Development of an Equivalent Porous Medium Model for a Tubular Receiver Equipped With Raschig Rings

The porous insert has become one of the promising methods for heat transfer enhancement in many industrial applications ranging from small electronic devices to nuclear reactors, and large solar fields. For the assessment of such systems, the CFD numerical studies are usually employed by scientists to investigate the heat and mass transfer inside the region in micro or macro scales. Although micro studies are accurate and provide a detailed analysis of the process, they cannot be used for every study due to complex and costly computational resource they may demand for the case under study. Therefore, sometimes macro-scale simulations become more favorable thanks to the reduction in time and cost as well as the simplification over the morphology of the porous medium they offer. For these reasons, this study aims at developing a macro model for a novel porous disc made of Raschig Rings, to be applied to the tubular solar absorber for future simulations. The methodology devised in this study was to exploit detailed micro-scale simulations, achieving the macro properties and then developing a new equivalent macro model of a porous medium, based on the obtained properties. Numerical data indicated that when the developed macro model is compared to the micro simulations, the thermo-hydraulic results are in good agreement. Applying the macro model to a solar absorber working under linear Fresnel heating showed that the proposed porous disc could reduce the temperature rise on the tube wall by 40%

Bacterial coinfections in dengue virus disease: what we know and what is still obscure about an emerging concern

Dengue virus is the most frequent arthropod-borne viral infection worldwide. Simultaneously to the growth of its incidence, cases of bacterial coinfection in dengue have been increasingly reported. The clinical course of dual infections may worsen for reciprocal interactions and delays in the diagnosis, so that clinicians should be aware of this eventuality. Therefore, we reviewed literature to provide an overview of the epidemiological, clinical, and physiopathological issues related to bacterial coinfections and bacteremia in dengue.Clinical studies and case reports regarding bacteremia and bacterial coinfections in dengue and the interactions between the pathogens published on PubMed were reviewed.We found 26 case reports, only 3 studies on concurrent bacteremia and 12 studies reporting data on bacterial coinfections in dengue. According to the three available studies, the 0.18-7 % of dengue infections are accompanied by concurrent bacteremia, while the 14.3-44.4 % of dengue-related deaths seem associated to bacterial coinfections. Comorbidities, advanced age, and more severe dengue manifestations could be risk factors for dual infections. A longer duration of fever and alterations in laboratory parameters such as procalcitonin, hyponatremia, leukocyte count, and renal function tests can raise the suspicion.Despite the real burden and consequences of this emerging concern is still not computable accurately due to the lack of a significant number of studies on large cohorts, clinicians need a greater awareness about it to early recognize warning signs, to properly use available diagnostic tools and to readily start antibiotic treatment able to prevent worsening in mortality and morbidity

Experimental and numerical investigation of a porous receiver equipped with Raschig Rings for CSP applications

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 analyzed1. 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

Experimental investigation on an air tubular absorber enhanced with Raschig Rings porous medium in a solar furnace

An experimental study was carried out to assess the performance of a tubular absorber enhanced with Raschig Rings (RR) porous medium for CSP applications. Two alternative designs with different porous lengths of 20 and 40 mm were fabricated and compared with two conventional tube designs with and without surface coating. Several tests were conducted at the solar furnace SF60 of the Plataforma Solar de Almeria (PSA) within the international access program of the SFERA III project, financed by the EU. The main scope of the study was to provide comprehensive detail on the hydraulic and thermal characteristics of the modified tube for further optimization and deployment in point-focusing solar systems. Therefore, evaluations were directed to determine the effects of each design on the pressure losses and the tube wall temperature, as well as on the useful heat gain. Results indicated that although the porous inserts rise the pressure losses through the fluid flow, the higher wetted area in the porous zone for heat transfer between the air and the heated plate reduces the wall tem-perature significantly. Moreover, applying the PYROMARK 2500 as the surface coating has a high influence on increasing solar absorption and reducing thermal losses. Further investigations revealed that the integration of the porous medium changes the temperature profile formed all over the tube, transforming a Gaussian shape in the plain pipes to a spline shape with two peaks in the modified tubes. Increasing the energy and exergy effi-ciencies of the solar absorber up to 30-50% and 60-70%, respectively, demonstrated the improving effects of the proposed porous material for future applications in the solar industry

Test and modeling of the hydraulic performance of high-efficiency cooling configurations for gyrotron resonance cavities

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

Analysis of the Flow Distribution in the Back Supporting Structure Manifolds of the HCPB Breeding Blanket for the EU DEMO Fusion Reactor

The European Union Demonstration Fusion Power Reactor (EU DEMO) is facing its preconceptual design phase. In this phase, the research and development activities make extensive use of computational tools, to, e.g., verify the design calculations or to perform parametric analyses aimed at optimization. The design of the breeding blanket (BB), which will be a first-of-a-kind component in EU DEMO, is supported from the thermal-hydraulic point of view by local three-dimensional (3-D) computational fluid dynamics (CFD) analyses, mainly aimed at verifying the heat removal capabilities of the system, and by analyses at the system level using one-dimensional (1-D) codes. This work presents the development and application of a detailed 1-D model of the coolant manifolds for the helium-cooled pebble bed BB concept for EU DEMO. This model, implemented in the GEneral Tokamak THErmal-hydraulic Model (GETTHEM), allows fast analyses to be performed at the global level but still maintain a good level of detail concerning the coolant distribution. The first results obtained with the model prove that 3-D CFD analyses of the manifolds may provide misleading results due to nonrepresentative boundary conditions (BCs), which must be used to avoid having a domain that is too complex. The application of a global model, which is indeed characterized exploiting local analyses, can in turn provide better BCs to the detailed 3-D CFD analyses

A validation roadmap of multi-physics simulators of the resonator of mw-class cw gyrotrons for fusion applications

For a few years the multi-physics modelling of the resonance cavity (resonator) of MW-class continuous-wave gyrotrons, to be employed for electron cyclotron heating and current drive in magnetic confinement fusion machines, has gained increasing interest. The rising target power of the gyrotrons, which drives progressively higher Ohmic losses to be removed from the resonator, together with the need for limiting the resonator deformation as much as possible, has put more emphasis on the thermal-hydraulic and thermo-mechanic modeling of the cavity. To cope with that, a multi-physics simulator has been developed in recent years in a shared effort between several European institutions (the Karlsruher Institut für Technologie and Politecnico di Torino, supported by Fusion for Energy). In this paper the current status of the tool calibration and validation is addressed, aiming at highlighting where any direct or indirect comparisons with experimental data are missing and suggesting a possible roadmap to fill that gap, taking advantage of forthcoming tests in Europe

A validation roadmap of multi-physics simulators of the resonator of mw-class cw gyrotrons for fusion applications

For a few years the multi-physics modelling of the resonance cavity (resonator) of MW-class continuous-wave gyrotrons, to be employed for electron cyclotron heating and current drive in magnetic confinement fusion machines, has gained increasing interest. The rising target power of the gyrotrons, which drives progressively higher Ohmic losses to be removed from the resonator, together with the need for limiting the resonator deformation as much as possible, has put more emphasis on the thermal-hydraulic and thermo-mechanic modeling of the cavity. To cope with that, a multi-physics simulator has been developed in recent years in a shared effort between several European institutions (the Karlsruher Institut für Technologie and Politecnico di Torino, supported by Fusion for Energy). In this paper the current status of the tool calibration and validation is addressed, aiming at highlighting where any direct or indirect comparisons with experimental data are missing and suggesting a possible roadmap to fill that gap, taking advantage of forthcoming tests in Europe