Influence of Molecular Complexity on Nozzle Design for an Organic Vapor Wind Tunnel

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Alberto Guardone ◽  
Andrea Spinelli ◽  
Vincenzo Dossena
Keyword(s):  
High Pressure ◽  
Wind Tunnel ◽  
Operating Conditions ◽  
Critical Conditions ◽  
Working Fluid ◽  
Saturation Curve ◽  
Blow Down ◽  
Real Gas ◽  
Molecular Complexity ◽  
Organic Fluids

A novel blow-down wind tunnel is currently being commissioned at the Politecnico di Milano, Italy, to investigate real-gas behavior of organic fluids operating at subsonic-supersonic speed in the proximity of the liquid-vapor critical point and the saturation curve. The working fluid is expanded from a high-pressure reservoir, where it is kept at controlled super-heated or super-critical conditions, into a low-pressure reservoir, where the vapor is condensed and pumped back into the high-pressure reservoir. Expansion to supersonic speeds occurs through a converging-diverging Laval nozzle. Siloxane fluid MDM (octamethyltrisiloxane-C8H24O2Si3) is to be tested during the first experimental trials. A standard method of characteristics is used here to assess the influence of the molecular complexity of the working fluid on the design of the supersonic portion of the nozzle by considering different fluids at the same real-gas operating conditions, including linear and cyclic siloxanes, refrigerant R245fa, toluene, and ammonia. The thermodynamic properties of these fluids are described by state-of-the-art thermodynamic models. The nozzle length and exit area are found to increase with increasing molecular complexity due to the nonideal dependence of the speed of sound on density along isentropic expansion of organic fluids.

scholarly journals A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5049
Author(s):  
Xiaojian Li ◽  
Yijia Zhao ◽  
Huadong Yao ◽  
Ming Zhao ◽  
Zhengxian Liu
Keyword(s):  
Design Method ◽  
Operating Conditions ◽  
Low Flow ◽  
Working Fluid ◽  
Centrifugal Compressors ◽  
Flow Angle ◽  
Real Gas ◽  
Total Condition ◽  
Swallowing Capacity ◽  
Cycle Efficiency

Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.

Brush Seals Used in Steam Environments: Chronological Wear Development and the Impact of Different Seal Designs

2015 ◽  
Author(s):  
M. Raben ◽  
J. Friedrichs ◽  
J. Flegler ◽  
T. Helmis
Keyword(s):  
Abrasive Wear ◽  
Contact Force ◽  
Operating Conditions ◽  
Test Facility ◽  
Working Fluid ◽  
Two Stage ◽  
Blow Down ◽  
Frictional Contacts ◽  
Brush Seals ◽  
The Impact

During the last decades a large effort has been made to continuously improve turbomachine efficiency. Besides the optimization of the primary flow path, also the secondary flow losses have been reduced considerably, due to the use of more efficient seals. Brush seals, as a compliant contacting filament seal, have become an attractive alternative to conventional labyrinth seals in the field of aircraft engines as well as in stationary gas and steam turbines. The aim of today’s research related to brush seals is to understand the characteristics and their connections, in order to be able to make performance predictions, and to ensure the reliability over a defined operating period. It is known that inevitable frictional contacts lead to an abrasive wear on the rotor side as well as on the bristle side. The wear situation is essentially influenced by the resulting contact force at the seal-to-rotor interface during the operating time. This contact force depends on the seal’s blow down capability, which is mainly determined by the geometrical design of the bristle pack, e.g. the axial inclination of the investigated seal design, in combination with the design and material of the surrounding parts, as well as the thermal boundary conditions. For realistic investigations with representative circumferential velocities the TU Braunschweig operates a specially developed steam test rig which enables live steam investigations under varying operating conditions up to 50 bar and 450 °C. Wear measurements and the determination of seal performance characteristics, such as blow down and bristle stiffness, were enabled by an additional test facility using pressurized cold air up to 8 bar as working fluid. This paper presents the chronological wear development on both rotor and seal side, in a steam test lasting 25 days respectively 11 days. Interruptions after stationary and transient intervals were made in order to investigate the wear situation. Two different seal arrangements, a single tandem seal and a two-stage single seal arrangement, using different seal elements were considered. The results clearly show a continuous wear development and that the abrasive wear of the brush seal and rotor is mainly due to the transient test operation, particularly by enforced contacts during shaft excursions. Despite the increasing wear to the brushes, all seals have shown a functioning radial-adaptive behavior over the whole test duration with a sustained seal performance. Thereby, it could be shown that the two-stage arrangement displays a load shift during transients, leading to a balanced loading and unloading status for the two single brush seals. From load sharing and in comparison with the wear data of the tandem seal arrangement, it can be derived that the two-stage seal is less prone to wear. However, the tandem seal arrangement, bearing the higher pressure difference within one configuration, shows a superior sealing performance under constant load, i.e. under stationary conditions.

