Data-Driven Predesign Tool for Small-Scale Centrifugal Compressor in Refrigeration

Violette Mounier, Cyril Picard, Jürg Alexander Schiffmann
2018
Article

Résumé

Domestic scale heat pumps and air conditioners are mainly driven by volumetric com-pressors. Yet the use of reduced scale centrifugal compressors is reconsidered due to their high efficiency and power density. The design procedure of centrifugal compressors starts with predesign tools based on the Cordier line. However, the optimality of the obtained predesign, which is the starting point of a complex and iterative process, is not guaranteed, especially for small-scale compressors operating with refrigerants. This paper proposes a data-driven predesign tool tailored for small-scale centrifugal com-pressors used in refrigeration applications. The predesign model is generated using an experimentally validated one-dimensional (1D) code which evaluates the compressor performance as a function of its detailed geometry and operating conditions. Using a symbolic regression tool, a reduced order model that predicts the performance of a given compressor geometry has been built. The proposed predesign model offers an alternative to the existing tools by providing a higher level of detail and flexibility. Particularly, the model includes the effect of the pressure ratio, the blade height ratio, and the shroud to tip radius ratio. The analysis of the centrifugal compressor losses allows identifying the underlying phenomena that shape the new isentropic efficiency contours. Compared to the validated 1D code, the new predesign model yields deviations below 4%on the isen-tropic efficiency, while running 1500 times faster. The new predesign model is, therefore, of significant interest when the compressor is part of an integrated system design process.

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https://infoscience.epfl.ch/record/257764?ln=fr

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Violette Mounier, Cyril Picard, Jürg Alexander Schiffmann
2018
Article

Résumé

Official source

https://infoscience.epfl.ch/record/257764?ln=fr

À propos de ce résultat

Concepts associés (16)

Concepts associés

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Publications associées (4)

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Domestic scale heat pumps and air conditioners are mainly driven by volumetric compressors. Yet the use of reduced scale centrifugal compressors is reconsidered due to their high efficiency and power density. Recent work has demonstrated the technical feasibility of a 20 mm centrifugal compressor on gas lubricated bearings operated with R134a by achieving isentropic efficiencies in excess of 75%. The design procedure of such centrifugal compressor starts by using pre-design tools based on the Cordier line. However, the optimality of the obtained pre-design, which is the starting point of a complex and iterative process, is not guaranteed, especially when small-scale compressors operating with organic fluids are targeted. This paper proposes an updated data-driven pre-design tool tailored for small-scale centrifugal compressors used in refrigeration applications. The pre-design model is generated using an experimentally validated 1D code which evaluates the compressor performance as a function of its detailed geometry and operating conditions. Using a symbolic regression tool, a reduced order model that predicts the performance of a given compressor geometry has been built. The proposed pre-design model offers an alternative to the tools available in literature by providing a higher level of detail and flexibility . Particularly, the model includes the effect of the pressure ratio PR and additional geometrical features such as blade height ratio b4 and the shroud to tip radius ratio r2s for addressing the inlet and exhaust areas. The analysis of the centrifugal compressor losses allows identifying the underlying phenomena that shape the new isentropic efficiency contours. As a consequence, for a specific operating condition, a compressor can have different geometries that yield the same efficiency. Low Ns compressors with high b4 are limited by blade loading and recirculation losses and operate closer to the surge limit. Compressors with low b4 and high Ns are exposed to high tip clearance and skin friction losses. Finally, the design space is limited at high Ns due to choke at the compressor inlet, while high incidence losses occur at low Ns at a constant r2s. Since incidence losses relate to the impeller inlet area, increasing r2s enables to achieve higher Ns, while decreasing r2s enables to explore lower Ns conditions. Compared to the 1D model the new pre-design model yields deviations below 4% on the isentropic efficiency , while running 1500 times faster . The new pre-design model is therefore of significant interest when the compressor is part of an integrated system design process.

2018

Chargement

Modeling and Experimental Investigation of an Oil-Free Microcompressor-Turbine Unit for an Organic Rankine Cycle Driven Heat Pump

Jonathan Demierre, Antonio Rubino, Jürg Alexander Schiffmann

Domestic heating and cooling will more and more have to rely on heat pumps (HPs) in order to support a more rational use of primary energy consumption. The HP market is mainly dominated by electrically driven vapor compression cycles and by thermally driven sorption processes. The drawback of electrically driven vapor compression cycle is their dependence on an electrical grid and the fact that they increase the winter or summer electricity peak demands. Hence, a thermally driven vapor compression cycle would offer substantial advantages and flexibility to the end user for heating and cooling applications. This paper presents the investigation of an oil-free compressor-turbine unit (CTU) used for a thermally driven HP (TDHP) based on the combination of a HP compression cycle and an organic Rankine cycle (ORC). The CTU consists of a radial inflow turbine and a centrifugal compressor of the order of 2 kW each, directly coupled through a shaft supported on gas lubricated bearings. The CTU has been tested at rotor speeds in excess of 200 krpm, reaching compressor and turbine pressure ratios up to 2.8 and 4.4, respectively, and isentropic efficiencies around 70%. Comparisons between the experimental data and predictions of models, that are briefly described here, have been carried out. A sensitivity analysis based on the experimentally validated models shows that tip clearance, for both compressor and turbine, and surface roughness of the compressor are key parameters for further improving performance.

American Society of Mechanical Engineers2015

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

Violette Mounier, Jürg Alexander Schiffmann

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 the HP centrifugal compressor, offering an oil free and high power density solution. The radial compressor and the radial turbine have tip diameters of the order of 20mm and the system has been tested at rotor speeds in excess of 200 krpm with shaft powers up to 2.4 kW, running with R134a. The compressor and the turbine were operated at pressure ratios of up to 2.8 and 4.4, while reaching thermal COP of the order of 1.5 and isentropic compressor and turbine efficiencies in excess of 70%, thus validating the HP-ORC concept based on small-scale turbomachinery. However, performance limitations were encountered due to suboptimal heat exchanger, working fluid and turbomachinery design. This article presents a full thermo-economic optimization of the HP-ORC enabling the identification of the best trade-off Investment Cost/ COP. Several working fluids have then been compared, revealing that a compromise is to be found between best cost/efficiency trade-off, highest performances achievable and technical feasibility. It also showed a thermal COP improvement potential up to 30% compared to the existing experimental system. Finally, the thermo-economic results of the HP-ORC have been compared with other typical TDHPs, such as absorption heat pump.

2017

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2018