1 – Recirculation fan for a solid oxide fuel cell system
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High-temperature solid oxide fuel cells (SOFC) are able to operate at electrical net efficiencies close to the ones achieved by modern combined cycle power plants. State-of-the-art fuel cell systems can be further improved by recirculating the hot anode off gas, containing hydrogen and steam. In this project we aim to design and demonstrate a new recirculation fan for a SOFC system with an electrical output of 10 kW. Maximum SOFC efficiency is reached with a recirculation rate of 55 to 60%, corresponding to a mass flow of a few kg/h. Hence, a small high-speed fan is necessary. Gas lubricated journal and thrust bearings are considered to ensure a long lifetime, also at elevated recirculation temperatures up to 790° C. An integrated optimization approach of the SOFC and the recirculation fan is used to identify the optimal system layout.The project is sponsored by the Canton de Vaud under the program “100 millions for renewable energy and energy efficiency.” |
Related publication:
P. H. Wagner, Z. Wuillemin, S. Diethelm, J. Van herle, J. Schiffmann, Modeling and Designing of a Radial Anode Off-Gas Recirculation Fan for Solid Oxide Fuel Cell Systems, Journal of Electrochemical Energy Conversion and Storage (ASME), vol. 14(1), p.011005, 2017. doi:10.1115/1.4036401.
2 – Thermal heat pump
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In this project we develop a thermally driven heat pump system for domestic applications. An Organic Rankine Cycle (ORC) drives the vapor compression heat pump cycle such that both condensers share the same temperature and pressure. This tri-thermal system can use a widesrange of heat sources such as solar, biomass or wood pellets and is designed for both heating and cooling applications. The radial single stage heat pump compressor is driven by the radial inflow turbine of the ORC. Both the compressor and the turbine are located on the same gas bearing supported rotor, yielding low mechanical losses, increased lifetime and a very compact and oil-free solution. The research focuses on the mechanical design optimization of the small-scale compressor-turbine-unit with regards to the thermal management, bearings, sealing and global performance, on the optimization of the thermal system including fluid screening and finally on experimental validation.The project is sponsored by the Canton de Vaud under the program “100 millions for renewable energy and energy efficiency”. |
Related publications:
V. Mounier, L. C. Mendoza Toledo and J. A. Schiffmann. Thermo-economic optimization of an ORC driven heat pump based on small scale turbomachinery and comparison with absorption heat pumps, International Journal of Refrigeration, vol. 81, p. 96-110, 2017. doi:10.1016/j.ijrefrig.2017.05.021
Modeling and Experimental Investigation of an Oil-Free Microcompressor-Turbine Unit for an Organic Rankine Cycle Driven Heat Pump, Transactions- ASME Journal of Engineering for Gas Turbines and Power, vol. 137, num. 3, p. 032602, 2015. doi:1115/1.4028391
3 – Small-scale ORC turbo-generator
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Due to more and more stringent vehicle emission regulations, road vehicles and especially heavy-duty vehicles such as long-haul trucks are pushed to reduce their fuel consumption. Such a reduction can be reached by improving engine efficiency and in particular through waste heat recovery (WHR) from the exhaust gases. Organic Rankine cycles (ORC) are promising candidates to harvest such low-grade heat sources while the use of small-scale turbo-expanders allows for system compactness, which is an important requirement for such an application.
This project aims at developing and testing a small-scale ORC turbo-generator, suitable for truck WHR. As turbine design and operating conditions are strongly affected by the choice of working fluid, thermodynamic and aerodynamic aspects must be coupled during the design process, in order to ensure a realistic solution. Moreover, small-scale turbomachinery is inherently associated with high rotational speeds, thus making other design aspects such as the rotor shaft, the bearings, the electrical machine and the power electronics challenging. In order to improve system performance and lifetime, a major design criterion is the absence of petroleum-based lubricant. This constraint drives the use of gas-lubricated bearings, well indicated for low loads and high rotational speeds. Finally, presence of hot vapor in the turbine passage and important heat generation from the electrical machine imposes robust thermal management strategies. |
4 – Compressed air storage
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This project’s focus is energy storage via compressed air. In order to maximize the round-trip efficiency isothermal compression and expansion are sought after. Therefore the 4-stage system is split into two initial volumetric compressors followed by two liquid pistons. Our objective is a reversible volumetric compressor-expander for the first two stages that can be operated safely without oil-lubrication and with significant water injection to approach an isothermal process. The principle of a co-rotating Scroll-machine is being investigated.
