Liquid metal technology for concentrated solar power systems: Contributions by the German research program

Concentrated solar power (CSP) systems can play a major role as a renewable energy source with the inherent possibility of including a thermal energy storage subsystem for improving the plant dispatchability. Next-generation CSP systems have to provide an increased overall efficiency at reduced specific costs and they will require higher operating temperatures and larger heat flux densities. In that context, liquid metals are proposed as advanced high temperature heat transfer fluids, particularly for central receiver systems. Their main advantages are chemical stability at temperatures up to 900 ℃ and even beyond, as well as largely improved heat transfer when compared to conventional fluids like oil or salt mixtures, primarily due to their superior thermal conductivity. However, major issues here are the corrosion protection of structural materials and the development of technology components and control systems, as well as the development of indirect storage solutions, to circumvent the relatively small heat capacity of liquid metals. On the other hand, using liquid metals might enable alternative technologies like direct thermal-electric conversion or use of solar high-tem­perature heat in chemical processes. This article aims at describing research areas and research needs to be addressed for fully evaluating and subsequently utilizing the potential of liquid metals in CSP systems. A second aim of the article is a brief overview of the liquid metal research capabilities of Karlsruhe Institute of Technology (KIT), their background and their relation to CSP and the aforementioned research pathways

Multiscale thermo-hydraulic modeling of cryogenic heat exchangers

The cryogenic industry has experienced a continuous growth in the last decades, partially sustained by the worldwide development of Liquefaction of Natural Gas (LNG) projects. LNG technology provides an economically feasible way of transporting natural gas over long distances, and currently accounts for nearly 30% of the international trade of this resource. The economic feasibility of these projects, in terms of both capital and operating costs, is to a large extent controlled by the performance of the main cryogenic two-phase flow heat exchanger. This industrial scenario provides then the motivation for a detailed study of the heat exchanger from a design perspective. On the one hand, it is widely accepted that a highly detailed analysis is required at a micro scale to properly take account of the two phase heat transfer process. On the other hand, a process-level description corresponds to larger time and space scales. In general, determining the proper methodology for considering these scales and their interaction remains a challenging problem. For this reason, current techniques focus in only one particular scale. The main objective of this project is then to develop a multiscale model applicable for two-phase flow heat exchangers. In this context, a three-scale framework is postulated. This thesis was divided into macro, meso (medium) and micro scale analysis. First, a macroscopic analysis provides a broad description in terms of overall heat transfer and pressure drop, using simple models without taking into account the details of physical phenomena at lower scales. Second, at mesoscale level, flow in parallel channels is considered following a homogenization approach, thus including the effects of flow maldistribution and partial mixing. Third, the microscopic description conceives a phenomenological representation of boiling flows, following multifluid formulations, for two specific flow patterns: annular-mist and post-dryout regimes. Finally, a multiscale design algorithm is proposed

Asymmetric decay heat removal in MYRRHA: experiments in the E-SCAPE facility

MYRRHA is an accelerator-driven system, coupling a proton accelerator to a subcritical reactor cooled by lead-bismuth eutectic (LBE), under development by SCK CEN in Belgium. The reactor design is based on a pool configuration, all components of the primary system housed within the main vessel. In this context, the thermal-hydraulic experimental program considers separately the performance of individual reactor components, and the integral pool dynamics in steady-state and in anticipated transients. The E-SCAPE (European SCAled Pool Experiment) facility is a thermal hydraulic 1/6-scale model of the primary system of the MYRRHA reactor. Replicas of the main components are placed in the main vessel, while pumps and heat exchangers are located in two external circuits. Operating conditions in LBE are representative of (scaled) decay heat removal in terms of mass flow rate (up to 120 kg/s), core power (up to 100 kW) and temperature (200 – 340 °C). This arrangement allows the study of different scenarios, including forced circulation, natural circulation, flow transitions and asymmetric operation. Two specific asymmetric scenarios, corresponding to possible initiating events for design-basis accidents, are studied in the present experimental campaign, framed within the European collaborative project PASCAL (2020-2024). First, a single pump failure is investigated. Second, partial loss of heat sink is simulated by stopping the flow of secondary coolant in only one circuit. These scenarios are compared to a reference symmetric case. Their evolution depends on the fluid mixing in the cold and hot plena

Comparison of RANS and LES heat transfer results for a 19-rod bundle experiments with wire spacers cooled by lead bismuth eutectic

This work presents the main results of a CFD benchmark exercise completed by partner institutions from Europe and USA aiming to achieve a better understanding of the heat transfer characteristics and flow behavior in fuel assemblies cooled by heavy liquid metals. The selected scenario is a 19-rod bundle with wire spacers representative of the MYRRHA reactor under development at SCK CEN (Belgium), with uniform heat flux and cooled by lead-bismuth eutectic (LBE) in steady state conditions of forced convection. Reynolds Averaged Navier Stokes (RANS) simulations using commercially available CFD codes were performed by NRG (Netherlands), UGent (Belgium) and ENEA (Italy). These partial results were presented previously, focusing on a code to code comparison. Experimental data from an LBE test at ENEA became later available, including temperature measured at selected sub-channels. High fidelity Large Eddy Simulation (LES) were recently performed by ANL (USA) using spectral elements. Comparing the two types of numerical results and including the experimental data, is an important step towards a verification and validation of numerical tools used in design and licensing. The comparison of RANS with LES indicates to which extent the current liquid metal modeling methods are sufficiently capable of capturing the most relevant thermal-hydraulic features and helps to highlight remaining issues. Preferably, experimental data are used for validation, although at a lower level of detail. Two cases are studied, representative of nominal conditions (high power and flow) and of conditions after a protected loss of flow accident (PLOFA) (low power and flow)

