EXPERIMENTAL INVESTIGATION AND DISCUSSION OF HEAT TRANSFER MECHANISMS DURING FLOW BOILING IN MINI-CHANNELS USING REFRIGERANT R134A

The main objective of this work was to investigate the heat transfer characteristics of elongated bubbles in 0.5mm diameter mini-channels using R134a as working fluid. In particular to identify the contribution of the nucleate and film boiling to the heat transfer mechanism at low thermodynamical qualities. The measurements were performed in a glass test section with several diabatic and adiabatic regions. The adiabatic region was heated by Joule effect using an ITO coating as heater. The measurement of heat transfer coefficient for elongated bubbles without the presence of bubble nucleation were compared with the case with nucleation showing that heat transfer in elongated bubbles is only larger than the case with nucleation at very small heat fluxes. In addition, heat transfer coefficient showed a dependence with the thermodynamic quality.