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Im 21. Jahrhundert haben einige Länder als Reaktion auf die Nuklearkatastrophe von Fukushima bereits den Ausstieg aus der Kernkraft beschlossen oder zumindest in Erwägung gezogen. Das Ende der Kohleverstromung ist in einigen Ländern bereits umgesetzt oder wie in Deutschland für 2038 zumindest beschlossen, um den globalen Klimawandel zu verlangsamen. Es stellt sich also die Frage, ob die „Dampfmaschine“, das heißt der Rankine-Kreisprozess noch eine Zukunft hat?

Entgegen dem aktuellen Trend, Abwärme im kleinen Leistungsbereich unter 100 kW(el.) mittels einer ORC-Anlage in Strom umzuwandeln, wird im vorliegenden Beitrag das Konzept eines Mikro-Dampfkraftwerks verfolgt. Nachfolgend wird erläutert, warum die Wahl der Turbine auf eine geschwindigkeitsgestufte zweikränzige Curtis-Turbine gefallen ist und das dafür verwendete 1-D-Turbinendesign-Tool wird kurz vorgestellt. Der parametrisierte Ansatz des Turbinenentwurfs in 3-D-CAD/CFD wird erläutert und schließlich werden das CFD-Strömungsfeld und die Leistungskennfelder der entworfenen Turbine diskutiert.

The article describes the results from the research and development of a cantilever microturbine designed for ORC power plants. The main objective of the paper was to compare different types of rotor seals and their effect on the turbine efficiency and rotor forces. The turbine stage and the numerical models used in the CFD system NUMECA FINE/Turbo are briefly described. The results are compared with the values obtained from measurements and previous simulations. The results show a relatively limited influence of the seal design on the turbine efficiency. The results also show the effect of the seal on the rotor axial force. The article describes the results from the research and development of a cantilever microturbine designed for ORC power plants. The main objective of the paper was to compare different types of rotor seals and their effect on the turbine efficiency and rotor forces. The turbine stage and the numerical models used in the CFD system NUMECA FINE/Turbo are briefly described. The results are compared with the values obtained from measurements and previous simulations. The results show a relatively limited influence of the seal design on the turbine efficiency. The results also show the effect of the seal on the rotor axial force.

Wrist worn mobile sensors have proven to be applicable for various applications, including fitness tracking or gesture recognition. In time- and security-critical application scenarios, the commonly used Radio frequency based communication technologies may pose a bottleneck for further advancements. In this work, we present a simulation environment implemented in Matlab/Simulink that enables the precise simulation of wristbands that are equipped with light emitting diodes, which take over the task of data transfer by means of visible light communication in a fast and secure way.

Fingerprinting-based Visible Light Positioning is a promising candidate to perform large-scale indoor positioning tasks. In fingerprinting, signal characteristics are grouped in a fingerprint map together with the respective locations inside the indoor environment. By comparing live signal measurements with the fingerprint map, the closest match is selected as the current position estimate. However, the fingerprint map has to be generated beforehand in the so-called offline phase, which is the time-consuming process of sampling the environment, in which the positioning task is desired, for signal characteristics. Here, we propose a fingerprint-based positioning approach for which we mitigate the need for the offline phase by taking advantage of the VLC data transmission capabilities of the LED luminaires of the obligatory room lighting. Based on the transmitted data on room and luminaire configurations to the receiving device, the illumination characteristics in the room can be calculated by simplified analytical formalisms, substituting the need for an experimentally measured offline phase. We demonstrate the effectiveness of our approach with the help of ray-tracing simulations and under the assumption that the receiving device is equipped with an angular sectored receiver. The results of the ray-tracing simulations mimic real world measurements with the receiver in the online phase. We show that decimeter level accuracies down to centimeter level accuracies are achievable for such an approach.

