Hi, I've searched the definition of conjugate heat transfer and cannot get it. What condition can we call it a conjugate heat transfer problem? Thanks.

A good starting point is when there is heat exchange between solid material(s) and fluid material(s).

Why is that not simply called heat transfer?

Because "heat transfer" alone doesn't imply multiple materials. Conduction of heat from the hot end of an iron bar to the cold end, for example, is heat transfer but not conjugate heat transfer.

Conjugate refers to the fact that both conduction and convection contribute to the transfer of heat.

The term conjugate heat-transfer simulation is most often used to indicate that the simulation includes both the solid material and the fluid in and/or around the solid object.

For example, if you do a conjugated heat-transfer analysis of a turbine blade you would do a large simulation which included a CFD simulation of the hot gas-channel flow passing by the blade coupled to a simultaneous heat-transfer simulation of the temperature in the metal of the blade (possibly also coupled to a second CFD simulation of any cooling flows inside the blade).

Thanks all of you for your responses. So conjugate heat transfer is for the phenominum of Solid+Air Convection.

Thanks for that.