Abstract
Flow boiling and evaporation heat transfer in mini-channels was examined by using water. The cross-sections tested were in a range of 0.163 mm x 3mm-1.25 mm x 3 mm. The length of the flow channel was 260 mm. When the flow channel gap became smaller than 0.273 mm, the single-phase flow pressure drop coefficient maintained the characteristics of laminar flow in the turbulent flow region. The single-phase flow heat transfer coefficient was smaller than the value predicted with the correlation for the usual size and the trend itself was also different in the turbulent flow region. In forced flow boiling and evaporation, the evaporation was dominant. The flow channel was filled with a large-long bubble. The critical heat flux condition was triggered by the formation of dry areas in the film under the large-long bubble. When the channel gap became smaller than 0.327 mm, the evaporation heat transfer coefficient became smaller than the value predicted with the usual correlation. The provable reason was the use of the usual turbulent flow heat transfer correlation to correlate the results. The effect of narrowing the channel gap on the thermal-hydraulics seemed to appear as the channel gap became smaller than 0.35 mm.
