Impeller

Résumé

An impeller or impellor is a driven rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid. Strictly speaking, propellers are a sub-class of impellers where the flow both enters and leaves axially, but in many contexts the term "impeller" is reserved for non-propellor rotors where the flow enters axially and leaves radially, especially when creating suction in a pump or compressor. In pumps An impeller is a rotating component of a centrifugal pump that accelerates fluid outward from the center of rotation, thus transferring energy from the motor that drives the pump to the fluid being pumped. The velocity achieved by the impeller transfers into pressure when the outward movement of the fluid is confined by the pump casing. An impeller is usually a short cylinder with an open inlet (called an eye) to accept incoming fluid, vanes to push the fluid radially, and a s

Source officielle

https://en.wikipedia.org/wiki/Impeller

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The effects of the tip clearance on the performance of small-scale turbopumps for ORC applications; analysis and modeling

Jürg Alexander Schiffmann, Sajjad Zakeralhoseini

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 used to generate a wide range of turbopumps and their fluid domains to carry out three-dimensional computations across the impeller stage. Impellers are investigated at different operating conditions and the accomplished results are analyzed to characterize the performance at design and off-design conditions. The CFD calculations demonstrate that the slip factor is dependent not only on its geometrical parameters as considered by most correlations but also on its operating conditions. The slip factor decreased almost linearly as the flow rate increased. In addition, the tip clearance ratio influences the slip factor and its influence is non-linear. The head rise decreases as the tip clearance ratios increased, however, for radial impellers, the higher head rise was observed for small tip clearance ratios.

Technical University of Munich2021

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This paper proposes a novel approach to predict the machining time of small-scale radial-inflow turbine impellers for organic Rankine cycle power systems based on preliminary design parameters. The time prediction method uses machining databases of different milling tools for the estimation of the cutting parameters, on which basis the flow channel volume and surfaces are discretized for the generation of preliminary milling toolpaths. The parameter selection comprises the material selection, the volume removed, the demanded surface quality and the tool selection governed by the accessibility due to geometrical limitations induced by the blades. The model is verified using computer-aided manufacturing software for two radial-inflow turbines cases: a state-of-the-art turbine using air and a turbine using the working fluid Novec 649 for a heat recovery application. The results highlight the governing role of the tool slenderness ratio on the actual manufacturing time. The relative time distribution among roughing, semi-finishing and finishing operations remain similar when considering the same production chain. The tool roughing strategy holds potential for optimization by contributing to approximately 60 % of the total milling time. Furthermore, the results indicate that the turbine manufacturing time can be improved by up to approximately 44 % when the maximum permissible load limits of the tools are exploited by customized cutting data. The presented machining time model can be applied in future works to predict the manufacturing costs of impellers and to quantify the influence of individual design features on the total cost by performing a sensitivity analysis. Moreover, the design space for optimal designs of small-scale radial-inflow turbines for organic Rankine power applications considering both the manufacturing time and the performance of the expander can be explored.

Technical University of Munich2021

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Impact of large tip clearance ratios on the performance of a centrifugal compressor

Markus Diehl, Jürg Alexander Schiffmann

Ultra-compact and fast spinning turbomachinery is a key technology to increase performance of domestic heating applications and to address decentralization of power and heat as a consequence of the rise of renewable energy sources. Recently, a heat pump using a reduced-scale centrifugal compressor with an impeller diameter of 20 mm supported on gas bearings was tested successfully and higher system performance compared to commonly used positive displacement compressors was achieved. Nonetheless, due to the small feature size as well as manufacturing tolerances, the performance of such compressor systems is deteriorated compared to large-scale systems. The tip gap necessary to ensure a free spinning of the rotor on gas bearings is relatively large compared to industrial compressors. Unfortunately, limited experience about centrifugal compressors running on relative large clearance exists. This paper investigates the impact of tip leakage on the performance of centrifugal compressor systems for relative clearance ratios, ranging from 3 up to 15 %. The tip leakage analysis is conducted numerically on an experimentally validated centrifugal compressor system operating with refrigerant R134a. In order to investigate the behavior of the compressor by altering its clearance ratio, impellers with different blade heights are used to adjust the tip gap. The change in efficiency is investigated and empirical correlations available in literature are assessed. A new method to predict change in efficiency as function of relative clearance ratio is provided, thus extending current correlations to much higher relative clearance ratios.

2019

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