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To increase system efficiency and power density, the cathode air path of Polymer Electrolyte Membrane Fuel Cells (PEM FCs) is supercharged using electrically driven air bearing centrifugal compressors. To maximize system efficiency, the cathode air supply system must be designed to optimally fulfill the requirements of the PEM FC system while obeying the design constraints imposed by the electric compressor drive and the air bearing system. This article proposes a dedicated design process for PEM FC cathode air compressors. Using physically based component models, the impact of varying cathode stoichiometry and operating pressure on PEM FC system performance is assessed to derive the system efficiency optimal compressor operating strategy. The centrifugal compressor stage is subsequently designed to achieve optimum efficiency on this operating line using meanline performance models and three-dimensional computational fluid dynamics simulations. Novel test procedures and measurement equipment are employed to validate the compressor design. The design process is demonstrated using a PEM FC passenger car application as an example. It is shown that significant performance and efficiency gains are achievable when tailoring the cathode air supply system to the application at hand. In the given example, effective compressor efficiency is increased by Δηeff = 12%. Along with an optimized compressor operating strategy, an overall PEM FC system efficiency gain of Δηsys = 2.7% is achieved. [ABSTRACT FROM AUTHOR]

Nanofluid-based finned collector designs have been explored to enhance solar spectrum utilization and thermal efficiency in photovoltaic-thermal (PV/T) systems. Combining nanofluids with finned collector designs improves heat transfer processes. Over the past five decades, various research methods have been used to analyze system performance, including experimental studies, theoretical analysis, design modification, advanced technologies, and soft computing techniques. This research examines the impact of fin geometry on energy conversion of Water/Al2O3-based PV/T systems using 3D CFD modeling simulations using ANSYS Fluent and ANSYS Steady State Thermal software. This study found that the quadrilateral fin geometry produced the lowest PV temperatures, followed by each concentration's pentagon and triangle fin geometries. The PV temperature decreased as the electrical efficiency increased, with the quadrilateral fin geometry with 1% Water/Al2O3 fluid producing the highest efficiency of 12.83%. The amount of PV heat absorbed by the working fluid affects the output temperature, which causes thermal energy conversion to be inversely proportional to electrical efficiency. Pentagon fin geometry with 4% Water/Al2O3 fluid produces the highest thermal conversion of 22.28%. In addition, this study also found significant differences in results for the three fin geometries on the collector, but no significant differences for the six Water/Al2O3 working fluids studied. [ABSTRACT FROM AUTHOR]

This research uses 3D Computational Fluid Dynamics (CFD) simulations to investigate the downhole Natural Gas Separation Efficiency (NGSE) for multiphase pumping wells in the heterogeneous churn flow regime. Results explain the effects of key parameters such as liquid viscosity, intake port sizes/diameter, and casing diameter, on the NGSE. Methods are thus suggested to enhance the NGSE in oil field operations, and key improvements to the widely used mathematical formulations for viscous service are proposed. Transient numerical simulations were performed for a section of an experimental flow loop extracted from the literature, and the flow solution was obtained with the Volume of Fluid (VOF) model. For most simulations, turbulence effects were modelled with the [Formula: see text] turbulence model. The [Formula: see text] SST turbulence model was however considered for the sensitivity analysis on liquid viscosity. The final numerical results validated against the corresponding experimental data showed an average error of less than 6%. Combining past literature and current results confirms that (i), the NGSE is affected by the downhole geometry (i.e annulus space and pump intake port flow area geometry) and (ii), current analytical NGSE models are not ideal for multiphase viscous service (high viscosity Newtonian flow) in the heterogeneous flow regime. The widely used steady-state formulations might thus not be adequate for this flow regime.

