Lokust:
There are a number of companies who distribute and sell absorbent product like silica gel. Many of them have information to calculate the absorption rates and total amount of gel necessary to determine how much gel is required to keep a volume at the proper humidity. Here is one such link.
http://www.sorbentsystems.com/desic...harts.html You can find more by search the phrase - silica gel absorption rate
Niel Leon
engineering.com