Masakwa dry season cropping in the Chad Basin

In the inundation area - the basin of the former larger Lake Chad - a special type of sorghum is grown on the clay soils (firgi). This dry-season guinea corn is also called dwarf sorghum or masakwa. In Kanuri, the dominant language in the region, sorghum is called ngawuli. The dry-season types are called ngawuli firgibe (lit. translated: sorghum of the firgi). During the dry season when the natural vegetation becomes dry and yellow, masakwa fields appear in prominent green covering large areas of the clay plains. The most important natural factor for this specialized dry season cropping is the presence of soils with a high clay content. For a better understanding of masakwa and its related issues, a multidisciplinary sub-project (G1) has been established within the SFB 268 (Joint Research Project: History of Culture and Language in the Natural Environment of the West-African Savannah). This project in which all disciplines participate is entitled: "Natural basis for masakwa cultivation and its meaning for the settlement history of the clay plains (firgi) in the Chad basin"

Heat load budgeting of a superconducting induction heater‘s commercial cryocooler-based cryostat

Within a project funded by the German Federal Ministry for Economic Affairs and Energy (BMWI), the Karlsruhe Institute of Technology (KIT) collaborates with the Theva GmbH and Bültmann GmbH to develop a superconduct-ing magnetic heater. The Theva GmbH designs and supplies the high-temperature superconducting (HTS) coil. It will be integrated in a cryostat designed and supplied by KIT and cooled to ca. 25 K via a GM-cryocooler. Granted successful test results at KIT, the cryostat with the superconducting coil will serve to operate an induction heater at the Bültmann GmbH and be assessed there under industrial conditions. The challenge within the cryogenic design lies in the simultaneous requirement of relatively low production costs, robustness and extremely limited operation downtimes to form a competitive product. This contribution presents aspects of the cryogenic system’s conceptional design, with a focus on its heat load budgeting. Due to the limited cooling capacities of cryocoolers on each stage, the main aim of the design is to distribute the estimated heat loads as suitably as possible between the cryocooler stages. In the cryostat we designed, the total heat loads on both cryocooler stages will have three significant contributions: heat conduc-tion along connected components, Joule heating and thermal radiation. The respective estimation methods for these heat loads and their results are briefly shown and evaluated in this contribution. In this context, specific examples for the results‘ influence on the cryostat design within the scope of thermal and economical design are given. The heat load approximations’ eligibility to serve as a determination basis of an appropriate cryocooler model is discussed as well. On this basis, finally, we give suggestions for specific cryocooler models currently on the market

Sensoren zur Messung von Rißfortschritt und Rißgeschwindigkeit

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Compact cryogen-free modular cooling system for large scale offshore superconducting wind turbines

High temperature superconducting (HTS) generators are expected to pave the way to scale up offshore wind turbines to 10 MW and beyond. Although study of HTS wind generators has been of great interest and several designs have been proposed, the commercialization has not yet come. Despite the demonstrated feasibility and realized technical advantages, cryogenic cooling is still the key barrier to make the use of HTS technology in the field of offshore wind applications more transparent. In order to fulfill the requirements of handling, transportation, maintenance and reliability of long-term offshore operation, we have proposed a compact cryogen-free modular cryogenic cooling system for large scale HTS wind generators. The HTS generator usually contains many identical superconducting coils and each coil is allocated one identical modular cryostat in order to achieve the working temperature of 20-40 K. The modular cryostat enveloping the HTS coil adopts rectangular shape and consists of a vacuum vessel, a thermal shield with multi-layer insulation and corresponding supporting structures. Rods made of titanium alloy are selected as support structures to reduce the heat load. A small scale two-stage Stirling or pulse tube cryocooler driven by oil-free linear compressor will be implemented in each modular cryostat to deliver the required cooling power

Development of a rotary union for Gifford-McMahon cryocoolers utilized in a 10 MW offshore superconducting wind turbine

Superconducting generators (SCG) show the potential to reduce the head mass of large offshore wind turbines. By evaluating the availability and required cooling capacity in the temperatures range around 20 K, a Gifford-McMahon (GM) cryocooler among all the candidates was selected. The cold head of GM cryocooler is supposed to rotate together with the rotating superconducting coil. However, the scroll compressor of the GM cryocooler must stay stationary due to lubricating oil. As a consequence, a rotary helium union (RHU) utilizing Ferrofluidic® sealing technology was successfully developed to transfer helium gas between the rotating cold head and stationary helium compressor at ambient temperatures. It contains a high-pressure and low-pressure helium path with multiple ports, respectively. Besides the helium line, slip rings with optical fiber channels are also integrated into this RHU to transfer current and measurement signals. With promising preliminary test results, the RHU will be installed in a demonstrator of SCG and further performance investigation will be performed.This research is primarily supported by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement 308793. Thanks for the technical support from Tom Black and Mark Granoff at Ferrotec

Magnetlagerauslegung unter Nutzung der Particle-Swarm-Optimization

Die Auslegung von Magnetlagern erfolgt in der Regel durch Fachpersonal in einem iterativen zeitaufwendigen Prozess. Dies stellt einen großen Kostenfaktor bei der Entwicklung magnetgelagerter Maschinen oder der Umrüstung konventionell gelagerter Maschinen dar. Aus diesem Grund wurde ein Softwarewerkzeug entwickelt, welches eine automatisierte, optimale Auslegung von Magnetlagern auf Basis der Particle-Swarm-Optimization ermöglicht. Dabei wurden auch Temperatureinflüsse berücksichtigt, sodass eine Auslegung von Magnetlagern für erweiterte Temperaturbereiche möglich ist (Hochtemperatur-Magnetlager).The design of magnetic bearings is usually carried out by specialist personnel in an iterative time-consuming process. This represents a major cost factor in the development of machines with magnetic bearings or the retrofitting of machines with conventional bearings. For this reason, a software tool was developed that enables an automated, optimal design of magnetic bearings based on Particle-Swarm Optimization. Temperature influences were also taken into account, so that a design of magnetic bearings for extended temperature ranges is possible (high-temperature magnetic bearings)