Experimental data for thermal resistance measured on an ETD44 transformer. The temperature rose from 19.7°C to 54.0°C (so change of 34.3°C), with the loss of 3.38W, which gives the thermal resistance of 10.2°C/W. Various sources (e.g. Epcos) give the value for ETD44 between 11 and 12 K/W (see also: thermal resistance of ferrite transformers), so this measurement comes close with the table value.
Data measured by Stan Zurek.
thermal_resistance_etd44_magnetica.png
You are permitted and indeed encouraged to use this image freely, for any legal purpose including commercial, and with any modifications (the permission is hereby given, so there is no need to ask for it explicitly again), but you MUST always give the following credits:
S. Zurek, Encyclopedia Magnetica, CC-BY-4.0
We would appreciate if you let us know of any use: info@e-magnetica.pl