Diffuser Geometry Research Articles

Performance Measurements of a Low Specific Speed TurboClaw® Compressor

Low specific speed compressors have been historically based on positive displacement machines. Attempts to bring advantages of turbomachinery such as oil free, low parts counts, low cost of manufacture, and reliability to low flow rate applications have not been sparse, but the principle difficulty has always been that the conventional turbomachine design operates at ultra-high speed to deliver low volume flow rates. This is synonymous with low efficiency due to higher losses (windage, surface finish, and tip clearances). The innovative TurboClaw® design is a low specific speed turbomachinery with forward swept impeller geometry. It owes its high efficiency and operational stability to careful design of its nearly tangential forward swept blading and diffuser geometry.

Chlorination reaction kinetics of CsI under cladding hull waste treatment condition: a TGA study

The reaction between cesium iodide (CsI) and chlorine gas was quantitatively investigated using a thermo-gravimetric analysis system. A comparison between calculated and experimental results on the chlorine molar flow rate revealed that the reaction lies within the gas phase diffusion limited region under the condition of this work. Using the experimental data, the second-order nucleation and growth model was identified as the best geometry function to describe the morphological changes of CsI during the chlorination reaction. Combining the gas phase diffusion equation and geometry function, a reaction rate equation was proposed for the reaction between CsI and Cl2.

0518 潮流発電用の往復流型ディフューザーの数値解析

The bi-directional impulse turbine and the bi-directional diffuser for tidal energy conversion is investigated in this paper. The bi-directional impulse turbine with fixed guide vanes is adopted because the turbine has a large efficiency and an advantage of maintenance. The turbine characteristics is obtained experimentally by the air turbine test rig. As a bi-directional diffuser suitable for the bi-directional impulse turbine, the diffuser geometry is proposed, which has a straight part and a semicircular brim part. By using a CFD analysis, the diffuser geometries are selected for the water flow turbine. Numerical results showed that the install of the brim can reduce the flow resistance.

STUDY OF THE CONFIGURATION AND PERFORMANCE OF AIR-AIR EJECTORS BASED ON CFD SIMULATION

This paper describes a numerical study of gas-gas ejector performance for different operating conditions and geometrical configurations. The performance of ejector obtained based on a simulation procedure of linearized and axisymmetric subsonic and supersonic flow using Fluent Package. A conventional finite-volume scheme utilized to solve two-dimensional transport equations with the standard k-ω SST turbulence model. The model is solved in three regions namely, the primary flow nozzle, the secondary flow channel, and the region of interaction between the supersonic nozzle jet and the secondary flow. The effect of gas motive pressure the mixing part and tail section (pipe or diffuser) geometry on the ejector performance are studied. The computational results are validated using published experimental data with acceptable agreements. The numerical results indicate that the ejector geometry has a pronounced effect on the flow parameters (i.e., pressure and gas velocity) and the ejector performance. In addition, predicted numerical results indicate that when the motive-stream velocity exceeds the speed of sound, shock waves are unavoidable inside ejectors and that shock wave pattern in mixing part has a dominant effect on ejector performance. In addition, the results indicate that the shock location inside the nozzle and the separation point are affected by the motive pressure. The results show also that configuration with convergent-divergent mixing section is much better for mixing process than the other tested configurations.

Performance of vertical diffusers carrying Gas-solid flow: experimental and numerical studies

