Asymmetric Compound Research Articles

Kinetic energy and momentum correction coefficients in straight compound channels with vegetated floodplain

Summary In this paper, the effect of flow relative depth (ratio of the floodplain to the main channel flow depths) and vegetation density on the kinetic energy and momentum correction coefficients (termed as α and β , respectively) was described based on an experimental study. A series of experiments was run using rigid dowels with seven flow relative depths and four vegetation densities in an asymmetric compound channel. The local flow velocities were measured using an acoustic Doppler velocimeter (ADV). Using regression analysis, velocity data were considered and equations were developed for calculating the kinetic energy and momentum correction coefficients as a function of the flow relative depth and vegetation density. The results show that the values of α and β decrease as the relative depth increases. Also, as the vegetation density increases, the effects of the vegetation on α and β increase too. Finally, by comparing with the findings of the previous researchers, it was found that the average values of the α for asymmetric compound channels with vegetation are 26.5% and 43.3% greater than those for asymmetric and symmetric compound channels without vegetation respectively while these values for β are 12.7% and 18.1%, respectively. Furthermore, the floodplain vegetation can increase the average values of coefficients α and β by 52.8% and 21.6%, respectively, in comparison with single channels.

Remote monitoring of volumetric discharge employing bathymetry determined from surface turbulence metrics

AbstractCurrent methods employed by the United States Geological Survey (USGS) to measure river discharge are manpower intensive, expensive, and during high flow events require field personnel to work in dangerous conditions. Indirect methods of estimating river discharge, which involve the use of extrapolated rating curves, can result in gross error during high flow conditions due to extrapolation error and/or bathymetric change. Our goal is to develop a remote method of monitoring volumetric discharge that reduces costs at the same or improved accuracy compared with current methods, while minimizing risk to field technicians. We report the results of Large‐Scale Particle Image Velocimetry (LSPIV) and Acoustic Doppler Velocimetry (ADV) measurements conducted in a wide‐open channel under a range of flow conditions, i.e., channel aspect ratio (B/H = 6.6–31.9), Reynolds number (ReH = 4,950–73,800), and Froude number (Fr = 0.04–0.46). Experiments were carried out for two different channel cross sections (rectangular and asymmetric compound) and two bathymetric roughness conditions (smooth glass and rough gravel bed). The results show that the mean surface velocity normalized by the depth‐averaged velocity (the velocity index) decreases with increasing δ*/H, where δ* is the boundary layer displacement thickness and that the integral length scales, L11,1 and L22,1, calculated on the free‐surface vary predictably with the local flow depth. Remote determination of local depth‐averaged velocity and flow depth over a channel cross section yields an estimate of volumetric discharge.

Design and experiment of a new solar air heating collector

This paper presents the design and experiment of a CTAH (Concentrating Transpired Air Heating) system. A newly designed solar air heating collector comprised of an inverted perforated absorber and an asymmetric compound parabolic concentrator was applied to increase the intensity of solar radiation incident on the perforated absorber. An extensive literature review was carried out to find the vital factors to improve optical and thermal efficiency of solar air heating systems. A stationary optical concentrator has been designed and experimented. Experimental thermal efficiency remained high at higher air flow rates. The average thermal efficiency was found to be approximately 55%–65% with average radiation above 400 W/m2 for flow rates in the range of 0.03 kg/s/m2 to 0.09 kg/s/m2. Experimental results at air flow rates of 0.03 kg/s/m2 and 0.09 kg/s/m2 showed temperature rise of 38 °C and 19.6 °C respectively at a solar radiation intensity of 1000 W/m2. A comparative performance study shows the thermal performance of CTAH. As the absorber of the CTAH facing downward, it avoids radiation loss and the perforated absorber with tertiary concentrator reduces thermal losses from the system.