By utilizing the technology of Visible Light Sensing in a non Line-of-Sight setup, we present a novel approach for establishing human-system interaction without the necessity for any active sensor or component to be worn by the user. In our proposed system, different wrist postures can be determined by employing a retroreflective foil attached to the wrist of the user in combination with a low-complexity electronic transceiver unit. Our solution approach is verified in two experimental setups and the achieved results depict that our solution cannot only determine the wrist postures with a fine resolution in terms of rotation angle, but that furthermore the rotation direction of the wrist as well as the speed of the rotation movement can be ascertained. In an exemplary real world application, we demonstrate how our system can be used to control the dimming of the room lighting. Moreover, our proposed solution approach combines the obligatory room illumination task of luminaires with a precise sensing functionality and can therefore be easily implemented with low installation effort.

Systems based on visible light sensing can relief some of the anticipated challenges arising from the predicted massive increase in connected Internet of Thing devices. For example, identification and speed determination of mobile objects can be achieved without the necessity to place actively powered devices or sensors on the object itself. Instead, the surfaces of the objects are simply equipped (coded) with sequences of differently colored foils, which affect the respective spectral compositions of reflected light. In this work, we present an innovative approach for classifying differently colored retroreflective foils in varying size configurations on a moving object by utilizing the supervised machine learning algorithm of random forest. For the respective experimental setup, consisting of a single light source (as a transmitter) and a single RGB sensitive photodiode (as a receiver for the reflected light from the coded mobile object), we can show that not only the task of identification, but also the task of determining the speed of the object can be achieved with 98.8 % accuracy. By utilizing a minimal feature set to create the random forest, the proposed approach requires only minimal computational effort for model generation and classification. The therewith-achieved results are directly compared to an algorithm based on the more complex and resource demanding method of Euclidian distances. The satisfying congruence discloses the applicability of the random forest model for such tasks, especially in scenarios with highly limited memory resources and limited available computational performance.

Achieving precise information on the position of a subject without changing the luminaire infrastructure is a big challenge in positioning approaches that rely on visible light positioning. Achieving high positioning accuracy on a centimeter scale is done by implementing complex receiver unit designs or adapting the existing luminaries. In this context, we suggest a visible light positioning based approach that can determine the position of a person in certain areas of a room without the need of lighting infrastructure modifications. With this approach, one can identify the position with the help of the existing luminaires for the obligatory room lighting. The receiver, represented by a RGB sensitive photodiode, is positioned in an optimized way in order to support both the positioning task as well as the comfort of the user. Based on received signal strength measurements in the red, green and blue channels, we achieve the positioning task by a segmentation of the room into different areas corresponding to the respective impinging light and by utilizing machine learning clustering. Our results show the influence of different segmentation strategies and parameters on the number and size of the distinguishable areas inside the room. Then, we demonstrate the achievable accuracy of our solution approach in real world experiments. Our results show that such light-based positioning data can be fused with IMU sensor data for recognizing human activity.

Experimentally determined efficiency characteristics of two micro turbines are discussed in this paper. One turbine (15 kW) is working with cyclopentane, the other turbine (12 kW) expands hexamethyldisiloxane (MM). The two turbines are designed and built in accordance to the concept of a micro-turbine-generator-construction-kit (MTG-c-kit) for small-scale Organic Rankine Cycle (ORC) waste heat recovery. The motivation for this MTG-c-kit and its architecture will be briefly introduced. Both single stage impulse turbines show a high design point total-to-static isentropic efficiency: the 15 kW cyclopentane turbine achieves 65.0%, the 12 kW hexamethylidisiloxane turbine achieves even 73.4%. Furthermore, the discussed off-design characteristics of the turbines prove that their operating behavior is very advantageous for small waste heat recovery plants - the turbine efficiency keeps a high level over a wide range of pressure ratio and rotational speed.

Článek popisuje poznatky z výzkumu a vývoje radiální mikroturbíny navržené pro práci v ORC elektrárnách. Stručně je popsán stupeň experimentální turbíny a použité numerické modely. První část se zabývá porovnáním naměřených a spočtených výsledků. Druhá část se zabývá vlivem geometrie výstupní části na pracovní parametry turbíny. Výsledky jsou významné pro další studie ve výzkumném a vývojovém procesu. The article deals with a description of results from research and development of the cantilever micro-turbine designed for the ORC power plants. The experimental turbine stage and used numerical models are briefly described. In the first part the comparison of measured and CFD results is presented. The second part deals with an investigation of the outlet geometry influence on the turbine working parameters. The results are relevant for next studies in the research and development process.

