Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.
Evaporation of dielectric coolants and refrigerants flowing in microgap channels and tubes, is a most promising - though as yet insufficiently understood - technique for a wide range of energy conversion applications and of particular interest in the thermal management of high flux semiconductor chips, chip stacks, and other microelectronic components. In such microgap channels, Annular flow has been found to be the dominant flow regime and to provide substantial evaporative heat transfer rates at the wetted walls. This Keynote lecture will review two-phase flow regimes in microgap channels and the M-shaped heat transfer coefficient variation induced by the axial progression from Bubble to Annular flow. Attention will then be turned to the observed spatial and temporal variations in the wetted wall temperature and to the articulation of an inverse technique for extracting local heat transfer coefficients from such data. Recent results for the parametric dependence of the wall temperature fluctuations and zonal heat transfer coefficients, as well as the impact of microgap channel orientation and externally imposed vibrations on wall temperature, will be described.