Increasing power densities of electric machines in e-vehicles in addition to the resulting quest for enhanced cooling concepts are bringing forward the importance of defining adequate heat transfer correlations in air gaps. This is a highly challenging topic, as there exist no generally applicable flow and heat transfer phenomena descriptions for air gaps due to their highly variable geometrical properties and operating conditions. As an answer to this challenge, this paper presents a workflow that defines an adequate 3D CFD model for an arbitrary air-gap design that includes its system-dependent boundary conditions. The workflow is built on the recognition of underlying air-gap flow phenomena, which are used to steer the subsequent design of the 3D CFD model in a systematic step-by-step manner. Consequently, the complexity of the 3D CFD model gradually increases to the point where it provides an adequate flow and heat transfer description. Validation of the workflow is presented for a wide range of air-gap designs and flow conditions. It is demonstrated that the 3D CFD models obtained with the workflow match the experimentally obtained data from various flow cases that have been documented in the literature. Considerable optimization of computational costs, offering potentially an order-of-magnitude reduction in computational time, is achieved as a result of computational domain span optimization and transient simulations being applied only when required. The validation confirms that this workflow facilitates construction of valid 3D CFD models without the prior knowledge of flow and heat transfer phenomena in a specific air gap. This workflow thus provides a reliable and computationally efficient tool for valorization of convective heat transfer, and opens up prospects for time- and cost-efficient optimizations of electric machines' cooling system designs. [ABSTRACT FROM AUTHOR]

Transient flow characteristics and dissipation mechanism in pressurized pipeline were investigated based on 1D friction models and 3D turbulence models, where the pressure–density model was combined into the 3D continuity equation allowing for the elasticity of the fluid and the pipes. The applicability of 3D realizable k–ε and 3D SST (shear stress transport) k–ω turbulence models was verified with comparison to 1D traditional water hammer models and the experimental data for fast closing of the valve in the reservoir–pipe–valve system. The valve closure rule was instantaneously carried out using the grid slip CFD (computational fluid dynamics) technique. The SST k–ω turbulence model has the highest accuracy in predicting the pressure attenuation of transient flows. The 3D detailed flow field confirms that the asymmetric flows induced by the change of valve opening within approximately three-fourths of the pipe inner diameter before the valve are captured. In the pressure wave cycles, the unsteady inertia, axial pressure gradient, viscous shear stress and turbulent shear stress mainly influence the velocity variations. During the pressure wave propagation, the viscous and turbulent dissipation are critical in the pressure attenuation in the wall region; the viscous dissipation is mainly concentrated in the viscous sublayer, while the turbulent dissipation increases to the maximum values at y+ = 13–23. HIGHLIGHTS The 3D weakly compressible and dissipation mechanism models are introduced to investigate transient flow characteristics.; The asymmetric flows induced by the change of valve opening are captured well within approximately three-fourths of the pipe inner diameter before the valve.; The viscous dissipation is mainly concentrated in the viscous sublayer, while the turbulent dissipation has maximum influence at y+ = 13–23.;

A model for the approximation of cavitation-induced air release in three-dimensional flow simulations is proposed. A cavitating orifice flow is investigated. It is assumed that vapor vanishes in the proximity of the orifice, and bubbles further downstream consist essentially of air. The model is based on a homogeneous mixture assumption and comprises one main parameter, which needs to be adjusted to the experimentally measured degassing fraction. Experimental validation is based on transmission light images downstream of the orifice. In the proximity of the orifice, the inclusion of air release in the CFD simulation yields a better agreement to experimentally measured cavitation intensity than the consideration of pure vapor only. It is concluded that a considerably larger amount of air is released than is dissolved in the evaporated amount of liquid. The simulation results suggest that the released air mass corresponds to about 1% of the evaporated liquid mass. These observations may be a good basis for purposeful future experiments, which are indispensable for the development of a more predictive approach of cavitation-induced air release in 3D CFD methods. [Display omitted] • A compressible solver for cavitating flow is extended by air release. • Air release is modeled by a homogeneous mixture approach. • Inclusion of released air improves the match to shadowgraphy data. • Mass of released air equals about 1% of evaporated liquid mass. [ABSTRACT FROM AUTHOR]

