Grzegorz Żywica

The influence of selected design and operating parameters onthe dynamics of the steam micro-turbine

Abstract The topic of the article is the analysis of the influence of selected design parameters and operating conditions on the radial steam micro-turbine, which was adapted to operate with low-boiling agent in the Organic Rankine Cycle (ORC). In the following parts of this article the results of the thermal load analysis, the residual unbalance and the stiffness of bearing supports are discussed. Advanced computational methods and numerical models have been used. Computational analysis showed that the steam micro-turbine is characterized by very good dynamic properties and is resistant to extreme operating conditions. The prototype of micro-turbine has passed a series of test calculations. It has been found that it can be subjected to experimental research in the micro combined heat and power system.

The Experimental Investigation of the Biomass-Fired ORC System with a Radial Microturbine

The paper presents the results of experimental investigation of the ORC system with a droplet separator (which was used to improve the quality of working medium vapour), a radial microturbine and a multi-fuel boiler. The research aimed at verifying the correctness of prototype microturbine performance in the ORC installation, equipped with a heat source in the form of the multi-fuel boiler. During these tests, a detailed assessment of the functioning of the microturbine and the boiler has been devoted more attention. The paper contains the characteristics of the heat exchangers installation that were obtained for the ORC system variant using a regenerative cycle. The multi-fuel boiler was fired with biomass (wood pellets). Two series of measurements were conducted for various flow rates and several selected temperatures of the working medium, glycol solution and thermal oil. On the basis of research carried out on the ORC with a radial microturbine, one can say that, physicochemical parameters of the HFE7100 medium obtained during the first measuring series, were as follows: temperature at the microturbine inlet 158.9 °C, pressure at the microturbine inlet 9.66 bar, flow rate 178.9 g/s at the microturbine discharge pressure of 1.75 bar. The second series of measurements gave the following results: temperature at the microturbine inlet 163.2 °C, pressure at the microturbine inlet 9.86 bar, flow rate 179.2 g/s at the microturbine discharge pressure of 1.88 bar. The maximum electrical power generated with the use of radial microturbine working in the regenerative ORC system reached about 1150 We.

Experimental investigation of the ORC system in acogenerative domestic power plant with a scrollexpanders

Abstract The paper presents the results of experimental investigations of the ORC system with two scroll expanders which have been used as a source of electricity. Theworking fluidwas HFE7100 – a newly engineered fluid with a unique heat transfer and favourable environmental properties. In the ORC system three heat exchangers were used (evaporator, regenerator, condenser) and before expanders the droplet separator was installed. As a source of heat an innovative biomass boiler was used. Studies have been carried out for the expanders worked in series and in parallel. The paper presents the thermal and fluidflow properties of the ORC installation for the selected flow rates and different temperatures of the working medium. The characteristics of output electrical power, operating speed and vibrations for scroll expanders were also presented.

Numerical Model of the High Speed Rotors Supported on Variable Geometry Bearings

The reported investigations aim at developing the theoretical model of a bearing characterized by variable geometry. The method used for calculating the non-linear response to an arbitrary excitation takes into account factors characteristic of the variable bearing geometry, including friction in the supports. The article presents part of the study referring to numerical analyses oriented towards developing the model of a high-speed rotor supported on bump-foil or tilting pad bearings.

The Sensitivity Analysis of the Method for Identification of Bearing Dynamic Coefficients

This article presents the sensitivity analysis of the method for determination of mass, damping and stiffness coefficients using the impulse excitation technique for a rotor-bearing system. Such an experimental approach is an adequate tool for the estimation of 24 dynamic coefficients, that is 4 damping coefficients, 4 mass coefficients and 4 stiffness coefficients for each bearing. As yet, the literature is exclusive of any researches into the sensitivity of this experimental method itself. However, the influence of several parameters (e.g. supply pressure, bearing geometry, etc.) on the calculation results concerning bearing dynamic coefficients had already been examined in detail. The preparation of the numerical model of the rotor made it possible to assess how influential are the input parameters—such as position and angle of an excitation force or movements of the sensor heads used to measure the displacements of bearing journals—to the results. The potential impact of changing parameters, such as stiffness of rotor material, its unbalance or its geometry, on the values of calculated stiffness, damping and mass coefficients in tested rotor-bearing system was also verified. The paper presents the calculation results of dynamic coefficients for the bearings along with their relative errors. It was shown how the calculated values change according to the different input parameters. The excitation signals and the corresponding system responses were also provided. Moreover, the article contains information on how to enhance the accuracy of calculations.

The Experimental Determination of Bearings Dynamic Coefficients in a Wide Range of Rotational Speeds, Taking into Account the Resonance and Hydrodynamic Instability

Methods for the experimental determination of dynamic coefficients are commonly used for the analysis of various types of bearings, including hydrodynamic, aerodynamic and foil bearings. There are currently several algorithms that allow estimating bearing dynamic coefficients. Such algorithms usually use various excitation techniques applied to rotor–bearings systems. So far only a small number of scientific publications show how calculated dynamic coefficients of bearings change as speed rises. In the literature, there are no computation results that demonstrate changes in these coefficients either in a broad range of speeds (that would cover resonant speeds) or at speeds at which a phenomenon of hydrodynamic instability can be observed. This article fills the literature gap in question. For calculation purposes, the impulse response method based on an in-house algorithm (with a linear approximation using the least squares method) was applied. On its basis, the stiffness, damping and mass coefficients of a rotor–bearings system were calculated. It turns out that some of the obtained values of damping coefficients are negative at the resonant speed. Moreover, if the values are calculated at a speed at which the hydrodynamic instability phenomenon is present they are accompanied by considerably higher standard deviations. On the basis of our computation results and the literature review, capabilities and limitations of the method used for the experimental identification of dynamic coefficients of hydrodynamic bearings were discussed.

