Abstract: The interest area covered the issues of heat transfer to the subcooled working fluid (refrigerant R-123) flowing upward through a narrow rectangular channel (1 x 40 x 360 mm), vertically oriented with one wall heated uniformly and others approximately adiabatic. Liquid crystals thermography was applied to determine two-dimensional temperature distribution on the heating surface. The current study concentrated on heat transfer transition phenomenon during laminar flow, from single phase convection, to boiling incipience and further, to fully developed nucleate boiling. Particular attention was paid to boiling incipience coditions. Experimental investigations were meant to specify the location of the "boiling front", which demonstrated that the phenomenon callud "nucleation hysteresis" or "zero boiling crisis" took place when the boiling incipience occurred. Observations of the hysteresis phenomena, including the impact of various factors (the liquid subcooling at inflow, flow velocity and pressure) on the incipience boiling in narrow channels were also presented. Results are shown in the form of boiling curves plotted for selected points in the channel where heat flux density depends on the heating surface superheating T[w]-T[sat]. The shapes of the curves, in which "nucleation hysteresis" or "zero boiling crisis" are visible, were analysed. The correlation concerning the determination of heat transfer coefficient for refrigerant R-123 boiling incipience in a narrow vertical channel was put forward.
YADDA/CEON