Free surface heat transfer and innovative designs for thin and thick liquid walls

Design windows on free surface flows in the APEX (advanced power extraction ) study are derived from the viewpoints of the free surface heat transfer, the adaptation of liquid flows to the topological constraints, and temperat ure requirements for plasma operation and power conversion efficiency. With in these constraints, the temperature of the free liquid surface facing the plasma is the most critical parameter governing the amount of liquid that evaporates into the plasma chamber. Present analyses show that a 2 cm or a 40 cm thick lithium layer can be established throughout the ARIES-RS reacto r using a velocity of 10 m s(-1) while operating under the plasma compatibl e surface temperature. However, like solid metallic walls, the liquid lithi um walls require the use of electrical insulators to overcome the MHD drag. As for Flibe free surface flows, the MHD effect caused by interaction with the mean flow is negligible, while a fairly uniform flow of 2 or 45 cm thi ck can be maintained throughout the reactor based on 3-D hydrodynamics calc ulations. However, being a low thermally conducting medium, the Flibe surfa ce temperature highly depends on the extent of the turbulent convection. Th e heat transfer analyses based on the K-E model of the turbulence, includin g MHD effects and various boundary conditions, predict a range of temperatu res that may be beyond the plasma compatible temperatures. If indeed the Fl ibe surface temperature is high relative to the plasma operation limit, fur ther design adjustments will be required to accommodate this deficiency. (C ) 2000 Elsevier Science B.V. All rights reserved.