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

Environmentally Sustainable Tourism Problem and Prospects in Bangladesh: A Study on Coastal Region at Cox’s Bazar

Coastal region in Bangladesh is always includes floodplains mangroves marshes and fringing coral reefs. Tourism is considered as the world’s largest and rapid growing industry of modern business world. But tourism industry is directly related to the environment. The quality of the environment, both natural and man-made is essential to tourism. The negative impacts of tourism development can gradually destroy environmental resources like loss of marine resources due to destruction of coral reefs overfishing pollution of marine and freshwater resources soil degradation and loss of land resources, air pollution, natural hazards and sea level rise and climate change. Environmental Education must be nurtured from root level to the last day of life to provide the best fruit of sustainable development. This study focuses on the guidelines of the way and contents of different level of environmental Education. Environmentally educated society can carry out the sustainable tourism development of coastal Bangladesh. Keywords: Sustainable Tourism Development, Sustainable Coastal Zone, Eco-tourism, Coastal Tourism., Environmental Impacts

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