I was very glad to find an internet job service as CFD-online, which supplies the jobs database for postdoc. Unfortunately, my research field is mainly on numerical heat transfer. Does anybody know if there is a special internet career service on heat transfer? Your assistance is highly appreciated in advance.

I haven't seen anything like that. There are very few job services that are as specialized as the CFD Jobs Database. I've been thinking about starting similar "databases" for fields related to CFD, like Heat Transfer, Turbomachinery, Aerospace, .... It would essentially just be to "copy" all my scripts and query/replace "CFD" with "Heat Transfer" or whatever. Would also have to find an editor who volunters to moderate it and "touch up" the posts. Anyone interested?