Bu çalışmada doğalgazla çalışan direkt enjeksiyonlu benzinli bir motorda ateşleme zamanının yanma ve emisyonlar üzerine etkileri incelenmiştir. Farklı ateşleme zamanları için motorun 3000 devir şartlarında simülasyonlar gerçekleştirilmiştir. Yanma karakteristikleri ve emisyon oluşumlarını incelemek için üç boyutlu hesaplamalı akışkanlar mekaniği kodu olan ANSYS-Forte 19.0 kullanılmıştır. Tüm simülasyonlar farklı ateşleme zamanları için gaz kelebeğinin tam açık konumunda tekrarlanmıştır. Erken ateşleme zamanlamasında silindir içi basıncın yükseldiği görülürken, HC ve CO emisyonlarında düşüş gözlenmiştir. Ayrıca, erken ateşleme şartlarında düşen HC ve CO emisyonlarına rağmen NOx emisyonlarında artış görülmüştür. Sonuç olarak doğalgazlı motorlarda erken ateşleme zamanında daha yüksek yanma verimi elde edilmiştir.

Increasing power densities of electric machines in e-vehicles in addition to the resulting quest for enhanced cooling concepts are bringing forward the importance of defining adequate heat transfer correlations in air gaps. This is a highly challenging topic, as there exist no generally applicable flow and heat transfer phenomena descriptions for air gaps due to their highly variable geometrical properties and operating conditions. As an answer to this challenge, this paper presents a workflow that defines an adequate 3D CFD model for an arbitrary air-gap design that includes its system-dependent boundary conditions. The workflow is built on the recognition of underlying air-gap flow phenomena, which are used to steer the subsequent design of the 3D CFD model in a systematic step-by-step manner. Consequently, the complexity of the 3D CFD model gradually increases to the point where it provides an adequate flow and heat transfer description. Validation of the workflow is presented for a wide range of air-gap designs and flow conditions. It is demonstrated that the 3D CFD models obtained with the workflow match the experimentally obtained data from various flow cases that have been documented in the literature. Considerable optimization of computational costs, offering potentially an order-of-magnitude reduction in computational time, is achieved as a result of computational domain span optimization and transient simulations being applied only when required. The validation confirms that this workflow facilitates construction of valid 3D CFD models without the prior knowledge of flow and heat transfer phenomena in a specific air gap. This workflow thus provides a reliable and computationally efficient tool for valorization of convective heat transfer, and opens up prospects for time- and cost-efficient optimizations of electric machines’ cooling system designs.

According to the IEC 60041 standard, the pressure-time method (1D PTM) can be employed to determine the flow rate in hydraulic turbines. This method assumes a one-dimensional flow and applies to straight pipes with uniform cross-sections, with specific restrictions on the pipe length, fluid velocity, and distance between the measurement sections from any irregularities in the pipeline. However, challenges arise when applying this method in low-head hydropower plants due to the short lengths, irregularities like bends and developing flows in the intake. The present paper aims to improve the performance of the method in the presence of a bend. To this end, a test rig has been developed and measurements performed, including such geometry. The data are evaluated using the development of a newly proposed approach combining the 1D PTM based on an energy balance formulation and three-dimensional computational fluid dynamics (3D CFD) developed for axis-symmetrical accelerating flows. The updated methodology includes a correction of the experimental pressure measurements used in the 1D PTM to account for the effects of the Dean vortices present after the bend as well as the kinetic energy correction factors which deviate from known values in transient conditions. The results obtained under conditions involving the presence of bends either between or in close proximity to one show a significant improvement compared to the standard one-dimensional pressure-time method. • A laboratory setup is specially designed and built for testing the pressure-time method outside IEC-60041 recommendations. • A novel introduced which extends the method's applicability to account for developing flows affected by bends by incorporating 3D CFD. • Combining experimental data and 3D CFD analysis aims to enhance the traditional 1D PTM methodology. [ABSTRACT FROM AUTHOR]

This study investigates using tailor-developed combustion and air-handling system concepts to achieve high-efficiency, clean gasoline compression ignition (GCI) combustion, aimed at addressing a future heavy-duty ultralow NOx standard of 0.027 g/kWh at the vehicle tailpipe and the tightening CO2 limits around the world by combining GCI with a cost-effective engine aftertreatment system. The development activities were conducted based on a 15 L heavy-duty diesel engine. By taking an analysis-led design approach, a first-generation (Gen1) GCI engine concept was developed and tested, encompassing tailor-designed piston bowl geometry, fuel spray pattern, and swirl motion paired with a customized, fixed-geometry, two-stage turbocharging system and a high-pressure EGR loop with two-stage cooling. Across four key steady-state operating points, the Gen1 GCI concept demonstrated 85–95% lower smoke and 2–3% better diesel-equivalent gross indicated fuel consumption compared to the diesel baseline at 1 g/kWh engine-out NOx. By upgrading to a Gen2 air-handling concept that was composed of a prototype, single-stage, variable-geometry turbocharger and a less restrictive EGR loop, 1D system-level analysis predicted that the pumping mean effective pressure was reduced by 43–54% and the diesel-equivalent brake-specific fuel consumption was improved by 2–4%, thereby demonstrating the performance enhancement potential of refining the air-handling system.

