Jürg Alexander Schiffmann

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To improve the industry benchmark of solid oxide fuel cell (SOFC) systems, we consider anode off-gas recirculation (AOR) using a small-scale fan. Evolutionary algorithms compare different system design alternatives with hot or cold recirculation. The syste ...

A test facility to investigate flow pattern transitions of vertical two-phase flow of CO2 has been built within the scope of the high-luminosity detector upgrades at the European Organization for Nuclear Research (CERN). Adiabatic flow pattern observations ...

Hermetic, small-scale turbo compressors supported on gas-lubricated bearings and driven by high-speed electric motors represent a promising technology to increase the efficiency of domestic heat pumps and air conditioners. Moreover, thanks to the oil-free ...

Waste heat recovery (WHR) is expected to contribute to reducing CO2 emissions from trucks. Organic Rankine cycle (ORC) systems show the highest potential for this application, but still lack efficient small-scale expansion devices, in practice. A novel tur ...

Gas bearings use pressurized gas as a lubricant to support and guide rotating machinery. These bearings have a number of advantages over traditional lubricated bearings, including higher efficiency in a variety of applications and reduced maintenance requi ...

Hybrid absorption heat pumps (Osenbrück cycle and Hybrid wet compression cycle) are known for high temperature lifts, low-pressure ratios and wide capacity control. They are well suited for processes with the occurrence of significant heat sink and heat so ...

Multi-objective optimization is increasingly used in engineering to design new systems and to identify design trade-offs. Yet, design problems often have objective functions and constraints that are expensive and highly non-linear. Combinations of these fe ...

Here, we present a methodology for the generalized quantification of the carbon (C)-formation risk in hydrocarbon mixtures based on the normalized chemical activity. An open-source computational thermodynamics tool is coupled to a solid oxide fuel cell (SOFC) stack model to apply and validate this approach with literature data based on methane-fueled SOFC systems with anode off-gas recirculation. Two- and three-dimensional C-formation risk maps valid for all C-H-O mixtures are proposed for a practical, accu

The proper orthogonal decomposition (POD) is successfully employed in a variety of projection-based methods for parametric model order reduction (pMOR) of large dynamical systems. It extracts the most energetic modes describing the dynamics of a system fro ...

A micro steam turbine with a tip diameter of 15mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kgh-1 and 2, respectively, the turbine yields a power of 34W and a total-to-static isent ...

The blade tip clearance loss was studied experimentally and numerically for a micro radial fan with a tip diameter of 19:2mm. Its relative blade tip clearance, i.e., the clearance dividedby the blade height of 1:82mm, was adjusted with different shims. The ...

Herringbone grooved journal bearings (HGJBs) are widely used in micro-turbocompressor applications due to their high load-carrying capacity, low friction, and oil-free solution. However, the performance of these bearings is sensitive to manufacturing devia ...

The presence of oil in domestic heat pumps is a hindrance, particularly for enhanced surface evaporators and for advanced concepts based on two-stage cycles. Very compact oil-free dynamic compressor directly driven by high speed electric motors and supported on refrigerant vapor bearings represent a promising alternative. This paper presents a design analysis of the first stage prototype with the various tradeoffs between the impeller characteristics to follow the seasonable heat demand, the bearing and rot

In this paper, the influence of tip clearance on the performance of small-scale turbopumps is studied numerically on extensive parameter ranges suitable for organic Rankine cycle applications. A novel and fully parameterized design model is developed and u ...

Herringbone-grooved journal bearings (HGJBs) for high-speed turbo-machinery are often supported on O-rings due to their favorable stiffness and damping characteristics for stability and alignment reasons. They yield limited lifetime at high temperatures, i ...

Pressure is one of the constitutional quantities governing the flow field in gas lubricated bearings. Knowledge of the pressure is of principal importance in the fundamental understanding of such bearings and for the calibration of reduced order models. Th ...

High-speed small-scale turbomachinery for waste heat recovery and vapor compression cycles is typically supported on gas-lubricated bearings operating close to the saturation conditions of the lubricant. Under particular conditions, the gas film might loca ...

This study experimentally validates robust designs for herringbone grooved journal bearings (HGJBs) in micro-turbocompressors, addressing manufacturing deviations that lead to rotor instabilities. Experiments on a Pelton-driven rotor system focused on maxi ...

A hybrid-twin for gas-bearing supported, high-speed turbocompressor is suggested to be an aide to increase the operational reliability and to provide valuable insights to improve its design. The bearing clearances of a few micrometers imply that excessive ...

This work presents an experimental investigation of heat transfer and pressure loss in high–aspect–ratio nominally rectangular channels with a single ribbed wall, representative of wall-integrated turbine blade cooling. In such designs, separate cooling passages lie directly beneath the blade’s pressure and suction surfaces, so only the wall facing the hot gas path requires enhancement. Despite their relevance, systematic data for high–aspect–ratio, single-sided ribbed multi-pass channels at engine-relevant

Jürg Alexander Schiffmann

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Modeling and Designing of a Radial Anode Off-Gas Recirculation Fan for Solid Oxide Fuel Cell Systems

Flow pattern observations and flow pattern map for adiabatic two-phase flow of carbon dioxide in vertical upward and downward direction

Brine-to-water heat pump test system for small-scale oil-free turbo compressors

Experimental Investigation of a Small-Scale Organic Rankine Cycle Turbo-Generator Supported on Gas-Lubricated Bearings

Parametric Reduced Order Model of a Gas Bearings Supported Rotor

Theoretical Study of a Novel Oil-Free Co-Rotating Scroll Compressor Integrated into a Hybrid Absorption Heat Pumps

Realistic Constrained Multi-Objective Optimization Benchmark Problems from Design

Chemical activity-based carbon-deposition risk maps for solid oxide fuel cell systems with off-gas recirculation

A new method to interpolate POD reduced bases-Application to the parametric model order reduction of a gas bearings supported rotor

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

Influence of Large Relative Tip Clearances for a Micro Radial Fan and Design Guidelines for Increased Efficiency

Robust Design of Herringbone Grooved Journal Bearings using Multi-Objective Optimization with Artificial Neural Networks

High-Speed Low Power Radial Turbocompressor For Oil-Free Heatpumps

Analysis and modeling of the tip leakage flow on the performance of small-scale turbopumps for ORC applications

Flexible Support for Gas-Lubricated Bearing Bushings

An Instrumented High-Speed Rotor with Embedded Telemetry for The Continuous Spatial Pressure Profile Measurement in Gas Lubricated Bearings: A Proof of Concept

Thin Gas Film Isothermal Condensation in Aerodynamic Bearings

Robust design optimization of gas-lubricated herringbone grooved journal bearings: Surrogate modeling and experimental validation

Towards a real-time capable hybrid-twin for gas-bearing supported high-speed turbocompressors

Thermal–hydraulic performance and roughness-function modelling in high-aspect-ratio single-sided ribbed multi-pass channels