Welcome to this month’s installment of “Ben bumbles an analogy.” This is the place where I attempt to take something that people go to graduate school to understand, chop it into pieces based on half-informed Internet searches and a few well-placed phone calls, and hopefully squeeze out some kernel of shareable knowledge. So hop in, let’s take this ride . . .
I’m feeling masochistic this month and going straight for the cliff dive. We’re talking vapor, permeance, permeability, wet cups, dry cups, rates, pressures, oh my! I’m not going to go into why water vapor is something to pay attention to—suffice to say, moisture causes problems—but we’re going to talk about how vapor does its thing. It’s a convoluted and nuanced subject that often leaves me—and, as I discovered while researching this post, many others—flummoxed.
Back to pasta
For a brief explanation of water vapor, I’ll revisit my boiling pasta analogy. Essentially, vapor is the gas form of what we use to cook pasta. The steam coming off the pot is vapor in a concentration so strong we can see it. Ultimately, it spreads out to the point that we can’t see it, but it’s still there—all around us, bouncing off and through everything. Unless we’re in the vacuum of aerospace, there’s water vapor in some quantity everywhere. We measure it with the common metric of humidity, which is a measurement of the relative vapor pressure in a given space. If we put a lid on our pot of pasta, the space under that lid is going to have a higher vapor pressure than the space outside of it—you with me?
Vapor is like a box of bouncy balls
Vapor always wants…