The article describes an interpolation–analytical method of reconstruction of the IAPWS-95 equations of state and the modified Benedict–Webb–Rubin equations of state with 32 terms (mBWR32). The method enables us to provide the thermodynamic closure in 3D computational fluid dynamics (CFD) calculations of turbomachinery flows with real working media, such as steam and Organic Rankine Cycle (ORC) fluids. The described approach allows for the sufficient accuracy of 3D flow calculations and does not require a significant increase in computational cost over perfect gas calculations. The method is validated against experimental data from measurements and compared with computational results from the model using the Tammann equation of state. Three turbine blading systems are considered—a multi-stage configuration from a low-pressure cylinder of a large-power steam turbine and two ORC microturbines working with organic media HFE7100 and R227ea. The calculation results obtained using the described method of approximation of the IAPWS-95 and mBWR32 equations exhibit satisfactory agreement with the experimental data, considering pressures, temperatures and enthalpies in key sections, as well as turbine power and efficiency in a wide range of changing thermodynamic parameters. In contrast, the Tammann equation of state provides acceptable results only for relatively small changes of thermodynamic parameters.

The key issue associated with the thermal power plant is the disposal of ash-water slurry and the process of its transportation is accomplished using long length pipelines. The designing of such pipelines is a vital endeavor of researchers and designers globally. In this perspective, numerical simulation of 42 mm diameter three-dimensional slurry flow pipeline carrying high concentration of mono-dispersed fine ash particles has been carried out. The study is enunciated by employing Eulerian- Eulerian two-phase model with RNG k-ɛ turbulence model with the aim of visualizing and understanding the characteristics of the slurry flow behavior. The coal ash slurry concentration varies between 50% to 70% (by weight) for velocity ranges, 1-3 ms-1. The modeling is done using Fluent commercial software with the intention of predicting the characteristics of flow for 300 μm particle size. It is observed that pressure drop upsurges non-linearly with solid concentrations and slurry velocity across pipeline. The obtained results of predetermined pressure drop are analytically compared with the experimental results. Moreover, the results are also compared with that of Eulerian-Langrange model using SST K-ω turbulence model and it is found that RNG k-ɛ turbulence model yields more accurate and desirable results. [ABSTRACT FROM AUTHOR]

Alteration of the flow characteristics in coronary vessels is correlated with coronary heart disease (CHD). In particular, wall shear stress (WSS) appears to be a hemody-namic key factor in the genesis of CHD. Since computational fluid dynamics (CFD) is a well-known method for the inves-tigation of WSS, it may be a valuable tool for the prediction of CHD. Latest imaging techniques, such as optical coher-ence tomography (OCT) in conjunction with angiography deliver precise 2D data sets of patient-specific vessel geome-try, which can be used for CFD analysis. Current CFD stud-ies utilize patient-specific geometries, but are lacking well defined physiologic inflow conditions.

