Simulation of a Safe Start-Up Maneuver for a Brayton Heat Pump

With about 50 % of the final energy used as heat in Europe, reducing fossil fuel consumption in this sector is crucial to achieve significant greenhouse gas emission reduction. Heat pumps using renewable electricity can potentially cover the heat demand below 500 °C. The DLR’s prototype CoBra (Cottbus Brayton cycle heat pump) aims at demonstrating the feasibility of a turbomachine driven closed-loop Brayton cycle heat pump with a thermal output of 200 kW and a heat sink temperature of up to 350 °C. In order to achieve safe operation, transient operation of the heat pump, such as start-up, must be analyzed. Temperature gradients must be kept below a limit, defined mostly by thermal stresses in the heat exchangers. At the same time, compressor surge and resonant frequencies of rotating components must be avoided during transient maneuvers of the system. In the current work, the heat pump prototype has been modeled with Modelica based on the component geometries and with the use of compressor and turbine maps obtained from 3D CFD simulations. For the start-up of the prototype, a suitable control strategy is developed and analyzed in order to minimize operational risks. Control parameters are compressor shaft speed, secondary mass flows and the turbine bypass. It is shown that a turbine bypass is necessary to avoid compressor surge during start-up. The conflicting requirements of crossing natural frequencies quickly while ensuring tolerable temperature gradients in the heat exchangers can be met. The results also show that pressure rise delay through volume dynamics is in the order of seconds. Slow transient effects in the evolution of fluid and heat exchanger temperatures arise from the thermal inertia of the heat exchangers

Part Load Capability of a High Temperature Heat Pump with Reversed Brayton Cycle

This paper studies the part load behavior and capability of a high temperature heat pump that operates with the Brayton cycle. A novel concept of a high temperature heat pump which is currently under construction in Cottbus (Germany) is presented. It goes far beyond temperature levels of current high temperature heat pumps and will provide process heat at above 250 °C. The heat pump uses a closed Brayton cycle driven by axial turbomachinery and provides up to 200 kW of thermal energy. The thermal output can be adjusted by variation of compressor shaft speed, use of internal recuperation and additionally by variation of the fluid inventory. The latter allows operation of our prototype within a broad part load range down to 25 % of the nominal power at nearly constant efficiencies and output temperatures. Brayton cycle heat pumps can be adapted to a wide range of industrial processes and enable highly efficient thermal energy storage systems to balance grid fluctuations

Wearable technology in healthcare

Despite increasing reliability of data generated by wearable devices, not many institutions in the healthcare sector use wearables for patient care or safety. The benefit of having accurate patient data over a certain period of time is often neglected by the fact that the medical personnel and patients do not fully accept the technological improvement. Another issue is the interoperability between the device itself and the hospital information systems, e.g. data generated may not be further processed due to lacking data standards or interfaces. In order to investigate the acceptance of stakeholders of wearable devices, a survey based on use cases was sent out to medical and administrative staff of Swiss hospitals. Finally, a technical feasibility study was conducted to investigate the technical requirements and challenges for the integration of wearable devices in the hospital IT environment

Transient analysis and control of a Brayton heat pump during start-up

This paper aims to investigate the transient response of the DLR's CoBra prototype, an innovative Brayton-cycle heat pump intended to provide heat above 250 °C and currently under commissioning at the DLR facility in Cottbus, Germany. First, a comprehensive transient thermodynamic model of the system is developed, accounting for heat exchangers and piping thermal inertia. Furthermore, a control logic is presented that ensures safe operation throughout off-design conditions and start-up manoeuvres. In particular, several control parameters are considered to avoid potential operational issues, such as critical temperature gradients, compressor surge, and critical mechanical vibration phenomena due to resonance. The performed simulations aim to reduce start-up time and energy consumed during start-up. Results show that with the help of the described controller, the system can reach design operation via a transient trajectory safely and quickly. Therefore, the capability of the CoBra prototype to flexibly supply high-temperature heat is demonstrated

Hybrid cosmic ray measurements using the IceAct telescopes in coincidence with the IceCube and IceTop detectors

IceAct is a proposed surface array of compact (50 cm diameter) and cost-effective Imaging Air Cherenkov Telescopes installed at the site of the IceCube Neutrino Observatory at the geographic South Pole. Since January 2019, two IceAct telescope demonstrators, featuring 61 silicon photomultiplier (SiPM) pixels have been taking data in the center of the IceTop surface array during the austral winter. We present the first analysis of hybrid cosmic ray events detected by the IceAct imaging air-Cherenkov telescopes in coincidence with the IceCube Neutrino Observatory, including the IceTop surface array and the IceCube in-ice array. By featuring an energy threshold of about 10 TeV and a wide field-of-view, the IceAct telescopes show promising capabilities of improving current cosmic ray composition studies: measuring the Cherenkov light emissions in the atmosphere adds new information about the shower development not accessible with the current detectors, enabling significantly better primary particle type discrimination on a statistical basis. The hybrid measurement also allows for detailed feasibility studies of detector cross-calibration and of cosmic ray veto capabilities for neutrino analyses. We present the performance of the telescopes, the results from the analysis of two years of data, and an outlook of a hybrid simulation for a future telescope array

Tailored implementation of internet-based cognitive behavioural therapy in the multinational context of the ImpleMentAll project: a study protocol for a stepped wedge cluster randomized trial.

BACKGROUND: Internet-based Cognitive Behavioural Therapy (iCBT) is found effective in treating common mental disorders. However, the use of these interventions in routine care is limited. The international ImpleMentAll study is funded by the European Union's Horizon 2020 programme. It is concerned with studying and improving methods for implementing evidence-based iCBT services for common mental disorders in routine mental health care. A digitally accessible implementation toolkit (ItFits-toolkit) will be introduced to mental health care organizations with the aim to facilitate the ongoing implementation of iCBT services within local contexts. This study investigates the effectiveness of the ItFits-toolkit by comparing it to implementation-as-usual activities. METHODS: A stepped wedge cluster randomized controlled trial (SWT) design will be applied. Over a trial period of 30 months, the ItFits-toolkit will be introduced sequentially in twelve routine mental health care organizations in primary and specialist care across nine countries in Europe and Australia. Repeated measures are applied to assess change over time in the outcome variables. The effectiveness of the ItFits-toolkit will be assessed in terms of the degree of normalization of the use of the iCBT services. Several exploratory outcomes including uptake of the iCBT services will be measured to feed the interpretation of the primary outcome. Data will be collected via a centralized data collection system and analysed using generalized linear mixed modelling. A qualitative process evaluation of routine implementation activities and the use of the ItFits-toolkit will be conducted within this study. DISCUSSION: The ImpleMentAll study is a large-scale international research project designed to study the effectiveness of tailored implementation. Using a SWT design that allows to examine change over time, this study will investigate the effect of tailored implementation on the normalization of the use of iCBT services and their uptake. It will provide a better understanding of the process and methods of tailoring implementation strategies. If found effective, the ItFits-toolkit will be made accessible for mental health care service providers, to help them overcome their context-specific implementation challenges. TRIAL REGISTRATION: ClinicalTrials.gov NCT03652883 . Retrospectively registered on 29 August 2018