Using FLOTHERM and the Command Center to Exploit the Principle of Superposition Paul Gauché Flomerics Inc. 257 Turnpike Road, Suite 100 Southborough, MA 01772 Phone: (508) 357-2012 Fax: (508) 357-2013 Email: paul@flomerics.com Abstract A set of computational analyses was performed for a system level model to show that the principle of superposition can easily be exploited in a new parametric tool called the Command Center (CC), a module that will be included with Flomerics software from the next release. Thermal superposition implies that the effect of a set of independent sources in an analysis can be studied one by one and a combination of these sources can be added to provide a solution for a system. This implies that the thermal effect of the sources is linearized to enable the superposition principle. For forced convection systems, this assumption is valid for a broad range of boundary conditions whilst for natural convection systems, this principle will only work in a narrow range of source values. The concept of the adiabatic heat transfer coefficient (AHTC) and superposition kernel function (SKF) has been used as a basis for understanding thermal superposition, a very useful tool enabling thermal analysis before the power list for a new design is available. Because CFD solves the physics of flow and heat transfer implicitly for a model, the concept of the AHTC can be used directly without additional analysis methods except for a quick matrix multiplication process. The method in CFD requires that each heat source is activated as a unit value in turn and the results are stored for any number of probed points in the system. These points are then tabulated and post-processed with the actual system heat load to determine the system temperatures. For forced convection systems where radiation and natural convection effects are minimal, the results of this study have shown excellent correlation. Key words: CFD, Adiabatic Heat Transfer Coefficient, Superposition Kernel Function Introduction Thermal analysis using advanced computational tools for the cooling design of electronic equipment is becoming more common and, in many cases essential. The increasing power densities in electronic packages and the increased demand for reliability have forced hardware designers to look closer at the thermal design and optimization of equipment. To satisfy this demand of thermal design optimization in electronics, Flomerics has developed a new module for FLOTHERM used to perform parametric sets of analyses automatically. This module is called the Command Center. Performing a computational analysis on a system requires enough data to model the important geometry of the concept or design, the material properties and the thermal boundary conditions. The thermal boundary conditions include: 1) the ambient or environmental conditions that effect the equipment and 2) the power dissipation rating of each electrical or electronic device. One of the biggest problems in accurate modeling of electronic systems is the reliability or simply the lack of power dissipation ratings. State of the art computational fluid dynamics (CFD) software can perform accurate analyses of complex systems, but if the power rating is off by 100% or more, the model will not provide correct results. The issue of knowing the power in the system has been one of the biggest stumbling blocks in the analysis of equipment that does not yet exist. This is no longer a problem when a prototype exists, but by then it’s too difficult to affect the design in any effective way. Knowing