Vibroacoustic diagnostics of a radial microturbine and a scroll expander operating in the organic Rankine cycle installation

The article presents the results of vibroacoustic research on a prototypical 4-stage radial microturbine and a scroll expander operating in the organic Rankine cycle with the low-boiling fluid HFE7100. The high-speed microturbogenerator had the electrical capacity of 3 kWe at the nominal speed of 24000 rpm. The low-speed expander with a capacity of 1 kWe and a nominal speed of 3600 rpm was made by Air Squared. The frequency characteristics and overall vibration level (vibration velocity Vrms) measurements were conducted for both the microturbine and the expander, depending on the rotational speed and on the power consumption of electrical energy receivers. The level of noise emitted by the microturbine and expander was also determined. The research was carried out for various electrical loads of the expansion devices generators running in the ORC system. The devices were tested in the following electric power ranges: from 550 We to 1150 We (scroll expander) and from 800 We to 1800 We (radial microturbine). Based on the obtained results, dynamic state assessment of the tested machines was performed and their noise and vibration levels were analysed

Investigation of dynamic properties of the microturbine with a maximum rotational speed of 120 krpm – predictions and experimental tests

Advances in the development of analysis and design methods for fluid-flow machines have enabled both their multi-criteria optimisation and miniaturisation. To decrease the size of such a machine whilst, at the same time, maintaining its output power level, the rotor’s rotational speed needs to be increased. It is the reason for serious difficulties with respect to the rotor dynamics and the selection of a bearing system. This article discusses the simulation analysis and experimental research carried out on a prototypical microturbine, designed for use in a domestic ORC (organic Rankine cycle) cogeneration system. During the design process, the basic assumption was to develop a turbomachine, whose dimensions would have been as small as possible and whose output electric power would have been about 1 kilowatt. A supersonic impulse turbine, with a nominal rotational speed of 100,000 rpm, was used in order to obtain high flow efficiency. The maximum speed of the rotor was determined at a level of 120,000 rpm. The article presents the results of analyses made at the design stage and preliminary results of the experimental research. The numerical simulations covered the bearing system optimisation and the rotor dynamics analysis. Next, based on the outcomes of these analyses, a decision was made to use non-conventional gas bearings which are fed by the low-boiling medium’s vapour that comes from the ORC system. Within the framework of the experimental research, the dynamic behaviour of the turbogenerator was examined in terms of the rotational speed and produced energy. The performed measurements are proof of very good dynamic properties of the tested machine and after the research was over it was concluded that there were absolutely no signs of wear of the turbogenerator’s subassemblies

Investigation of dynamic properties of the microturbine with a maximum rotational speed of 120 krpm – predictions and experimental tests

Advances in the development of analysis and design methods for fluid-flow machines have enabled both their multi-criteria optimisation and miniaturisation. To decrease the size of such a machine whilst, at the same time, maintaining its output power level, the rotor’s rotational speed needs to be increased. It is the reason for serious difficulties with respect to the rotor dynamics and the selection of a bearing system. This article discusses the simulation analysis and experimental research carried out on a prototypical microturbine, designed for use in a domestic ORC (organic Rankine cycle) cogeneration system. During the design process, the basic assumption was to develop a turbomachine, whose dimensions would have been as small as possible and whose output electric power would have been about 1 kilowatt. A supersonic impulse turbine, with a nominal rotational speed of 100,000 rpm, was used in order to obtain high flow efficiency. The maximum speed of the rotor was determined at a level of 120,000 rpm. The article presents the results of analyses made at the design stage and preliminary results of the experimental research. The numerical simulations covered the bearing system optimisation and the rotor dynamics analysis. Next, based on the outcomes of these analyses, a decision was made to use non-conventional gas bearings which are fed by the low-boiling medium’s vapour that comes from the ORC system. Within the framework of the experimental research, the dynamic behaviour of the turbogenerator was examined in terms of the rotational speed and produced energy. The performed measurements are proof of very good dynamic properties of the tested machine and after the research was over it was concluded that there were absolutely no signs of wear of the turbogenerator’s subassemblies

Pool boiling of water-Al2O3 and water-Cu nanofluids on horizontal smooth tubes

Experimental investigation of heat transfer during pool boiling of two nanofluids, i.e., water-Al2O3 and water-Cu has been carried out. Nanoparticles were tested at the concentration of 0.01%, 0.1%, and 1% by weight. The horizontal smooth copper and stainless steel tubes having 10 mm OD and 0.6 mm wall thickness formed test heater. The experiments have been performed to establish the influence of nanofluids concentration as well as tube surface material on heat transfer characteristics at atmospheric pressure. The results indicate that independent of concentration nanoparticle material (Al2O3 and Cu) has almost no influence on heat transfer coefficient while boiling of water-Al2O3 or water-Cu nanofluids on smooth copper tube. It seems that heater material did not affect the boiling heat transfer in 0.1 wt.% water-Cu nanofluid, nevertheless independent of concentration, distinctly higher heat transfer coefficient was recorded for stainless steel tube than for copper tube for the same heat flux density

