Further development in cutting-edge technologies (micro-electronics, lithographic systems, high-performance power switches and battery packs) becomes increasingly reliant upon dedicated thermal management. Key challenges are massive heat removal and thermal homogenization. Fluid boiling affords solutions to both thermal issues and has found first applications in state-of-the-art electronics-cooling systems. However, the risk of “burn-out” at higher heat fluxes (catastrophic temperature jumps due to the formation of vapor films) severely limits current boiling-based schemes.
The presented study aims at realizing a control strategy by which to actively avoid burn-out and allow thermal-management systems to maximally exploit the potential of boiling heat transfer. Key indicator of impending burn-out is the formation of essentially heterogeneous and highly unstable boiling states, characterized by rapid progressions through patterns of vapor patches (“dry spots”), in the fluid-heater interface. Obtaining insight into the dynamics of such boiling states and gaining control over their behavior are the principal goals of the study. To this end a compact model has been proposed that describes the system-level dynamics of a wide range of practical devices entirely by the internal temperature and incorporates interaction with the boiling medium via a nonlinear Nusselt relation.
Discussion and investigation of the model system is divided into two parts. The first part concerns its open-loop dynamics and concentrates on multiplicity, heterogeneity and stability of steady states and their consistency with realistic system behavior. The second part concerns design of a control strategy by way of a spectral representation of the compact model in a Fourier-Chebyshev state space. The modal state-feedback controller thus designed enables stabilization of (at least a subset of) the unstable heterogeneous boiling states solely by regulation of the mean heat generation on the basis of temperature monitoring in discrete positions on the heater boundary. This serves as first proof of principle of this approach for practical thermal-management schemes.
Michel Speetjens is affiliated with the Energy Technology Laboratory, Department of Mechanical Engineering at the Eindhoven University of Technology (TU/e) in The Netherlands. Michel received his MSc in Mechanical Engineering (Energy Technology) in 1996 and his PhD in Physics (Fluid Dynamics) in 2001, both at TU/e. After two post-doc projects, one at Australia’s national laboratory CSIRO in Melbourne (2002-2003) and one at the Department of Mathematics, Technical University of Aachen (RWTH), Germany (2004-2005), he returned to his “home” institution in 2006 to take up his present position. Michel currently is at UCSB on a sabbatical in the research group of professor Mezic. His research activities include Lagrangian description and analysis of (thermal) transport phenomena, dynamical behaviour of thermal systems and spectral methods for transport processes.
