Abo Bibliothek: Guest

ISSN Online: 2377-424X

International Heat Transfer Conference 12
August, 18-23, 2002, Grenoble, France

Microscale evaporative heat transfer: modelling and experimental validation

Get access (open in a dialog) DOI: 10.1615/IHTC12.3330
13 pages

Abstrakt

Microscale evaporative heat transfer has grown to an important research field in thermophysical sciences. The reasons for this trend are the miniaturization of systems and the recognition that microscale phenomena can be very important for the understanding and performance prediction of macroscopic devices. The paper concentrates on the description of microscale heat and mass transfer phenomena in evaporating thin films, and its interaction with macroscopic transport processes in engineering devices. Important microscale aspects for the mathematical description of heat and mass transfer in evaporating thin films are: intermolecular forces of adsorption, capillary forces, molecular phase change resistance, effect of internal and external forces on phase equilibrium, contact angles etc. A research strategy is presented to combine microscale and macroscale models with the aim to build design tools for specific heat transfer devices or processes. Two examples are presented: (1) advanced capillary structures with microgrooves for heat pipes and capillary pumped loops, (2) nucleate pool boiling of binary mixtures. Typical microscale results are discussed. Very high spatial gradients of heat flux and mixture concentration occur. Overall (macroscale) results are compared with experimental data. Thereby, a deeper understanding of the transport processes is gained. Some experimentally observed, characteristic thermal behavior can be traced back to microscale effects (e.g. the maximum heat transfer coefficient at intermediate temperatures in NH3-heat pipes, or the reduced heat transfer coefficient in fluid mixtures compared with pure fluids). Microscale temperature measurements with thermochromic liquid crystals underneath an evaporating thin film are presented. The geometrical resolution is less than 1μm. Qualitatively, the measured temperature profiles agree with the results from the microscale heat and mass transfer model.