That's correct. I would like to raise the transistor temperature by 25C using as little a power as possible, hence 25mW dissipation.
I am monitoring VBE to assess the cooling effect of the airstream. A surface mount device has very small thermal mass so the response should be quite fast.
That being your application, I think I would have you look at part number BC857CT-7-F. http://www.diodes.com/datasheets/ds30275.pdf
It has a high thermal resistance, while haveing one of our lowest power dissipation ratings. So I would think it will produce the most amount of heat for the smallest amount of power.
Thanks a lot, Levy, that looks exactly what we were looking for. One more question, is the thermal barrier on the underside, in which case we should invert it to get best exposure to the airflow?