Identification and sensing are two of the main tasks a wireless sensor node has to perform in an Internet of Things (IoT) environment. Placing active powered nodes on objects is the most usual approach for the fulfillment of these functions. With the expected massive increase of connected things, there are several issues on the horizon that hamper the further deployment of this approach in an energy efficient, sustainable way, like the usage of environmentally hazardous batteries or accumulators, as well as the required electrical energy for their operation. In this work, we propose a novel approach for performing the tasks of identification and sensing, applying visible light sensing (VLS) based on light emitting diode (LED) illumination and utilizing retroreflective foils mounted on a moving object. This low cost hardware is combined with a self-developed, low complex software algorithm with minimal training effort. Our results show that successful identification and sensing of the speed of a moving object can be achieved with a correct estimation rate of 99.92%. The used foils are commercially available and pose no threat to the environment and there is no need for active sensors on the moving object and no requirement of wireless radio frequency communication. All of this is achievable whilst undisturbed illumination is still provided.

Absorption power cycle (APC) using water-lithium bromide (LiBr) as a working fluid is a novel concept especially suitable for micro scale low temperature distributed power systems. Theoretical investigations provide various benefits in comparison to alternatives such as organic Rankine cycles, but technical design poses many challenges as well. Regardless of similarities with LiBr absorption chillers, no LiBr APC has been to authors’ knowledge experimentally operated. This paper focuses on an experimental development of a proof-of-concept APC operating with LiBr solution. The first part contains an introduction of the experimental system built, the first tests and experimental results of the cycle. The main part of this work focuses specifically on the expander design and performance. After discussing turbine considerations, axial steam micro turboexpander with plastic 3D printed components (rotor and stator) with design power output of approx. 300 W is described. Experimental performance is presented and compared to the design point.

This work introduces a modular experimental micro turboexpander system designed to perform air turbine tests of a radial impulse cantilever turbine. The system has high modularity and is intended primarily to test flow-path components which are manufactured by 3D printing and rapid prototyping. System design from the fluid dynamic viewpoint is based on a previously described tool proven and validated during the design of micro turboexpanders in range of mainly dozens of kW. In order to achieve maximal simplicity, the system uses a converted aeromodelling motor as a permanent magnet generator and housing for bearings. Overall parameters are obtained from electrical performance and known generator’s characteristics. The mechanical design then takes into account request of simplicity, modularity and properties of materials in additive manufacturing, especially plastics. First experimental tests show a comparison between different manufacturing technologies and resulting flow components surface roughness and the impact of pressure ratio on the isentropic efficiency.

The spectral composition of light has a significant influence on human wellbeing, emotion and health. Natural sunlight is often considered as the ideal light source in this regard. Therefore, artificial lighting solutions that mimic natural sunlight are a central research topic in the lighting industry. Another global trend is the monitoring and evaluation of the vital parameters of human beings to improve their health status and their personal lifestyle. Here, we present VitaLight, a laboratory sample for a smart lighting system that aims to interconnect these global trends and consists of VitaWatch, a wristband with functionally integrated sensors that is comfortable to wear on the body, and VitaLUMI, a lighting unit with access to the internet.

Recently, indoor activity monitoring of human beings has gained more and more relevance. In particular, the determination of the spatial and temporal context of a user is of utter importance in many applications like monitoring or safety. In this paper, we present a framework that can identify what, where and how long a user is performing a certain activity by the utilization of a low cost and low complex system. Our system only comprises of a single inertial measurement unit and a single RGB sensitive photodiode, with no prerequisite for infrastructural modifications. By using independent decision trees, also the training effort can be kept minimal. Additionally, we verify experimentally the optimal set of features to be used for the framework. Overall, the achieved results are above 90 % in correct determinations of the room the user is in, the activity the user is performing and in which direction the activity is undertaken.

