Experimental investigation of void fraction variation in subcooled boiling flow under horizontal forced vibrations

•A subcooled flow boiling experiment with horizontal forced vibrations has been carried out.•Variations of void fraction and fluid temperature under vibrations have been observed and analyzed.•Effective subcooled boiling flow conditions were shown on non-dimensional plots.•Potential variations of TBL and heat transfer enhancement were analyzed to explain the changes of void fraction. An experimental investigation of horizontal forced vibration effect on void fraction variation of subcooled boiling flow was carried out in this study. In order to simulate the fuel assembly subchannel of a boiling water reactor (BWR), an annular test section with inner and our diameters of 19.1 and 38.1mm was utilized for subcooled boiling tests under atmospheric pressure. The annular test section was attached to an eccentric-cam vibrator, which was driven by a low-speed motor and can produce horizontal forced vibrations with frequency up to 20Hz and maximum displacement of 22.2mm. The inlet liquid velocity and subcooling were set as vf,in=0.25–1.00m/s and ΔTSub=5–20°C. Different heat fluxes of q″=0.058–0.193MW/m2 were loaded through the center heater rod, and the void fraction and fluid temperature were measured during the tests under stationary (no vibration) and vibration conditions. Test results show that in the subcooled boiling region, the void fraction and fluid temperature can vary under horizontal forced vibrations, and the variation trends were presented in NZu-NSub and vf,in-〈α〉 plots. These variations can be explained by the potential changes of thermal boundary layers (TBL) and the heat transfer enhancement under vibrations. In addition, no significant change of void fraction and fluid temperature was found in or near the saturated boiling conditions under vibrations.