convective boiling, micro-channels, two-phase flow, surface wettability, R-134a
In this study, we have examined the convective flow boiling performance of R-134a on various micro-structured aluminum surfaces produced using advanced manufacturing techniques. More specifically, we have calculated the boiling heat transfer coefficient of R-134a on a bare aluminum surface and three micro-structurally enhanced surfaces. Two of these surfaces were produced using photolithography and reactive ion etching techniques, and the third surface was produced by means of laser-ablation. Experiments were performed in a conventional two-phase, single-pass loop which allowed for heat transfer and pressure drop measurements over a range of inlet qualities with only small quality changes occurring in the test section. There was also optical access to the test specimen to permit flow visualization. To begin, both single-phase and two-phase flow experiments were performed on the bare aluminum surface to compare these baseline results with data found in the literature. Once baseline testing and validation were complete, the sample was exchanged and the three micro-structured surfaces were then each subsequently tested. The temperature and pressure of the refrigerant were measured at stations in the flow upstream and downstream of the test section, and the temperature of the test surface was measured using five T-type thermocouples in contact with the sample. The evaporation of the refrigerant was driven by thin ceramic heaters in contact with the underside of the test samples. The pressure, temperature, and quality within the test section were prescribed using an upstream heat exchanger, and the mass flow rate of the refrigerant was controlled using a magnetic gear pump and measured using a positive displacement flow meter. Experiments were performed for mass fluxes between 75 and 600 kg/m2s and for heat fluxes between 5 and 25 kW/m2.