Effects of heat flux on boiling heat transfer and flow performance in a wavy-finned minichannel

This study experimentally investigates flow boiling heat transfer in a wavy minichannel designed with a 0.3 mm open gap above the heated surface to facilitate vapor escape and enhance liquid–vapor interaction. Experiments were performed at inlet temperatures of 80°C, 85°C, and 90°C under constant mass flux conditions, while the applied heat flux was varied from 11.61 to 37.55 kW/m² to examine boiling behavior, heat transfer performance, and flow stability. The wavy channel geometry induces periodic flow acceleration and deceleration, promoting bubble nucleation, detachment, and efficient vapor removal. High-speed visualization and surface-mounted thermocouples were utilized to identify boiling regimes and quantify local thermal responses over a wide range of operating conditions. The local heat transfer coefficient exhibited a nonuniform distribution along the channel length, with maximum values near the inlet, a reduction in the mid-section, and a subsequent increase downstream; higher heat fluxes markedly enhanced the heat transfer coefficients. The pressure drop increased with both inlet temperature and heat flux, displaying oscillatory behavior associated with transitions among nucleate, slug, and annular flow regimes. Wall superheat rose sharply near the inlet due to subcooled boiling and stabilized downstream as fully developed nucleate boiling was established. Increasing the inlet temperature shifted the onset of boiling closer to the channel inlet and reduced the required wall superheat.