In the present work, numerical and experimental studies are carried out to investigate the performance of vertical straight-walled conical diffusers carrying air-solid two-phase flow. Eulerian-Lagrangian approach is used to numerically simulate the two phases using the Chen-Kim k-ε turbulence model. The continuous phase (gas) is simulated using Eulerian frame by solving Reynolds-Averaged Navier-Stokes equations (RANS), while the dispersed phase (solids) is simulated using particle tracking method. Coupling between the two phases is established by adding particle source terms and void fraction in the continuous phase equations. A 4-way coupling is adapted to include the effect of particle-particle collisions. Lift forces, particle dispersion and particle-wall collisions are also considered in the simulation of solid-phase. The experimental study is carried out on a pilot scale vertical pneumatic transport system. Four different diffuser geometries are tested at various inlet-Reynolds numbers and mass loading ratios. Sand particles of different sizes and mass flow rates are used to represent the solid phase. Comparisons between numerical predictions and experimental results indicated good agreement. The effects of solid parameters are significant for small angled-diffusers and decrease as the diffuser angle increases. It is also found that, there is a significant decrease in the separation zone within diffuser due to the presence of solid particles. Energy is transferred from the gas phase to the solid phase in the upstream pipe. This energy is transferred again to the gas phase through the diffuser and its downstream tangent pipe. The rate of energy transfer is enhanced by increasing the solid mass flow rate and decreasing the particle size. The results show that the mass loading and size of solid particles have significant effects on the diffuser loss coefficient.

과급기의 고압력비 원심압축기 공력설계 및 시험평가

ABSTRACT It is necessary to design a compressor with high pressure ratio that satisfies the IMO(international maritime organization) NOx emission regulation for the marine diesel engine. Impeller was designed using the modified slip factor with the flow coefficient. The main purpose of this study is to investigate the sensitivity of the compressor performance by the vaned diffuser geometries. The first vaned diffuser type was based on a NACA airfoil, the second was channel diffuser, and the third was conformally transformated configuration of a NACA65(4A10)06 airfoil. The sensitivity of the performance was calculated using a commercial CFD program for three different diffuser geometries. The channel diffuser showed the wide range of operation and higher pressure characteristics, comparing with the others. This is attributed to the flow stability at diffuser. Combined with this results with impeller design, the optimized compressor was designed and verified by the test results. Unit ValuePower kW 1,200Volumetric flow rate m

A linear gradient line source facilitates the use of diffusion models with high order approximation for efficient, accurate turbid sample optical properties recovery.

In this paper, we demonstrate that a scanning MEMS mirror can be employed to create a linear gradient line source that is equivalent to a planar source. This light source setup facilitates the use of diffusion models of increased orders of approximation having closed form solution, and thus enhance the efficiency and accuracy in sample optical properties recovery. In addition, compared with a regular planar light source, the linear gradient line source occupies much less source area and has an elevated measurement efficiency. We employed a δ-P1 diffusion equation with a closed form solution and carried out a phantom study to understand the performance of this new method in determining the absorption and scattering properties of turbid samples. Moreover, our Monte Carlo simulation results indicated that this geometry had probing depths comparable to those of the conventional diffuse reflectance measurement geometry with a source-detector separation of 3 mm. We expect that this new source setup would facilitate the investigating of superficial volumes of turbid samples in the wavelength regions where tissue absorption coefficients are comparable to scattering coefficients.

Simulation of Complete Liquid-Vapor Phase Change inside Divergent Porous Evaporator

Complete phase change process within a divergent porous evaporator is numerically investigated in this paper. A smoothing algorithm, proposed by the present authors, is used in order to deal with the discontinuity in effective diffusion coefficient. Effects of various parameters on the temperature distribution are carefully investigated, which clearly indicate that operating conditions and the geometry of diffuser strongly influence the outlet condition of steam, whereas, porous media properties have only minor impact.

Experimental and geologic evaluation of monazite (U–Th)/He thermochronometry: Catnip Sill, Catalina Core Complex, Tucson, AZ

