Jürg Alexander Schiffmann

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Small-scale turbomachines in domestic heat pumps reach high efficiency and provide oil-free solutions, which improve heat-exchanger performance and offer major advantages in the design of advanced thermodynamic cycles. An appropriate turbocompressor for do ...

Coupling a biomass gasifier with a solid oxide fuel cell system through a high-temperature syngas compressor holds great promise to achieve low-emission, small-scale combined heat and power, since it reduces the number of heat exchangers and increases the ...

Currently the herringbone grooved journal bearing (HGJB) has applications in the domain of small, low power energy related applications, where high rotational speeds are required for reaching reasonable efficiency and where standard oil lubricated bearings are limited or even unable to operate over the life time required. Furthermore the presence of oil requires auxiliary control systems reducing the overall system efficiency and reliability. High-speed rotors running in hermetic units processing refrigeran

The organic Rankine cycle (ORC) system is considered a promising technology to exploit thermodynamic potential of waste heat. Small-scale ORC applications, including both vehicular applications and stationary power plants, would greatly benefit from more c ...

This paper investigates the waste heat recovery potential of internal combustion engines, using organic Rankine cycles running on small-scale radial turbomachinery. ORC are promising candidates for low-grade thermal sources and the use of dynamic expanders ...

A micro steam turbine with a tip diameter of 15 mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kg/h and 2, respectively, the turbine yields a power of 34 W and a total-to-static isen ...

Although robustness is an important consideration to guarantee the performance of designs under deviation, systems are often engineered by evaluating their performance exclusively at nominal conditions. Robustness is sometimes evaluated a posteriori throug ...

In a large share of industrial process, heat demand is required as steam. One possibility for steam generation is to evaporate water against condensing refrigerant in a heat pump and compress it with a separate compressor to the desired final pressure. This work aims to demonstrate this process with a 70-kW butane (R600) heat pump and a small- scale centrifugal compressor for steam recompression. The high-temperature heat pump was built with a 6-cylinder reciprocating compressor, flat plate heat exchangers

ORC driven Heat Pumps (HP-ORC) offer a promising technology of thermally driven heat pumps (TDHPs) for domestic applications. Recently, a 40 kW HP-ORC unit based on gas supported turbomachinery has been investigated in which the ORC radial turbine drives t ...

This research introduces an innovative framework to engineering design to tackle the challenges of robustness against manufacturing deviations and holistic optimization simultaneously in a multi-disciplinary, multi-subsystems context. The methodology is ba ...

Supercritical power cycles offer a unique opportunity to utilize low temperature heat sources to reduce waste heat and offer new opportunities for renewable energy sources. Although it is established that supercritical power cycles have high efficiencies at low temperatures, the real gas effects which lead to this have not been comprehensively studied. Here, we study the impact of real thermophysical properties on the relation between efficiency and turbine inlet temperature for Brayton cycles. We introduce

Highly loaded impellers, typically used in turbocharger and gas turbine applications, exhaust an unsteady, transonic flow that is nonuniform across the span and pitch and swirling at angles approaching tangential. With the exception of the flow angle, conf ...

Replacing fossil fuels with alternative energy sources for steam production in industry can help fulfill the targets towards a more sustainable energy landscape. In this work, a high-temperature heat pump and a gas-bearing supported turbocompressor are com ...

The devlopment of domestic heat pump systems is mainly based on the use of volumetric oil lubricated compressors. Following the implementation of economizer based rotary compressors, which represented a major improvement step, one major opportunity to improve both efficiency and heat rate, in particular for high temperature lift heat pumps, is to use two stage cycles. However the reliability of those can be strongly impaired by oil migration, resulting in oil level unbalance when using oil lubricated compre

The design process followed by mechanical engineers is undergoing significant changes with the development of rapid prototyping techniques [1] and of artificial intelligence (A.I.) supported tools [2]. The job market is highly affected by these changes. However, Deininger et al. [3] show that novice designers do only rarely take advantage of the new tools and if they do, their use is unintentional. There is a clear need for mechanical engineers to be trained to use A.I.-based tools. Created in 2016-2017, th

In the endeavor towards distributed power systems, not seasonal-dependent micro-power generation technologies are expected to integrate the energy scenario in the years to come. In this context, the Organic Rankine Cycle (ORC) in the (1e10) KWe scale has c ...

The nonlinear behavior of a rigid rotor supported by herringbone grooved journal gas bearings (HGJBs) was investigated in this study. The two-dimensional narrow groove theory (2D-NGT) was adopted to model the HGJBs. A set of integrated rotor-bearing state ...

Small-scale, oil-free radial compressors on gas lubricated bearings represent a promising alternative to state-of-the-art compressor technology for driving domestic sized heat pumps. The inherent characteristics of turbocompressors manage to fit the heat p ...

The hydraulic design, computational analysis, and experimental investigations of a high-speed small-scale turbopump for mobile waste heat recovery applications based on organic Rankine cycle systems are presented in this paper. Such applications demand hig ...

Jürg Alexander Schiffmann

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Integrated Design and Multi-objective Optimization of a Single Stage Heat-Pump Turbocompressor

A High-Speed, High-Temperature, Micro-Cantilever Steam Turbine for Hot Syngas Compression in Small-Scale Combined Heat and Power

Multi-Objective Optimisation of Herringbone Grooved Gas Bearing Supporting a High Speed Rotor, Taking into account Rarefied Gas and Real Gas Effects

Experimentally validated pre-design maps and performance estimation methods for small-scale turbopumps for organic rankine cycles

Potential of Small-Scale Turbomachinery for Waste Heat Recovery on Automotive Internal Combustion Engines

A High-Speed, High-Temperature Micro-Cantilever Steam Turbine for Hot Syngas Compression in Small-Scale Combined Heat and Power

Theoretical and Experimental Investigation of a 34 Watt Radial-Inflow Steam Turbine with Partial-Admission

Robust design using multiobjective optimisation and artificial neural networks with application to a heat pump radial compressor

Experimental results from a 70 kW steam-generating butane heat pump using off-the-shelf components

ORC Driven Heat Pump Running on Gas Bearings for Domestic Applications: Proof of Concept and Thermo-Economic Improvement Potential

An Integrated Approach to Designing Robust Gas-Bearing Supported Turbocompressors through Surrogate Modeling and Constrained All-At-Once Multi-Objective Optimization

Impact of real gas effects relating efficiency and turbine inlet temperature for supercritical power cycles

The Role of Impeller Outflow Conditions on the Performance of Vaned Diffusers

Efficient steam generation in industry - Combined heat pump cycle with mechanical vapor recompression

Theoretical Design of a High Speed, Oil Free Radial Compressor for Domestic Heat Pumps

Assessing student learning of design and project management skills in a project-based course

Dimensionless correlations and performance maps of scroll expanders for micro-scale Organic Rankine Cycles

Nonlinear study on a rigid rotor supported by herringbone grooved gas bearings: Theory and validation

Turbocompressors for Domestic Heat Pumps – A Critical Review

Design, computational and experimental investigation of a small-scale turbopump for organic Rankine cycle systems