or helium in your system. Is that ok?

ChaoticLlama Aug18-09 10:28 PM

Re: Purging air from system
 
Yes, that is a catch indeed.

The tube system will be a closed loop, and therefore the nitrogen or helium would act as diluents; reducing the performance of the cell.

FYI: The pressure build-up is very small, so that is not a concern. There is a gauge which reads from 0 to 5 psig, and the needle as never been observed to move.


Thanks for taking time to read this.

Danger Aug19-09 01:04 AM

Re: Purging air from system
 
Could you perhaps insert some sort of 'hydrogen trap' in your purge port? (Chilled magnesium, maybe?) Or, even simpler, purge the line into a storage container such as a balloon that won't let it vent to atmosphere?

berkeman Aug19-09 01:23 AM

Re: Purging air from system
 
How about just pumping down the tubing first?

Q_Goest Aug19-09 07:01 AM

Re: Purging air from system
 
Yes, as mentioned by berkman, systems can also be vacuum pumped to eliminate air. Generally, this is followed up by breaking vacuum with an inert gas (nitrogen and helium) and then pumping again.


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