DEVELOPMENT OF PIN-LEVEL NEUTRONICS/THERMAL-FLUID ANALYSIS COUPLED CODE SYSTEM FOR A BLOCK-TYPE HTGR CORE

Recently, the coupling between computer codes that simulate different physical phenomena has attracted for more accurate analysis. In the case of high-temperature gas-cooled reactor (HTGR), the coupling between neutronics and thermal-fluid analysis is necessary because of large change of temperature in the reactor core. Korea Atomic Energy Research Institute (KAERI) has developed the coupled code system between a reactor physics analysis code CAPP and a thermal-fluid system safety analysis code GAMMA+ for a block-type HTGR. The CAPP/GAMMA+ coupled code system provides more accurate block-wise distribution data than CAPP or GAMMA+ stand-alone analysis. However, the block-wise distribution data has the limitation in order to predict safety parameters such as the maximum temperature of the nuclear fuel. It is necessary to calculate refined distribution, for example, pin-level (fuel compact level) distribution. In this study, we tried to solve this problem by coupling CAPP and a high-fidelity thermal-fluid analysis code CORONA. CORONA can perform a high-fidelity thermal-fluid analysis of Computational Fluid Dynamics (CFD) level by dividing a block-type HTGR core into small lattices. On the other hand, CAPP can provide a pin power distribution. It is expected that the refined, more accurate distribution data for a block-type HTGR can be obtained by coupling these two codes. This paper presents the development of coupled code system between CAPP and CORONA, and then it is tested on a simple HTGR column problem with encouraging results.

Architecture choices for high-temperature synchronous machines

The article proposes an analysis of the possible architectures of synchronous machines with an ability to operate at high temperatures of over 200°C in their environment. Two machine principles have been considered: the permanent magnet synchronous machine and the synchronous reluctance machine. The numerical analyses are carried out with 3D-coupled electromagnetic-fluid-thermal models; the electromagnetic one provides the local losses that give the input data to the coupled thermal-fluid analysis model for computing the temperatures inside the machines. The simulation results are used for estimating the temperature limit of each machine architecture, considering the characteristics of their critical parts.

Evaluation of localized heat transfer coefficient for induction heating apparatus by thermal fluid analysis based on the HSMAC method

With the development of electrical machines for achieving higher performance and smaller size, heat generation in electrical machines has also increased. Consequently, the temperature rise in electrical machines causes unexpected heating of components and makes it difficult to operate properly. Therefore, in the development of electrical machines, the accurate evaluation of temperature increase is important. In the thermal design of electrical machines, heat-conduction analysis using the heat-transfer boundary set on the surface of a heated target has been frequently performed. However, because the heat-transfer coefficient is dependent on various factors, it is often determined based on experimental or numerical simulation results. Therefore, setting the heat-transfer coefficient to a constant value for the surface of the heated target degrades the analysis accuracy because the actual phenomenon cannot be modeled. To enhance the accuracy of the heat-transfer coefficient, the coupled electromagnetic field with heat-conduction analysis finite element method (FEM), thermal-fluid analysis using FEM, and the highly simplified marker and cell method is applied to the estimation of the distribution of the heat-transfer coefficient. Moreover, to accurately calculate the localized heat-transfer coefficient, the temperature distribution and flow velocity distribution around the heated target are analyzed in the induction-heating apparatus.

Heat Transfer and Thermal Management of Interior Permanent Magnet Synchronous Electric Motor

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.