scholarly journals Flux-Reducing Tendency of Pd-Based Membranes Employed in Butane Dehydrogenation Processes

Membranes ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 291 ◽  
Author(s):  
Thijs A. Peters ◽  
Marit Stange ◽  
Rune Bredesen
Keyword(s):  
Competitive Adsorption ◽  
Prolonged Exposure ◽  
Hydrogen Permeation ◽  
State Of The Art ◽  
Operating Temperature ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Hydrogen Flux ◽  
Membrane Performance ◽  
Wide Range

We report on the effect of butane and butylene on hydrogen permeation through thin state-of-the-art Pd–Ag alloy membranes. A wide range of operating conditions, such as temperature (200–450 °C) and H2/butylene (or butane) ratio (0.5–3), on the flux-reducing tendency were investigated. In addition, the behavior of membrane performance during prolonged exposure to butylene was evaluated. In the presence of butane, the flux-reducing tendency was found to be limited up to the maximum temperature investigated, 450 °C. Compared to butane, the flux-reducing tendency in the presence of butylene was severe. At 400 °C and 20% butylene, the flux decreases by ~85% after 3 h of exposure but depends on temperature and the H2/butylene ratio. In terms of operating temperature, an optimal performance was found at 250–300 °C with respect to obtaining the highest absolute hydrogen flux in the presence of butylene. At lower temperatures, the competitive adsorption of butylene over hydrogen accounts for a large initial flux penalty.

A State-of-the-Art CFD Setup for Axial Compressors: Details and Validation

2020 ◽  
Author(s):  
Lorenzo Cozzi ◽  
Filippo Rubechini ◽  
Andrea Arnone ◽  
Savino Depalo ◽  
Pio Astrua ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Power Plants ◽  
State Of The Art ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Cfd Modelling ◽  
Axial Compressors ◽  
Surge Margin ◽  
Wide Range

Abstract The overall fraction of the power produced by renewable sources in the energy market has significantly increased in recent years. The power output of most of these clean sources is intrinsically variable. At present day and most likely in the upcoming future, due to the lack of inexpensive and reliable large energy storage systems, conventional power plants burning fossil fuels will still be part of the energy horizon. In particular, power generators able to promptly support the grid stability, such as gas turbines, will retain a strategic role. This new energy scenario is pushing gas turbine producers to improve the flexibility of their turbomachines, increasing the need for reliable numerical tools adopted to design and validate the new products also in operating conditions far from the nominal one. Especially when dealing with axial compressors, i.e. machines experiencing intense adverse pressure gradients, complex flow structures and severe secondary flows, CFD modelling of offdesign operation can be a real challenge. In this work, a state-of-the art CFD framework for RANS analysis of axial compressors is presented. The various aspects involved in the whole setup are discussed, including boundary conditions, meshing strategies, mixing planes modelling, tip clearance treatment, shroud leakages and turbulence modelling. Some experiences about the choice of these aspects are provided, derived from a long-date practice on this kind of turbomachines. Numerical results are reported for different full-scale compressors of the Ansaldo Energia fleet, covering a wide range of operating conditions. Furthermore, details about the capability of the setup to predict compressor performance and surge-margin have been added to the work. In particular, the setup surge-margin prediction has been evaluated in an operating condition in which the turbomachine experiences experimental stall. Finally, thanks to several on-field data available at different corrected speeds for operating conditions ranging from minimum to full load, a comprehensive validation of the presented numerical framework is also included in the paper.

