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This investigation explores the utilization of semiconductor zinc oxide (ZnO) based nanocomposite in decolorization of textile dyes. The structural, morphological and optical characteristics of semiconductor ZnO nanoparticles fabricated by hydrothermal process are scrutinized thoroughly and maneuvered with reduced graphene oxide (rGO) to yield superior properties and consequent preferable performance. The modification of the properties of zinc oxide nanoparticles by fabrication of a nanocomposite with an efficient electron acceptor like reduced graphene oxide results in excellent catalytic characteristics. The photocatalytic activity of the nanocomposite is carried out by photodegradation of Rhodamine B (a toxic colorant used in textile and medical industry) in aqueous solution under solar light irradiation. The synthesized nanocomposite along with the prepared zinc oxide nanoparticles are characterized by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray (EDX), and Ultraviolet-Visible (UV-Vis) spectroscopy.This investigation explores the utilization of semiconductor zinc oxide (ZnO) based nanocomposite in decolorization of textile dyes. The structural, morphological and optical characteristics of semiconductor ZnO nanoparticles fabricated by hydrothermal process are scrutinized thoroughly and maneuvered with reduced graphene oxide (rGO) to yield superior properties and consequent preferable performance. The modification of the properties of zinc oxide nanoparticles by fabrication of a nanocomposite with an efficient electron acceptor like reduced graphene oxide results in excellent catalytic characteristics. The photocatalytic activity of the nanocomposite is carried out by photodegradation of Rhodamine B (a toxic colorant used in textile and medical industry) in aqueous solution under solar light irradiation. The synthesized nanocomposite along with the prepared zinc oxide nanoparticles are characterized by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ra...

Due to the over-harvesting of low valued wood for the production of low and medium density particle boards the forest resources are decreasing day by day and hence finding new substitutes for producing particle board is a major concern nowadays. This study attempts to fabricate and examine the structural and mechanical properties of banana pseudo-stem-based particle boards that are capable to serve as a cost effective and technologically viable substitute to the conventional wood chip. Banana pseudo-stem has been used as the raw material with commercially used urea formaldehyde resin as the binder. A systematic experimental study is carried out to examine the effects of parametric variation (particle-board density, resin concentration and thickness of the sample) on the physical and mechanical properties of the particle-boards such as tensile, compressive and maximum crushing strength, screw holding strength etc. The fabricated particle-boards exhibit excellent mechanical and physical properties. It is found that the physical properties greatly vary with thickness, density and percentage of binder used in the particle board. For a constant density of the particle board, 12 mm thick boards exhibit the maximum internal bond strength and the strength decreases with increasing thickness. Both the maximum crushing strength and screw withdrawal force are obtained at a resin concentration of 9%, while both higher and lower resin concentration give inferior results. The particle-boards fabricated in this study can have significant potential for substituting wood-based particle-boards in a range of applications.

Fire in a seven-storied ready-made garments (RMG) factory building, based on the actual drawing of an existing RMG building, is simulated and the tenability of the occupants isanalyzed. The modeling is conducted by using PyroSim,a computational fluid dynamics (CFD) tool with the capability of simulating fire and optimized for low-speed, thermally-driven flow. A number of factors including temperature, visibility, and CO concentration are analyzed to examine their effects on the tenability of different zones and floors. The source of the fire is considered to be the fabric storage of the ground floor andnylon, a commonly used fiber in the RMG industries with a high heat release rate, is selected as the fuel. It is found that within 3 min of the initiation of the fire, fire-smoke spreads very rapidly through the hallways and stairways and completely blocks the escape routes of the building. From the point of view of an efficient evacuation process, the conditions in the 1st floor are found to be the most critical as fire and dense smoke surround the escape routes with a high degree of visibility reduction within 2 min. The available safety egress time is found to be small unless the smoke migration ismitigated by the use of fire doors and other smoke management techniques. Findings of this study will be helpful in the assessment of fire risk in the RMG buildings in Bangladesh and would enable to suggest design measures to control the propagation of fire and smoke and improve tenability, thus minimizing the life and property damages.

