Experimental and LBM simulation study on the effect of bubble departure and bubbles merging on subcooled flow boiling of pure water and surfactant solution

In the present study, flow boiling experiment using Ni-resistance method of temperature determination and numerical simulation by means of lattice Boltzmann method (LBM) are carried out to confirm the effect of bubble departure and bubbles merging on subcooled flow boiling heat transfer in pure water and CTAC/NaSal(1:1) solutions. Tests are performed with the same cross-section channel of 6.0 mm × 3.5 mm, inlet fluid temperature of T_in = 80 ℃, and outlet pressure of P_out = 101.3 kPa. With microlens and high-speed camera, the bubble departure process and flow patterns are recorded at different concentrations, gravity directions, and mass velocities. The improved Shan–Chen model with large density ratio (T_S = 0.8T_C, ρ_l/ρ_v = 36.55) is applied to simulate the bubble departure and bubbles merging process with changing gravity. The present results show that the superheat of CTAC/NaSal solution has a positive relationship with the bubble departure time and heat transfer coefficient (HTC) of pure water is almost unaffected by surfactant additives without bubble departure. Without bubble departure, the dry spot at the bottom of bubble causes the higher superheat, and the increasing velocity of liquid phase is the main reason of subcooled flow boiling heat transfer.