Degradation of pool boiling heat transfer of mixtures on an enhanced tube

Pool boiling experiments have been carried out on a smooth tube and an enhanced tube with sub-surface structures. Pure propane, pure iso-butane and three mixtures of propane and iso-butane were used as working fluids. For boiling of mixtures, the enhanced tube shows a higher decrease of the heat transfer coefficient than the smooth tube, due to a reduced performance of the sub-surface structures. This is supported by some special bubble behaviors, e.g. a sharp turn of the bubble curvature near the wall, the generation of small bubbles, jets of small bubbles on the bottom surface, etc.. The obtained bubble dynamics data also prove that the amount of vapor generated during boiling of mixtures is lower than that for pure components.