Why does foaming increase pressure? 1

[matcheee]

Does anyone know why foaming in a closed vessel increases the pressure?

 

[jproj]

You are releasing gas from the liquid. Think of a 2-liter of pop. If you open it to release the initial pressure, then close it, you will be able to squeeze the sides in pretty far. Now, shake the bottle up.... the result is a foam & liquid filled bottle that is pressurized (try squeezing it again).

jproj

 

[matcheee]

Sorry, that's not what I'm trying to ask. I'm asking about a foam created by agitation not a degassing situation. We had a case of no dissolved gases in a reactor but a foam formed due to intense agitation and the pressure increased 5 psi. No temperature change.

 

[eyadamk]

what reactants do u use?? check side & non required reactions in the reactor, reactants may contain some impurities that cause gas formation. foam comes from gases in liquids.

 

[hacksaw]

agitation is one of the ways that you release gas from solution.

The change from a solvated gas to a free gas results in a considerable increase in volume and hence the pressure that you report. think about it

 

[25362]

To get a foam you need gas, either extraneous to the liquid or formed in situ by a chemical reaction or released from solution. The intensive stirring provides the hydrodynamic shearing forces needed to break-up large bubbles into smaller bubbles. Surface active chemicals (such as proteinaceous materials in beers) may prevent these smaller bubbles to fuse, or coalesce, stabilizing the foam.

 

[chemiengg]

Agitation leads to the entrapment of gas in liquid, hence formation of foam takes place. Pressure in closed vessel is on the account of pressure exerted by gas/vapor on the surface on liquid. Hence, pressure increases due to foaming.
Regds

 

[samienela]

Hello matcheee

The pressure is going up because the gas pressure inside the bubbles is larger than the gas pressure outside them. Picture a bubble with a continuous film of liquid around it. Consider a plane passing exactly through the middle of the bubble. The force pulling the two halves of the bubble together is the perimeter length of the bubble multiplied by the surface tension of the liquid, force per unit length. Times two I think because there is an inner and an outer surface. To keep the bubble from collapsing, that tension is opposed by the air pressure inside the bubble, so that the opposing force is delta-p times the area of the circle described by the plane passing through the bubble.
Then, 4*pi*r*(surfacetension) = pi*r^2* deltaP

and deltaP = 4(surfacetension)/r. The smaller the bubble the higher the interior pressure. So if you have agitation producing a fine grained foam, when that foam fills up the vessel the pressure will go up.

Have you tried adding an antifoam? For fermentations we use corn oil or a silicone oil antifoam. A single drop of the silicone stuff can take down several liters of foam in seconds. I have also heard of mechanical foam breakers for fermentations, that spin in the air space above the liquid and break up the bubbles, but I've never used one.