Heat transfer in liquid metal cooled fusion blankets

Experiments on the magnetohydrodynamic (MHD) heat transfer under fusion relevant conditions have been performed in order to quantify the heat transfer capability of such flows especially of the highly heat loaded first wall of a self-cooled liquid metal blanket. Results on heat transfer without and with additional turbulence promotion by means of mechanical and electromagnetic turbulence promoters (TPʹs) are presented for both electrically insulated ducts and thin walled, electrically conducting ducts of rectangular shape. The experimental results are compared with data from theoretical models. A cost-benefit analysis for the use of turbulence promoters is given and engineering correlations are derived which give guidelines for a MHD adapted blanket design. The heat transfer measured in a thin walled conducting rectangular duct is improved by turbulent transport at fusion conditions by a factor of about two compared to slug flow. The corresponding dimensionless pressure gradient keeps constant although the flow changes its state from laminar to turbulent. Using electromagnetic TPʹs installed close to the heated wall no measurable enhancement of the heat transfer has been observed within the range of Re=103–105. Mechanical TPʹs used in the test section with insulated walls improve the heat transfer up to 7 times compared to slug flow, but the corresponding pressure drop increases within the measured range of Reynolds numbers by up to 300%. Based on the analysis of the results design criteria are derived for the orientation and shape of the first wall coolant ducts of self-cooled liquid metal blankets.