Elctrostatic field distribution for Air Cleanner Units.

Hello everybody,
I've research about Electrostatic precipitation for cleaning of air. actually there is a high electrostatic voltage on the electrode surrounded by neutralize surface of metal tube. for mounting electrodes at the center of tubes we need use one or two windows that they catch these electrodes .
question is one window is better or a pair of windows according to electric field distributions on electrodes?
my friend told me a pair of windows decrease electric field inside of tube! and we must use one window! is it true?
Is there any way for simulate this electric field distribution?
Sorry for my bad English!