The use of modern plastics for the construction of high speed fluid-flow machinery

* Dr inż. Grzegorz Żywica (gzywica@imp.gda.pl), dr inż. Tomasz Z. Kaczmarczyk (tkaczmarczyk@imp.gda.pl), dr inż. Eugeniusz Ihnatowicz (gieihn@imp.gda.pl) – Instytut Maszyn Przepływowych Polskiej Akademii Nauk Omówiono zagadnienia związane z doborem tworzyw sztucznych na wybrane elementy wysokoobrotowych maszyn przepływowych. Oprócz kryteriów stosowanych przy doborze materiału przedstawiono przykład analizy wytrzymałościowej tarczy wirnikowej z tworzywa sztucznego. Celem tych prac było zastąpienie powszechnie stosowanych stopów metali nowoczesnymi tworzywami sztucznymi, co może się przełożyć na skrócenie czasu produkcji i obniżenie kosztów. SŁOWA KLUCZOWE: budowa maszyn, tworzywa sztuczne, polimery wysokotemperaturowe, maszyny przepływowe, mikroturbiny

Analysis of the Rotor Supported by Gas Foil Bearings Considering the Assembly Preload and Hardening Effect

This article discusses a new method for modelling elastic deformations of a foil bearing’s structure, taking into account key phenomena influencing its characteristics. Special attention was paid to the assembly preload, which has an impact on the stiffness of the supporting system and thus also on the static and dynamic properties of the rotor. There has been proposed the method which allows for the inclusion of a selected preload into the bearing model. A new FEM model of the foil bearing’s structure has been described. This model was coupled with an in-house developed flow model of the bearing and the entire rotating system. Computations were made for several assembly preload values, taking into account changes in the bearing structure stiffness as the load increases. The changes in stiffness associated with the load changes were due to the nonlinear geometry of the foils, and also due to the contact phenomena, including friction between components. The applied calculation algorithm allowed to take into account all these phenomena. The results obtained using the developed model confirm the very high influence of the foil bearing’s pre-clamp and the progressive stiffness on the properties of the rotating system. Numerical models of this type can pave the way for a further development of foil bearings and for their wider use in modern high-speed fluid-flow machines.

Selection of the Bearing System for a 1 kW ORC Microturbine

The article describes an analysis of various bearing systems for the rotor of an ORC turbine with an electric power of 1 kW. The nominal rotational speed of the newly designed single-stage axial-flow turbine is 100,000 rpm. The turbine is supplied with a low-boiling medium’s vapor and this medium is not compatible with all typical materials used for constructing power turbines. Additionally, the turbine must be an oil-free machine. In one of the design variants, the turbine rotor disk is to be made of plastic and the temperature of the working medium directed to the vanes will be approx. 150°C (at a pressure of 10 bar). Three different bearing systems were considered: 1. bearings lubricated with a low-boiling medium’s liquid; 2. gas bearings lubricated with a low-boiling medium’s vapor; 3. rolling bearings. After initial analysis, it was found that hydrodynamic bearings lubricated with a low-boiling medium did not work properly in this case and it was decided to conduct a detailed analysis of the second and third type of bearings. The two bearing systems are associated with changes in the geometry of the rotor, which in turn strongly affect the dynamic performance of the entire rotating system. The dynamic analysis of the rotor is the subject of the conducted research and constitutes part of the bearing selection process. This article presents the process of selecting and optimizing the bearing system for the rotor of a 1 kW turbine.

Analysis of Thermal Damage in the High-Speed Foil Bearing

The article discusses experimental research and simulation testing on prototypical foil bearings. All experimental tests were conducted on a special test rig which makes it possible to operate in various conditions and within a wide range of speeds. As a result of the study, it turned out that adverse operating conditions caused almost instant bearing damage, accompanied by a significant rise in temperature. The main factors affecting the durability of foil bearings were material covering mating surfaces, bearing geometry, way of assembling the bearing, rotational speed and load. To better understand the physical phenomena occurring in foil bearings, a numerical model has been developed which allowed carrying out thermal analyses. The analysis of heat flow in the bearings structure showed that, because of the system geometry, significant problems with proper removal of large amounts of heat continued to be experienced, which may have led to an accelerated rate of fatigue damage and shorter bearing life. This phenomenon can occur in bearings operating under tough conditions (e.g. at low speeds or under heavy loads). The research showed that the development of a new foil bearing is a very difficult task and requires many aspects to be taken into account, including the aspects directly related to the operation of the bearing itself, as well as those related to the rotors operation and characteristics of the machine.