PRESSURE DRIVEN WALL JET FLOW NEAR CHANNEL EXIT AT MODERATE REYNOLDS NUMBER

The wall jet flow driven by a pressure gradient near channel exit at Reynolds Number ranging from the order of 10 to 100, emerging from a two-dimensional channel is examined theoretically in this study. Poiseuille flow conditions are assumed to prevail far upstream from the exit. The problem is solved using the method of matched asymptotic expansions. The small parameter involved in the expansions is the inverse Reynolds number. The flow and pressure fields are obtained as composite expansions by matching the flow in the boundary-layer region near the free surface, flow in the outer layer region near the stationary plate, and the flow in the core region. The fluid is assumed to be Newtonian and it is found that the jet contracts downstream from the channel exit. The influence of inertia on the shape of free surface is emphasized and the boundary layer structure near the free surface is explored. To leading order, the problem is similar to the case of the free jet (Tillett 1968) with different boundary conditions. A similarity solution can be carried out using a similarity function which is then determined by solving a boundary-value problem, where the equation is integrated subject to the boundary conditions and a guessed value of the slope at the origin. The slope is adjusted until reasonable matching is achieved between the solution and the asymptotic condition far from the free surface. The level of contraction is essentially independent of inertia, but the contraction moves further downstream with increasing Reynolds number. The present work provides the correct conditions near exit, which are required to determine the jet structure further downstream. If the jet becomes thin far downstream, a boundary layer formulation can be used with the presently predicted boundary conditions for steady and possibly transient flows

Fog Collection on Plant Surfaces and Biomimetic Applications

Shortages of fresh water affect around one billion people world-wide; mostly in arid and semi-arid climates. Fog, in certain regions, may be an important source of water that is often overlooked. Inspired by the distinctive fog-collection mechanisms of certain plants surviving in these climatic conditions, biomimetic fog collectors are an innovation that could enable us to alleviate the water shortages. The influence of leaf shape, surface microstructure and hierarchical architecture, and wettability of plant and biomimetic samples on their fog-collection efficiency is analyzed. A pinnate leaf shape shows higher efficiency compared to perforate or simple leaf shapes as a result of a lower flow resistance of the fog droplets transported by air, as well as sufficient space on the surfaces for their deposition. Pinnate and perforate leaf shapes were prepared by experimental modification of simple leaves. Directed channels on the surfaces and a drip tip at the lower edge of leaf samples improve the transport of water. Adhesion of a thick water layer at the bottom edges of the samples without the drip tip results in the saturation of the surfaces and a lower efficiency. Microstructured surfaces show two to three times higher efficiency over smooth surfaces. A continuous fog droplet deposition, an effective water transport to the target and a very efficient fog collection is found in dry hydrophilized Hordeum vulgare (barley) awn with hierarchical architecture. A unique fog-collection ability is demonstrated by the structured trichomes of Ptilotus manglesii. Polymer fibers with microgrooved surface demonstrates a higher water transport (drainage efficiency) than different other fiber profiles with smooth surface, resulting in the increase of total fog collection. Numerical simulation supports the findings. Superhydrophilic surface property plays a major role to enhance the deposition efficiency as well as transport of water droplet, i.e., superhydrophilic meshes collect twice as much fog as hydrophobic meshes and five times as much fog as hydrophilic meshes. Therefore, fibers with a combination of optimized diameter and microgrooved superhydrophilic surface can enhance the efficiency. In conclusion, a new fiber design with a hierarchical architecture and superhydrophilic surface is proposed to develop optimized meshes for fog collection.Weltweit leiden rund eine Milliarde Menschen unter Frischwassermangel; vor allem in den ariden und semiariden Klimaten/Gebieten der Erde. Dabei kann Nebel, was oft übersehen wird, in bestimmten Regionen als eine wichtige Quelle für Wasser angesehen werden. Nebel-Sammelmechanismen, welche für einige, unter solchen klimatischen Bedingungen vorkommende, Pflanzen charakteristisch sind, können dabei eine Inspiration für biomimetische Nebelkollektoren darstellen. Diese sind eine Innovation, die es uns ermöglichen könnte die Wasserknappheit zu lindern. In dieser Studie werden die Einflüsse unterschiedlicher Blattformen, der Oberflächenmikrostruktur und hierarchischer Architektur, sowie der Benetzbarkeit von pflanzlichen und biomimetischen Proben auf ihre Nebelsammeleffizienz hin analysiert. Versuche mit unterschiedlich modifizierten Blattformen zeigen eine höhere Effizienz bei einer gefiederten Form im Vergleich zu einfachen oder perforierten Blattformen. Dies ist auf einen geringeren Strömungswiderstand, für die Nebeltröpfchen transportierende Luft, und die Größe, der zur Anlagerung geeigneten, Oberfläche zurückzuführen. Gerichtete Rillen auf den Oberflächen und eine Träufelspitze an der unteren Spitze der Blattproben verbessern den Abtransport von Wasser ebenfalls. Proben ohne diese Träufelspitze sammeln Wasser an der unteren Spitze, was zur Sättigung der Oberfläche und einer geringeren Effizienz führt. Mikrostrukturierte Oberflächen weisen eine zwei- bis dreimal höhere Effizienz als glatte Oberflächen auf. Eine trockene hydrophilisierte Granne von Hordeum vulgare (Gerste) hat eine hierarchische Architektur und weißt eine kontinuierliche Nebeltröpfchen Abscheidung, einen wirksamen Wassertransport und eine sehr effiziente Nebelsammlung auf. Eine einzigartige Nebelsammelfähigkeit durch strukturierte Trichome wird auch durch Ptilotus manglesii demonstriert. Polymerfasern mit mikrogerillter Oberfläche zeigen einen höheren Abtransport des Wassers (Entwässerungseffizienz) als verschiedene andere Faserprofile mit glatten Oberflächen, was zu einer Erhöhung der Effizienz führt. Numerische Simulationen unterstützen die Ergebnisse. Superhydrophile Oberflächeneigenschaften spielen eine wichtige Rolle, um die Abscheidungseffizienz zu verbessern sowie den Transport von Wassertropfen. Superhydrophile Netze beispielweise sammeln doppelt so viel Nebel wie hydrophobe Netze und fünfmal so viel Nebel wie hydrophile Netze. Daher können Fasern mit einer Kombination aus optimiertem Durchmesser und mikrogerillter superhydrophiler Oberfläche die Effizienz verbessern. Abschließend wird ein neues Faserdesign mit einer hierarchischen Architektur und superhydrophilen Oberflächenchemie vorgeschlagen, um optimierte Netze für die Nebelsammlung zu entwickeln