We present an approach to enable 3D Visible Light Positioning (VLP) utilizing the fingerprinting method combined with the approach of track analysis. Especially in rooms with a highly symmetric arrangement of the luminaires, fingerprinting suffers from high ambiguity of the received signals. We demonstrate an approach to overcome this ambiguity by expanding fingerprinting by track analysis in 3D VLP based on angle diverse receivers. Furthermore, we give a more detailed insight on the impact of the number and the kind of the segmentations of the related optical elements for the receivers and their effect on the performance of the designed algorithm. We demonstrate that by such an approach the success rate for correct 3D position estimation can be enhanced between 29 % and 64 % in dependence of the respective angular segmentation of the receiver.

For a long time, the sole function of a luminaire was to illuminate its surrounding. Nowadays, with the rise of light-emitting diode (LED) based luminaires also functionalities beyond illumination become more and more of relevance. Recent attempts in this regard focus on communication, localization and, most recently, also on sensing on the base of the light that is emitted from the luminaire. Recently, we demonstrated a simple approach in regard to visible light sensing (VLS), which allows us to identify and to distinguish between different surface colors of an object. The effectiveness of the approach was demonstrated using a cube having different surface colors as an object together with an LED and an RGB photodiode as emitter and receiver. Still, for further improvements, it is of relevance to get a better insight into the coherences of illuminance and distance values on the accuracy of correct color determinations, which again lays the basis for a tailored design of the (electronic) VLS system.

In this paper, we discuss a system-level tool based on Simulink/Matlab, Simscape, and Stateflow that allows us to simulate the received power of light reflected from surfaces in visible light sensing environments. Simulink and Stateflow are used in parallel to consider both continuous and instantaneous changes, while block parameters of physical modeling components are designed in Simscape, which consider data from manufacturer datasheets and/or measurements. With the help of this tool, one can evaluate the power of light, which is emitted from a light-emitting diode (LED), reflected at a surface and finally impinges on a photodiode, which acts as a receiver. This power depends on a variety of parameters, such as the spectral power distribution of the light source, the illuminance level at the reflective surface, the reflectivity properties of the reflective surface and the distances between LED, reflective surface and photodiode. Furthermore, we use differently colored surfaces, such as golden, reddish, and silvery surfaces and study their impact on the output voltage of the photodiode in different distances between the LED and the photodiode. In the end, we analyze and compare the results of the simulation with experimentally determined ones to demonstrate the applicability of the approach.

We present a novel approach to perform passive visible light sensing of retroreflective foils mounted on a moving object by utilizing low-cost hardware combined with a self-developed, low complex software algorithm with minimal training effort for successful classification. Therewith, we show the feasibility of utilizing the visible light spectrum not only for illumination, but also to perform sensing tasks, which consequently will lead to less energy consumption, no need for active sensors on the moving object, and finally no necessity of wireless radio frequency communication between the object and the processing device.

