CI3: Will sess_expiration value end a session that is active?

Can I use sess_expiration as an "inactive timeout" function?

If sess_expiration=100, and the end user refreshes the page once a second, will the session expire 100 seconds after it started? Or will it never end?

Also, if I set sess_expiration to a year, would that session last even as the user's browsers is closed & opened? I do not think so. I assume that it always expires on close, but I've read some confusing posts.

Thanks!