Enhancement of flow boiling in meso scale channels with subsonic vibrations

Abstract

Heat transfer coefficients were measured for forced convection refrigerant mixture (R-407C) flow in meso-scale heat exchangers enhanced by subsonic vibration. Flow in three horizontal meso-channels (ID 1.0 mm, 2.0 mm, and 4 mm), and a length of 60 mm for subcooled and saturated boiling conditions are reported in this study. Experiments were conducted at heat fluxes of 2 and 11 kW/m2 for subcooled boiling, and 15 and 29 kW/m2 for saturated boiling. The mass flow rate was varied from 0.45 to 1.85 kg/min. The frequency was varied, freq = 0–70 Hz. An experimental setup composed of heating elements provided heat flux variations in the meso-channels and excitation elements were attached to the side of the channels to produce the subsonic vibrations. The heat transfer coefficient was found to be dependent on both the heat flux as well as mass flux levels. Results show that subsonic vibration enhanced the heat transfer performance over that of non enhanced meso-channels by 8% as compared to regular flow convective boiling process.