This work presents an experimental investigation of the ester oil ISO VG10-refrigerant R134a mixture flashing flow with foam formation through a straight horizontal 3.22 mm-diameter-6.0 m- long tube. An experimental apparatus was designed to allow the measurement of both pressure and temperature profiles along the tube as well as the visualization of the flow patterns. Tests were performed at different mass flow rates, several refrigerant mass fractions at the inlet of the flow, and inlet mixture temperatures around 28 and 39 °C. A liquid mixture flow with constant temperature and pressure gradient could be noticed at the inlet of the tube. As the flow proceeded towards the exit of the tube the pressure drop produced a reduction of the refrigerant solubility in the oil yielding to formation of the first bubbles. Initially, small and few bubbles could be noticed and the flow behaved as a conventional two-phase flow. Eventually, the bubble population increased and foam flow was observed at the exit of the tube. Due to the great formation of bubbles, both the temperature and pressure gradient of the mixture were greatly reduced in this region of the flow.
Performance of a small diameter two-phase closed thermosyphon in geyser boiling condition