Working Fluid Selection for Organic Rankine Cycles from a Molecular Structural Point of View

2013 ◽  
Vol 805-806 ◽  
pp. 649-653
Author(s):  
Bing Zhang ◽  
Shuang Yang ◽  
Jin Liang Xu ◽  
Guang Lin Liu
Keyword(s):  
Critical Temperature ◽  
Heat Source ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Point Of View ◽  
Operating Conditions ◽  
Working Fluid ◽  
Working Fluids ◽  
Organic Fluids ◽  
Cycle Efficiency

The optimum working conditions of 11 working fluids under different heat source temperatures for an organic Rankine cycle (ORC) were located in our previous work. In the current work, the system irreversibility of each candidate were calculated and compared at their optimal operating conditions. Obvious variation trends of both the cycle efficiency and irreversibility were found for different types of organic fluids. It is suggested, when selecting working fluid for our ORC system, the critical temperature should be as close as possible to the heat source temperature to achieve high cycle efficiency but avoid large irreversibility. The relationships between the structure of the molecules and the critical temperature of the working fluids are investigated qualitatively and potentially meaningful for the rational selection of proper organic fluids for certain ORCs.

The Influence of Real Gas Effects on ICE-ORC Turbine Flow Fields

2014 ◽  
Author(s):  
Lei Zhang ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Jie Peng
Keyword(s):  
Thermodynamic Parameters ◽  
Gas Flow ◽  
Combustion Engine ◽  
Incidence Angle ◽  
Flow Fields ◽  
Operating Conditions ◽  
Specific Power ◽  
Working Fluid ◽  
Perfect Gas ◽  
Real Gas

This paper presents a quantitative comparison of the flow fields of a radial turbine between real gas and perfect gas models for the internal combustion engine (ICE) organic Rankine Cycle (ORC) application. Three-dimensional turbulent Navier-Stokes simulations are carried out using CFD code NUMECA FINE™/TURBO, which is linked to an accurate thermodynamic model for organic working fluid R123 in the form of thermodynamic tables. Four turbine operating conditions including the design point and three part-load points, the inlet compressibility factors of which are 0.82–0.89, are analyzed to discuss the differences of flow fields. Obvious derivations of thermodynamic parameters are investigated in the turbine flow fields. The derivations of speed of sound and density at the nozzle inlet are about 15–20%. There exist about 10m/s value differences in the nozzle outlet velocity evaluation, and furthermore a difference of 10 degrees in the rotor inlet incidence angle comparison. The derivations of relative Mach number are about 20–35% in the rotor outlet near the shroud surface. More than 30% differences are shown in the comparison of turbine total temperature drops. Other thermodynamic parameters show much smaller derivations. The differences of thermodynamic parameters lead to a 1–3% larger in mas flow rate, 1–2% larger in isentropic efficiency and 6–8% smaller in specific power comparison. However, there do not exist obvious differences on thermodynamic parameters distributions in the flow fields. The similar flow fields provide a suggestion that perfect gas model may be an acceptable model for turbine preliminary design and one-dimensional analysis in this gas thermodynamic region, and also the real gas flow fields simulated can be used as a start point to refine the turbine design.

Performance Predictions of Axial Turbines for Organic Rankine Cycle (ORC) Applications Based on Measurements of the Flow Through Two-Dimensional Cascades of Blades

2014 ◽  
Author(s):  
Karsten Hasselmann ◽  
Felix Reinker ◽  
Stefan aus der Wiesche ◽  
Eugeny Y. Kenig ◽  
Frithjof Dubberke ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Low Temperature ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Two Dimensional ◽  
Real Gas ◽  
Specific Loss ◽  
Performance Predictions ◽  
Flow Through ◽  
Organic Fluids

