Loop heat pipe and capillary pumped loop design: About heat transfer in the isolated bubbles zone of condensers

Heat transfer in the isolated bubbles zone of a circular cross-section micro condenser was investigated. This zone is of interest, on the one hand for designing the condensers and, on the other hand because some bubbles may be entrained by the flow towards the evaporator involving some disturbances in the capillary pumping. Low mass fluxes were considered, of the order of magnitude of those encountered in capillary pumped loops or loop heat pipes. The test section was made using transparent material allowing visualization of bubble collapse. Thanks to image processing, the evolution of vapour quality was experimentally determined. The energy balance was then used to calculate the temperature of the liquid in the isolated bubbles zone, showing that liquid and vapour were not in thermal equilibrium. The sensible heat transfers and latent heat transfers were then compared. Sensible heat transfers appeared to be non-negligible.