Monazite is a petrologically important and analytically promising target for (U–Th)/He thermochronology. Previous studies have reported highly variable He diffusion results from monazite from a single sample and demonstrated that composition can significantly affect He diffusion parameters. In this study, we performed incremental heating of single monazite grains to experimentally determine the 4He diffusion properties of reference monazite ‘554’ that occurs within a peraluminous two-mica granite from the Catnip Sill within the Catalina Core complex, Arizona. Assuming that the grain size defines the diffusion geometry, the six experiments yielded Ea values of 212 to 238±5 kJmol−1 (1σ) and Do values of 15.7 to 103 cm2s−1 with one value of 784 cm2s−1. Monazite (U–Th)/He data from five grains yielded closure temperatures of 291 to 262 °C (± c. 15 °C) and ages of 23.8–20.3(±∼1.2;2σ) Ma; the weighted mean age is 21.8±0.73 (MSWD=1.83, n=5) and the weighted mean closure temperature is 282±6°C (MSWD=0.96, n=5;1σ). We tested the accuracy of these results by comparing our monazite thermochronology data with monazite Th/Pb depth profiling results, the 40Ar/39Ar thermal history for the Catnip Sill constrained using coexisting muscovite, biotite, and K-feldspar, and published regional zircon and apatite fission track results. The monazite Th/Pb data indicate emplacement of the Catnip Sill at ∼45 Ma. The 40Ar/39Ar muscovite and biotite data indicate cooling from 460 to 350 °C from 27 to 26 Ma. K-feldspar MDD modeling suggests cooling from 360 to 240 °C from 26 to 24 Ma. Zircon fission track data indicate cooling through 250 °C between 29 and 20 Ma. Additional cooling through 110 °C is recorded by apatite fission track ages of 19–16 Ma. Because the monazite thermochronology results are reproducible and consistent with the thermal history constrained by the other chronometers, our results 1) confirm the accuracy of the 4He diffusion kinetics from monazite ‘554,’ and 2) demonstrate that monazite can be an effective (U–Th)/He thermochronometer, provided that He diffusion properties are either measured or reasonably assumed for each sample.

Flow control of a boundary layer ingesting serpentine diffuser via blowing and suction

The use of serpentine boundary layer ingesting (BLI) diffusers offers a significant benefit to the performance of Blended Wing Body (BWB) aircraft. However, the inherent diffuser geometry combined with a thick ingested boundary layer creates strong secondary flows that lead to severe flow distortion at the engine face, increasing the possibility of engine surge. This study investigated the use of enabling active flow control methods to reduce engine-face distortion. An ejector-pump based system of fluidic actuators was used to directly manage the diffuser secondary flows. This system was modeled computationally using a boundary condition jet modeling method, and tested in an ejector-driven wind tunnel facility. This facility is capable of simulating the high-altitude, high subsonic Mach number conditions representative of BWB cruise conditions, specifically a cruise Mach number of 0.85 at an altitude of 12,000 m. The tunnel test section used for this experiment was designed, built, and tested as a validation tool for the computational methods.

Affine Invariant Geometry for Non-rigid Shapes

Shape recognition deals with the study geometric structures. Modern surface processing methods can cope with non-rigidity--by measuring the lack of isometry, deal with similarity or scaling--by multiplying the Euclidean arc-length by the Gaussian curvature, and manage equi-affine transformations--by resorting to the special affine arc-length definition in classical equi-affine differential geometry. Here, we propose a computational framework that is invariant to the full affine group of transformations (similarity and equi-affine). Thus, by construction, it can handle non-rigid shapes. Technically, we add the similarity invariant property to an equi-affine invariant one and establish an affine invariant pseudo-metric. As an example, we show how diffusion geometry can encapsulate the proposed measure to provide robust signatures and other analysis tools for affine invariant surface matching and comparison.

37.3: Viewing Direction Measurements with Hemispherical Diffuse Illumination on E‐Paper Displays

AbstractViewing direction measurements on reflective e‐paper displays under hemispherical diffuse illumination are an essential part of characterizing reflectance under common usage conditions such as outdoor shade, or indirect indoor lighting. This paper proposes a hemispherical diffuse illumination geometry based on splitting a sampling sphere into two hemispheres to allow the light measuring device to be pointed at the display at different angles. First results on e‐paper agree well with conventional sampling sphere data, show the effects of top layer and surface reflection, and were used to predict the viewing direction distribution of ambient contrast ratio.

