Abstract
This paper presents visualization of boiling phenomena and formation of the two-phase flow pattern in a mini tube which has a 0.30mm inner diameter. Test fluid is refrigerant HCFC123. ITO film is formed by vapor deposition over the outer surface of the glass tube. This film is transparent and electrically conductive. Refrigerant HCFC123 is pumped into the glass tube in liquid phase; it then is boiled away by electrical heating. Bubble formation and growth near the onset point of nucleate boiling and the two-phase flow pattern in the low-quality region is recorded via high-speed video camera (10,000 - 50,000 fps). Appearance of bubble formation and growth in a mini-tube depends on heat flux and mass flux. For low heat flux, an isolated bubble grows to occupy the whole tube cross section, and flows in a form resembling a bullet. Liquid film is not observed between this vapor bubble and the inner tube surface, and evaporation is not so dominant. For high heat flux and low mass flux, bubbles grow to coalesce immediately into a long vapor plug; and both nucleate boiling and evaporation from liquid film between the vapor plug and the inner tube surface remain dominant.