Heat Treatment of Titanium-Aluminum-Compounds Made by Co-Extrusion of Asymmetric Compound Profiles

Combining different materials allows designing lightweight structures with tailor-made properties at the macroscopic as well as at the microscopic scale. In this context co-extrusion by lateral angular co-extrusion process (LACE) offers a great potential for advanced products by joining different light alloys, such as titanium and aluminum alloys. While titanium alloys show particular high mechanical strength values and a good corrosion resistance, aluminum alloys feature a considerable high specific bending stiffness at low materials costs. Within the presented research study metallic compounds were manufactured by co-extrusion using a LACE process. Since the mechanical properties of metallic composites highly depend on the existence and formation of an intermetallic layer, the bonding zone of the compounds were investigated. Experiments were carried out at the example of the material combinations Al99.5 & Ti99.2 and AlSi1MgMn & Ti99.2, respectively. The results of co-extruded samples concerning the intermetallic layer that was formed during heat treatment were compared with those directly after the co-extrusion. The investigations were focused on the formation of the bonding zone after both co-extrusion and the subsequent heat treatment. The bonding zone was characterized by scanning electron microscopy as well as electron probe micro analysis. Finally, the bond strength of each compound variant was determined and evaluated.

Performance analysis of a novel rotationally asymmetrical compound parabolic concentrator

Abstract The low-concentration photovoltaic (LCPV) system has been identified as one of the potential solutions in lowering the overall installation cost of a building integrated photovoltaic (BIPV) system. This paper evaluates the performance of a novel type of LCPV concentrator known as the rotationally asymmetrical compound parabolic concentrator (RACPC). A specific RACPC design with a geometrical concentration ratio of 3.6675× was fabricated and integrated with a 1 cm by 1 cm monocrystalline laser grooved buried contact silicon solar cell. This design was tested indoors to evaluate its current–voltage ( I – V ), angular response and thermal characteristics. Under standard test conditions, it was found that the RACPC increases the short circuit current by 3.01× and the maximum power by 3.33× when compared with a bare solar cell. The opto-electronic gain from the experiment showed good agreement when compared with the simulation results, with a deviation of 11%.

Assessment of stage–discharge predictors for compound open-channels

The accurate prediction of flood levels and velocities is a prerequisite to any appropriate management of river valleys, where the mitigation of environmental, economic or human losses caused by flood events is of paramount importance. During these events, rivers frequently acquire a compound channel configuration.Due to the 3D nature of compound channel flows, the stage–discharge curves are not as easily predicted as in single channels. Despite the availability of 2D and 3D flow models that may solve this question, 1D methods are often preferred due to the reduced data required and to the much shorter processing time. In the last five decades, important research efforts have been devoted to the improvement of 1D predictors of stage–discharge curves in compound channels. In this study, the accuracy of seven of those methods is assessed by comparing their predictions with a large experimental dataset, comprising symmetrical and asymmetrical compound channels with vertical and inclined main channel sidewalls, and smooth and rough floodplains. To the authors’ best knowledge, this is the most comprehensive assessment of stage–discharge predictors for straight compound channels since it involves the highest number of predictors applied to the widest data set.It was concluded that the methods that account for the momentum transfer between the main channel and the floodplains display considerably better results than the traditional methods. For relative depth (ratio between floodplain and main channel flow depths) higher than 0.25, predicted discharges for the methods that account for the turbulent momentum exchange are within 5% of observed values. Depending on whether the flow depth or the flow discharge is the pertinent variable, two different methods seem to be the most appropriate to produce precise and safe predictions.

An empirical discharge prediction model for smooth asymmetric compound rectangular channel validated using area method

This paper presents an empirical, non-linear, multivariable regression model for predicting discharge in smooth asymmetric compound rectangular channel. The model is developed using experimental discharge data generated from testing nine different channel cross-sections with varied geometric dimensions. The predictive strength of the developed regression model is validated using several major statistics. All deployed statistics have indicated that the developed model is highly significant. In addition, the area method has been used to validate the model’s discharge predictive strength. The area method predicts discharge mainly based on the cross-section geometry and apparent shear stress. As obtained from the literature, a sample of three different regression-based models has been used to estimate the apparent shear stress. Therefore, three different sets of discharge have been predicted using the area method. The four sets of discharge predicted using the developed regression model and area method have been compared to their corresponding experimental values using the sum of squared errors (SSE). The outcome is that seven channel cross-sections out of nine tested ones resulted in minimum SSE values when discharge predicted using the developed regression model.

