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Abstract The vertical targets in fusion divertors are the main component which are exposed to very high heat flux generally exceeding 10 MW/m2. In addition, since the heat is non-uniformly imposed to the cooling channels by unique one-side heating, the local heat flux can easily reach up to 20 MW/m2. It is a very challenging engineering target even when considering the latest cooling technology. In this study, CFD-based shape optimization is applied in order to find the optimal channel cross-sectional shape for minimizing local heat flux on the cooling surface. For simplicity, 2-D thermal analysis is adopted as the first step and it estimates preliminary optimized shapes. In this 2-D analysis, heat transfer model is simply reflected on the boundary conditions by analytic method using heat transfer correlations. Then, the optimized shapes are validated using detailed 3-D CFD simulations based on Eulerian two-phase flow models with/without boiling heat transfer. Maximum heat flux on the cooling channel surface is defined as the objective function in the optimization process. Finally, it is found that the maximum heat flux and temperature in the cooling channel can be significantly reduced compared to the original circular channel shape by simple modification to the ellipse-like cross-section. Effects of boiling heat transfer and manufacturability are also discussed in this paper. [ABSTRACT FROM AUTHOR]

Highlights • Analysis of thermo-hydraulic behavior in helium-cooled divertor module with nozzle-to-target distance. • Revealing the detrimental effect with the change of cartridge diameter due to fluidic behavior. • Suggestion of thermal design guideline for nozzle-to-target distance in helium-cooled divertor. Abstract The power exhaust from high temperature plasma at the level of divertor is one of the biggest technological challenges in the path to establish fusion power reactors. At the Karlsruhe Institute of Technology (KIT), a novel helium-cooled divertor using jet impingement cooling array has been investigated as one of the possible solutions for a DEMO tokamak. The concept, consisting of tungsten armour slabs fixed on a tungsten-laminate tube inside which a jet distribution cartridge is placed, has undergone an extensive optimization process. Among other things, the heat transfer coefficient (HTC) and pressure drop over a divertor unit have been thoroughly looked upon in order to improve the divertor thermohydraulic performance. The present paper is presenting such an optimization study in which the effect on the divertor performances of the distance between the cartridge and the heat loaded surface is investigated. Given the geometrical constraints, the nozzle-to-target surface distance is changed either by increasing the diameter of the inlet manifold, or, by varying the cartridge position, starting from a coaxial configuration, to various positions closer to the impingement surface. [ABSTRACT FROM AUTHOR]

Safety analysis for the design basis accident (DBA) is essential to support DEMO blanket concept design. It is necessary to study the pressure behaviour in the blanket and the connected systems during the loss of coolant accident (LOCA) in a blanket module, as well as the temperature evolution in the coolant flow and the associated structures. For the Helium Cooled Pebble Bed (HCPB) blanket concept (version 2014) three representative accidental sequences of LOCA have been simulated using system code MELCOR 1.8.6 for fusion. The LOCA is identified to be the failure of cooling channels in the stiffening grid, in the FW or in the breeder unit. Simulation results are discussed in this paper. [ABSTRACT FROM AUTHOR]

Increased cooling performance is eagerly required for many cutting edge engineering and industrial technologies. Nanofluids have attracted considerable interest due to their potential to enhance the thermal performance of conventional heat transfer fluids. However, heat transfer in nanofluids is a controversial research theme, since there is yet no conclusive answer to explain the underlying heat transfer mechanisms. This study investigates the physics behind the heat transfer behavior of Al 2 O 3 –H 2 O nanofluids under natural convection. A high spatial resolution flow velocimetry method – Particle Image Velocimetry – is employed in dilute nanofluids inside a Rayleigh-Benard configuration with appropriate optical access. The resulting mean velocity and flow structures of pure water and nanofluids are reported and their overall heat transfer performances are compared for Rayleigh numbers, Ra , of the order of 10 9 . This paper aims to identify the contribution of the suspended nanoparticles on the heat and mass transfer mechanisms in low flow velocity applications, as those occurring during natural convection. The outcome of this work is a first step towards the evaluation of the applicability of nanofluids in applications where more complex heat transfer modes, namely boiling and Critical Heat Flux, are involved that are of great importance for the cooling of Fusion reactors. [ABSTRACT FROM AUTHOR]

• Radiation analysis of SMARTEX-C to estimate the maximum temperature on different parts. • Detailed thermal hydraulic analysis of cooling and baking scheme attached externally around the vessel and over the flanges of SMARTEX-C. • A possible cooling scheme has been designed to resolve the high temperature of different parts of vessel with limited external surface area. • Pressure drop, heat transfer coefficient and temperature have been evaluated for the designed cooling and baking scheme. In this paper, a unified cooling and baking scheme has been designed and analyzed, which aids in maintaining the vacuum levels of an experimental system SMARTEX-C. It is a SM all A spect R atio T oroidal Ex periment in a 'C' (SMARTEX-C) shaped geometry. It is a trap meant for confining electron plasma i.e. non-neutral plasma. A vacuum ∼ (1.5 ± 0.5) x 10−10 mbar is maintained inside the vessel. Electrons are emitted from a heated tungsten filament, which eventually deteriorates the vacuum of the vessel with time. To perform reproducible electron plasma experiments it is essential to maintain vacuum levels constant. The designed cooling scheme helps in maintaining it. Additionally, flow of hot Nitrogen has been incorporated in this scheme which serves baking of the vacuum vessel making the dedicated baking system redundant and makes the operation of the system hassle-free. The scheme is modeled in CATIA© and analyzed in ANSYS CFX©. The thermal-hydraulic performance has been analyzed and parametric results in terms of temperature, heat transfer coefficient and pressure drop have been provided for the cooling and baking of the vessel. [ABSTRACT FROM AUTHOR]

• This paper use CFD method to simulate the cooling of the high-temperature divertor components. • This paper gives a clear overview of heat transfer and impingement jet profile in HEMJ divertor. • Our work shows the optimizing results of H/D ratio of divertor design. As part of the EU-DEMO prospective design studies, a He-cooled divertor concept has been developed by Karlsruhe Institute of Technologies (KIT). Using multi-jet cooling, the aim is to provide a robust solution that is capable of coping with heat fluxes as high as 10 MW/m2 under stationary loading conditions. Using the CFD simulations the cooling performance was evaluated and a configuration providing the lowest pipe temperature was identified. [ABSTRACT FROM AUTHOR]

This paper is the continuation of the first report on investigations of heat transfer in the first wall of Helium-Cooled-Pebble-Bed Test Blanket Module for ITER submitted to this Journal (see Ilić et al. [1] ). The investigations have been performed experimentally by manufacturing and testing of a mock-up and numerically through the development of corresponding 3D CFD models. The experimental tests have been conducted for HCPB TBM relevant conditions – the test channel made of Eurofer steel, helium coolant at pressure of 8 MPa and inlet temperature of 300 °C and heat flux of 270 kW/m 2 at the channel side representing plasma facing side of the first wall. In total six measuring series have been performed in which surface roughness, helium inlet temperature and heater power have been considered as parameters. For each measuring series corresponding 3D CFD computational scenarios have been conducted. By use of experimental data for Eurofer temperature it was possible to verify 3D CFD models. On the other side, 1D CFD approaches failed in comparison with experimental data. Further, a critical analysis of the use of microscopic surface roughness as a method for heat transfer improvement in the first wall has been presented. Finally, based on a detailed analysis of experimental and 3D CFD data obtained in the framework of these activities the main directions for an improvement of cooling channels in the first wall could be proposed. [ABSTRACT FROM AUTHOR]