Liquid Metals as Efficient High-Temperature Heat-Transport Fluids

Liquid metals appear to be attractive heat-transport fluids, in particular if looking at their high thermal conductivities and low viscosities. Despite some pioneering technical applications in the past, complex handling, special requirements, safety concerns, and structural degradation of the materials have prevented their widespread application. However, progress in research and development on liquid-metal science and technology has advanced considerably in the last decade, and this has opened the gate to their broader use in the short term. This requires a more differentiated view on liquid metals, particularly on the specific properties of individual fluids within the context of specific applications. By doing so, many commonly mentioned prejudices vanish or are of minor significance. At the Karlsruhe Institute of Technology, a comprehensive research program on liquid-metal technology has been pursued for more than 50years, and some of the advances in different applications will be outlined in this article

Towards validated prediction with RANS CFD of flow and heat transport in a wire-wrap fuel assembly

Liquid metal fast reactors (LMFRs) are foreseen to play an important role in the future of nuclear energy, thanks to their increased fuel utilization and safety features profiting from the optimal heat transfer performance of the metallic coolants. Accurate thermal-hydraulic analysis of their fuel assemblies, typically employed with wire-wraps as spacers, is recognized as a crucial scientific and engineering contribution to support the deployment of such technology. This challenges the modeling and simulation community. To this aspect, various reference databases (both experimental and numerical) for different wire-wrapped fuel assembly configurations have been created recently and are being used for validation of engineering simulation approaches based on Reynolds Averaged Navier Stokes (RANS) modelling. These databases include: • 7-pin rod bundle: A detailed experiment with Particle Image Velocimetry (PIV) is performed. In order to allow accurate measurements of the flow topology, a matched-index-of-refraction technique was used employing water as working fluid. • 19-pin bundle: A series of experiments is performed covering a wide range of Reynolds and Peclet numbers as well as thermal powers. The experiments use liquid lead-bismuth eutectic as working fluid. The measurements include pressure drop and local temperatures. • 61-pin rod bundle: This large eddy simulation including conjugate heat transfer from the pin cladding to the coolant allows to bridge the gap from small bundles (less than 37 pins) to large bundles (more than 37 pins). In literature, a fundamental different behavior has been observed for small bundles compared to large bundles. • 127-pin bundle: Isothermal experiments using lead-bismuth eutectic characterizing pressure drop are performed on a full scale fuel assembly representative for the MYRRHA reactor. • Infinite pin bundle: This reference quasi-direct numerical simulation profits from periodicity in all directions. It provides a detailed view into the flow field and in addition reveals details of the heat transfer from the rod bundle into the flow.Reference databases aim to serve the nuclear scientific community to validate engineering simulation approaches. The paper will introduce these reference databases, and how they have been used to validate RANS based turbulence modelling approaches within a mainly European context.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.RST/Reactor Physics and Nuclear Material

Influence of Ethanolic Plant Extracts on Morphology and Size Distribution of Sol-Gel Prepared TiO2 Nanoparticles

The influence of ethanolic extracts of three common plants (Equisetum arvense, Syzygium aromaticum and Camellia sinensis) on the morphology and size distribution of TiO2 nanoparticles prepared using the sol-gel method is presented. The phytochemicals extracted from the plants acted as surfactants, modifying the growth mechanism and stabilizing high-quality small, quasi-spherical, non-aggregated TiO2 nanoparticles with sizes in the range from 20–50 nm. The most satisfactory result was achieved using extracts of E. arvense. The structural, morphological, and optical properties of TiO2 nanoparticles prepared using E. arvense ethanolic extracts are discussed. After thermal treatment at 550 °C, the TiO2 nanoparticles were present only in the anatase crystalline phase, with a bandgap of 3.27 eV, as confirmed by X-ray diffraction and UV-vis analyses, respectively. These small morphologically homogeneous TiO2 nanoparticles stabilized by low-cost, abundant and eco-friendly capping agents may be useful as components in photovoltaic cells, pharmaceutical and cosmetic products, as well as for photocatalytic uses.Fil: Rodríguez Jiménez, Rafael Aurelio. Benemérita Universidad Autónoma de Puebla; MéxicoFil: Panecatl Bernal, Yesmin. Universidad Interserrana del Estado de Puebla-Ahuacatlán; MéxicoFil: Carrillo López, Jesús. Benemérita Universidad Autónoma de Puebla; MéxicoFil: Méndez Rojas, Miguel Ángel. Universidad de las Américas Puebla; MéxicoFil: Romero López, Anabel. Benemérita Universidad Autónoma de Puebla; MéxicoFil: Pacio Castillo, Mauricio. Benemérita Universidad Autónoma de Puebla; MéxicoFil: Vivaldo, Israel. Benemérita Universidad Autónoma de Puebla; MéxicoFil: Morales Sánchez, Alfredo. Instituto Nacional de Astrofísica; MéxicoFil: Arce, Roberto Delio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Caram, Jorge Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Villanueva-Cab, Julio. Benemérita Universidad Autónoma de Puebla; MéxicoFil: Alvarado, Joaquín. Benemérita Universidad Autónoma de Puebla; Méxic