An experimental investigation on bubble dynamics of alternating saturated flow boiling of R-407C with oscillating refrigerant flow rates

Abstract In this work, an experimental investigation is accomplished on the bubble dynamics of alternating saturated flow boiling of refrigerant R-407. The refrigerant flow rate is oscillated with time approximating the form of the inverted triangular wave to study bubble behaviors of saturated flow boiling. The effects of different parameters, including average mass flux G ¯ , period of oscillating mass flux tp, amplitude of oscillating mass flux ΔG, and mean saturation temperature T ¯ sat of refrigerant R-407, on bubble structures, mean bubble departing size and frequency, and mean density of active nucleation site are investigated. Measured results show that the times in which the bubble nucleation phenomenon is started or terminated are associated with the oscillatory flow conditions. The bubble departure size is raised considerably with the decreasing mass flux in the first half of the alternating cycle. However, an opposite trend is observed in the second half of the temporal alternating cycle where the mass flux is raised. The period of oscillation in the mass flux has negligible influence on the bubble dynamics. Finally, more changes in the bubble departing frequency and the densities of the active bubble nucleation sites are observed as the amplitude of oscillation in the mass flux increases.