Multi-disk bladeless turbines, also known as Tesla turbines, are promising in the field of small-scale power generation and energy harvesting due to their low sensitivity to down-scaling effects, retaining high rotor efficiency. However, low (less than 40%) overall isentropic efficiency has been recorded in the experimental literature. This article aims for the first time to a systematic experimental characterization of loss mechanisms in a 3-kW Tesla expander using compressed air as working fluid and producing electrical power through a high speed generator (40krpm). The sources of losses discussed are: stator losses, stator-rotor peripheral viscous losses, end wall ventilation losses and leakage losses. After description of experimental prototype, methodology and assessment of measurement accuracy, the article discusses such losses aiming at separating the effects that each loss has on the overall performance. Once effects are separated, their individual impact on the overall efficiency curves is presented. This experimental investigation, for the first time, gives the insight into the actual reasons of low performance of Tesla turbines, highlighting critical areas of improvement, and paving the way to next generation Tesla turbines, competitive with state of the art bladed expanders.

Tesla bladeless turbomachines are recently being investigated due to many advantages such as its simple design and ease of manufacturing. If an efficient design is achieved, this will be a promising machine in the area of small-scale power generation and energy harvesting. This paper focuses on the experimental performance investigation of 3 kW (rated power) Tesla bladeless expander. The Tesla expander and electric generator are housed in a single casing making it first of its kind being tested with such configuration. The expander is fed with air and operated at high rotational speeds up to 40000 rpm. The test is carried out with different number of nozzles to understand its effect on the performance. Results show that the peak efficiency for two nozzles is better than one nozzle and four nozzle configurations for the same inlet pressure conditions. Experimental tests revealed that this turbine is most efficient Tesla turbine till now with air as a working fluid. Furthermore, one of the most important losses in Tesla turbomachines, nozzle loss, is experimentally characterized. Specific vibrational tests were carried out to obtain complete machine dynamical characterization. The vibrational response characterization of the turbine enabled us to recognize a disk mode family solicited by the air flow and to perform a proper machine maintenance and balancing aiming to reduce the energy of its operational vibration.

Interest in small scale turbines is growing mainly for small scale power generation and energy harvesting. Conventional bladed turbines impose manufacturing limitations and higher cost, which hinder their implementation at small scale. This paper focuses on experimental and numerical performance investigation of Tesla type turbines for micro power generation. A flexible test rig for Tesla turbine fed with air as working fluid has been developed, of about 100W net mechanical power, with modular design of two convergent-divergent nozzles to get subsonic as well as supersonic flow at the exit. Seals are incorporated at the end disks to minimize leakage flow. Extensive experiments are done by varying design parameters such as disk thickness, gap between disks, radius ratio and outlet area of exhaust with speeds ranging from 10000 rpm to 40000 rpm. A quasi-1D model of the whole setup is created and tuned with experimental data to capture the overall performance. Major losses, ventilation losses at end disks, nozzle and exhaust losses are evaluated experimentally and numerically. Effect of design parameters on the performance of Tesla turbines is discussed.

This paper shows experimental results obtained from a T100 microturbine connected with different volume sizes. The activity was carried out with the test rig developed at the University of Genoa for hybrid system emulation. However, these results apply to all the advanced cycles where a microturbine is connected with an additional external component responsible for volume size increase. Even if the tests were performed with a microturbine (for laboratory scale and for the related research interest in innovative cycles), similar analyses can be extended to on large size turbines. The main power systems including the effect of an additional volume connected with a turbine are: fuel cell based hybrid plants, humid cycles, externally fired layouts and innovative systems including high temperature thermal storage devices. Since in this case a 100 kW turbine was used, the volume was located between the recuperator outlet and the combustor inlet as in the typical cases related to small size plants. A modular vessel was used to perform and to compare the tests with different volume sizes. To highlight the volume size effect, preliminary experimental results were carried out considering the transient response due to an on/off bleed valve operation. So, the main differences between system parameters obtained for a bleed line closing operation are compared considering three different volume sizes. The main results reported in this paper are related to surge operations. This analysis was carried out to extend the knowledge about this risk condition: the systems equipped with large volume size connected with the machine present critical issues related to surge prevention especially during transient operations. For instance, if the T100 machine is operating with large volume components, the standard shutdown procedure can produce surge condition. This behavior is due to a slow depressurization rate in comparison with a standard microturbine. So, to produce surge conditions in this test rig, a valve operating in the main air path was closed to generate unstable behavior. It was possible to compare the effect of different volume sizes on main properties of the system using a modular vessel. Particular focus was devoted to the operational curve plotted on the compressor map. The system was equipped with different dynamic probes to measure the vibrations during normal and surge operations. The frequency analysis showed significant vibration increase not only during surge events but also close to the unstable condition. In details, possible surge precursor indicators were obtained to be used for the detection of risky machine operations. Since these surge precursors are considered important parameters for the control system point of view, an extensive experimental analysis was carried out considering the influence of volume size. These precursors were defined to produce control data (e.g. an on/off signal for a bleed valve) for surge prevention. The experimental data collected during these tests are analyzed with the objective of designing control systems to prevent surge conditions.