Eksperymentalna ocena właściwości dynamicznych mikroturbiny energetycznej w obecności defektów układu wirującego

Today’s energy systems increasingly use various types of microturbines to produce electricity. A specific feature of such machines is a high-speed rotor, whose rotational speed can be higher than 100,000 rpm. Failure-free operation of highspeed microturbine rotors requires both special design and high precision during the manufacturing process. What is more, proper procedures must be followed during run-up and coast-down phases; and also, dedicated diagnostic systems have to be used. This article discusses the experimental research conducted on a 2.5 kW vapour microturbine that operated in a prototypical combined heat and power plant. A series of measurements was carried out to evaluate the dynamic performance of the machine during normal operation. After the appearance of certain defects in the rotating system, it was necessary to perform a new series of measurements in order to assess the dynamic properties of the machine. The measurements results obtained in the form of vibration velocity spectrums made it possible to define diagnostic symptoms corresponding to particular defects. Similar diagnostic symptoms can occur during the operation of this class of turbomachines.We współczesnych systemach energetycznych coraz częściej do wytwarzania energii elektrycznej stosowane są różnego typu mikroturbiny. Charakterystyczną cechą takich maszyn są wysokoobrotowe wirniki, których prędkości obrotowe mogą przekraczać nawet 100 000 obr/min. Praca wirnika w takich warunkach wymaga zastosowania specjalnych rozwiązań konstrukcyjnych i bardzo dużej precyzji wykonania, a podczas eksploatacji zachowania odpowiednich procedur przy rozruchu i odstawieniu, a także stosowania dedykowanych systemów diagnostycznych. W niniejszym artykule zostały omówione badania eksperymentalne mikroturbiny parowej o mocy 2,5 kW, pracującej w prototypowym układzie kogeneracyjnym. Wykonane pomiary obejmowały ocenę stanu dynamicznego podczas normalnej pracy maszyny oraz badania jej właściwości dynamicznych w obecności defektów układu wirującego. Uzyskane wyniki pomiarów, w postaci rozkładów częstotliwościowych drgań, pozwalają na zdefiniowanie symptomów diagnostycznych typowych dla różnych defektów, które mogą pojawić się podczas eksploatacji tej klasy maszyn wirnikowych

Pool boiling of nanofluids on rough and porous coated tubes: experimental and correlation

The paper deals with pool boiling of water-Al2O3 and water- Cu nanofluids on rough and porous coated horizontal tubes. Commercially available stainless steel tubes having 10 mm outside diameter and 0.6 mm wall thickness were used to fabricate the test heater. The tube surface was roughed with emery paper 360 or polished with abrasive compound. Aluminium porous coatings of 0.15 mm thick with porosity of about 40% were produced by plasma spraying. The experiments were conducted under different absolute operating pressures, i.e., 200, 100, and 10 kPa. Nanoparticles were tested at the concentration of 0.01, 0.1, and 1% by weight. Ultrasonic vibration was used in order to stabilize the dispersion of the nanoparticles. It was observed that independent of operating pressure and roughness of the stainless steel tubes addition of even small amount of nanoparticles augments heat transfer in comparison to boiling of distilled water. Contrary to rough tubes boiling heat transfer coefficient of tested nanofluids on porous coated tubes was lower compared to that for distilled water while boiling on porous coated tubes. A correlation equation for prediction of the average heat transfer coefficient during boiling of nanofluids on smooth, rough and porous coated tubes is proposed. The correlation includes all tested variables in dimensionless form and is valid for low heat flux, i.e., below 100 kW/m2

Experimental study of the prototype of a Roto-Jet pump for the domestic ORC power plant

The purpose of the work was to experimentally determine the characteristics of the prototype of a Roto-Jet pump (the Pitot tube pump) during its operation under conditions typical for the domestic micro power plant. The low-boiling fluid, sold under the trade name of HFE7100 and characterised by a zero ozone depletion potential (ODP) coefficient, was used as a working medium in the organic Rankine cycle (ORC). An electric thermal oil heater with a maximum power of 2×24 kWe was used as a heat source. The pump of Roto-Jet type was specially designed for the operation with the following rated parameters of the thermodynamic cycle: nominal flow rate of the working fluid 0.17 kg/s, operating pressure 1.2 MPa. The pump was put under load using an expansion valve that simulated the operation of an expansion machine. The article discusses thermodynamic and flow conditions to be met by the pumping engine as well as results of the experimental research. Moreover, the article includes the operational characteristics of the ORC installation and the Roto-Jet pump obtained during the operation with the target working medium – HFE7100. The engineering problems the authors of this article faced when designing and testing the pumping engine prototype are also presented

Experimental investigation of the ORC system in a cogenerative domestic power plant with a scroll expanders

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