The Organic-Rankine-Cycle (ORC) offers a great potential for waste heat recovery and use of low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low temperature level, and it is, therefore, of major importance to design ORC components with high efficiencies and minimized losses. The use of organic fluids creates new challenges for turbine design, due to real-gas behavior and low speed of sound. The design and performance predictions for steam and gas turbines have been mainly based on measurements and numerical simulations of flow through two-dimensional cascades of blades. In case of ORC turbines and related fluids, such an approach requires the use of specially designed closed cascade wind tunnels. In this contribution, the specific loss mechanisms caused by the organic fluids are reviewed. The concept and design of an ORC cascade wind tunnel are presented. This closed wind tunnel can operate at higher pressure and temperature levels, and this allows for an investigation of typical organic fluids and their real-gas behavior. The choice of suitable test fluids is discussed based on the specific loss mechanisms in ORC turbine cascades. In future work, we are going to exploit large-eddy-simulation (LES) techniques for calculating flow separation and losses. For the validation of this approach and benchmarking different sub-grid models, experimental data of blade cascade tests are crucial. The testing facility is part of a large research project aiming at obtaining loss correlations for performance predictions of ORC turbines and processes, and it is supported by the German Ministry for Education and Research (BMBF).

scholarly journals Evaluation of Aerial Spray Technologies for Adult Mosquito Control Applications

2013 ◽  
Vol 53 (3) ◽  
pp. 222-229 ◽  
Author(s):  
Wesley Clint Hoffmann ◽  
Bradley Keith Fritz ◽  
Muhammad Farooq ◽  
Todd William Walker ◽  
Zbigniew Czaczyk ◽  
...  
Keyword(s):  
High Pressure ◽  
Wind Tunnel ◽  
Vector Control ◽  
Droplet Size ◽  
High Speed ◽  
Laser Diffraction ◽  
Operating Conditions ◽  
Adult Mosquito ◽  
Size Spectrum ◽  
Spray Droplet

Abstract Spray droplet size has long been recognized as an important variable that applicators of vector control sprays must be aware of to make the most effective spray applications. Researchers and applicators have several different techniques available to assess spray droplet size from spray nozzles. The objective of this study was to compare the droplet size spectrum produced by three nozzles commonly used in vector control in a high-speed wind tunnel, when characterized using three different laser-based droplet size measurement systems. Three droplet sizing systems: Malvern Spraytec laser diffraction, Sympatec HELOS laser diffraction, and TSI Phase Doppler Particle Analyzer (PDPA), were simultaneously operated, but under different operating conditions, to measure the spray droplet size-spectra for three spray nozzles. The three atomizers: a TeeJet® 8001E even flat fan nozzle, a BETE® PJ high pressure fog nozzles, and a Micronair ® AU5000 rotary atomizer were evaluated in a high speed wind tunnel at airspeeds of 53 and 62 m/s (120 and 140 mph). Based on the results of this work, only the BETE® PJ high pressure fog nozzles met the label requirements for both Fyfanon® and Anvil®. While the other nozzle might met the Dv0.5 (VMD - volume median diameter) requirement for Fyfanon®, the resulting Dv0.9 values exceeded labeled size restrictions. When applying Anvil with the BETE PJ high pressure fog nozzles, it is important to use the smaller two orifice sizes. The larger sizes tended to result in Dv0.9 values that exceeded label recommendations

Design, Simulation, and Construction of a Test Rig for Organic Vapors

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Andrea Spinelli ◽  
Matteo Pini ◽  
Vincenzo Dossena ◽  
Paolo Gaetani ◽  
Francesco Casella
Keyword(s):  
Dynamic Simulation ◽  
Thermal Power ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Main Process ◽  
Test Rig ◽  
Experimental Conditions ◽  
Blow Down ◽  
Working Fluids ◽  
Real Gas

A blow-down wind tunnel for real-gas applications has been designed, validated by means of dynamic simulation, and then built. The facility is aimed at characterizing an organic vapor stream, representative of the expansion taking place in organic Rankine cycle (ORC) turbines, by independent measurements of pressure, temperature, and velocity. The characterization of such flows and the validation of design tools with experimental data, which are still lacking in the scientific literature, is expected to strongly benefit the performance of future ORC turbines. The investigation of flow fields within industrial ORC turbines has been strongly limited by the unavailability of calibration tunnels for real-gas operating probes, by the limited availability of plants, and by restricted access for instrumentation. As a consequence, it has been decided to design and realize a dedicated facility, in partnership with a major ORC manufacturer. The paper thoroughly discusses the design and the dynamic simulation of the apparatus, presents its final layout, and shows the facility “as built”. A straight-axis planar convergent-divergent nozzle represents the test section for early tests, but the test rig can also accommodate linear blade cascades. The facility implements a blow down operating scheme, due to high fluid density and operating temperature, which prevent continuous operation because of the prohibitive thermal power required. A wide variety of working fluids can be tested, with adjustable operating conditions up to maximum temperature and pressure of 400 °C and 50 bar, respectively. Despite the fact that the test rig operation is unsteady, the inlet nozzle pressure can be kept constant by a control valve. In order to estimate the duration of the setup and experimental phase, and to describe the time evolution of the main process variables, the dynamic plant operation, including the control system, has been simulated. Design and simulation have been performed with both lumped-parameter and 1D models, using siloxane MDM and hydrofluorocarbon R245fa as the reference working fluids, described by state-of-the-art thermodynamic models. Calculations show how experiments may last from 12 seconds up to several minutes (depending on the fluid and test pressure), while reaching the experimental conditions requires few hours, consistently with the performance of daily-based experiments. Moreover, the economic constraints have been met by the technical solutions adopted for the plant, allowing the construction of the facility.

