1,720,961 research outputs found
Thermal energy storage based on cold phase change materials: Charge phase assessment
No full textIntegration of thermal energy storage in energy systems provides flexibility in demand-supply management and in supporting novel operational schemes. In a combined heat and power cycle, it has been shown that integration of cold thermal energy storage is beneficial to fine-tune electric power and heating/cooling production profiles to better match the load demand. Latent heat storage systems have the advantage of compactness and low temperature swing, however storage performance analysis on large scale setup operating around the density inversion temperature is still limited. In this work, a shell & tube, latent heat based cold thermal energy storage was studied around the density inversion temperature of ice-water at 4 degrees C and the performance was characterized. Sensitivity analyses on heat transfer fluid flow rate, flow direction and inlet temperature were performed. The results show 27% power increase with doubled mass flow and 18% shorter charge time with 2 degrees C lower charge temperature. Contrary to general expectations during solidification, the cold thermal energy storage actually shows between 5% and 6% better thermal performance and reducing instant icing power jump of 36% due to supercooling with downwards cold heat transfer fluid flow in cooling charge cycle due to buoyancy change around density inversion temperature. This fact highlights the importance of accounting for the buoyancy effect due to density inversion when designing the operational schemes of large size cold thermal energy storage
A guideline to link the off-design performance of a micro-gas turbine to a heavy-duty gas turbine in a test rig that aim to investigate flexibility of GTCC
No full textIn the era of coal power station phase-out, natural gas fired combined cycle will drive the energy transition towards sustainable power generation. In a panorama of strong requirement for grid flexibility and non-dispatchable renewable penetration, the survival of a thermal power plant is strictly linked with operating successfully in compensating the renewable fluctuating production through flexible generation. The Italian case is taken as reference, considering that energy transition and renewable energy penetration may have similar effects also in different countries. In this direction, a test rig to investigate gas turbine compressor inlet conditioning techniques has been developed at the Tirreno Power laboratory of the University of Genoa, Italy. This is based on a Turbec T100 micro gas turbine (or microturbine), a Mayekawa heat pump and a phase-change material energy storage. The whole test-rig is virtually scaled up, through a cyber-physical system, to emulate a real 400MW combined cycle, with the heat pump governing the inlet conditions at the compressor. The microturbine is therefore used as the physical feedback for the system, whilst the steam bottoming cycle is simulated in real-time according to microturbine operation. The scope is to present the test rig and the procedure adopted to virtually scaleup a microturbine to a heavy-duty GT. the advantage of using microturbine for testing combined cycle flexibility options lays also on the possibility to make accelerated tests and to simulate multiple situations in compressed time windows
Model predictive control of a phase-change-material thermal energy storage device at industrial relevant scale
No full textThermal energy storage (TES) systems are widely used in the power generation, industrial and residential sectors, frequently coupled with concentrated solar power systems, heat pumps or dedicated heat exchangers to recover waste heat from industrial processes. They are characterized by high reliability, slow degradation and low costs, in terms of both investment and maintenance. Among the available technologies, latent heat storage systems employing phase change materials (PCMs) have the advantage of high compactness and small temperature variations. However, knowledge of operation of PCM devices is still limited, in particular regarding their dynamic response and performance of control systems devoted at regulating the thermal power exchanged. This article analyses the dynamic response of a shell-and-tube PCM-TES device, operated in laboratory but featuring industrial scale storage capacity (180 kWh) which provides cooling power exploiting the latent heat of water/ice. Experimental tests were carried out to observe its performance in various operating conditions and different states of charge, highlighting strongly non-linear behavior during transients, making the design of the controllers particularly challenging. First, a detailed system identification process was carried out, introducing new nondimensional parameters to characterize the TES platform thermal response. Then a second order transfer function was developed to simulate the PCM-TES device and used to support the development of two control systems: the first one based on a conventional PID, and the second one developed according to a model predictive control (MPC) approach. These controllers were separately tested and compared in a software-in-the-loop setup and later installed on the actual PCM-TES device, demonstrating that (i) conventional linear control approaches might be unsuccessful with system non-linearities, causing instabilities, and that (ii) advanced control techniques, such as MPC, can compensate for system non-linearities and achieve successful regulation of the PCM-TES device
Butane-based heat pump for advanced GTCC applications: Static and dynamic model validation
