Construction of a Test Facility for Demonstration of a Liquid Lead-bismuth-cooled 10 kW Thermal Receiver in a Solar Furnace Arrangement - SOMMER

AbstractLiquid metals have been proposed in the past as high temperature heat transfer media in concentrating solar power (CSP) systems. Until the mid 80s test facilities were operated with liquid sodium-cooled central receivers. After a period of reduced interest in that approach, several new efforts have been reported recently, particularly from the US, South Africa and Australia. In addition, several recent publications have highlighted the attractive properties of liquid metals for CSP applications. A new contribution to this topic has been launched by Karlsruhe Institute of Technology (KIT) and the Solar Institute of the German Aerospace Center (DLR), combining their experience in CSP and liquid metal technology. The overall goals of this project are planning, design, construction and operation of a small concentrating solar power system in the 10kW thermal range (named SOMMER) using liquid metal as heat transfer fluid for re-gaining operation experience and validating design methodology and providing a complete design concept for a large pilot CSP plant based on liquid metal technology, up to evaluation of O&M cost and levelized cost of electricity. This paper describes the current status of the work on the design and setup of SOMMER, the research goals of this facility, first results of numerical activities in view of the liquid metal cooled receiver design and the connection to the design activities for the pilot plant

Direct numerical simulation and RANS comparison of turbulent convective heat transfer in a staggered ribbed channel with high blockage

A turbulent convective flow of an incompressible fluid inside a staggered ribbed channel with high blockage at ReH≈4200 is simulated with direct numerical simulation (DNS) and Reynolds-averaged NavierStokes (RANS) techniques. The DNS results provide the reference solution for comparison of the RANS turbulence models. The kϵ realizable, kω SST, and v2f model are accurately analyzed for their strengths and weaknesses in predicting the flow and temperature field for this geometry. These three models have been extensively used in literature to simulate this configuration and boundary conditions but with discordant conclusions upon their performance. The v2f model performs much better than the kϵ realizable while the kω SST model results to be inadequate

Review of data and correlations for turbulent forced convective heat transfer of liquid metals in pipes

Within the present work the dataset of experimental points and the heat transfer correlations available in literature for liquid-metal fully-developed, forced-convective heat transfer in pipes are reviewed and critically analyzed. Over 1,100 data points from 21 different sources are considered for constant heat flux, covering a wide range of operating conditions (velocity, heat flux, diameter, among others). Among 15 evaluated correlations, four appropriate ones are recommended for forced turbulent convection: one covering all the data points and the other three respectively related to alkali liquid metals, lead alloys and mercury. Moreover, a new correlation has been derived as a best fit of the limited number of available data points for constant wall temperature, while an alternative evaluation method is also described for this boundary condition

Veicolo plug-in con modulo di riscaldamento e deumidificazione aria

Un veicolo plug-in comprendente una spina elettrica (2) connettibile ad un’alimentazione elettrica esterna, ed almeno un modulo di riscaldamento e deumidificazione aria (10). L’almeno un modulo di 10 riscaldamento e deumidificazione aria (10) comprende: un condotto di ingresso d’aria (20) configurato per miscelare una prima portata d’aria prelevata dall’esterno di detto veicolo e una seconda portata d’aria prelevata da un abitacolo (120) di detto veicolo; un condotto di uscita d’aria trattata (30) configurato per immettere in detto abitacolo (120); un 15 condotto di uscita d’aria esausta (40) configurato per immettere in un ambiente esterno, in alternativa a detto condotto di uscita d’aria trattata (30); un reattore (60) comprendente sostanze assorbenti, detto reattore (60) interposto tra detto condotto di ingresso d’aria (20) e detto condotto di uscita d’aria trattata (30) o detto condotto di uscita d’aria esausta (40); 20 una sezione di riscaldamento (50) a monte di detto reattore (60) o integrata in detto reattore (60), detta sezione di riscaldamento (50) essendo selettivamente attivabile mediante alimentazione tramite detta spina elettrica (2), per riscaldare una corrente d’aria da circolare in detto reattore (60)

Numerical and experimental analysis of airborne particles control in an operating theater

