Cooling and Separation (CSEP)

This research line focuses on industrial and domestic cooling systems.

Microscale Heat Transfer

The present trend is for mechanical and electrical components to become smaller and smaller. Since most component produce heat when operating, it is essential to cool them to perform well and to its life span. A method of cooling at such small scales is by micro-channels through which liquids flow and/or evaporate. These channels are placed on top of the hot spots. A main advantage of these micro-channels is that the surface-volume ratio becomes better. Another advantage is that distance to the local heat source is decreased. Furthermore, the heat transfer can locally be increased tremendously by evaporation in the micro-channels. However in that case the limits for a continuum approach will be reached since small scale effects become dominant. Accurate solutions can only be achieved when the physical processes at the different scales are coupled. A novel hybrid method is being developed for this purpose, combining molecular-dynamics analyses close to the wall with Monte Carlo simulations and a continuum apprach for the region away from the channel wall. In addition, new optical techniques for velocity and temperature measurements at the microscale level are being implemented and developed (micro-PIV and micro-LIF). Experiments on micro-electronic cooling are being performed in close collaboration with Philips.

More information: A.J.H. Frijns, dr. S.V. Gaastra - Nedea

Thermal Transport in Compact Systems

Research concentrates on (thermal) transport phenomena in compact fluid-dynamical systems. Topics of interest are heat and mass transfer in the laminar flow regime (relevant to e.g. compact equipment for thermo fluids engineering and micro-fluidics applications) and the system-level dynamics of phase-change cooling schemes as e.g. employed in electronics cooling.

The first topic involves development of a unified Lagrangian description for fluid transport and heat transfer for a wide range of laminar transport problems (e.g. heat transfer, mixing, dispersion of additives) in industry. This facilitates alternative ways for studying heat and mass transfer, e.g. heat-transfer visualisation in a similar manner as flow visualisation and analysis of heat transfer by methods from mixing technology, that are expected to afford new insight into the underlying transport phenomena. Applications currently studied include heat-transfer visualisation in industrial heat exchangers and heat-transfer enhancement in micro-flows.

The second topic involves development of a compact model for phase-change heat transfer in small devices (e.g. electronics cooling). This model hinges on description of phase-change heat transfer entirely in terms of the temperature distribution within the heater and incorporation of the fluid-heater interaction by a non linear boundary condition. key advantage of this approach is that it enables investigation of the system-level behaviour of phase-change heat transfer without the need for detailed description of microscopic (multi-phase) phenomena. The compact model thus has great potential for analyses of realistic (industrial) configurations. Both topics employ a variety of numerical and experimental techniques including spectral methods, 2D/3D PTV, (micro-)PIV and (micro-)LIF.

More information: M.F.M. Speetjens

Individual Thermal comfort

The built environment is one of the largest users of fossil fuels. With the current technology huge savings on energy usage can be realized. However, a lot of the theoretically possible targets are not realized in practice, because too little attention is given to the physiology, health and behavior of the individual occupant.

Human thermal comfort depends on many thermal processes. Optimal thermal comfort requires a thermal equilibrium between the human body and its surroundings. For this purpose numerical heat transfer models are developed. In cooperation with Maastricht University we are developing such model, ThermoSEM, that also incorporates thermophysiology. This model can be used to optimize the thermal indoor climate in the built environment taking individual differences and preferences into account: minimizing the energy consumption while ensuring or even improving men’s well-being (thermal comfort and health).

More information: A.J.H. Frijns, D.M.J. Smeulders, A.A. van Steenhoven