Advanced Components for PEMFC Stacks

2006 ◽  
Author(s):  
Chinbay Fan ◽  
Michael Onischak ◽  
William Liss
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
State Of The Art ◽  
Low Cost ◽  
Polymer Membrane ◽  
Operating Conditions ◽  
Metal Alloy ◽  
Membrane Electrode ◽  
Corrosion Rates ◽  
Wide Range

Currently, fuel cell cost reduction and long life are major priorities for fuel cells to be commercially successful for vehicle, stationary, or portable power applications. In the last five years, Gas Technology Institute (GTI) has formulated and developed a low cost, long lifetime, high conductivity proton exchange membrane (PEM) yielding state-of-the-art fuel cell performance. Additionally, a non-coated, corrosion-resistant metal alloy bipolar separator plate has been patented and tested for both hydrogen-fueled and direct methanol fueled PEMFC applications. Tests in fuel cells plus out-of-cell ASTM corrosion tests have shown very low corrosion rates under fuel cell operating conditions. Metal alloy separator plates have run for over 23,000 hours in cells with corrosion rates an order of magnitude less than the DOE target of 1 μA/cm2. GTI’s fuel cell polymer membrane research focused on three criteria: (1) use of low cost materials; (2) polymer structures stable under fuel cell operating conditions; and (3) performance equal or better than current Nafion membrane electrode assemblies (MEAs). Fluorine-containing polymers were eliminated due to cost issues, environmental factors, and the negative influence fluorine ion loss has on metallic separator plates. The polymer membrane material was synthesized and cast into films, then fabricated into MEAs. The cost of the membrane (raw materials plus film processing materials) is estimated to be less than $10/m2 — or less than 10% of available technology. A variety of out-of-cell testing showed the membrane has sufficient strength, flexibility, and conductivity to serve as an ion conducting membrane for fuel cells. A series of 60 cm2 active area single cells and short stacks were operated over a wide range of fuel cell conditions, showing state-of-the-art MEA performance with long-term polymer stability.

Condition Management of HP/HT Pipelines: A New Approach

2008 ◽  
Author(s):  
Hroar Nes ◽  
Birger Etterdal ◽  
Stian Svardal
Keyword(s):  
Survey Data ◽  
Failure Modes ◽  
Hot Spot ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Design Criteria ◽  
Integrity Assessment ◽  
Safety Margins ◽  
Wide Range ◽  
Relative Utilization

StatoilHydro operates a large number of High Pressure/High Temperature (HP/HT) pipeline systems in the Norwegian Sea. These lines connect remote subsea templates to floating processing and storage units. Flowlines are designed for a maximum temperature up to 155 °C and a pressure in the range of 390–500 bar. Design pressure for injection lines are in general 500 bar. In addition to high operating loads, the infield lines are exposed to challenging seabed conditions and a potential for interference with on-bottom trawl gear. The objective of this paper is to present the principles and the methodology used for integrity assessment of the HP/HT lines, which provides the basis for specification of optimum maintenance requirements. The risk of integrity failure, associated with any hot-spot location, is consistently estimated based on safety margins predicted for the actual design criterion and as a function of the pre-defined Safety Class. The developed methodology assumes that the pipeline configuration and associated response parameters are accurately determined for relevant operating conditions. This requires finite element models that are calibrated according to survey data and corresponding operating parameters. A cyclic load history is applied to the post-buckled pipeline model in order to simulate actual operating conditions. Design criteria for relevant degradation and failure modes are established for a wide range of operating configurations and conditions. These criteria are used both to identify potential hot-spots and to estimate the relative utilization. The relative utilization may be estimated for an extreme single event, i.e. a design condition, or due to long term degradation. The risk of integrity failure is then determined as a function of the Safety Class and the relative utilisation, expressing the consequences and the probability of failure, respectively. A risk matrix, configured according to design safety principles, determines the risk of integrity failure. A software interface has been developed to compare and to visualize pipeline simulation results, survey data and corresponding design criteria. This information is used for documentation of the pipeline operating condition, and finally, for specification and follow-up of maintenance measures. The new integrity assessment methodology has been implemented as part of the condition management system for more than 30 HP/HT pipelines operated by StatoilHydro.

scholarly journals Thermal Analysis of Direct Liquid-Immersed Solar Receiver for High Concentrating Photovoltaic System

