Jürg Alexander Schiffmann

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High-aspect-ratio cooling channels with single-sided rib roughness are increasingly used in wall-integrated turbine blade designs; however, generalized thermal–hydraulic scaling frameworks for such asymmetric multi-pass configurations remain limited, particularly for channels combining high aspect ratio, single-wall ribbing, turning regions, and engine-relevant Reynolds numbers. This study develops a validated numerical framework to investigate heat transfer and pressure loss in high-aspect-ratio nominally

We present an algorithm for constructing efficient surrogate frequency-domain models of (nonlinear) parametric dynamical systems in a non-intrusive way. To capture the dependence of the underlying system on frequency and parameters, our proposed approach combines rational approximation and smooth interpolation. In the approximation effort, locally adapted sparse grids are applied to effectively explore the parameter domain even if the number of parameters is modest or high. Adaptivity is also employed to bu

High-speed turbomachinery is commonly designed to achieve high power densities. Limited space for active cooling results in a challenging thermal management. A thermal modeling approach leveraging modern declarative programming capabilities is presented, y ...

Although gas-lubricated herringbone grooved journal bearings (HGJB) are known for high rotordynamic stability thresholds, small clearance to diameter ratios are required for stable rotor operation. Tight clearances not only increase bearing losses but also yield challenging manufacturing and assembly tolerances, which ultimately translate into cost. Traditionally, the grooves of HGJB are of helical nature with constant cross section and pitch. The current paper aims at increasing the clearance to diameter r

Gas lubricated bearings are capable of supporting high speed rotors with satisfactory load capacities. Pressure is one of the constitutional quantities governing the flow field in gas lubricated bearings. Knowledge of the pressure is of principal importanc ...

This study investigates the technical and economic feasibility of replacing throttling valves with smale-scale, oil-free turbomachinery in industrial steam networks. This is done from the perspective of the turbomachine, which has to be integrated into a n ...

Automated design tools are seldom used in industry. Their potential, however, is high, especially in companies mostly active in variant design, where custom tools could help cut down development time in the early stages. The design of geared electro-mechan ...

Foil bearings are strong candidates to support oil -free turbomachinery. Although foil bearings are a widely used technology, models describing their behavior are not validated using the film pressure, which is the fundamental variable of any fluid film be ...

The aggravation of climate change calls for the timely development and implementation of highly efficient, renewable, zero- or negative-emission energy solutions with high technological readiness and feasibility levels. Solid oxide fuel cells (SOFC) consti ...

This paper presents neural network regression models for predicting the nonlinear static and linearized dynamic reaction forces of spiral grooved gas journal bearings. The partial differential equations (PDEs) are sampled, based on a full factorial and ran ...

This paper presents the integration of a novel scroll expander into a combined power and cooling cyclethat can be driven by low grade heat sources such as solar and waste heat. The scroll device used here is based on a co-rotating technology which allows to work without internal lubrication. The mathematical model adopted for the cycle incorporates a simplified semi-empirical model that predicts the performance of the scroll expander. Ammonia-water has been selected as the working fluid because of its natur

Domestic heat pumps have been identified as a key-technology to decrease the energy consumption of the domestic sector, which represents 29% of the world final energy consumption. Space & water heating represent more than two third of the domestic sector e ...

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 ...

A theoretical case study on steam generation has been performed. Different methods of producing steam by vapour compression, direct electrical heating, gas heating, heat pumping, use of waste heat, and a mixture thereof, were theoretically analysed. The fi ...

With a growing energy demand in a carbon-constrained society, fuels cells powered by renewable fuels, and specifically solid waste, are seen as interesting contributors to the energy portfolio. The alternative energy industry needs to reduce costs, enhance ...

The measurement results of various nitrile butadiene rubber (NBR) O-Ring sizes are pre-sented, and reduced-order models are developed in order to predict the stiffness and damping coefficient as a function of O-Ring geometry, Shore hardness, squeeze, and e ...

High-speed bearings and electrical motors are gradually getting available. This is of particular interest for the application of thermal turbomachinery. The availability of high speed bearing and motor components opens the way to new applications for low power, compact, oil-free and high speed radial compressors. This paper describes the basic design of a high speed single stage radial compressor for high pressure ratios and a wide flow range using a vaneless diffuser. The target application is aimed at dom

Heat transfer measurements of flow boiling Carbon Dioxide (CO2) in vertical upward direction have been carried out with a dedicated test facility at the European Organization for Nuclear Research (CERN). The experiments have been conducted in a vertical up ...

Emerging energy-efficient, oil-free radial centrifugal compressors seem promising for small to mid-capacity air conditioning and refrigeration applications. Compressor design must balance trade-offs among impeller diameter, bearing type, and refrigerant se ...

Motivated by the use of aerodynamic bearings lubricated with high-pressure gases in energy conversion cycles, the Reynolds equation is adapted in order to include effects of real-gas and turbulence. Three geometries (Rayleigh-step slider, plain and herring ...

Jürg Alexander Schiffmann

Chattez avec Graph Search

Numerical thermal–hydraulic modeling and generalized roughness-function correlations for high-aspect-ratio single-sided ribbed channels

Plug-and-play adaptive surrogate modeling of parametric nonlinear dynamics in frequency domain

Thermal management for gas lubricated, high-speed turbomachinery

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

An Instrumented High-Speed Rotor With Embedded Telemetry For The Continuous Spatial Pressure Profile Measurement In Gas Lubricated Bearings: A Proof Of Concept

On the Application of Small-Scale Turbines in Industrial Steam Networks

Automated Design Tool for Automotive Control Actuators

Pressure Profile Measurements Within The Gas Film Of Journal Foil Bearings Using An Instrumented Rotor With Telemetry

Readiness evaluation of SOFC-MGT hybrid systems with carbon capture for distributed combined heat and power

Prediction of the reaction forces of spiral-groove gas journal bearings by artificial neural network regression models

Analysis of a Combined Absorption Cycle for Power and Cooling Production Using a Novel Oil-Free Co-Rotating Scroll Expander

Experimental investigation of a two-stage oil-free domestic Air/Water heat pump prototype powered by an oil-free high-speed twin-stage radial compressor rotating on gas bearings

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

Theoretical analysis of steam generation methods - Energy, CO 2 emission, and cost analysis

Techno-Economic Optimization of an Integrated Biomass Waste Gasifier–Solid Oxide Fuel Cell Plant

Data-Driven Model for the Dynamic Characteristics of O-Rings for Gas Bearing Supported Rotors

Theoretical Design of a High-Speed Low Power Radial Turbocompressor

Heat transfer of flow boiling carbon dioxide in vertical upward direction

Small, High-Speed, Oil-Free Radial Turbo-compressors for Cooling Applications: Refrigerant Selection

Real-gas effects on aerodynamic bearings