The design of a ventilation system for operating theaters (OT) is aimed to reduce the patient infection risk while maintaining adequate comfort and productivity for the surgical staff. Nowadays, Computational Fluid Dynamics (CFD) represents an important tool to simulate the airflow pattern in an operating theater and its ability to remove airborne particles. The CFD advantages, compared to experimental campaigns, consist in the ability to test different configurations, in the ease of implementation and in time and money savings. The aim of this work is to numerically and experimentally investigate an OT with a layout according to the Standard DIN 1946-4. Moreover the effectiveness of a differential airflow diffusion system on reducing the particle concentration above the operating table is analyzed. The supply air comes from a ceiling filter system composed of 23 H14 filters, which assures an unidirectional flow with differential air velocities over the protected area. In order to experimentally evaluate the performance and the protection grade SG, according to DIN 1946-4, and to validate the numerical results, a measuring campaign has been carried out within a laboratory setup of an OT. Two different scenarios have been adopted to evaluate the protection level against the entry of external and internal contaminant loads into the protected area. For both cases, the simulated and measured particle concentration in the protected area agree well, and the differential air flow diffusion system is able to maintain the desired protective effect (SG) against contamination load in both the design and the off-design conditions

Single stage centrifugal air sampler: a theoretical and experimental approach for cut-off size (d50) evaluation

This work focuses on the study of the particle sampling efficiency of a small single stage centrifugal air sampler under different air sampling flow rates and particles diameters. The centrifugal force perpendicular to the mean airflow motion within the circular cavity is opposed to the viscous one, which depends on the particle aerodynamic diameter. The particles hitting the outer surface of the sampler stick on it and are trapped. Experimental tests have been done for the lowest particle size sampled by the instrument, usually called d 50 or cut-off size, at different air sampling flow rates. Experimental results for particle´s diameters higher than 2 µm agree quite well with those obtained by the theoretical model and by computational fluid dynamics simulations. Furthermore, it has been shown how the particles sampling efficiency of the instrument increases with the airflow rate

Heat transfer experiments in rod bundles cooled by lead-bismuth uutectic (LBE)

Heavy liquid metals (HLMs), such as lead-bismuth eutectic (LBE) and pure lead are prominent candidate coolants for critical assemblies and accelerator-driven systems based on fast neutrons. With a strong focus on safety, key thermal-hydraulic aspects of these systems must be considered. The main challenge for modeling the heat transfer in liquid metals is given by their characteristically low Prandtl number (Pr << 1), separating the scales of turbulent transfer of momentum and heat. For that reason, specific experimental investigations are required for validating according models, particularly for complex geometries such as rod bundles. This work presents the experimental evaluation of two tests sections, both consisting of electrically-heated 19-pin hexagonal bundles, although with different characteristics. The setup #1 has grid spacers and a relatively large pitch-to-diameter ratio P/D=1.4. In this recently completed experimental campaign, extensive heat transfer and pressure drop information was obtained at typical reactor conditions of temperature (up to 450 °C), power density (up to 1.0 MW m ) and bulk velocity (2.2 m s ). With a good repeatability, these results agree well with information available in literature and are a suitable source of data for the validation of predicting models. The setup #2 is a similar bundle, with wire spacers and P/D=1.28. It is currently in the last stages of construction and commissioning. Its main characteristics, instrumentation and envisaged experiments are presented in this work

A comparison between transient CFD and FEM simulations of solar central receiver tubes using molten salt and liquid metals

The design of central receivers in solar thermal power plants is crucial for efficiency and operating behavior of the plant. The local heat flux distribution on the absorber tubes varies, depending on time, weather conditions and aim point strategy. A proper receiver design needs accurate thermodynamic models to detect local temperature distribution, especially hot spots on the absorber tubes. Moreover, due to highly transient boundary conditions, the dynamic behavior of the model is important. Starting with a detailed CFD model of a single receiver tube several simplified FEM models were investigated. The influence of an inhomogeneous heat flux distribution on the absorber and the dynamic behavior after a sudden change of heat flux (e.g. due to passage of clouds) were analyzed. In order to consider radiation exchange between surfaces, simulations with a whole receiver panel were also conducted. The FEM model with one-dimensional fluid elements and constant heat transfer coefficients shows a very good agreement with the detailed CFD model. Further simplifications like the presented model, where the tubes are discretized as projected surfaces are computationally very efficient and can be used for relative comparison between receiver configurations. However, this simplification has deviations in the prediction of tube temperatures and radiation losses. Finally, the receiver simulation of the Solar Two power plant validates the FEM model with the measured data for solar salt. The investigation of liquid metals considers a single tube with an inhomogeneous heat flux on its surface. The detailed analysis shows, that the Nusselt number correlation plays an important role for the tube wall temperature. If the Nusselt number is overestimated in the region of the peak heat flux, the simplified model results in a lower tube wall temperature