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Xinyue Han ◽  
Qian Wang ◽  
Jun Zheng ◽  
Jian Qu
Keyword(s):  
Solar Cells ◽  
Conversion Efficiency ◽  
Flow Rate ◽  
Triple Junction ◽  
Concentration Factor ◽  
Operating Temperature ◽  
Operating Conditions ◽  
Dense Array ◽  
Wide Range ◽  
Solar Receiver

Concentrator solar cells that operate at high solar concentration level must be cooled. In this paper, direct liquid immersion cooling of triple-junction solar cells (InGaP/InGaAs/Ge) is proposed as a heat dissipation solution for dense-array high concentrating photovoltaic (HCPV) systems. The advantages of triple-junction CPV cells immersed in a circulating dielectric liquid and dish HCPV technology are integrated into a CPV system to improve the system electrical conversion efficiency. An analytical model for the direct liquid-immersed solar receiver with triple-junction CPV cells is presented. The main outputs of the model are the components temperatures of the receiver and the system electrical efficiency. The influence of concentration factor, mass flow rate, and inlet liquid temperature on the operating temperature of the triple-junction CPV cells and the system electrical conversion efficiency are discussed. It is shown that the system electrical conversion efficiency is very high for a wide range of operating conditions. The three operating parameters have a major effect on the operating temperature of the triple-junction CPV cells and, by extension, system output power. The flow rate selection should match concentration factor to keep the triple-junction CPV cells temperature lower and increase the electrical conversion efficiency of the dense-array HCPV system.

scholarly journals Identification of a Material–Lubricant Pairing and Operating Conditions That Lead to the Failure of Porous Journal Bearing Systems

2020 ◽  
Vol 68 (4) ◽  
Author(s):  
Guido Boidi ◽  
Stefan Krenn ◽  
Stefan J. Eder
Keyword(s):  
Mixed Lubrication ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Asperity Contact ◽  
Operational Conditions ◽  
Practical Applications ◽  
Custom Made ◽  
Wide Range ◽  
Lab Test ◽  
Wear Tests

AbstractIn this study, we perform accelerated wear tests with porous journal bearings (PJBs) on a lab test rig, providing statistically reliable results under realistic operational conditions. To this end, a custom-made tribometer consisting of 5 mechanically independent but centrally controlled units was used to test five identical bearings in parallel. The test parameters were tuned to promote enough wear under mixed lubrication by increasing the clearance gap and the radial load, while minimizing the bidirectional rotational speed. A wide range of lubricant and material combinations were evaluated, the vast majority of which performed excellently (i.e., negligible wear and low friction). Only one notable combination of a low-density iron bearing paired with a standard PAO-based lubricant failed when operating at low rotational speeds, exhibiting highly unstable frictional behavior and 10–20 times the typical wear in practical applications. An analysis of Stribeck curves, recorded periodically during the wear tests as a diagnostic tool, proved that this particular combination of materials and parameters failed to run in properly, with deteriorating tribological behavior over time. A direct relation between the total wear and the maximum temperature in the tribocontact during testing helped identify this pairing as the only one operating solely under mixed lubrication (high asperity contact), explaining the excessive wear. Graphical Abstract

Extremely Low Mass Flow at High Blade to Jet Speed Ratio in Variable Geometry Radial Turbines and its Influence on the Flow Pattern: A CFD Analysis

2017 ◽  
Author(s):  
José Ramón Serrano ◽  
Antonio Gil ◽  
Roberto Navarro ◽  
Lukas Benjamin Inhestern
Keyword(s):  
Mass Flow ◽  
Flow Instability ◽  
State Of The Art ◽  
Flow Behavior ◽  
Weight Ratio ◽  
Operating Conditions ◽  
Speed Ratio ◽  
Cfd Simulations ◽  
Wide Range ◽  
Low Mass