Standardization the effect of shape of aggregates with respect to compressive strength of concrete

It is proved that aggregate’s types have the severe effect on physicomechanical properties of concrete as aggregate covered almost 70 to 80 percent of the total volume of concrete. The effect of Flaky and Elongated aggregates on strength, durability, and workability of concrete has often been qualitatively expressed. The aim of this work is establishing the same quantitatively. M25 grade concrete for different ratios of weights of Elongated to normal aggregate, Flaky to normal aggregate and combined Flaky & Elongated aggregate to normal aggregate was tested for compressive strength at 28 days concrete. Three different types of aggregates were employed in the investigation, namely; normal aggregate, Elongated aggregate, and Flaky aggregate. Density and water absorption also kept constant to identify the effects on properties of concrete only for differences in shape. Thirty-six concrete cylinder was cast at 28 days. Varying dosages of Normal aggregate (60%, 65%, 70%, 75%,80% 85%), flaky aggregate (40%, 35%, 30%, 25%, 20%, 15%), elongated aggregate (40%, 35%, 30%, 25%, 20%, 15%), by mixture volume and length of 12inch (304.8 mm) & diameter of 6inch (152.4 mm) cylinder were used to test. Compaction was done by temping rod. Concrete cylinder was tested at the age of 28 days of curing. This study proposed of mixing three different types of aggregate in concrete. Compressive strength of concrete was measured by the effect of three different shapes of aggregates of varying dosages

Modified differential evolution based on global competitive ranking for engineering design optimization problems

Engineering design optimization problems are formulated as large-scale mathematical programming problems with nonlinear objective function and constraints. Global optimization finds a solution while satisfying the constraints. Differential evolution is a population-based heuristic approach that is shown to be very efficient to solve global optimization problems with simple bounds. In this paper, we propose a modified differential evolution introducing self-adaptive control parameters, modified mutation, inversion operation and modified selection for obtaining global optimization. To handle constraints effectively, in modified selection we incorporate global competitive ranking which strikes the right balance between the objective function and the constraint violation. Sixteen well-known engineering design optimization problems are considered and the results compared with other solution methods. It is shown that our method is competitive when solving these problems.Fundação para a Ciência e a Tecnologia (FCT

A modified differential evolution based solution technique for economic dispatch problems

Economic dispatch (ED) plays one of the major roles in power generation systems. The objective of economic dispatch problem is to find the optimal combination of power dispatches from different power generating units in a given time period to minimize the total generation cost while satisfying the specified constraints. Due to valve-point loading effects the objective function becomes nondifferentiable and has many local minima in the solution space. Traditional methods may fail to reach the global solution of ED problems. Most of the existing stochastic methods try to make the solution feasible or penalize an infeasible solution with penalty function method. However, to find the appropriate penalty parameter is not an easy task. Differential evolution is a population-based heuristic approach that has been shown to be very efficient to solve global optimization problems with simple bounds. In this paper, we propose a modified differential evolution based solution technique along with a tournament selection that makes pair-wise comparison among feasible and infeasible solutions based on the degree of constraint violation for economic dispatch problems. We reformulate the nonsmooth objective function to a smooth one and add nonlinear inequality constraints to original ED problems. We consider five ED problems and compare the obtained results with existing standard deterministic NLP solvers as well as with other stochastic techniques available in literature.Fundação para a Ciência e a Tecnologia (FCT