Optimal Arrangement of Combined-Hole for Improving Film Cooling Effectiveness

Film cooling technique is widely used to protect the components from being destroyed by hot mainstream in a modern gas turbine. Combining round-holes is a promising way of improving film cooling effectiveness. A DoE (design of experiment) simulation of 396 cases focusing on the arrangement of the combined-hole with double holes for improving film cooling performance is carried out in this work, and the influence of an aerodynamic parameter, blowing ratio is considered as well. The dimensionless lateral distance (PoD) and compound angle (CA) of the double holes have relative influence on the film cooling performance of the combined-hole unit. At the low blowing ratio, increasing symmetrical compound angle (SCA) has positive influence on the area-average effectiveness (EFF) of the combined-hole. But at the intermediate and large blowing ratio, the influence of SCA on the area-average EFF depends on the range of PoD. At the small PoD, the area-average EFF ascends basically along SCA axis. However, the area-average EFF first ascends and subsequently descends along SCA axis at the large PoD. Asymmetrical compound angle (ACA) is also considered to fit the antikidney vortexes produced in the combined-hole film cooling compared to their ideal schematic. However, the film cooling effect of the cases with ACA is not as good as expected. The area-average EFF of ACA cases locates in the level between that of the adjacent SCA cases. The optimal arrangement of combined-hole unit for improving film cooling effectiveness is relative to the local flow field. The optimal arrangement of PoD and CA for improving the combined-hole film cooling performance is different at different blowing ratios.

Optical Performance Comparison of Six ACPCs for Concentrating Radiation on All-Glass Evacuated Solar Tubes

In this work, six asymmetric compound parabolic concentrators (ACPC) were designed for concentrating radiation on all-glass evacuated solar tubes (EST). The ACPCs are required to be horizontally oriented in the east-west direction and to collect direct sunlight for at least 6 hrs in any day of a year. The angular dependence of optical efficiency of six ACPCs, identical in the height of both reflectors after the higher reflector being truncated, was investigated by ray-tracing method, and the annual radiation on EST concentrated by ACPCs was estimated based on solar geometry and monthly horizontally radiation. Results shows that the ACPC designed based on “hat shaped” virtual absorber with a V-groove at the bottom of reflectors is the best in terms of the optical efficiency averaged over the acceptance angle, followed by the one designed based on “hat-shaped” absorber without a V-groove at the bottom, and the one designed based on the cover tube of EST is the worst. However, from the point of annual radiation on EST, the ACPC designed based on the cover tube is the best solution, followed by the one designed based on “ice-cream shaped” absorber and the one designed based on “hat shaped” absorber is the worst due to the smallest geometric concentration factor.

A highly selective fluorescence sensor for Zn2+ and Cu2+ based on diarylethene with a piperazine-linked amidoquinoline unit

A new asymmetrical diarylethene compound with a piperazine-linked amidoquinoline unit was synthesized and its multi-controllable switching behaviors induced by light and chemical stimuli were investigated.

Crystal structure of (4R,5S)-4-methyl-3-methyl-sulfinyl-5-phenyl-1,3-oxazolidin-2-one.

The absolute structure of the chiral asymmetric indole precursor title compound, C11H13NO3S, was confirmed by refinement of the Flack and Hooft parameters and is that expected based on the starting materials for the synthesis. The phenyl group subtends a dihedral angle of 56.40 (5)° with the mean plane of the oxazolidinone ring, which adopts an envelope conformation, with the C atom bearing the methyl group as the flap. In the crystal, no significant directional inter­actions beyond van der Waals contacts are observed.