State of the art car engines are fed by compressed air, coming from a turbocharger compressor, to increase the power to weight ratio and to allow downsizing the combustion engine. The used compressor is driven by a radial turbine taking advantage of the hot and pressurized exhaust gases of the engine. Thus, the turbine acts under highly unsteady conditions, working at very different turbine map regions. In urban driving the turbine faces even higher changes due to frequent acceleration and deceleration so that extremely low mass flow can occur. However, the flow behavior in turbocharger turbines at these extreme off-design conditions is rather unknown. So the development of physically-based models for extrapolating the usually narrow experimental turbine maps and advanced measurements to increase the range of turbine maps has been in the focus of many researchers. To provide valuable information about those flow characteristics, this paper supplies a detailed analysis at low mass flow in a radial turbocharger turbine. The turbine has been experimentally characterized under steady flow from normal operating working conditions up to extreme off-design points, where the turbine could even work with negative efficiency. Since heat transfer significantly affects the turbine efficiency calculation when turbine power is low, the experiments have been executed under quasi-adiabatic conditions and residual heat fluxes have further been corrected. This paper takes advantage of these data to validate adiabatic CFD simulations in a wide operating range, from optimum efficiency point up to negative turbine power. Stationary and transient three-dimensional CFD simulations of the turbocharger turbine have been performed. The numerical campaign covers a wide range of operating conditions, providing different flow patterns. The obtained results show that the secondary flow field changes appreciably with mass flow rate. At low mass flows, a further backflow region develops over the entire circumference close to the hub, significantly constricting the effective turbine area and provoking mass flow instability. The highlighted flow phenomena will allow to improve state of the art extrapolation models and might help designers to understand turbine flow operating under extreme off-design conditions.

scholarly journals Modeling of H2 Permeation through Electroless Pore-Plated Composite Pd Membranes Using Computational Fluid Dynamics

Membranes ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 123
Author(s):  
Alberto Fernández ◽  
Cintia Casado ◽  
David Alique ◽  
José Antonio Calles ◽  
Javier Marugán
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Hydrogen Permeation ◽  
Membrane Surface ◽  
Molar Fraction ◽  
Operating Conditions ◽  
Cfd Modeling ◽  
Wide Range ◽  
The Impact

This work focused on the computational fluid dynamics (CFD) modeling of H2/N2 separation in a membrane permeator module containing a supported dense Pd-based membrane that was prepared using electroless pore-plating (ELP-PP). An easy-to-implement model was developed based on a source–sink pair formulation of the species transport and continuity equations. The model also included the Darcy–Forcheimer formulation for modeling the porous stainless steel (PSS) membrane support and Sieverts’ law for computing the H2 permeation flow through the dense palladium film. Two different reactor configurations were studied, which involved varying the hydrogen flow permeation direction (in–out or out–in). A wide range of experimental data was simulated by considering the impact of the operating conditions on the H2 separation, such as the feed pressure and the H2 concentration in the inlet stream. Simulations of the membrane permeator device showed an excellent agreement between the predicted and experimental data (measured as permeate and retentate flows and H2 separation). Molar fraction profiles inside the permeator device for both configurations showed that concentration polarization near the membrane surface was not a limit for the hydrogen permeation but could be useful information for membrane reactor design, as it showed the optimal length of the reactor.

scholarly journals An Introduction to Indoor Localization Techniques. Case of Study: A Multi-Trilateration-Based Localization System with User–Environment Interaction Feature

2021 ◽  
Vol 11 (16) ◽  
pp. 7392
Author(s):  
Bruno Andò ◽  
Salvatore Baglio ◽  
Ruben Crispino ◽  
Vincenzo Marletta
Keyword(s):  
System Architecture ◽  
Indoor Localization ◽  
State Of The Art ◽  
Operating Conditions ◽  
Environment Interaction ◽  
End User ◽  
Localization System ◽  
Wide Range ◽  
Continuous Estimation

