" sessions in the Web Application expire" .. When the session is inactive for time more than the specified timeout in the web.xml ,the session is considered as expired. but does that count for the sessions for which the browser window is closed?
"the browser window is closed" is a client-side concept. The server has no idea whether the browser has been closed, the user is looking out the window, eating lunch, gone to the rest room or has fallen asleep.
Sessions expire when there has been no activity for the set perios of time regarless of why that period of inactivity has occurred.