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• Solar tubular receiver equipped with Raschig Rings tested in solar furnace. • Discrete Element Method (DEM) used to model the porous media. • CFD model validated against hydraulic and thermal experimental data. • Performance Evaluation Criteria (PEC) calculated to assess the thermal enhancement. In the context of central solar tower systems, tubular receivers are among the most appealing absorber solutions: the absorbed solar radiation is transferred from the tube external surface to the heat transfer fluid (HTF) flowing within the absorber. In the case of air as HTF, very high temperatures of the coolant can be obtained in principle, thus increasing the efficiency of the downstream thermodynamic cycle. To explore the possible applicability of a porous medium made of Raschig Rings (RRs), already successfully adopted in the heat removal from the resonant cavity of a technological device, the gyrotron, where the heat flux can go up to 20–25 MW/m2 and removed by subcooled water, a mock-up of a planar receiver equipped with RRs has been tested in a solar furnace, using air as coolant. The test results are presented here and analyzed 1 1 Based on experiments carried out at the Plataforma Solar de Almeria.. Furthermore, a numerical model of the mock-up, where the RRs are modeled in detail by the Discrete Element Method, is presented and its capability to reproduce the measured data demonstrated. The model shows, for the tested configuration, an enhancement of the heat transfer of a factor of ~5 with respect to a plain channel with the same envelope, and a Performance Evaluation Criteria of 2–2.5 when the device is compared to the same receiver configuration, but without RRs. [ABSTRACT FROM AUTHOR]

Distance learning has been used as one method to increase access for students who have otherwise been underrepresented in college preparatory courses like Advanced Placement (AP). This study evaluated the impact of a statewide Virtual Advanced Placement (VAP) program on access to AP courses for students from underrepresented populations. Survey and interview data indicate a heavy focus on recruiting students from diverse racial and ethnic backgrounds. However, English language learners and students with disabilities continued to be underrepresented in VAP programs. A discussion of the findings and implications for research and practice are also provided. [ABSTRACT FROM AUTHOR]

• The flow distribution around a MW-class gyrotron cavity is ameliorated. • Evolutionary CD simulations developed based on a genetic algorithm. • The heat removal capability is enhanced by inducing impinging jet effect. • The optimized design is improved in both flow and temperature homogeneity. The steadily increasing performance requested to gyrotrons, to comply with their function of heating and current drive in fusion reactors, put a progressively increasing burden on the heat removal from the interaction cavity, where the heat flux can easily reach 20 MW/m2 on its inner surface. The cavity is actively cooled by subcooled water in forced flow in an annular region, and the water flow typically enters and exits through a single inlet and outlet. The high-speed flow entering from the inlet potentially drives an inhomogeneous flow azimuthally in the cavity region, but helps in locally bursting the heat removal due to the impinging effect of the cold-water flow. Here a new design of the water inlet in the cavity region is performed through a simplified genetic algorithm, in such a way that the flow homogeneity in the gyrotron cavity is maximized, without reducing the beneficial cooling due to the impact of the water jet on the cavity wall. The presence of multiple holes feeding the cavity, with their azimuthal location driven by the genetic algorithm, is analyzed through Computational Fluid Dynamics (CFD) simulations. Once the multi-inlet location is optimized, the dimension of the inlet holes is tuned to burst the heat transfer effect, reaching a high level of temperature and flow homogeneity in the cavity. [ABSTRACT FROM AUTHOR]

The design of the superconducting magnet system of the EU-DEMO tokamak reached the end of the pre-conceptual design phase, and a careful investigation of the parasitic heat load from the room-temperature environment is needed. A possible route for the parasitic heat to enter the toroidal field (TF) coils is by conduction through their Gravity Supports (GSs), which provide mechanical support to the TFs, the Vacuum Vessel (VV) and attached coils, acting as a thermal bridge to the TF casing. A thermal anchoring of the GS using Supercritical helium (SHe) at 4.5 K, re-routing a fraction of the coolant from the TF casing cooling loop, downstream of the casing, is addressed in this study. A 3D thermal model is developed for a plausible design of the EU-DEMO GS, coupled to fluid lines that account for the active cooling by SHe. The effect of the location of the Thermal Anchor (TA) at different heights of the GS plates is investigated parametrically and the beneficial reduction of the parasitic heat load to the TF coil is demonstrated. The reduction of the static heat load to the TF winding pack, when the TA is enabled, is computed and discussed. [ABSTRACT FROM AUTHOR]

The design and manufacturing of different full-size mock-ups of the resonance cavity of gyrotrons, relevant for fusion applications, were performed according to two different cooling strategies. The first one relies on mini-channels, which are very promising in the direction of increasing the heat transfer in the heavily loaded cavity, but which could face an excessively large pressure drop, while the second one adopts the solution of Raschig rings, already successfully used in European operating gyrotrons. The mock-ups, manufactured with conventional techniques, were hydraulically characterized at the Thales premises, using water at room temperature. The measured pressure drop data were used to validate the corresponding numerical computational fluid dynamics (CFD) models, developed with the commercial software STAR-CCM+ (Siemens PLM Software, Plano TX, U.S.A.) and resulting in excellent agreement with the test results. When the validated models were used to compare the two optimized cooling configurations, it resulted that, for the same water flow, the mini-channel strategy gave a pressure drop was two-fold greater than that of the Raschig rings strategy, allowing a maximum flow rate of 1 × 10−3 m3/s to meet a maximum allowable pressure drop of 0.5 MPa. [ABSTRACT FROM AUTHOR]

In high-power fusion gyrotrons, the maximum heat-load on the wall of the interaction section is in the order of 2 kW/cm2, which is the major limiting technological factor for output power and pulse-length of the tube. The ongoing gyrotron development demands a very effective cavity cooling system for optimum gyrotron operation. In this work, the experimental investigation of a mini-channel cavity cooling using a mock-up test set-up is described. The mock-up test set-up will be used to experimentally validate the predictive simulation results and verify the mini-channel cooling performance. It is crucial for validation of the mini-channel cooling properties to determine the amount of the heat load introduced in the cavity wall by an induction heater. In order to estimate that heat load, full 3D electromagnetic simulations have been performed using the CST Studio Suite® software. A suitable calibration factor for the load deposited in the mock-up inner wall is identified after numerical investigation by a 3D thermal model. Calorimetry measurements are performed and the experimental results are compared with the simulation results obtained with a 3D thermal-hydraulic model, using the commercial software STAR-CCM+. When the calibration factor is applied, the experimental calorimetry is well reproduced by the simulations. [ABSTRACT FROM AUTHOR]