The problem of estimating the indoor position of a person or an object, also known as indoor localization, has gained a lot of interest in the last decades. Actually, this feature would be valuable in many application contexts, from logistics to robotic and Assistive Technology. Different solutions have been proposed in the literature, exploiting a wide range of approaches. This paper aims to provide a brief review of the state-of-the-art approaches in the field, as well as to present the RESIMA case study. The latter exploits an ultrasound-based indoor localization system and a User–Environment Interaction functionality, which allows for performing the continuous estimation of the distance between the end-user and objects in the environment. The latter is valuable to provide the end-user with efficient assistance during the environment exploitation. The main focus of this work is related to the overall description of the system architecture, the trilateration algorithm adopted for the sake of user localization and the estimation of the delay time produced by user-distance computation under different operating conditions.

Gear surface temperature monitoring

2005 ◽  
Vol 219 (2) ◽  
pp. 99-105 ◽  
Author(s):  
J Yi ◽  
P D Quiñónez
Keyword(s):  
Surface Temperature ◽  
Frictional Heating ◽  
Temperature Monitoring ◽  
Operating Conditions ◽  
Tooth Surface ◽  
Maximum Temperature ◽  
Computer Data ◽  
Contact Points ◽  
Wide Range ◽  
Gear Surface Temperature

Frictional heating from rolling and sliding contacts of gear teeth is of extreme importance for monitoring the condition of a gear transmission under its continuing operation. The surface temperature holds the critical information about the condition of a gear. A new power circulating gear test rig with a multichannel computer data acquisition system was built to develop various sensor technologies for gear surface temperature monitoring. In this paper, gear surface temperature monitoring will be presented by using miniature thermocouples. Five miniature type-K thermocouples of 125 μm in diameter were embedded underneath the tooth surface of a spur gear, and real-time surface temperature variations from a wide range of operating conditions were measured. The various effects of load, rotating speed, and meshing point on the surface temperature are discussed. The results attained in this study indicate that the maximum temperature rise occurs on the dedendum, close to the dedendum circle, and the maximum surface temperature difference at the various contact points along the tooth profile was 13°C. Among the various temperature monitoring techniques, the thermocouple is a very reliable and practical means for online gear condition monitoring.

Experimental Investigation of a Flat-Plate Oscillating Heat Pipe With Groove-Enhanced Minichannels

2020 ◽  
Vol 12 (6) ◽  
Author(s):  
Matthew J. Rhodes ◽  
Scott M. Thompson
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Heat Pipe ◽  
Operating Temperature ◽  
Operating Conditions ◽  
Working Fluid ◽  
Oscillating Heat Pipe ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Wide Range

Abstract The thermal and capillary performance of a groove-enhanced, or “microchannel-embedded,” flat-plate oscillating heat pipe (MC FP-OHP) was experimentally investigated while varying heating width, orientation, working fluid and operating temperature. The copper MC FP-OHP possessed two layers of 1.02 × 1.02 mm2 square channels, with the center 14 channels possessing two embedded microchannels (0.25 × 0.13 mm2) aligned coaxially with the primary minichannels. A FP-OHP without embedded microchannels, but with deeper minichannels (DC FP-OHP), was also tested for comparison. The FP-OHPs were filled with Novec 7200 or water (both at 80% ± 2% by volume), and the heating widths were varied between full-width and localized configurations: 38.71 cm2 and 14.52 cm2, respectively. Experimental results demonstrate that the MC FP-OHP is significantly less sensitive to operating orientation and can perform with less detriment as heat flux increases. The MC FP-OHP has a lower startup heating requirement and provides more fluid wetting along the FP-OHP structure—which is advantageous for pumping liquid from the evaporator to the condenser. The MC FP-OHP has enhanced convective heat transfer during operation, as it was observed to have similar or lower thermal resistances to that of the DC FP-OHP for a wide range of operating conditions. The groove-enhanced minichannel within the MC FP-OHP also provides for enhanced heat transfer because there being more thin-film evaporation sites and vapor–liquid mixing between the minichannel and microchannels.

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