A transient thermal analysis using a simplified heat transfer coefficient model

A transient thermal analysis was performed on the Motorola Automotive be Industrial Electronics Group (AIEG) electronic module to determine the maximum temperatures of a bare transistor die during cyclic electrical loading. The Computational Fluid Dynamics (CFD) software - Icepak - was used to model system level transient thermal behavior. An initial steady state full CFD model was solved for mass, momentum, and energy based on Navier-Stokes and energy equations using the finite volume method. Heat transfer coefficients were obtained from object surfaces in contact with the convective fluid and plotted as a linear function of wall temperature for various power dissipation levels. A model with a reduced meshed region of 1/6 of the full CFD model was developed This model incorporates heat transfer coefficients, determined from full CFD steady state runs at various power dissipation levels, as boundary conditions on the walls of the computational domain coincident to the outer surfaces of the solid model and solves only for the energy equation. The heat transfer coefficient is input as a linear function of the wail temperature. The simplified heat transfer coefficient model can be accurately used to solve transient thermal analysis problems for various duty cycles. It reduces computation time by a factor of 10 relative to the full CFD model.