EMC3-EIRENE simulations of neon impurity seeding effects on heat flux distribution on CFETR

The numerical modelling of the heat flux distribution with neon impurity seeding on CFETR has been performed by the three-dimensional (3D) edge transport code EMC3-EIRENE. The maximum heat flux on divertor targets is about 18 MW m-2 without impurity seeding under the input power of 200 MW entering into the scrape-off layer. In order to mitigate the heat loads below 10 MW m-2, neon impurity seeded at different poloidal positions has been investigated to understand the properties of impurity concentration and heat load distributions for a single toroidal injection location. The majority of the studied neon injections gives rise to a toroidally asymmetric profile of heat load deposition on the in- or out-board divertor targets. The heat loads cannot be reduced below 10 MW m-2 along the whole torus for a single toroidal injection location. In order to achieve the heat load mitigation (<10 MW m-2) along the entire torus, modelling of sole and simultaneous multi-toroidal neon injections near the in- and out-board strike points has been stimulated, which indicates that the simultaneous multi-toroidal neon injections show a better heat flux mitigation on both in- and out-board divertor targets. The maximum heat flux can be reduced below 7 MWm-2 on divertor targets for the studied scenarios of the simultaneous multi-toroidal neon injections.

Boiling of FC-72 on Surfaces with Open Copper Microchannel

The paper presents the results of experimental research on pool boiling heat transfer of dielectric liquid FC-72. Measurements were made at atmospheric pressure on open surfaces with microchannels. Heat transfer surfaces, in the form of parallel milled microchannels, were made of copper. The rectangular cross-sectional microchannels were 0.2 to 0.5 mm deep and 0.2 to 0.4 mm wide. The surfaces, compared to a smooth flat surface, provided a five-fold increase in the heat transfer coefficient and a two-fold increase in the critical heat flux. The article analyses the influence of the width and height of the microchannel on the heat transfer process. The maximum heat flux was 271.7 kW/m2, and the highest heat transfer coefficient obtained was 25 kW/m2K. Furthermore, the experimental results were compared with selected correlations for the nucleate pool boiling.

A Simulation Method for the Optimization of Cooling Water Slot Structure in Slab Continuous Casting Mold Combined With SEN

The temperature field in the full 3D finite element mold model combined with submerged entry nozzle(SEN)(Full SEN-3D FEMM) is simulated with Fluent of ANSYS 18.0 Package to apply the maximum heat flux density on the heat face of mold copper plate obtained through this simulation to the element model of the copper plate, and thermal stress and strain simulations on the copper plate and stainless back ones are conducted with Workbench of ANSYS 18.0 Package to confirm the reasonable designing factors for the water slot structure on the copper plate. The maximum heat flux densities on the wide and narrow heat faces of the copper plates are given on the initial shock areas of molten steel flux injected through SEN. With constant heat flux density on the heat face, the more the thickness of copper plate increases, the more the max- and min temperatures increase and the difference between them decreases. Elastic and plastic deformations on the copper plate are made during continuous casting(CC) process; the former occurs around the water slots and the latter around the heat face with the highest temperature, which regards 20-18-17 as the most reasonable one among 4 plans for the water slot structure.

Boiling Heat Transfer Characteristics of Rotary Hollow Cylinders with In-Line and Staggered Multiple Arrays of Water Jets

Transient heat transfer studies of quenching rotary hollow cylinders with in-line and staggered multiple arrays of jets have been carried out experimentally. The study involves three hollow cylinders (Do/d = 12 to 24) with rotation speed 10 to 50 rpm, quenched by subcooled water jets (ΔTsub=50-80 K) with jet flow rate 2.7 to 10.9 L/min. The increase in area-averaged and maximum heat flux over quenching surface (Af) has been observed in the studied multiple arrays with constant Qtotal compared to previous studies. Investigation of radial temperature distribution at stagnation point of jet reveals that the footprint of configuration of 4-row array is highlighted in radial distances near the outer surface and vanishes further down toward the inner surface. The influence of the main quenching parameters on local average surface heat flux at stagnation point is addressed in all the boiling regimes where the result indicates jet flow rate provides strongest effect in all the boiling regimes. Effectiveness of magnitude of maximum heat flux in the boiling curve for the studied parameters is reported. The result of spatial and temporal heat flux by radial conduction in the solid presents projection depth of cyclic variation of surface heat flux in the radial axis as it disappears near inner surface of hollow cylinder. In addition, correlations are proposed for area-averaged Nusselt number as well as average and maximum local heat flux at stagnation point of jet for the in-line and staggered multiple arrays.

