Delete file on session end

I am recreating a web application that serves up search results in a CSV file.  I'm able to create the csv fil from a database query, then offer a download link to grab it from.

Question 1: In order to make the CSV files unique, I am appending them with the session id.  Is this a bad idea?  Should I use an encrypted session id instead?

Question 2: In order to prevent the server from filling up with csv files, I want to delete the file once it's been downloaded.  I'd like to do this on session end, but the session variable I used to name the file will be gone when the session ends, so this might not be the best idea.  Any suggestions?

Thanks!