Enhancing Lumped Parameter TMM Using Computational Fluid Dynamics and Scripting

Lumped parameter models are extensively used to calculate the thermal state of structures in a defined environment. Such models rely on the correct estimation of thermal couplings between the thermal nodes. Frequently, such conductances are difficult to establish using standard methods or given correlations. This paper presents methods to determine linear bulk flow conductances and linear conductances due to conduction and convection using computational fluid dynamics (CFD). The methods take advantage of grids of finite elements or finite volumes to model the structure, and the solution of the Navier-Stokes equations using CFD. Conductances due to conduction are determined in two ways. First, the conductance is calculated by means of geometric and material property analysis. Second, a thermal case was applied to compute the conductance. The results were compared subsequently. Fluid and convective conductances were calculated applying thermal and fluid dynamics cases.

Obstacles, such as holes, interface resistances and non-congruent interfaces could easily be handled with these methods.

CFDRC [1], a commercially available CFD package with implemented scripting capability, was used to implement and test the methodologies. Simple test cases are presented here and provide a basis for further exploration of these methodologies.