Graphical abstract Highlights • An Euler-Euler model for the two-phase flow (solid OC and gas fuel) is developed. • 3D unsteady numerical simulations of a CLC unit based on a DCFB are performed. • Good agreement between numerical results and experimental measurements is found. • Numerical results prove the ability of the approach to predict the CLC process. • The local and instantaneous CLC behavior is analyzed and discussed. Abstract In this paper, reactive unsteady three-dimensional numerical simulations of a chemical looping combustion (CLC) unit are presented. The configuration is a 120-kW pilot plant working with perovskite, CaMn 0.9 Mg 0.1 O 3− δ , as the selected oxygen carrier. Numerical simulations were performed using NEPTUNE_CFD code in the frame of an Euler-Euler approach by computing both gas and solid phases in an Eulerian technique, accounting for specific closures in order to model the interphase mass, and momentum and energy transfers. Heterogeneous reduction and oxidation (gas–solid) reactions were modeled by means of a grain model to account for the competing mechanisms of the chemical reaction onto the grain surface, the gaseous diffusion through the product layer around the grain, and the external transfer through the gas mixture surrounding the particle. Results from numerical simulations were assessed against experimental measurements and analyzed in order to acquire insight on the local behavior of reactive gas-particle flow in the CLC system. The theoretical/numerical tool developed in this work can be used for the design upgrade of crucial parts of the system in the stage of scaling-up from pilot to industrial plants. [ABSTRACT FROM AUTHOR]

Coronary diseases are the main reason for death in the western world. Bio-fluid mechanical correlations with arterial diseases are in the focus of our research. To treat occluded vessels, stents are implanted. Stent implantations can be associated with blood flow disruptions leading to restenosis or thrombosis formation. Numerical flow simulation is a promising tool to evaluate the hemodynamic performance of cardiovascular implants, but is resource-intensive in time and computational power. Therefore, a reduction in grid size would be beneficial due to economic exploitation of computational cost. The purpose of this numerical investigation is to substitute the computational domain of a distal stented bifurcation with a stented straight vessel by using the right inlet condition. The deviation of the results of the two different methods to simulate the blood flow situation in a bifurcation is marginal. This inlet can be used for standardised simulations of bifurcations were lesions commonly occur.

This paper presents an experimental and numerical hydrodynamic performance assessment of a 1:50 scale model offshore floating–moored Oscillating Water Column (OWC) wave energy converter. The device is a tension–leg structure with four vertical mooring lines. The performance of the OWC device was investigated for several design parameters including regular and irregular wave conditions of different heights and periods, power take–off (PTO) damping and mooring line pre–tension. A 3D Computational Fluid Dynamics (CFD) model using RANS–VOF approach was constructed and validated against experimental results for regular waves showing good agreement. It was found that the hydrodynamic efficiency of the floating–moored OWC device follows the same general trend as a fully–constrained (fixed) model, but the addition of surge motion in the floating device improved the energy production efficiency over a broader bandwidth around the chamber resonance. Increasing the incoming wave height resulted in a higher efficiency for low–frequency waves, but noticeable reductions in the efficiency were observed in the intermediate– and high– frequency zones. The effectiveness of utilizing offshore OWC devices in deep–water was demonstrated by increasing the extracted energy by a maximum of 7.7 times and 5.7 times when regular and irregular wave heights were doubled, respectively. Decreasing the mooring line pre–tension slightly increases the energy extraction efficiency in the intermediate–frequency zone. [ABSTRACT FROM AUTHOR]

A numerical study has been carried out to investigate heat transfer enhancing flow field in 28 geometrically different sinusoidally, spirally corrugated tubes. To vary the corrugation, the height of corrugation e / D and the length between two successive corrugated sections p / D are varied in the ranges 0–0.16 and 0–2.0 respectively. The 3D Unsteady Reynolds-averaged Navier–Stokes (URANS) equations combined with the transition SST turbulence model are solved using the finite volume method to obtain the fully-developed flow field in a repeatable section of the heat exchangers at a constant wall temperature and at Re = 10 , 000 . By studying the wide range of geometrically different tubes, the flow conditions vary significantly. At low corrugation heights, only a weak secondary flow centred in the corrugated section is present. At higher corrugations heights, the tangential velocity component increases and eventually exceeds the axial velocity component causing the highest pressure to be located at the centre of the corrugated section. At these high corrugation heights, a further increase in corrugation height will at best only result in a small increase in Nusselt number but at a significantly higher pressure loss. To assess the performance as a heat exchanger, the ratio of enhanced Nusselt number to enhanced friction factor η = ( Nu / Nu s ) / ( f / f s ) 1 / 3 compared to the non-corrugated tube is used. Using this parameter, the simulations show a decrease in performance at higher corrugation heights. To link the detailed flow fields to the performance as a heat exchanger, non-dimensional correlations for heat transfer, pressure loss, and performance parameter are given. [ABSTRACT FROM AUTHOR]