Rotationally asymmetrical compound parabolic concentrator for concentrating photovoltaic applications

This paper describes a novel type of solar concentrator – a rotationally asymmetrical compound parabolic concentrator (RACPC). The RACPC aims at addressing the following objectives: (i) to increase the electrical output of a concentrating photovoltaic (CPV) system by providing sufficient concentration gain; (ii) to minimise the usage of the PV material with the corresponding reduction of CPV system cost, and (iii) to eliminate the requirement of mechanical tracking by providing a wide field-of-view. This paper first provides a short review on variations of compound parabolic concentrator designs available to date. Next, the process of designing the RACPC is presented and the geometrical concentration gain of the concentrator is discussed. In addition, the optical concentration gain is also presented for various angles of incidence. Through simulations, it is demonstrated that the RACPC can provide significant optical concentration gains within its designed acceptance angle. An RACPC based system is an attractive alternative to conventional solar photovoltaic systems.

Solar cooking development in Algerian Sahara: Towards a socially suitable solar cooker

Abstract This paper presents a review of research works and studies carried out in the development of solar cooking in Algerian Sahara. The review is performed in such way to focus on diverse box type solar cookers that have been realized by the solar heating research team at the Research Unit in Renewable Energies in Sahara Medium (URER/MS-Adrar, Algerian Sahara). Research started with the realization of a simple solar box cooker with a tilted absorber-plate, then the construction of a double exposure solar cooker and then the development of a novel non-tracking solar box cooker, which is equipped with a fixed asymmetric compound parabolic concentrator (CPC) as booster-reflector and its absorber-plate, is in a form of a step. The last cooker can be fixed at a south building wall with its rear opening in kitchen; it can be more user friendly. This will allow a freedom of interactive cooking and it does not require the user to go out in the sun during its use. These qualities promote its uptake and made it a socially acceptable device.

Φ-indices approach and multivariable regression analysis for prediction of discharge in asymmetric straight compound open channel flows

This study is related to flow measurement structures of asymmetric compound cross section mostly suggested for sediment laden-rivers, streams and wadis. Nine different models of asymmetrical rectangular cross sections were tested for a wide range of discharges. In each model, the stages and corresponding discharges were measured. From these measurements, the average discharges utilizing the Φ-indices Approach were determined. In addition, a multivariable regression model was derived with high accuracy for the prediction of discharge in asymmetric compound channels using five dimensionless parameters.The measured discharges were compared with the predicted ones obtained from the Φ-indices methods with vertical, horizontal and diagonal interface planes; FI-V, FI-D and FI-H, respectively, with the use of three well-known methods for the computation of the apparent shear stress acting on the interface perimeter, τa, and the multivariable regression model for discharge prediction. At lower relative depth values, almost all the tested methods predict discharge with acceptable accuracy. In addition, as the relative depth increases, the results demonstrate a suitable accuracy of the FI-V with the vertical division lines and the multivariable regression model method. The multivariable regression model presented has been identified as the best-fit model in 26 cases out of 29 through minimization of the mean squared errors.

Geometry effect and generalization of velocity distribution in asymmetric compound channels

Nine different geometries with asymmetric rectangular compound cross-sections were tested in a laboratory flume in order to investigate effects of the geometry on the values of three different dimensionless velocity ratios. A generalized single variable regression model has been derived to predict each of the three dimensionless velocity ratios with high accuracy. Another set of the multiple-variable regression models has been derived using one additional dimensionless parameter which is the ratio of the upstream channel width to the main channel width. The application of several key statistics and validation procedures has indicated that the developed models predict the three mean dimensionless velocity ratios with high correlation coefficients.

ChemInform Abstract: Reaction of Tetrachlorinated Perylene Bisimide in a Strong Base to Form an Asymmetric Compound with Charge Transfer Optical Properties.

AbstractThe optical properties of the compound (III) are investigated in CH2Cl2, hexane, and DMF.

