Thomas Wetzel

Investigation of a Heavy Liquid Metal Free Surface Target Experiment

Several distinct reactor strategies are proposed within the context of the IP Eurotrans framework programme for the transmutation of nuclear waste. A pool type reactor filled with liquid heavy metal and containing a subcritical core is one of the promising designs. Additional neutrons required for the nuclear reaction are generated by a spallation reaction inside the core. A high power proton beam is guided through a vacuum tube from an accelerator into the liquid heavy metal pool i.e. into the reactor core. At the point where the beam hits the metal surface special construction effort is indispensable to handle the high heat production.A specific target design is used to ensure a high fluid velocity and a stable surface at the beam entry. This design employs a concentric vertical feeder establishing a free conical surface with velocity up to 2.5 m/s ensuring stable surface flow and appropriate heat removal. The proposed target geometry has been constructed using underlying rules developed by the MYRRHA design group for the free surface target in the MYRRHA research reactor.A full scale model of this design using lead bismuth eutectic (LBE) has been set up and experimentally investigated at the of the Karlsruhe Institute of Technology (KIT). Measurements taken by high speed digital imaging visualize both conical inner and outer jet free surface. They show a stable surface in a wide range of operating conditions starting from 35% of the nominal flow rate and agree well with numerical investigations using commercial CFD code Star-CD and Star-CCM+. Previous concerns related to splashing or cavitation during the start-up or shut-down procedure proofed unjustified.Copyright

Experimental Activities on Heavy Liquid Metal Thermo-Hydraulics

Heavy liquid metals, such as Pb and lead–bismuth eutectic (LBE), are fluids of interest for applications in fast reactors and accelerator-driven systems (ADS). For the development of such systems, thermal-hydraulics is a key discipline to be further investigated. The low Prandtl number of these fluids makes this problem particularly challenging and reliable experimental data is essential. In this work, an overview of the experimental activities at the Karlsruhe Liquid Metal Laboratory is presented.

Thermal management of Li-ion batteries and its influence on electrical performance

The current development activities for hybrid (PHEV/HEV) or full electric driven vehicles (FEV/BEV) focus on Li-ion batteries as energy storage. Since the amount of storable energy inside an automotive battery pack still prevents longer distances in the electric driving mode, the available energy has to be used as extensively as possible and high power throughput and maximum utilization of the nominal capacity are key development goals. Nevertheless, safe operation is limited to a certain temperature range which makes operation of Li-ion batteries in automotive application without reducing the battery’s life span and without exceeding recommended temperatures a challenging task. The temperature is one of the key factors that influence the electrical behaviour and the ageing characteristics of Li-ion batteries. At low temperatures the output power is significantly reduced [1, 2, 3] and high charging rates cannot be applied. The deposition of metallic lithium at the anode as a result of charging at lower temperatures can cause internal short circuits and can even initiate a thermal runaway of the battery [4]. However, charging at low temperatures occurs while decelerating a cold started electric vehicle with a thermally unconditioned battery pack. Batteries in adequate thermal state on the other hand facilitate a high power output because of reduced ohmic resistances [5] and raised diffusion coefficients inside the battery cell respectively. Whereas charging at higher temperatures is more feasible, the storage of Li-ion batteries (on stock, but also in the parked car) under elevated temperatures has a detrimental effect on the battery’s long-term endurance. More precisely, the calendar life ageing, which reduces the battery’s capacity and increases its ohmic resistances, intensifies with temperature [6, 7].

Kondensation reiner Stoffe

Kommt Dampf mit einer Wand, deren Temperatur kleiner als die Sattigungstemperatur des Dampfes ist, in Kontakt, kondensiert er an der Wand und schlagt sich als Flussigkeit nieder.

Einleitung und Definitionen

Die Warmeubertragung ist ein Teilgebiet der Warmelehre. Sie beschreibt die Gesetzmasigkeiten, nach denen der Transport von Warme zwischen Systemen unterschiedlicher Temperatur erfolgt. In der Thermodynamik werden Warmestrome und Warme, die von einem System zum anderen zu- oder abgefuhrt werden, als gegebene Prozessgrosen angenommen. Dabei bleibt unberucksichtigt, wie die Warme ubertragen wird und auf Grund welcher Gesetzmasigkeiten die Quantitat der transferierten Warme entsteht. Die Warmeubertragung behandelt die Mechanismen, die die Grose des Warmestromes bzw. der ubertragenen Warme bei den vorhandenen Temperaturdifferenzen und sonstigen physikalischen Bedingungen bestimmen.

Berechnung von Stoffwerten

Bei der Berechnung der Warmeubergangszahlen spielt die Beschaffung von Stoffwerten eine wichtige Rolle.

Wärmeleitung in ruhenden Stoffen

Die Warmeleitung ist ein Warmetransportmechanismus, der in festen, flussigen und gasformigen Stoffen auftritt. Trager des Energietransports sind dabei je nach Medium Atome, Molekule, Elektronen oder Phononen. Letztere sind Energiequanten elastischer Wellen, die in Nichtmetallen und – neben Elektronen – auch in Metallen fur den Transport thermischer Energie sorgen.

Condensation of pure vapors

When vapor comes into contact with a wall at a temperature below its saturation temperature, condensate is generated on the wall surface. The condensate can either build a film or droplets. A differentiation between film condensation and droplet condensation has to be made. Droplet condensation reaches higher heat transfer coefficients but requires special dewetting surfaces.

Thermal conduction in static materials

Thermal conduction in static materials is a heat transfer process in solids or static fluids. The carriers of the energy transfer can be molecules, atoms, electrons and phonons. The latter are energy quantums of elastic waves, in nonmetallic and metallic solids. Electrons transfer heat in metals, both in solid and fluid state.

Introduction and definitions

Heat transfer is a fundamental part of thermal engineering. It is the science of the rules governing the transfer of heat between systems of different temperatures. In thermodynamics, the heat transferred from one system to its surroundings is assumed as a given process parameter. This assumption does not give any information on how the heat is transferred and which rules determine the quantity of the transferred heat.