The aim if this paper is the analysis of a lubrication circuit adopting two simulation models to study the influence of three different lubrication oils. First, the oils pump performance were analyzed with a tri-dimensional simulation model, realized with the commercial code PumpLinx ® , which allowed to obtain the performance curves of the oil pump, varying the oils. Then the lubrication circuit was studied with a 1D model, realized with the commercial code LMS AMESim ® , and the behaviour of the lubrication circuit was analyzed in terms of pressure drops and components oil consumption. The adopted oils were: 0W30; 5W40 and10W60. In previous activities, both models showed good correlation with experimental data. Analyzing the models results, it was noted that the pressure behavior in the lubrication circuit is highly influenced by the oil, especially for low engine speed and high temperatures. The adopted methodology, that couples mono-dimensional and tri-dimensional models, allowed to analyze the oil influence in a lubrication circuit, avoiding excessive computational cost, but with an acceptable accuracy [ABSTRACT FROM AUTHOR]

Abstract: The main target of nowadays engine designers is to focus on exhaust emissions, fuel consumption and engine performance, so during the design phase of a new internal combustion engine, all the aspects related to friction and mechanical power loss must be deeply considered. And then, also the friction related to engine lubrication system must be analyzed and studied. In this paper a tridimensional CFD analysis of the lubrication circuit oil pump of a modern high-performance engine manufactured by Aprilia will be shown. The model was build up with PumpLinx®, a commercial CFD 3D code by Simerics Inc.®, taking into account all the phenomena associated to the fluid cavitation. The model was validated by data of an experimental campaign performed on a hydraulic test bench, at the Industrial Engineering Department of the University of Naples, Federico II. [Copyright &y& Elsevier]

This study investigates using tailor-developed combustion and air-handling system concepts to achieve high-efficiency, clean gasoline compression ignition (GCI) combustion, aimed at addressing a future heavy-duty ultralow NOx standard of 0.027 g/kWh at the vehicle tailpipe and the tightening CO2 limits around the world by combining GCI with a cost-effective engine aftertreatment system. The development activities were conducted based on a 15 L heavy-duty diesel engine. By taking an analysis-led design approach, a first-generation (Gen1) GCI engine concept was developed and tested, encompassing tailor-designed piston bowl geometry, fuel spray pattern, and swirl motion paired with a customized, fixed-geometry, two-stage turbocharging system and a high-pressure EGR loop with two-stage cooling. Across four key steady-state operating points, the Gen1 GCI concept demonstrated 85–95% lower smoke and 2–3% better diesel-equivalent gross indicated fuel consumption compared to the diesel baseline at 1 g/kWh engine-out NOx. By upgrading to a Gen2 air-handling concept that was composed of a prototype, single-stage, variable-geometry turbocharger and a less restrictive EGR loop, 1D system-level analysis predicted that the pumping mean effective pressure was reduced by 43–54% and the diesel-equivalent brake-specific fuel consumption was improved by 2–4%, thereby demonstrating the performance enhancement potential of refining the air-handling system. [ABSTRACT FROM AUTHOR]

Abstract: Spatially 1D simulations of exhaust gas catalysts are often used in the automotive industry because of short computation times. In fully 3D CFD-based model, the computational requirements increase by several orders of magnitude. A novel approach to 3D simulations of complete exhaust gas aftertreatment systems is proposed in this paper. It is based on a modular combination of standard CFD tool with a user-defined 1D channel model. The employment of external 1D channel model enables more effective computations and gives maximum freedom in definition of realistic reaction kinetics, including non-linear rate laws and fully transient solution of adsorbed components. The approach is validated by comparison of the results from the stand-alone 1D model and single channel CFD simulation. Dynamic simulations of CO oxidation light-off and lean/rich operation of NO x storage catalyst (NSRC, LNT) are then conducted in a test geometry with 10 representative channels and skewed inlet/outlet pipes. Finally, a complex system including bent pipes and conical expansion/constriction parts is simulated with 80 representative channels. It is demonstrated that relatively large deviations can exist between the individual channels. Non-uniform inlet flow distribution affects light-off behaviour as well as breakthrough of adsorbed components, and it may also lead to a different extent of catalyst ageing in individual channels. The combined 3D CFD and 1D channels simulation approach represents an effective tool for analysis of such problems and can help with the design of more efficient exhaust gas aftertreatment systems. [Copyright &y& Elsevier]

