Abstract
This paper presents an experimental investigation on forced convective boiling of refrigerant HCFC123 in a mini-tube, and visualization of boiling phenomena at the onset points of nucleate boiling is conducted. It was indicated in the former report that heat transfer characteristics of forced convective boiling in mini-tubes, of which inner diameter is φ0.51mm and φ0.30mm, were different from those in conventional tubes. In order to clarify this difference of heat transfer characteristics, bubble formation and growth at the onset points of nucleate boiling were observed and examined, using a glass tube on which ITO film is formed. For low heat flux, an isolated bubble grows up to occupy the whole tube cross section, and flows in the form such as a bullet. As heat flux becomes larger, plural bubbles grow to coalesce into a long vapor plug, and evaporation through liquid film between the vapor plug and the inner tube surface becomes dominant.
