[Thommo (OP)]

I do like a couple of real ales, but subsequently suffer from their flatulent effect on me.  On the up side, it does make me marvel at the ability of my bowels to separate the gas from solids, and transport it against gravity (which would be expected to pull the heavier solids down first) to my anus to be released.

How do bowels do this?
Can the process be mimicked with a manmade system? Would he ability to separate gas from solid and transport it separately within a single closed tube have a scientific or engineering application?

[chiralSPO]

As I understand it, the issue is gas moving from high pressure to low pressure, and the fact that it is going down and out is not really going "against gravity." Just as air escapes from the open end of an inflated balloon no matter what direction it is pointed in.

I am not really sure of the mechanism of the separation, but as long as the intestine isn't completely blocked off (air-tight), the gases probably have higher mobility than the solids. Then it is a simple matter of the intestines being able to effectively close off at the top, and open enough at the bottom periodically to allow pressure to release.

[evan_au]

Transportation of solids through the intestines & bowel is caused by rhythmic muscle contractions.
Gas transport requires no such muscle effort.

[Thommo (OP)]

the issue is gas moving from high pressure to low pressure,

Surely, within the bowels, the gas pressure will be equal when the anal sphincter is closed; the pressure differential is caused when the sphincter is open (like in the balloon analogy).  That being the case, there is nothing to cause the gas to collect at the sphincter.   There could be an argument that the solids prevent easy gas flow, and so maintain the pressure differential, but then there is again no reason for the gas to collect at the sphincter, and not merely push the solids towards the sphincter.

[Thommo (OP)]

I tried an experiment with a balloon, and the air doesn't flow out without forcing the solids out: https://   
m.youtube.com/watch?v=0cYjR3RimRY
Well, sometimes a little route opens out, allowing air out, but clearly this isn't how the bowels work, otherwise farting would be a very messy business!