Design of a Closed-Loop Optical-Access Supersonic Test Facility for Organic Vapours

2018 ◽  
Author(s):  
Martin T. White ◽  
Abdulnaser I. Sayma
Keyword(s):  
Test Section ◽  
Closed Loop ◽  
Operating Conditions ◽  
Test Facility ◽  
Lubricating Oil ◽  
Working Fluid ◽  
Settling Chamber ◽  
Flow Visualisation ◽  
Research Activities ◽  
Organic Fluids

Despite significant research activities into organic Rankine cycles for the conversion of low-temperature heat into power, there remain uncertainties with regards to non-ideal gas effects and their role in turbine performance. Moreover, existing performance models and numerical solvers have yet to be validated for turbines operating with organic fluids. This paper documents the design of a closed-loop supersonic test facility intended for experimental characterisation of the flow of organic fluids under typical operating conditions experienced within an ORC turbine. The test section forms part of a wider test facility, developed for the study of ORC expanders, which includes a screw compressor, the supersonic test section, a heat exchanger and an expander test section. The working fluid is R1233zd, and the test facility is sized to deliver test conditions up to 20 bar and 125 °C with a mass-flow rate of 1 kg/s. After an overview of the test facility, the detailed design of the upstream diffuser, settling chamber, contraction zone and converging-diverging nozzle to deliver a flow with a Mach number of 2 to the test section is discussed. The performance of the test section is confirmed by CFD simulations. Finally, the intended flow visualisation using particle-image velocimetry is discussed. This includes the identification of a suitable seeding method considering both liquid and solid tracer particles. The assessment is completed considering constraints such as the operating conditions, the required particle size to accurately trace the fluid flow, maintenance issues, and compatibility with the working fluid. In particular, the possibility of using the compressor lubricating oil as the seeding particle is evaluated.

Design and Flow Analysis of a Supersonic Small Scale ORC Turbine Stator With High Molecular Complexity Working Fluid

2014 ◽  
Author(s):  
Antti Uusitalo ◽  
Teemu Turunen-Saaresti ◽  
Alberto Guardone ◽  
Aki Grönman
Keyword(s):  
High Efficiency ◽  
Waste Heat ◽  
Flow Analysis ◽  
Organic Rankine Cycle ◽  
Working Fluid ◽  
Small Scale ◽  
Low Grade ◽  
Real Gas ◽  
Turbine Stator ◽  
Molecular Complexity

In small scale and low temperature waste heat recovery systems, Organic Rankine Cycle (ORC) technology can be identified as a promising solution in converting low-grade heat into electricity. The principle of ORC is based on a conventional Rankine process but an organic working fluid is adopted instead of steam. The use of high molecular complexity working fluids enables the design of high efficiency ORCs and are characterized by dry expansion and high pressure ratios over the turbine, as well as low speed of sound, which typically leads to highly supersonic flows in the ORC turbine stator. In order to design supersonic ORC turbines, the geometry of the turbine stator has to be based on design methods that accurately take into account the real gas effects of the working fluid during the expansion. In this study, a highly supersonic small scale ORC turbine stator using siloxane MDM as working fluid, is studied. The accurate real gas model was implemented in a CFD-flow solver in order to predict the flow field in the stator in design and in off-design conditions. The results of this study gives valuable information on realising small capacity ORC turbomachinery, characterized by highly supersonic stators, and on the off-design performance of supersonic radial turbine stator that has not been documented or discussed in the previous studies.

Sign in / Sign up

Export Citation Format

Share Document