Critical heat flux in subcooled water flow of one-side-heated screw tubes

The purpose of the International Thermonuclear Experimental Reactor (ITER) divertor, which is located at the bottom of the vacuum vessel, is to exhaust impurities and their power from the plasma. Divertor plates function to withstand and to remove a steady-state surface heat flux of 5 MW/m(2) and a transient peak heat flux up to 20 MW/m(2) for 10 s on the side that faces the plasma. These demanding heat loads require active cooling by a pressurized subcooled flow of water as well as the development of a high-performance cooling channel to avoid burnout. Previous experiments showed that a screw tube, which is a tube whose inner surface is machined like a nut, is an efficient means of removing high heat fluxes. New experiments have been carried out with a B 0205 M10 type of screw copper tube. The average inner diameter, i.e., at the midheight of the fin, is 10 mm, and the outer diameter is 14 mm. Different pitches have been investigated: 1.5, 1.25, 1, and 0.75 mm. Incident critical heat fluxes (ICHFs) between 25 and 47 MW/m(2) have been reached for local pressures ranging from 0.9 to 2.2 MPa, inlet temperatures from 17 to 33 degrees C, and axial velocities from 3.6 to 14 m/s. ICHF increases as axial velocity increases and depends slightly on local pressure. Experimental results confirm the potentialities of the screw tube as a reliable geometry for fusion cooling tubes.