Order, Viscoelastic, and Dielectric Properties of Symmetric and Asymmetric Alkyl[1]benzothieno[3,2-b][1]benzothiophenes

The morphology, the viscoelastic, the dielectric properties and the dynamics of phase transformation are studied in symmetrically and asymmetrically substituted alkyl[1]benzothieno[3,2-b][1]benzothiophenes (C8-BTBT) by X-ray scattering, rheology, and dielectric spectroscopy. The interlayer spacing reflects the molecular and supramolecular ordering, respectively, in the symmetrically and asymmetrically substituted BTBTs. In the asymmetric BTBT, the core layer is double in size with a broader network of intermolecular interactions though the increased S-S contacts that is prerequisite for the development of high performance OFET devices. Two crystal states with elastic and viscoelastic responses were identified in the symmetric compound. In contrast, the SmA phase in the asymmetric compound is a viscoelastic solid. A path-dependent dielectric environment with a switchable dielectric permittivity was found in both compounds by cooling below 0 °C with possible implications to charge transport. The kinetics of phase transformation to the crystalline and SmA phases revealed a nucleation and growth mechanism with rates dominated by the low activation barriers.

Development of Two-layered model for compound open-channel flow

Present study deals with the development of two-dimensional two-layered model for straight compound open-channel flow using Smagorinsky-based subgrid-scale turbulence model, based on large eddy simulation approach. The two-layer depth averaged governing equations are solved using finite volume method based on MacCormack predictor-corrector explicit scheme. Model results for symmetric and asymmetric straight compound channel flows are verified with the available numerical and experimental data. Variations of flow variables in symmetric and asymmetric straight compound channels in terms of shear stress distributions and spanwise and vertical velocities are analyzed at the horizontal interface between the lower layer and the upper layer. Spanwise and vertical velocities at the horizontal interface revealed the existence of horizontal vortices near the junction of the main channel and the floodplain where momentum exchange takes place. Further, the model result, showing the spanwise shear stresses distribution at the interface of symmetric and asymmetric compound channel, revealed the existence of peak shear stress near the channel junction. Sensitivity of the two important model parameters is also undertaken and their roles in longitudinal velocity distribution along the channel width are discussed.

Boundary shear stress in asymmetric rectangular compound channels

A series of nine experiments was performed in a physical model of an asymmetric compound channel to quantify the boundary shear stress at the interface of the bed of a main channel and floodplain. Commonly used equations of shear stress distributions across the bottoms of the main channel and floodplain interfaces were analyzed and tested for various types of asymmetric compound channels and their flow conditions. The lateral momentum transfer between the deep main channel and the adjoining shallow floodplains was found to greatly affect the shear stress distribution at the bottoms of the main channel and the flood plain subsections. Different dimensionless ratios of shear stress distributions were obtained and related to the relevant parameters. Some important results concerning the uniformity of the shear stress distribution, which is significant in sediment-laden rivers to state the possible locations of erosion and deposition, are presented.

Performance evaluation of concentrating solar photovoltaic and photovoltaic/thermal systems

Hybrid conversion of solar radiation, which allows simultaneous conversion of sunlight into thermal and electrical energy in the photovoltaic/thermal collector, is one of the most promising techniques of solar energy exploitation. In this study, low concentrating photovoltaic (PV) and photovoltaic/thermal (PVT) systems were designed and tested for a given spring climatic condition of the Tunisian Saharan city Tozeur. The system is basically an asymmetric compound parabolic photovoltaic concentrator. As this system’s performance deteriorates with rising the solar cells temperature, we proposed to convert it on a hybrid one in order to improve its electrical efficiency and to recuperate simultaneously thermal energy. The comparison of these systems operating confirmed the improvement of the electrical performance of the combined PVT system and its acceptable thermal energy production. A computational fluid dynamics “CFD” model which interprets the PVT system was then developed and validated against the experimental results, proving the validity of the developed model use to identify numerically this system limitations and predict the possible improvements.