Dear Eli, With zero flow rate, you have only radiation. The increasing of the flow rate is increasing the air/gas convection and more air/ gas molecules (with heat capacity) flow and cool or heat the substrate. So you will get radiation and convection in the same time. Best Regards Reuven ROKAH Pls Think green before printing this mail... Thanks -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Eli Sarig Sent: Wednesday, August 27, 2008 10:24 PM To: [log in to unmask] Subject: [TN] Question about heat transfer My question is related to the heat transfer at the cooling zones. I want to reduce the substrate temperature from 200º C to 100ºC; can you explain the relationship between the flowing air temperature and the flow rate? What is more important: the temperature of the air or the flow rate? Thanks, Eli. --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------