Development of micro ORC systems with 1-15 kW power output for micro-cogeneration and waste heat recovery at the Czech Technical University in Prague, University Centre for Energy Efficient Buildings (CTU UCEEB) has over ten years of history with many successes. These include 6 different ORC units, all with in-house designed rotary vane expanders (RVE) of many versions throughout this development. Among main advantages of the RVE belong relatively simple and robust design at low cost even at very small series of single-unit production and all that with acceptable efficiency. The ORC units operate with hexamethyldisiloxane (MM) working fluid at high pressure ratios and expansion ratios and the isentropic efficiency of RVE has a limit at these conditions around 60%, often however only at values around 50%. While this might be enough on a cost side for commercialization of this technology, in pursuit of higher efficiency solutions, different expander technology needs to be selected. A turbo-expander is a logical choice with prospect of higher efficiency. At the same time, a literature review has found a lack of reported detailed experimental data for micro (5-50 kW) turbo-expanders, possibly hindering global development towards economically feasible solutions. A project named Dexpand, “Optimised expanders for small-scale distributed energy systems” aims at these issues by objectives in designing, optimizing, manufacturing and testing several ORC expanders with MM and isobutane and their subsequent performance mapping and comparison. One major task is a design of a turboexpander for a 120 kWth biomass fired microcogeneration ORC unit currently operated at the CTU UCEEB. An axial impulse single stage turboexpander was selected as a suitable choice, providing a prospect of a decent efficiency at technically manageable rotational speed and size. This paper provides a detail of currently performed design activities, starting from boundary conditions specification, over development and optimization of a 1D model, preliminary 2D CFD calculations and finishing in a state of a robust and detailed 3D CFD model with a real gas model. Note that the working fluid, high molar mass organic vapour, is highly non-ideal in its behaviour and the flow conditions with pressure design ratio around 13 is highly supersonic (nozzle outlet isentropic Mach number exceeds 2). The current results based on 3D CFD indicate a prospect of an isentropic efficiency 71% at mechanical power output of 11 kW. Lastly, ongoing and future work is outlined, which includes aerodynamic optimization based on the developed 3D CFD model and construction design of the entire turbine assembly.

In order to meet the targets set out in the Paris climate agreement of 2015, the energy sector needs to be restructured. In Germany for example the goal is to move out of both nuclear and coal-fired power. In order to fulfil more demanding energy requests alternative sources of energy must be found and made available. One component is the usage of Waste Heat Recovery. This paper deals with the evaluation simulation of an Elektra turbine, which concept is a velocity compounded radial re-entry single wheel turbine. Based on the first turbine design, multiple simulations were carried out in order to maximize the efficiency. With these simulations, optimization opportunities are described and identified. The paper concludes with a comparison of the results achieved by numerical simulation and on the experimental test bench. The main focus for this paper is to analyze the actual flow phenomena to identify possibilities for further improvements. All simulations were calculated with the commercial software FINETM/TURBO 15.1.

Electricity generation from waste heat by means of Organic Rankine Cycle is a promising method to increase the efficiency of industrial processes. However, due to special boundary conditions, such systems have to be robust, efficient in full load as well as in part load and scalable down to the power range of less than 15 kW. This study presents experimental results on the behaviour of two small-scale turbines, an axial impulse turbine and a radial cantilever turbine with a maximum power of about 12 kW. The turbine characteristics (isentropic efficiency and swallowing capacity) are given with respect to pressure ratio (ranging from 12 to 24) and rotational speed (ranging from 18,000 to 30,000 rotations per minute). For the axial turbine, a maximum isentropic efficiency of 73.4% has been reached in the ORC test bed. The maximum isentropic efficiency of the cantilever turbine is even higher and reaches 76.8%. The values are compared to volumetric expanders and it is shown that micro-turbines can compete even in the power range addressed in this study. As the turbine characteristics are given for full load and part load conditions, they can be implemented in simulation tools to allow for a more realistic calculation of ORCs with fluctuating heat sources.

After the successful penetration of light-emitting diodes (LEDs) into the lighting market in the past, nowadays functionalities beyond illumination become more and more of relevance. Recent attempts in this regard focus on communication, localization and most recently also on sensing with light. In this paper, we demonstrate a simple and costeffective approach to identify different surface colors exemplarily shown on a differently colored cube as a passive object and an LED and an RGB sensitive photodiode as emitter and receiver in a visible light sensing setup. We introduce an algorithm, which after successive characterization, measurement and decision-making steps allows the determination of the individual surface colors by an RGB photodiode with high accuracy. We also present a simple correction procedure, which allows maintaining the accuracy in color identification without the need to repeat the timeconsuming characterization step for any change in the lighting conditions. This approach could become part of future visible light communication, positioning and sensing networks, which, besides exchanging information, also detect incidents in their surroundings.

