Hello Everyone,
The thread on dehumidifiers vs air conditioners got me thinking. I have a 24 gun safe in my home. Inside the age I have placed a dehumidifier to take care of ant moisture that might find its way in. This particular dehumidifier is passive, that is its not an electrically powered device. Inside the plastic case there are little beads that change color when wet. When the beads turn green I remove the device from the safe and plug it into an outlet. It warms up, dies the beads and is ready to use again.
My question is, how does the device collect water? With no fan in it, the air is not circulated through it. How does the water find it’s way into the beads? I put the device on a shelf at the top of the safe, how does it capture moisture present at the bottom?
The beads are hygroscopic meaning they attract and absorb water from the air. Suger is another example of a hygroscopic solid.
So far as absorbing moisture in your gunsafe, there’s probably some circulation as its not likely to be airtight. I know mine isn’t. Mine has seals that swell when heated. They are intended to create a seal if there’s a fire. I have a Goldenrod electric dehumidifier in mine.
Diffusion. The process starts when the beads absorb water vapor in their immediate vicinity. Now you have dry air in that part of the safe, and damp air everywhere else. The water molecules like their personal space and so the ones that are crowded in the damp parts of the safe will spread out to moisten the dry region near your dehumidifier, resulting in reduced humidity in regions far from the dehumidifier. Now the dehumidifier beads have more water near them that can be absorbed. This process continues until the dehumidifier has absorbed all of the water it can handle (or all of the water in the safe).
This process happens even in the absence of bulk convection; that is, you don’t need a fan in the safe to circulate the air, as the individual water molecules will move around on their own and will, over time, find the dehumidifier.