You must know that lower temperatures can decrease the drying process, but this method will not work for you. Since refrigerators have low temperatures it can increase the hardening of the paint on the outer surface, reasoning your paint brushes.  Not only this but you must be aware of the fact that these paints carry some elements that have a stinking smell. So, if you place these paint brushes inside a refrigerator it will destroy the inner environment. Also, the smell can affect the other food items in the refrigerator.