Ray-tracing based channel modeling is a powerful tool for the determination of the channel characteristics of VLC settings. In order to overcome the huge computational effort that is necessary in this regard, new strategies for less time-consuming ray-tracing based channel models are essential. Here we introduce a channel model that is based on optical simulations using non-sequential ray-tracing in combination with selfdeveloped algorithms in MATLAB. In addition, we discuss an approach, which allows for a time-effective determination of the dependence of the receiver position on the VLC characteristics along the diagonal of the floor of a room. Raytracing information of each ray impinging on a diagonal stripe (with a width of $\sim1.41$ cm) is exported to MATLAB for further analysis. By doing so, 26 different receiver positions along the diagonal axis of a room can be investigated using only one raytracing simulation run instead of repeating ray-tracing simulations for each of the 26 receiver positions. The error made by this simulation approach turns out to be negligible because of the small ratio between the area or the receiver stripe and the area of the whole floor.

The paper deals with the CFD simulation and investigation of an axial Micro-ORC-Turbine, running with the working fluid hexamethyldisiloxane (MM). The CFD results are compared to the experimental results of the turbine, which were determined at the Center of Energy Technology at the University of Bayreuth. The simulation software Fine/Turbo by NUMECA was used for the meshing and simulation of the turbine. After the mesh studys and optimization of the geometry grid have been carried out, different pressure ratios and rotational speeds have been simulated. The simulated efficiency maps were compared to the experimentally determined efficiency maps. The simulated efficiency characteristics show principally a very similar turbine operating behavior to the measured ones. However, the simulated efficiencies are about 2 to 3 percentage points higher than the measured data. Through the detailed analysis of the blade-to-blade flow fields, it was possible to plausibly trace the integral course of the efficiency curves. Thus, CFD turbine flow simulation proved to be a valuable tool to predict the efficiency characteristics of a Micro-ORC-Turbine.

Due to the various ORC applications, it is not expedient to design and build one standard turbogenerator. Therefore, authors developed a flexible “micro-turbine-generator-construction-kit (MTG-c-kit)” by means of which a customized turbogenerator can be made for any required power output between 1 and 200 kW, for a wide range of working fluids and boundary conditions – quickly, cost effectively and with high expander efficiency. The architecture and main features of this kit are briefly introduced. However, more focus is put on the developed 1D turbine design tool. It allows to quickly design and optimize a single stage turbine for any fluid and boundary conditions. The implemented models are presented on two specific design examples - an axial impulse and a radial inflow cantilever turbine. Also, the experimental results of the two micro turbines designed and built according to this approach, are presented and discussed. Focusing to further accelerate and cheapen the customized micro-turbogenerators for low temperature applications, we provide an outlook of possibilities of additive manufacturing methods like 3D printing of turbine nozzles and rotors. These new possibilities provide potential to improve the competiveness of small-scale ORC. A simple air turbine design with plastic and metal components has been manufactured and tested.

In the paper the behaviour of the five-stage experimental steam turbine 10 MW is described during the expansion transition from superheated steam to wet steam as well as the influence of wet steam on the flow path efficiency. The influence of wet steam occurrence on one to four last stages is given by setting the inlet steam parameters. The wetness of steam behind the last stage is calculated using two methods, first by enthalpy drop with the output measured by water brake and second by an optical probe. The results of both methods are compared. The impact of steam wetness increasing on a decrease in turbine efficiency is observed. In the paper the influence of steam wetness on the individual stage efficiency is also described and wetness loss coefficient is determined. Using the optical probe, assessment of poly-disperse structure of fine droplets is carried out, which is presented here by Sauter mean diameter. A pneumatic probe is used to define the distribution of velocities and pressures along the blade length after the last stage.

This paper describes an experimental study of the three-dimensional flow within two highly loaded turbine cascades subjected to the same overall load but different load distributions. Data were obtained using pneumatic probes, pressure tappings and a surface flow visualization technique. It is found that the general nature of the flow is similar for both cascades. In the exit plane the cascades show different spanwise loss distributions. However, the averaged secondary loss is quite similar in this plane. Examining the measurements further downstream and also by comparing the calculated mixed-out values it becomes clear that a higher magnitude of secondary loss is generated by the front-loaded cascade.Copyright © 1993 by ASME