Effect of porous coating on critical heat flux removed by subcooled water at low flow rates

The critical heat flux (CHF) is studied experimentally in vertical tubes heated directly using power current (direct current 2500 A, 15 V) and cooled with water at a low mass flow rate (0 to 0.2 Mg/m2.s) and at low pressure (0.1 to 0.8 MPa). A smooth tube and a tube with a porous coating layer sintered onto the inner surface were used. The tube and the porous coating layer are both made from INCONEL-600. The results (so far at moderate heat fluxes) are compared with each other and with correlations by Katto and by Weber. Enhancement of heat transfer was determined as well as a negative effect of the porous coating below the expected value of CHF. It seems that a disadvantage of the coated tube corresponds to the apparently annular flow regime alone; whereas, the CHFs can be enhanced by the porous layer as long as the bubbly flow pattern is maintained up to the location of maximum heat flux. Obviously, the later situation is established during high-heat-flux conditions, i.e., at high subcooling and high flow rate, which are the classical design characteristics of high-heat-flux components in fusion reactors. 27 refs., 7 figs