Minyoung Lee

Numerical Modeling of a Micro-Scale Stirling Cooler

Micro-scale coolers have a wide range of potential application areas, such as cooling for chip- and board-level electronics, sensors and radio frequency systems. Miniature devices operating on the Stirling cycle are an attractive potential choice due to the high efficiencies realized for macroscale Stirling machines. A new micro-scale Stirling cooler system composed of arrays of silicon MEMS cooling elements has been designed. In this paper, we use computational tools to analyze the porosity-dependence of the pressure and heat transfer performance in the regenerator. For laminar flow in the micro-scale regenerator, the optimal porosity is in a range of 0.85∼0.9 based on maximizing the system coefficient of performance (COP). The system’s thermal performance was then predicted considering compressible flow and heat transfer with a large deformed mesh in COMSOL. The Arbitrary Lagrangian-Eulerian (ALE) technique was used to handle the deformed geometry and the moving boundary. To overcome the computational complexity brought about by the fine pillar structure in the regenerator, a porous medium model was used to replace the pillars in the model, allowing for numerical predictions of full-element geometry. Parametric studies of the design demonstrate the effect of the operating frequency on the cooling capacity and the COP of the system.Copyright

A Novel Scheme in Thermal Modeling of Printed Circuit Boards

This paper presents a simple yet novel analytical approach to model the heat conduction in a Printed Circuit Board (PCB) by taking advantage of the large thermal conductivity contrast between the copper and glass-epoxy layers. The model provides a compact expression for the effective thermal resistance of a PCB and captures an approximate 2-dimensional temperature distribution within the PCB copper layer using simple one-dimensional fin equations in successive copper-glass epoxy layers. The results for effective thermal resistance and temperature distributions in copper layers agree within ±10% of those predicted using finite element (FEM) simulations. The present approach can significantly improve the system level thermal modeling and design of single and multi-component PCBs.Copyright