This paper describes the development and testing of a new algorithm to identify faulty sensors, based on a statistical model using quantitative statistical process history. Two different mathematical models were used and the results were analyzed to highlight the impact of model approximation and random error. Furthermore, a case study was developed based on a real micro gas turbine facility, located at the University of Genoa. The diagnostic sensor algorithm aims at early detection of measurement errors such as drift, bias, and accuracy degradation (increase of noise). The process description is assured by a database containing the measurements selected under steady state condition and without faults during the operating life of the plant. Using an invertible statistical model and a combinatorial approach, the algorithm is able to identify sensor fault. This algorithm could be applied to plants in which historical data are available and quasi steady state conditions are common (e.g. Nuclear, Coal Fired, Combined Cycle).

This paper presents the development of a new experimental facility for analysis and optimization activities on smart polygeneration grids. The test rig is being designed and built in the framework of the European project “Energy-Hub for residential and commercial districts and transport” (E-HUB), which targets optimal energy management of residential and commercial districts. The experimental rig, named “Energy aNd Efficiency Research Demonstration District” (E-NERDD), is located inside the University campus in Savona, and is based on four different prime movers able to produce both electrical and thermal energy: a 100 kWe micro gas turbine, a 20 kWe internal combustion engine, a 3 kWe Stirling engine, and a 450 kWe fuel cell/gas turbine hybrid system emulator based on the coupling of a micro gas turbine with a modular vessel. While the electrical side is based on the connection with the campus grid (further developments are planned for a local electrical grid including storage units), thermal energy is managed through a dual ring-based water distribution system. The facility is also equipped with thermal storage tanks and fan cooler units to study and optimize different thermal management algorithms generating different thermal load demands. The facility also includes an absorption chiller for cold water generation. As a result, trigeneration operation is possible in a physically simulated urban district. Moreover, the rig is equipped with six photovoltaic panels (significant for the electrical aspects) and 10 kWp of thermal solar panels to be integrated in the grid. Further technologies to be considered for the E-NERDD are power plants based on other renewable resource (e.g. with biomass fuel). These systems are planned to be analyzed through real plants (remote connection with the field) or through virtual models based on real-time dynamic approaches. Experimental tests related to the performance of the micro gas turbine are reported and discussed in this paper. The focus here is on machine correction curves essential to evaluate factors for quantifying ambient temperature influence on machine performance. This analysis is essential for setting the thermal distribution grid and for future optimization tests.

The aim of this work is the experimental analysis of steady-state and transient behavior of a primary surface recuperator installed in a 100 kW commercial micro gas turbine. The machine is integrated in an innovative test rig for high temperature fuel cell hybrid system emulation. It was designed and installed by the Thermochemical Power Group (TPG), at the University of Genoa, within the framework of the Felicitas and LARGE-SOFC European Integrated Projects. The high flexibility of the rig was exploited to perform tests on the recuperator operating in the standard cycle. Attention is mainly focused on its performance in transient conditions (start-up operations and load rejection tests). Start-up tests were carried out in both electrical grid-connected and stand-alone conditions, operating with different control strategies. Attention is focused on system response due to control strategy and on boundary temperature variation because of its influence on component life consumption. Further tests were carried out using the valves installed on the test rig to bypass the air side of the unit. Different operative conditions were analyzed to show the effect of different mass flow rates on recuperator behavior. Attention is mainly focused on recuperator performance when it operates in unbalanced flow rate conditions (i.e. different mass flow rate values in recuperator sides), as well as during advanced cycle start-up and shutdown operations.

The Thermochemical Power Group (TPG) of the University of Genoa, Italy, has developed a new “Gas Turbine” laboratory to introduce undergraduate students to Gas Turbines and Innovative Cycles course, and Ph.D.s to advanced experimental activities in the same field. In the laboratory a general-purpose experimental rig, based on a modified commercial 100 kW recuperated micro gas turbine, was installed and fully instrumented. One of the main objectives of the laboratory is to provide both students and researchers with several experimental possibilities to obtain data related to the gas turbine steady-state, transient and dynamic performance including the effect of interaction between the turbomachines (especially the compressor) and more complex innovative gas turbine cycle configurations, such as recuperated, humid air, and hybrid (with high temperature fuel cells). The facility was partially funded by two Integrated Projects of the EU VI Framework Program (Felicitas and Large-SOFC) and the Italian Government (PRIN project) and it was designed with a high flexibility approach including: flow control management, co-generative and tri-generative applications, downstream compressor volume variation, grid-connected or stand-alone operations, recuperated or simple cycles, and room temperature control. The layout of the whole system, including connection pipes, valves, and instrumentation (in particular mass flow meter locations) was carefully designed, for educational purposes, by a group of Ph.D. students using CFD tools (Fluent), and it is presented in detail in this paper. The paper also shows, as an example of the possibilities offered by the rig, experimental data obtained by both Master and Ph.D. students. The tests presented here are essential for understanding commercial microturbine performance, control strategy development, and theoretical model validation.

