Chimney Effect on Natural Convection Cooling of a Transistor Mounted on a Cooling Fin

The thermal impedance $Zth(jω)$ has been measured for the junction of a transistor mounted on a cooling fin. The setup was put inside a chimney in order to enhance the natural convection cooling. From the thermal impedance $Zth(jω)$ the influence of the chimney on the reduction in thermal resistance $Rth=Zth(jω=0)$ is clearly visible. A maximum improvement of almost 20% has been observed experimentally. Measuring the thermal impedance as a function of the angular frequency $ω$ provides specific information about the thermal path being influenced by the chimney.