Unlined pressure tunnels in sound rock, combined with pressurized sand traps at the downstream end, allow for low-cost construction of hydropower tunnel systems. This design concept is utilized in hydropower plants across the world. Currently, many such power plants are being upgraded with higher installed capacity, which may result in challenges with the sand trap efficiency. A physical scale model test, accompanied by 3D CFD simulations of a case study pressurized sand trap, has been studied for economic retrofitting. The geometric model scale is 1:36.67 while the velocity scale and sediment scale are 1:1 (same average flow velocity and sediment size in model and prototype). This is currently an uncommon scaling approach but with several advantages, as presented in this paper. Various options for retrofitting were investigated. A combined structure of ramp and ribs was found to significantly improve the sediment trap efficiency. The main novelties from this work are the proposed design of the combined ramp and rib structure. Secondary results include an efficient setup for physical scale models of pressurized sand traps and a methodology that combines the benefits of 3D CFD simulations with physical scale models testing for sand trap engineering and design. [ABSTRACT FROM AUTHOR]

The article describes an interpolation-analytical method of reconstruction of the IAPWS-95 equations of state and the modified Benedict-Webb-Rubin equations of state with 32 terms (mBWR32). The method enables us to provide the thermodynamic closure in 3D computational fluid dynamics (CFD) calculations of turbomachinery flows with real working media, such as steam and Organic Rankine Cycle (ORC) fluids. The described approach allows for the sufficient accuracy of 3D flow calculations and does not require a significant increase in computational cost over perfect gas calculations. The method is validated against experimental data from measurements and compared with computational results from the model using the Tammann equation of state. Three turbine blading systems are considered-a multi-stage configuration from a low-pressure cylinder of a large-power steam turbine and two ORC microturbines working with organic media HFE7100 and R227ea. The calculation results obtained using the described method of approximation of the IAPWS-95 and mBWR32 equations exhibit satisfactory agreement with the experimental data, considering pressures, temperatures and enthalpies in key sections, as well as turbine power and efficiency in a wide range of changing thermodynamic parameters. In contrast, the Tammann equation of state provides acceptable results only for relatively small changes of thermodynamic parameters.

• The 1D model is in good agreement with the CFD model. • Regenerators perform effectively at high speeds. • Heat transfer mechanisms are enhanced at high speeds. • Expressions for the heat transfer coefficient vs Reynolds number were generated. • The efficiency of the designed Vuilleumier machine increases with the speed. A one-dimensional analytical model and a three-dimensional CFD numerical model were used for the investigation of the effect that the rotational speed has on several thermodynamic quantities and the performance of a Vuilleumier machine. The machine, was designed as a combination of two opposing Stirling engines. The one-dimensional program was based on the energy balance at each control volume in order to calculate the energy flow inside the machine and then losses were added. On the other hand, the CFD model utilized fundamental conservation equations at each of the numerous computational cells which resulted to accurate calculations at every dimension. It was able to provide the heat transfer coefficients inside the heat exchangers that were in turn utilized by the analytical model. The pressure drop was computed directly at each space by the numerical model and with equations for flow losses from the bibliography by the analytical model. Pressure drop increased significantly with the speed. The effectiveness of the regenerators was evaluated by an existing analytical model and resulted to reduce drastically with the drop of speed. The effectiveness plays very important role on the efficiency of the machine. Furthermore, there appears to be a discrepancy between the heat flow in the heat exchangers and the wall-gas temperature difference at high speeds which has to be examined according to the oscillatory nature of the gas flow. Heat transfer coefficients were generated in relationship with the Reynolds number for each speed investigated, yielding less thermal resistance when the speed is high. Finally, the change of heat amounts through the four heat exchangers and change of the efficiency of the Vuilleumier machine with the speed, resulted to be similar with experimental data. [ABSTRACT FROM AUTHOR]