The project is sponsored by the Canton de Vaud under the program “100 millions for renewable energy and energy efficiency”. |
Related publication:
Testing and modelling of a novel oil-free co-rotating scroll machine with water injection, Applied Energy, vol. 185, p. 201-213, 2017. doi:10.1016/j.apenergy.2016.10.089
5 – Compact turbocompressor on gas lubricated bearings for fuel cell pressurization
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Ball bearings are not a suitable solution to support high speed rotors due to their limited lifetime and need of lubrication. Gas lubricated bearings offer many advantages like low friction, no wear at speeds above lift-off speed and no need for lubrication. Gas lubricated bearings however require very small clearance ratios to allow stable rotor operation which leads to high manufacturing cost, stringent misalignment tolerances and increased specific windage losses. The first objective of this project is to increase the bearing clearances in order to overcome these disadvantages while maintaining the rotordynamic performance of the bearings. In order to achieve this goal, enhanced groove geometries as well as the effect of bearing bushing support characteristics are studied. The second objective is the study of improved manufacturing procedures with the aim to reduce cost. The combination of the two objectives is expected to yield a Pareto front indicating the optimal compromise between bearing performance and manufacturing cost. |
Related publication:
Enhanced Groove Geometry for Herringbone Grooved Journal Bearings, ASME Journal of Engineering for Gas Turbines and Power, vol. 135, p. 102501, 2013. doi:10.1115/1.4025035
6 – Small-scale turbomachinery design
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Bottleneck for the breakthrough of decentralized power conversion based on tubomachinery is the lack of well understood small-scale turbomachinery equipment. The current project addresses the long standing challenges related to the design of high-speed turbomachinery which are (1) the appropriate design and choice of journal bearing technology, (2) efficient sealing technology, (3) the proper consideration of scaling issues on the aerodynamic turbomachinery design and (4) the efficient use of integrated design methodologies. The main objective is a proven and validated tool dedicated to the integrated design and optimization of small-scale turbomachinery supported on gas-lubricated bearings for decentralized power conversion systems. The SNF Assistant Professor Energy Grant project includes experimental investigations on turbomachinery, bearings and seals to validate the developed models. Dedicated test-rigs are being built and miniature probes are being developed for extending the current bandwidth an sensitivity of currently available systems. |
Related publication:
Integrated Design and Multi-objective Optimization of a Single Stage Heat-Pump Turbocompressor, ASME Journal of Turbomachinery, vol. 137, num. 7, p. 071002-071002-9, 2015. doi:10.1115/1.4029123
7 – Reduced-scale radial compressors for heat pump applications
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In this project we investigate the effect of variable inlet guide vanes and different types of diffusers on the performance of small-scale radial compressors for residential refrigeration applications. Robust design for performance is given a particular emphasis. Further analyses look into the effect of the compressor characteristics on the control of multistage heat pumps for high temperature lifts with various source temperature levels. |
Related publications:
8 – Fundamental Study of Gas Lubricated Bearings
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Gas foil bearings are pushed as strong contenders to support high speed turbomachinery. Nevertheless, the fundamental understanding of the technology is far from complete. The current project is focused on the conclusive validation of foil bearing models using state of the art measurement techniques.
Objectives:
This project is supported by the SNSF – Swiss National Science Foundation – Assistant Professor (AP) Energy Grants |
Related Publications:
K. Shalash, J. Schiffmann, On the manufacturing of compliant foil bearings. Journal of Manufacturing Processes, Volume 25, p. 357–368, 201. doi:10.1016/j.jmapro.2016.12.021
Foil Bearing Design Guidelines for Improved Stability, Journal of Tribology, vol. 135, num. 1, p. 011103, 2013. doi:10.1115/1.4007759
9 – High-pressure aerodynamic grooved bearings
| The use of small-scale high-speed turbomachinery in close-loop energy applications is a topic gaining in industrial interest. The use of grooved aerodynamic bearings lubricated with the process fluid at high pressure is well suited for this field, but the consequences and implications due to the high-pressure lubrication lack a convincing description. The current project aims to consolidate and extend the understanding of gas bearings operating in such conditions.
Objectives:
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Related Publication:
Schiffmann, J., Favrat, D., 2010. The effect of real gas on the properties of Herringbone Grooved Journal Bearings. Tribology International 43, 1602–1614. doi:10.1016/j.triboint.2010.03.006
10 – Integrated and optimal design for complex mechanical systems
| The need for more and more complex and performant systems calls for the development of new design methodologies that take advantage of the power of computers.
The goal of this project is to develop a unified design methodology that helps reduce the design time and allows new products to go faster to market. The approach leverages innovative integrated model generation and optimisation techniques to efficiently explore complex design spaces. |
11 – Rotary seals for reduced-scale turbomachinery
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Leakage has been identified as a major source of secondary losses in reduced-scale high speed turbomachines compared to large-scale machines. This research work focuses mainly on reduction of leakage loss and also to enhance rotordynamic performance in such reduced-scale high-speed turbomachines by using proper non-contacting seals. Damper seals, like pocket and hole pattern, have been identified as the most promising candidates for this application. The goal of this work is to build an experimental test-rig for reduced-scale seals including a validated mathematical seal model to determine leakage and rotordynamic force coefficients for different seals.
This project is supported by the SNSF – Swiss National Science Foundation – Assistant Professor (AP) Energy Grants |