In this research, the parameters affecting the Nusselt number of a generator rotor and stator under varying heat transfer rate are experimentally studied. In spite of the stator having no grooves, the rotor has four large triangular grooves. The temperature and then heat transfer rate of the rotor and stator are experimentally measured in three longitudinal and two angular positions. First, the effect of axial Reynolds number and rotor rotational speed on the rotor and stator Nusselt number with constant heat transfer rate ratio is studied. The range of the axial Reynolds number and rotational speed used is from 4000 to 30,000 and from 300 to 1500 rpm, respectively. Next, the effect of stator to rotor heat transfer rate ratio on the Nusselt number at constant axial Reynolds number and rotational speed is investigated. Three experiments were conducted at three heat transfer rate ratios ( 3, 5, and 8), defined as the ratio of heat transfer rate of the stator to the rotor. The results show that the higher the heat transfer rate ratio, the lower is the stator mean Nusselt number and the higher the rotor mean Nusselt number.