Imaging tumor hypoxia: Blood-borne delivery of imaging agents is fundamentally different in hypoxia subtypes

Hypoxic tissue subvolumes are a hallmark feature of solid malignant tumors, relevant for cancer therapy and patient outcome because they increase both the intrinsic aggressiveness of tumor cells and their resistance to several commonly used anticancer strategies. Pathogenetic mechanisms leading to hypoxia are diverse, may coexist within the same tumor and are commonly grouped according to the duration of their effects. Chronic hypoxia is mainly caused by diffusion limitations resulting from enlarged intercapillary distances and adverse diffusion geometries and — to a lesser extent — by hypoxemia, compromised perfusion or long-lasting microregional flow stops. Conversely, acute hypoxia preferentially results from transient disruptions in perfusion. While each of these features of the tumor microenvironment can contribute to a critical reduction of oxygen availability, the delivery of imaging agents (as well as nutrients and anticancer agents) may be compromised or remain unaffected. Thus, a critical appraisal of the effects of the various mechanisms leading to hypoxia with regard to the blood-borne delivery of imaging agents is necessary to judge their ability to correctly represent the hypoxic phenotype of solid malignancies.

Optimization of the automotive microturbine diffuser output geometry

The article considers development of the output axial-radial diffuser of automotive gas-turbine plant power turbine. The completed mathematical gas flow study optimized the diffuser geometry, which improves the power efficiency of stage power turbine, helping to achieve high efficiency of a microturbine.

Uncertainty quantification and race car aerodynamics

Car aerodynamics are subjected to a number of random variables which introduce uncertainty into the downforce performance. These can include, but are not limited to, pitch variations and ride height variations. Studying the effect of the random variations in these parameters is important to predict accurately the car performance during the race. Despite their importance the assessment of these variations is difficult and it cannot be performed with a deterministic approach. In the open literature, there have been no studies dealing with this uncertainty in car racing aerodynamics modelling the complete car and assessing the probability of a competitive advantage introduced by a new geometry. A stochastic method is used in this work in order to predict the car downforce under stochastic variations and the probability of obtaining a better performance with a new diffuser geometry. A probabilistic collocation method is applied to an innovative diffuser design to prove its performance with stochastic geometrical variations. The analysis is conducted using a complete three-dimensional computational fluid dynamics simulation with a k–ω turbulence closure, allowing the performance of the physical diffuser to be more accurately represented in a stochastic real environment. The random variables included in the analysis are the pitch variations and the ride height variations in different speed conditions. The mean value and the standard deviation of the car downforce are evaluated.

Optimization of Fractional Order Dynamic Chemical Processing Systems

In this work we address the dynamic simulation and optimization of chemical processing systems modeled in terms of fractional order differential equations. While fractional derivatives were first proposed by Liouville in 1832 [Samko et al. Fractional Integrals and Derivatives Theory and Applications; Gordon and Breach: New York, 1993; Oldham and Spanier. The fractional Calculus; Academic Press: New York, 1974], fractional differential equation (FDE) models have been only recently been explored. These have been proposed for a wide range of applications that include systems with nonlocal diffusion phenomena and geometries with fractal dimensions. FDE models have been shown to have advantages over traditional integer order models, as they often avoid scale dependent model parameters. For medium or large scale applications of FDEs normally no analytical solutions are available, and therefore, approximated numerical solutions ought to be sought. Moreover, little work has been done to solve fractional order dif...

Structural Study of Citrate Layers on Gold Nanoparticles: Role of Intermolecular Interactions in Stabilizing Nanoparticles

The structure of citrate adlayers on gold nanoparticles (AuNPs) was investigated. Infrared (IR) and X-ray photoelectron spectroscopy (XPS) analyses indicate citrate anions are adsorbed on AuNPs through central carboxylate groups. A unique structure of adsorbed citrate is determined, and a pH-induced structural transition is presented. IR analysis probes dangling dihydrogen anions (H2Citrate(-)) and hydrogen bonding of carboxylic acid groups between adsorbed and dangling citrate anions. A contribution of steric repulsion between citrate layers to particle stability is characterized. Structure-based modeling, which is consistent with scanning tunneling microscopy (STM) and transmission electron microscopy (TEM) images in the literature, suggests organization details relating to the formation of self-assembled layers on (111), (110), and (100) surfaces of AuNPs. Adsorption characteristics of the citrate layer include the interaction between hydrogen-bonded citrate chains, bilayer formation, surface coverage, and chirality. The enthalpic gain from intermolecular interactions and the importance of molecular structure/symmetry on the adsorption are discussed. Combining the enthalpic factor with surface diffusion and adsorption geometry of (1,2)-dicarboxyl fragments on Au(111), H2Citrate(-) anions effectively stabilize the (111) surface of the AuNPs. The detailed understanding of intermolecular interactions in the molecular adlayer provides insight for nanoparticle formation and stabilization. We expect these findings will be relevant for other nanoparticles stabilized by hydroxy carboxylate-based amino acids and have broad implications in NP-based interfacial studies and applications.

