Faculté des sciences et techniques de l'ingénieur STI, Section de génie mécanique, Programme doctoral Mécanique, Institut des sciences de l'énergie ISE (Laboratoire de transfert de chaleur et de masse LTCM)

Convective boiling heat transfer in a single micro-channel

Consolini, Lorenzo ; Thome, John Richard (Dir.)

Thèse sciences Ecole polytechnique fédérale de Lausanne EPFL : 2008 ; no 4024.

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    The current industrial need for compact high heat density cooling devices has conveyed an increasing interest on convective boiling in micro-channels. Although there is general agreement that these systems may be able to dissipate potentially very high heat fluxes, their heat transfer characteristics are still unclear and require investigation. The present study aims at providing further insight on two-phase single micro-channel heat transfer, through a sensitivity analysis on the effect of the different operational parameters, fluid properties, and channel size on thermal performance. The current database includes results for three different refrigerants, R-134a, R-236fa and R-245fa, two channel diameters, 510 and 790µm, and a multitude of heat fluxes and mass velocities, for a total of over 1800 data points. Two-phase flow instability, which represents one of the factors that has prevented a well-established understanding of the micro-scale phenomenon, has been also investigated, with results showing the potential error it may induce on the estimation of the heat transfer coefficients. Finally, a one-dimensional analysis based on the effect of interfacial shear on the temporal evolution of film thickness is proposed for a heat transfer model for slug flow, which has been shown to be the dominant flow mode at low and intermediate vapor qualities in micro-channel evaporators.