A high-performance solid-state electrocaloric cooling system

Electrocaloric (EC) cooling is an emerging technology that has broad potential to disrupt conventional air conditioning and refrigeration as well as electronics cooling applications. EC coolers can be highly efficient, solid state, and compact; have few moving parts; and contain no environmentally harmful or combustible refrigerants. We report a scalable, high-performance system architecture, demonstrated in a device that uses PbSc0.5Ta0.5O3 EC multilayer ceramic capacitors fabricated in a manufacturing-compatible process. We obtained a system temperature span of 5.2°C and a maximum heat flux of 135 milliwatts per square centimeter. This measured heat flux is more than four times higher than other EC cooling demonstrations, and the temperature lift is among the highest for EC systems that use ceramic multilayer capacitors.

Aerothermodynamic Shape Optimization for Re-entry Capsule Using Genetic Algorithms

Space hasn’t been for a long time now the final frontier, in the last years more and more spaceships have accessed outer space for different missions, some of them being required to return. The actual and main task of researchers is to find an optimal geometry for new generation of spacecraft which must be reusable and fit the imposed loads (heat flux, pressure, acceleration). The purpose of this paper is to optimize the design of a re-entry capsule configuration, in order to minimize the maximum heat flux on the thermal protection system and to obtain a wanted imposed drag coefficient. For the optimization process we use genetic algorithms and for the solving process, local inclination methods. Even if the latter are low-fidelity methods and do not offer satisfying results on all conditions, we consider them to be good enough for a preliminary study of an optimal design. Thus, this paper purpose is to describe the procedure to obtain an optimal configuration which can be better analyzed with high-fidelity methods.

A computational approach thermoelectric power generators to estimate heat flux

This paper focuses on establishing the limiting value of input heat flux for thermoelectric generators (TEG) under different environmental and operating conditions. The current study investigates the limiting input heat flux for TEG’s with allowable hot side temperature of 150.A fin block with 8 fin configuration and fin length of 60 mm is chosen as heat sink configuration for TEG. Computational Fluid Dynamics (CFD) model is developed and analyzed in this work after validation with published experimental results. CFD model consists of 4 TEGs encapsulated within a target block and a finned block, placed within a low speed wind tunnel. Forced laminar air flow in the wind tunnel up to 14 m/s simulates the outdoor wind conditions. Concentrated solar flux is applied to the face of the target block. Effect of ambient air temperature, fin material is studied. Angle of Attack (AOA) and wind direction which arises due to the 2 axis tacking of sun by Fresnel lens concentrator has also been studied and it is observed that maximum heat flux reaches 24,850 W/m2 for the TEG at 14 m/s wind speed, 24,000 W/m2 for 30Angle of Attack (AOA) under 5 m/s wind velocity. It is also observed that maximum heat flux varies by 147.77% with a change in wind velocity from 0 to 5 m/s, while the change is 11.43% when the change from 5 to 14 m/s.

Study on Thermal-Hydraulics Characteristics of the Flat and High-Thermal-Conductivity Core-Catcher

For mitigation of severe accident with core melting, core-catcher has been developed to catch and cool molten core. The core-catcher developed by Toshiba for Advanced Boiling Water Reactor was designed to be installed under Reactor Pressure Vessel (RPV) and catch molten core in basin with thermal-resistant material. It also has structure including risers and downcomers to generate natural circulation flow of cooling water. On the other hand, there is not enough space to install it in the existing plants due to the height of the inclined cooling channels. Then, we have been developing flat core-catcher with flat cooling channels for the existing plants to reduce total height of the structure. Finned channels will be adopted to increase heat transfer rate by increasing heat transfer area. However, the thermal-hydraulics characteristics of such core-catcher has not been clarified due to the specific configuration, that is, the horizontal rectangular finned channel with the heated surface from upper side. This present study investigated the natural circulation characteristics and heat transfer behavior in the horizontal rectangular finned channel by experiment. Pressure drop, natural circulation flow and temperature were measured by changing heat fluxes. The flow was visualized to obtain flow pattern in the finned channel by a high-speed camera. The maximum value of test range of heat flux was 250 kW/m2, which is the value when the total amount of the molten core would be dropped to the core-catcher. The partial simulated test section of finned channel with 3.5 m length was heated from upper side by heaters to simulate the heat flux from the molten core. This length is the same as the inner diameter of RPV pedestal of the existing plants. The natural circulation mass flux increased as the heat flux increased and then two-phase flow pressure loss also increased. Consequently, circulation flow turned to decrease. As a result of the test, when the heat flux was 50 kW/m2, the circulation mass flux got to the maximum value, 230 kg/m2s. Under all the conditions except for the maximum heat flux of 250 kW/m2, the fin surface temperature was around the saturated temperature. At maximum heat flux 250 kW/m2, the temperature got 540 K. However, the structural soundness was maintained because it is lower than melting temperature of the fin. It can be concluded that the flat and high-thermal-conductivity core-catcher has enough cooling performance to catch and stabilize the molten core.