High-Efficiency Shrouded Micro Wind Turbine for Urban-Built Environment

Shrouding (diffuser augmented) horizontal axis micro-wind turbine has been shown to be an effective ways to potentially increase the power output of micro wind turbine for applications in built environments. It is well understood that the degree of the performance enhancement depends on several factors including the diffuser shape and geometries, blade airfoils, and the wind condition at the turbine site. The effect of diffuser shape and geometries is reported in this paper. Computational fluid dynamic (CFD) simulations of a small wind turbine with a simple frustum diffuser shrouding have been carried out. The diffuser has been modeled with different shapes with the aim to understand the effect of length and area ratio on power augmentation phenomenon. The simulations provide some parameterized figures which present method to determine the beneficial range of frustum diffuser geometries for diffuser shrouded horizontal axis wind turbines.

Flow analysis of shrouded small wind turbine with a simple frustum diffuser with computational fluid dynamics simulations

Reported experimental and computational fluid dynamic (CFD) studies have demonstrated significant power augmentation of diffuser shrouded horizontal axis wind turbine compared to bare one with the same swept area of the diffuser. These studies also found the degree of the augmentation is strongly dependent on the shape and geometry of the diffuser such as the length and the expansion angle. In this paper, CFD simulations of a small commercial wind turbine have been carried out with a simple frustum diffuser shrouding. The diffuser has been modeled with different shapes with the aim to understand the effect of length and area ratio on power augmentation. The simulations provide some effective frustum diffuser geometries for the small commercial wind turbine. From the analysis, sub-atmospheric back pressure is found to be the most influential factor in power augmentation. This factor is significantly affected by diffuser area ratio. Meanwhile flow separation in the diffuser can lead to significant lowering of the pressure recovery coefficient which reduces the overall power coefficient. This phenomenon can be mitigated by adjusting the length of the diffuser. The results of this study present a method on how to determine effective frustum diffuser geometries for a small wind turbine. These results can be extended for any types of wind turbines designed for nominal wind speed.

Hypoxia in tumors: pathogenesis-related classification, characterization of hypoxia subtypes, and associated biological and clinical implications.

Hypoxia is a hallmark of tumors leading to (mal-)adaptive processes, development of aggressive phenotypes and treatment resistance. Based on underlying mechanisms and their duration, two main types of hypoxia have been identified, coexisting with complex spatial and temporal heterogeneities. Chronic hypoxia is mainly caused by diffusion limitations due to enlarged diffusion distances and adverse diffusion geometries (e.g., concurrent vs. countercurrent microvessels, Krogh- vs. Hill-type diffusion geometry) and, to a lesser extent, by hypoxemia (e.g., in anemic patients, HbCO formation in heavy smokers), and a compromised perfusion or flow stop (e.g., due to disturbed Starling forces or intratumor solid stress). Acute hypoxia mainly results from transient disruptions in perfusion (e.g., vascular occlusion by cell aggregates), fluctuating red blood cell fluxes or short-term contractions of the interstitial matrix. In each of these hypoxia subtypes oxygen supply is critically reduced, but perfusion-dependent nutrient supply, waste removal, delivery of anticancer or diagnostic agents, and repair competence can be impaired or may not be affected. This detailed differentiation of tumor hypoxia may impact on our understanding of tumor biology and may aid in the development of novel treatment strategies, tumor detection by imaging and tumor targeting, and is thus of great clinical relevance.