Speaker
Sebastian Ruck
(Institute of Neutron Physics and Reactor Technology)
Description
Rib-roughening the helium-gas cooled channels in plasma-facing components of DEMO (First Wall (FW), limiters or the divertor) enhances heat transfer and reduces structural material operation temperatures. The rib-elements induce a three-dimensional, unsteady flow field and heat transfer is augmented by mixing the fluid in the near wall regions and boundary layers. Whereas the overall heat transfer increases at rib-roughened channel wall, local decrease in heat transfer occurs at flow stagnation regions in the vicinity of rib-channel-wall junction. The present study examines the applicability of rib-arrays detached from the plasma-facing cooling channel wall for homogenizing the surface temperatures and raising the thermal efficiency within the helium-gas FW cooling concept. Furthermore, detached rib-arrays are expected to be advantageous in terms of cost-effective fabrication and local stresses compared to wall mounted ribs. Heat transfer and flow characteristics were computed by Detached-Eddy-Simulations (DES) at Reynolds numbers of ReDh=5E4 to ReDh=1.5E5 (corresponding to helium mass flow rates of 0.026 kg/s to 0.072 kg/s at 8MPa pressure). Thermal-hydraulics for rib-arrays of square rib-elements with a cross section of 1 mm x 1 mm and a clearance to the channel wall of c =0.1 mm, 0.3 mm and 0.5 mm were investigated. The channel cross section was 15 mm x 15 mm with round-edges of 2 mm radius, the rib-pitch-to-rib-height-ratio was p/e=10 and the rib-height-to-hydraulic-diameter-ratio was e/Dh=0.0653. A constant heat flux density of 750 kW/m22 ±250 kW/m22 and 80kW/m2 2 respectively were applied at the plasma-facing and breeder-unit-facing FW structural surface. The results show, that for increasing clearance-to-rib-height-ratios (a) peak values are reduced leading to homogenized surface temperatures and (b) the thermal performance factor for increased heat transfer decreases. For all simulations, mass flow rate dependent correlations for heat transfer coefficient and pressure drop prediction were derived.
Co-authors
Benedikt Kaiser
(Institute of Neutron Physics and Reactor Technology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
Frederik Arbeiter
(Institute of Neutron Physics and Reactor Technology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
Sebastian Ruck
(Institute of Neutron Physics and Reactor Technology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
