Geometric complexities and multi-physical phenomena add difficulties for predicting the thermal field and hence thermal management of an electric motor. A numerical design model that combined electromagnetic and thermal-fluid analysis was proposed for disclosing the detailed temperature distributions of each component in an electric motor. The thermal fluid analysis implemented ANSYS-Fluent code to unravel the thermal field of the interior permanent magnet synchronous electric motor fitted with a smooth or novel spirally twisted channel in the cooling water jacket of a stator with and without shaft cooling. In accordance with the thermal powers converted from the various electromagnetic losses of the electric motor, the complex heat conduction model with realistic thermal boundary conditions was formulated. Initially, the turbulent flow structures and channel averaged Nusselt numbers of the spiral channels without and with the sectional twist were comparatively examined for acquiring the convective thermal boundary conditions in the water jacket. With the high thermal conductivity of the aluminum water jacket, the heat-transfer improvements from the smooth-spiral-channel conditions by using the twisted spiral channel were effective for reducing the average temperatures by about 10% but less effective for altering the characteristic thermal field in the water jacket. At 1290 < Dn < 6455 or 5000 < Re < 25,000 for the spiral channel flows, the channel average Nusselt numbers ratios between the smooth and twisted spiral channels were elevated to 1.18–1.09 but decreased with the increase of Dn or Re. A set of heat-transfer correlations for estimating the Nusselt numbers of Taylor flow in the rotor-to-stator air gap was newly devised from the data available in the literature. While the cooling effectiveness of the water jacket and shaft was boosted by the sectional twists along the spiral channel of the water jacket, the presence of Taylor flow in the annual air gap prohibited the effective rotor-to-stator heat transmission, leading to hot spots in the rotor. By way of airflow cooling through the rotating hollow shaft, the high temperatures in the rotor were considerably moderated. As the development of Taylor flow between the rotor and stator was inevitable, the development of active or passive rotor cooling schemes was necessary for extending the power density of an electric motor. Unlike the previous thermal circuit or lumped-parameter thermal model that predicted the overall temperatures of motor components, the present coupled electromagnetic and thermal-fluid model can reveal the detailed temperature distributions in an electric motor to probe the local hot spots of each component in order to avoid overheating at the early design stage.

Increases in power density and thermal efficiency of a highly efficient gas turbine engine motivate an ever-mounting turbine entry temperature. The combined metallurgical and cooling advancements ensure the structural integrity of a gas turbine rotor blade that spins at high rotor speeds in a gas stream with temperatures above the melting point of the blade material. The cooling performances promoted by a variety of heat transfer enhancement methods typical of the coolant channels of the leading edge, the mid-chord region, and the trailing edge of a gas turbine rotor blade are reviewed. The manifested rotational effects on the aerothermal performances of impinging jets and swirl chambers for leading-edge cooling, multi-pass ribbed, dimpled, and/or wavy channels over the mid-chord region, as well as pin fin and latticework narrow ducts in the trailing edge of a gas turbine rotor blade, are summarized and cross-examined. Research orientations for future cooling studies aimed at preventing the development of hot spots in a gas turbine rotor blade are recommended.

As an attempt to enable a further increase in the power-to-weight ratio of an electric motor by improving its cooling performance, rotating thermosyphon loops in a rotor of a permanent magnet synchronous electric motor are proposed. The effective thermal conductivity and airflow heat-transfer rate of the rotating thermosyphon loop and the convective heat-transfer coefficient over the annular interior surface of the air chamber are measured to permit the definition of the thermal boundary conditions for simulating the temperature fields of the electric motors. The axial heat-transfer pathway with extremely high effective thermal conductivity attributing to the phase-change activities in the rotating thermosyphon loop acts synergistically with the heat convection enhancement induced by the stirring effect of the spinning condenser bend in the air chamber to improve the heat transmission out of the rotor core. The spatially average temperature gradients in the rotor with the thermosyphon loops are considerably moderated from those without the thermosyphon loop. At rotor speeds and electrical currents in the ranges of 1200–1500 rev/min and 1000–1200 A, the maximum temperatures in the rotors with the single- and twin-end rotating thermosyphon loops are, respectively, reduced 8–14 °C and 10–22 °C from those without a rotor-cooling scheme, affirming the effectiveness of a phase-change cooling device in a rotor for thermal performance improvement of an electric motor.

The innovative rotating looped thermosyphons (RLTs) with and without a coil insert were proposed with cooling applications in rotating machinery. The spatial gradients of body forces among the vapor–liquid mixture of the distilled water in a strong centrifugal acceleration field motivated the flow circulation in a RLT to facilitate the latent heat transmissions. The effective thermal conductivity (K_eff), the thermal resistance (R_th), the Nusselt numbers in the condenser (Nu_con) and evaporator (Nu_eva), and the Nusselt number of the airflow induced by the rotating bend of the condenser (Nu_ext,con) of each RLT were measured at various rotating speeds and heat powers with two filling ratios of 0.5 and 0.8. The increase of filling ratio from 0.5 to 0.8 to maintain a thin liquid film along the rotating inner leg of each RLT substantially improved the heat transfer performances. The K_eff, Nu_con, Nu_eva, and Nu_ext,con were increased with rotating speed, leading to the corresponding reduction of R_th. On the basis of the experimental data, the empirical correlations that were used to calculate R_th, K_eff, Nu_con, Nu_eva, and Nu_ext,con of the RLTs at the two filling ratios with and without coil were proposed to assist the relevant design applications.