Steady and transient conjugate heat transfer modelling of IGBTS subjected to liquid cooling by a membrane heat sink for rolling

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

A 3-D modeling technology based on Conjugate Heat Transfer (CHT) is developed to demonstrate numerically the thermal and hydrodynamic capabilities of a liquid cooled heat sink equipped with six high power semi-conductor modules of IGBT type. Calculated results are validated against experiments for three types of heat dissipating situations, where the diodes and transistors within the modules are heated simultaneously and separately. The CHT modeling is carried out with the commercially available software STAR-CCM+ from CDAdapco. The modeling accounts for all thin materials of the thermal stack of the six IGBT modules, the thermal compound, the aluminum based heat sink with surface enlargements and turbulent coolant flow. Encouraged by the agreement regarding numerical and experimental steady state results, a transient modeling practice is developed for the entire system. The transient modeling enables accurate and controlled studies of the thermal impedances of step responses that are often challenging to achieve in a laboratory. The novelty is the ability to return accurate time relaxation factors between heat sink and water for the whole system. Moreover, the transient results of the step responses are used to derive equivalent circuit models of Foster type. To that end, so-called H and Y models are devised and optimized that are able to predict essential mechanisms of the thermal cross talk of diodes and transistors. Such models are important in the daily work to provide swift and accurate results of the temperature response and life length analysis of dimensioning load cycles pertinent to rolling stock applications.