Transient Thermal Network Modeling Applied to Multiscale Systems. Part II: Application to an Electronic Control Unit of an Automobile

This paper applies the methodology of transient thermal network modelling (TTNM) introduced in Part I to the heat transfer analysis of an electronic control unit (ECU) located in the engine enclosure of a motorcar. The complexity of the geometry, the diverse heat transfer mechanisms involved and the duration of the operating cycle prevent the use of both simple, lumped models and detailed numerical simulations. The TTNM methodology relies instead in steady, approximate heat transfer correlations and a division of the system into the largest possible isothermal elements, based on the analysis of characteristic time and length scales. The dynamic heat balance of each element is then written down, conforming the TTNM of the system, which is numerically integrated with an adequate time step. The practical aspects of the TTNM methodology (design stage) are finally demonstrated; in this particular case-study, the model reveals a very high risk of damage of electronic components due to the radiative heat load received from the exhaust pipe of the engine. A design modification consisting of a radiative shield is proposed and model-tested, achieving an appropriate reduction of heat flux and temperatures, and thus an adequate protection of critical components.