No full textThe Thermochemical Power Group (TPG) of the University of Genoa is investigating innovative solutions to increase the flexibility of gas turbine combined cycles (GTCC) and extend their operative range by integrating large size high performance heat pumps. Achieving this goal would make GTCCs more competitive in the future energy market, which will be characterized by a heavy presence of non-dispatchable renewable energy sources. Within this framework, the authors designed and built a new experimental facility to emulate advanced GTCCs at laboratory scale, integrating a 100 kWel micro gas turbine (MGT), a 10 kWel heat pump (HP) and a 180 kWh cold thermal energy storage (TES), with scale-up equations and dynamic models, capable of hardware-in-the-loop tests. The focus of this article is on the HP, which uses n-butane (R600) as working fluid and can be used both to heat and cool down the MGT compressor intake. The HP features one superheater and a 6-cylinder reciprocating compressor, which rotational speed can be continuously varied from 900rpm to 1800rpm. A dynamic model of the HP was developed in TRANSEO, with dedicated Matlab-Simulink® models. This model includes all the components of the HP closed loop, making it possible to simulate its performance and monitor all the main process parameters, such as compressor operation and condensing pressure. This model can be used to simulate the HP in various conditions, including part-load and transient operations, and to aid the design of the advanced GTCC control system. The evaporator and condenser models solve a system of non-linear equations to compute pressure, temperature, and distribution of the different phases of the working fluid along the heat exchangers. Such phase distribution is computed following a moving boundary approach. An experimental campaign was carried out to collect data regarding the stationary performance of the HP. Values of COP and thermal power were analysed as a function of compressor speed and pressure at the condenser, keeping the conditions at the evaporator constant. Then, its transient behaviour was characterized, observing its response to step changes of both evaporator and condenser thermal loads. The model was then successfully calibrated and validated on both stationary and transient data, showing good accuracy. Based on these results, it will be possible to integrate the HP model within larger system simulation tools. Having an accurate digital twin of the whole GTCC integrating HPs and TES will make possible to develop and verify complex control logics on many different scenarios, relying on a safe model-in-the-loop setup, before actual implementation in the field
Centrifugal Compressor Surge in Innovative Heat Pump: Fluid Dynamic and Vibrational Analysis
No full textIn the current energy scenario, it is necessary to reduce fossil fuel consumption to achieve the far-sighted and stringent decarbonization goals. To date, heat is mainly produced through fossil fuels. Alternatively, electrically driven heat pumps can exploit renewable power to recover environmental and waste heat, offering energy efficient and environmentally friendly heating and cooling for applications ranging from domestic and commercial buildings to process industries. For this reason, they are expected to play a primary role in complementing or displacing natural gas boilers in the residential and industrial sectors in the near future. Centrifugal compressors are already used as prime movers of the working fluid in heat pumps, thanks to their industrial replicability, compact size, affordable costs, and good performance in terms of efficiency and low noise. However, they are subject to instabilities such as surge and stall like any other dynamic compressor and these phenomena develop quite differently than in classic open-loop systems such as gas turbines. In fact, such peculiarity is mainly due to the closed-loop configuration with real gases in two-phase conditions, occurring in typical heat pump cycles. In addition, heat exchangers also contribute to make these phenomena different from what is commonly studied. Compressor surge in closed-loop heat pump systems has received lower attention than other applications by the engineering community, lacking dedicated experimental characterization, and clear exposition of the phenomenon. The aim of this paper is to experimentally investigate the behavior of a centrifugal compressor installed into an innovative close loop heat pump system under stable and unstable conditions from both vibrational and fluid-dynamic points of view. The impact of the main process parameters on the evolution of the instability is shown, highlighting how surge cycles change by varying system operating conditions. The energy contents of surge cycles and pressure fluctuations are highlighted, using data postprocessing techniques such as fast Fourier transform and phase locked average. The vibro-acoustic analysis enrich the comprehension of the phenomena. The experimental results shown in this paper can be a basis for the future development of validated mathematical models of closed-loop heat pumps systems equipped with dynamic compressors operating under stable and unstable operating conditions
GAS TURBINE COMBINED CYCLE RANGE ENHANCER - PART 2: PERFORMANCE DEMONSTRATION
No full textIn the current energy scenario, gas turbine combined cycles (GTCCs) are considered key drivers for the transition towards fossil-free energy production. However, to meet this goal, they must be able to cope with rapid changes of power request, and to extend their operating range beyond the limits imposed by the environmental conditions in which they operate. The European H2020 project PUMPHEAT [1] aims at achieving this goal thanks to the integration of the GTCC with a heat pump (HP) and a thermal energy storage (TES). Both HP and TES are used to condition the air flow at the gas turbine compressor inlet, thus modifying the whole GTCC power output and extending its operative range. To study this setup, a dedicated cyber-physical facility was built at the University of Genova laboratories, Italy. The plant includes physical hardware, such as a 100kWel micro gas turbine, (mGT), a 10 kWel HP and a 180 kWh change phase material-based TES. These real devices are up-scaled thanks to performance maps and real-time dynamic models to emulate a full-scale heavy duty 400 MW GTCC with a cyberphysical approach. The three real key components (mGT, HP and TES) are run in the laboratory. Data collected by various sensors is monitored in real-time and used to feed both the simulated GTCC bottoming cycle model and the four-level control system. The control system determines the optimal configuration of the whole plant and the operative point of the real devices to minimize the mismatch with a real electric power demand curve. With the aim of analyzing the performance of the facility and to assess the potential of the proposed GTCC range enhancer, different operative configurations are tested: one for reducing the power production of the plant below the minimum environmental load (MEL) and two for augmenting the plant maximum power at certain ambient conditions. From the analysis of these tests it is possible to verify the effectiveness of the proposed concept and to characterize the transient behavior of the real components
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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