1,720,964 research outputs found
A new design method for two-phase nozzles in high efficiency heat pumps
No full textIn this paper an industrially established 1D model for two-phase nozzles design and analysis (Elliott, 1968) has been extended and validated with a wider range of experimental data, focusing on single component two-phase fluid expansion from initial quality in the 0%–25% range. The Authors focused on the correlations of the gas-liquid slip velocity and wall friction for two-flow regimes. The upgraded model has been tested on a converging nozzle showing accurate results under subcritical conditions (Ma<1). Furthermore, simulations have also been carried out on a convergent-divergent nozzle, concentrating on the diverging part at Ma>1, demonstrating that the new model obtained a significant reduction in error compared to the original Elliott model and to the well-known isentropic homogeneous approach (IHE). The extended model was also tested on a convergent-divergent nozzle produced by Carrier Corporation for the 19-XRT chiller, obtaining a satisfactory performance prediction. The validation process allowed to assess the limits of validity of the new model, which can be effectively used as design tool for subsonic or supersonic two-phase nozzles. In particular, the model capability to identify critical mass flow and critical expansion ratio has been investigated, showing good match for the critical expansion ratio, while margins of improvement remain for the critical mass flow prediction
Experimental Characterization of Losses in Bladeless Turbine Prototype
No full textMultidisk 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 (40 krpm). 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
A REVIEW OF PRESSURE GAIN COMBUSTION SOLUTIONS FOR AEROSPACE PROPULSION
No full textRecent developments in Pressure Gain Combustion (PGC) technology have demonstrated its ability to achieve higher thermal efficiencies and lower carbon emissions as compared to conventional gas turbine counterpart working in Brayton cycle. Ongoing studies suggest the possibility of implementing PGC in aircraft engines by replacing the high-pressure section (HP compressor, combustion chamber and HP turbine) with a PGC system. This, coupled with research on advanced materials and cooling solutions, offers the potential for higher overall gas turbine efficiency and fuel economy, contributing towards emission reduction of the aviation sector.
This paper aims at a comprehensive review of PGC technology solutions applied in the area of aero propulsion. Reported background covers the historic as well as ongoing research activities at the component level, the cycle level, and the propulsion application of Pulse Detonation Engine (PDE), Rotating Detonation Engine (RDE), Oblique Detonation Wave Engine (ODWE), Free Piston Composite Cycle Engine (FP-CCE), and wave rotor engines. The analytical, numerical, and experimental research work is reviewed, providing also a comparison of PGC engine conceptual designs with existing gas turbine engines used in aerospace propulsion
Experimental investigation on a 3 KW air tesla expander with high speed generator
No full textTesla 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
Performance Assessment of Bladeless Micro-Expanders Using 3D Numerical Simulation
No full textThis paper summarizes the development of fully 3D Computational Fluid Dynamics (CFD) analysis for bladeless air micro expander for 200 W and 3 kW rated power. Modelling of nozzle along with rotor is done using structured mesh. This analysis, for the first time, demonstrates the interaction between nozzle and rotor using compressible flow density-based solver. The Shear Stress Transport (SST) turbulence model is employed to resolve wall effects on the rotor and to determine the shear stress accurately. The results illustrate the flow field inside stator and rotor along with complicated mixing zone between stator and rotor. The comparison of rotor-stator CFD simulation results is done with experiments to preliminary validate the model. The losses in the turbine are discussed with the help of experimental and numerical data
Tesla Turbine : A Practical Design Guide for Boundary Layer or Bladeless Turbines
No full textThis book aims at providing the reader with up-to-date knowledge about Tesla turbine features, mechanical design, and performance characteristics. A Tesla machine, in general, is characterised by the absence of rotating blades, therefore it is also called bladeless or boundary layer machine. In this book, suitable numerical approaches for the fluid-dynamic analysis are described, with practical examples related to physical prototypes designed, built and operated by the Authors. Interest in small scale turbines is growing mainly for energy efficiency and power recovery in a variety of applications. Considering small scales, conventional bladed turbines impose manufacturing limitations, lower performance and higher cost, which hinder their implementation. Tesla bladeless turbomachines are being re-discovered due to many advantages such as their simple design and ease of manufacturing with acceptable performance, especially for small-scale power generation and energy harvesting. To contribute to the spread of efficient and viable Tesla turbines (or expanders), this book presents holistic design guidelines to Tesla turbines, encompassing geometrical definition of Tesla rotor, of Tesla stator, of Tesla rotor-stator-casing assembly, providing practical correlations to take into account various loss mechanisms, and discussing the optimal design point definition for such type of century-aged but always young turbines.</p
Energy Harvesting Technology for turbocompounding automotive engines with waste-gate valve
No full textThe reduction of CO2 and, more generally, GHG (Green House Gases) emissions imposed by the European Commission (EC) and the Environmental Protection Agency (EPA) for passenger cars has driven the automotive industry to develop technological solutions to limit exhaust emissions and fuel consumption, without compromising vehicle performance and drivability. In a mid-term scenario, hybrid powertrain and Internal Combustion Engine (ICE) downsizing represent the present trend in vehicle technology to reduce fuel consumption and CO2 emissions. Concerning downsizing concept, to maintain a reasonable power level in small engines, the application of turbocharging is mandatory for both Spark Ignition (SI) and Diesel engines. Following this aspect, the possibility to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world. One method to recover exhaust gas energy from ICEs is the adoption of turbo-compounding technology to recover sensible energy left in the exhaust gas by-passed through the waste-gate valve. In the paper, an innovative option of advanced boosting system is investigated through a bladeless micro expander, promising attractive cost-competitiveness. The numerical activity was developed on the basis of experimental data measured on a waste-gated turbocharger for downsized SI automotive engines. To this aim, mass flow rate through the by-pass valve and the turbine impeller was measured for different waste-gate settings in steady-state conditions at the turbocharger test bench of the University of Genoa. The paper shows that significant electrical power can be harvested from the waste-gate gases, up to 94 % of compressor power, contributing to fuel consumption reduction
Performance Investigation of a Bladeless Air Compressor
No full textThis study aims to investigate the reversible operation of a bladeless air expander prototype operated reversibly in compressor mode to understand the performance by numerical method and compare its results experimentally. A bladeless machine can reverse its operation by simply inverting the rotational speed. However, expander and compressor performance may differ significantly since losses are exacerbated in the compressor mode. The prototype was previously tested as an expander (experimental highest isentropic efficiency of 36.5%). In this work, the reverse mode is discussed, when the prototype is actuated as a compressor, with and without diffuser at variable rotational speeds. In compressor mode, the fluid enters through the center axially, passes radially outwards through disk gaps, and exits throughout the diffuser. The momentum transfer and pressure gain are carried out by the shear force produced on the surface of the rotating disk. An experimental/theoretical analysis focused on the pressure ratio, mass flow, and efficiency of bladeless compressor is conducted. High losses (main leakage across the rotor) were noticed during the experiments, affecting the overall Tesla compressor performance. Numerical calculations are carried out to estimate leakage losses by comparison with experimental results. It is shown that the original expander design would require specific modifications to reduce end disk leakages, which are higher in compressor mode than in expansion mode, significantly affecting the elaborated net mass flow. Improved diffuser, scroll, disk end gaps, and sealing mechanisms are discussed in order to augment overall performance of the bladeless prototype in compressor mode
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