The aim of this work is the experimental analysis of a primary-surface recuperator operating in a 100 kW micro gas turbine, as in a standard recuperated cycle. These tests, performed in both steady-state and transient conditions, have been carried out using the micro gas turbine test rig developed by TPG at the University of Genoa, Italy. Even if this facility has mainly been designed for hybrid system emulations, it is possible to exploit the plant for component tests, such as experimental studies on recuperators. The valves installed in the rig make it possible to operate the plant in the standard recuperated configuration, and the facility has been equipped with new probes essential for this kind of tests. A wide-ranging analysis of the recuperator performance has been carried out with the machine operating in stand-alone configuration, or connected to the electrical grid, to test different control strategy influences. Particular attention has been given to tests performed at different electrical load values and with different mass flow rates through the recuperator ducts. The final section of this paper reports the transient analysis carried out on this recuperator. The attention is mainly focused on thermal transient performance of the component, showing the effects of both temperature and flow steps.

This paper reports on the latest application of a generic time-dependent real-time simulation tool, originally developed for fuel cell gas turbine hybrid systems, and now applied to an actual micro gas turbine test rig. Real-time modeling is a recognized approach for monitoring advanced systems and improving control capabilities: applications of real-time models are commonly used in the automotive and aircraft fields. The overall objective is improving of calculation time in existing time-dependent simulation models, while retaining acceptable accuracy of results. The real-time modeling approach already applied to fuel cell gas turbine systems has here been validated against the experimental data from the micro gas turbine Turbec T100 test rig in Savona, Italy. The real-time model of the microturbine recuperator has been newly developed to fit such an application. Two representative transient operations have been selected for verification: the heating and cooling phases of the connected volume. The results already show an acceptable agreement with measurements, and they have contributed to a better insight into performance prediction for the entire plant.

The aim of this work, focused on natural gas fired distributed power systems, is the experimental analysis of the start-up and shutdown for high temperature fuel cell hybrid systems. These critical phases have been emulated using the micro gas turbine test rig developed by TPG at the University of Genoa, Italy. The rig is based on the coupling of a modified commercial 100 kWe recuperated gas turbine with a modular volume designed to emulate fuel cell stacks of different dimensions. It is essential to test the dynamic interaction between the machine and the fuel cell, and to develop different operative procedures and control systems without any risk to the expensive stack. This paper shows the preliminary experimental results obtained with the machine connected to the volume. The attention is mainly focused on avoiding surge and excessive stress on the machine components during the tests. Finally, after the presentation of the valve control system, this paper reports the emulation of the hybrid system start-up and shutdown phases. They have been performed to produce a gradual heating up and cooling down of the fuel cell volume, using the cold bypass line, three high temperature valves, and the machine load control system. This approach is necessary to avoid high thermal stress on the cell material, extremely dangerous for the plant life.

The Thermochemical Power Group (TPG) is building at the laboratory of the University of Genoa, Italy, a new high temperature fuel cell - micro gas turbine physical emulator based on commercial machine technology. The aim of this new test rig is the experimental analysis of the coupling of commercial machines with fuel cell stacks focusing the attention on the critical phases of start-up, shutdown and load changes. The experimental facility is composed of a Turbec T100 micro gas turbine package modified for the fuel cell emulator connection, a set of pipes designed for by-pass, measurement or bleed reasons, and a high temperature volume designed for the RRFCS stack dimension physical emulation. This experimental approach is essential for model validations, and to test different transient operative procedures and control systems without any risk for an expensive real fuel cell stack. This paper shows the preliminary experimental data obtained with the machine in stand alone configuration, focusing the attention on the comparison of these results with the tests performed with the external pipes. Furthermore, a theoretical transient model of this new experimental facility has been developed with the TRANSEO tool. It is essential for the rig design and to perform preliminary results necessary to prevent dangerous conditions during the tests. This paper reports a preliminary verification of this model performed with the facility.

The aim of this work is the experimental validation of a transient ejector model for hybrid system applications. This is a mandatory step in performing the transient analysis of the whole plant to avoid critical situations and to develop the control system. So, the anodic recirculation test rig already used in previous works to study the ejector design validating the steady-state 0-D and CFD models, was used in this work to perform tests at transient conditions and to validate the ejector transient model. An initial validation was carried out at steady-state conditions, then the ejector transient model was successfully compared with the experimental data, also under unsteady conditions. A second step was carried out to better investigate the whole anodic recirculation system. So, the validated ejector transient model was connected to the components necessary to simulate the pipes, the valves and the anodic volume. Also in this case, the calculated results were successfully compared with the experimental data obtained with the laboratory test rig. The final part of the paper is devoted to the results obtained at impulse conditions. In fact, this work investigates the effects on the anodic ejector and on the whole anodic circuit coming from fuel line impulses caused by possible unsteadiness conditions. The results obtained with impulses at different frequency values were successfully compared with the experimental data.