Energy harvesting technology has the ability to create self-powered electronic systems that do not rely on battery power for their operation. Wind energy can be converted into electricity via a piezoelectric transducer during the air flow over a cylinder. The vortex-induced vibration over the cylinder causes the piezoelectric beam to vibrate. Thus useful electric energy at the range 0.2-0.3V is found which can be useful for self-powering small electronic devices. In the present study, prototypes of micro-energy harvester with a shape of 65 mm × 37 mm × 0.4 mm are developed and tested for airflow over D-shaped bluff body for diameters of 15, 20 and 28mm in an experimental setup consisting of a long wind tunnel of 57cm × 57cm with variable speeds of the motor for different flow velocities and the experimental setup is connected at the downstream where flow velocity is the maximum. Experimental results show that the velocity and induced voltage follows a regular linear pattern. A maximum electrical potential...

Reduced core weight and material cost, higher corrosion resistance are some of the major eye catching properties to study polymers over metal in heat exchanger applications in spite of the former’s relatively low thermal conductivity and low strength. In the present study, performance of polymer parallel thin tube heat exchanger is numerically evaluated for cross flow liquid to air applications for a wide range of design and operating parameters such as tube diameter, thickness, fluid velocity and temperature, etc. using Computational Fluid Dynamics (CFD). Among a range of available polymeric materials, those with a moderate to high thermal conductivity and strength are selected for this study. A 90 cm × 1 cm single unit of polymer tubes, with appropriate number of tubes such that at least a gap of 5 mm is maintained in between the tubes, is used as a basic unit and multiple combination in the transverse direction of this single unit is simulated to measure the effect. The tube inner diameter is varied fr...

The present study aimed to evaluate the feasibility of coconut coir pads, jute fiber pads and sackcloth pads as alternative pad materials. Experimental measurements were conducted and the experimental data were quantitative. The experimental work mainly focused on the effects of different types and thicknesses of evaporative cooling pads by using forced draft fan while changing the environmental conditions. Experiments are conducted in a specifically constructed test chamber having dimensions of 12’X8’X8’, using a number of cooling pads (36”X26”) with a variable thickness parameters of the evaporative cooling pads i.e., 50, 75 and 100 mm. Moreover, the experimental work involved the measurement of environmental parameters such as temperature, relative humidity, air velocity, water mass flow rate and pressure drops at different times during the day. Experiments were conducted at three different water mass flow rates (0.25 kgs−1, 0.40 kgs−1 & 0.55 kgs−1) and three different air velocities (3.6 ms−1, 4.6 ms−1& 5.6 ms−1). There was a significant difference between evaporative cooling pad types and cooling efficiency. The coconut coir pads yielded maximum cooling efficiency of 85%, whereas other pads yielded the following maximum cooling efficiency: jute fiber pads 78% and sackcloth 69% for higher air velocity and minimum mass flow rate. It is found that the maximum reduction in temperature between cooling pad inlet and outlet is 4°C with a considerable increase in humidity. With the increase of pad thickness there was an increment of cooling efficiency. The results obtained for environmental factors, indicated that there was a significant difference between environmental factors and cooling efficiency. In terms of the effect of air velocity on saturation efficiency and pressure drop, higher air velocity decreases saturation efficiency and increases pressure drop across the wetted pad for maximum flow rate. Convective heat transfer co-efficient has an almost linear relationship with air Velocity. Water consumption or evaporation rate increases with the increase in air velocity. Finally, the present study indicated that the coconut coir pads perform better than the other evaporative cooling pads and have higher potential as wetted-pad material. The outcomes of this study can provide an effective and low-cost solution in the form of evaporative cooling system, especially in an agricultural country like Bangladesh.

Casualty of garment factory workers from factory fire in Bangladesh is a recurring tragedy. Smoke, which is more fatal than fire itself, often propagates through different pathways from lower to upper floors during building fire. Among the toxic gases produced from a building fire, carbon monoxide (CO) can be deadly, even in small amounts. This paper models the propagation and transportation of fire induced smoke (CO) that resulted from the burning of synthetic polyester fibers using two open source platforms, CONTAM and Fire Dynamics Simulator (FDS). Smoke migration in a generic multistoried garment factory building in Bangladesh is modeled using CONTAM where each floor is compartmentalized by different zones. The elevator and stairway shafts are modeled by phantom zones to simulate contaminant (CO) transport from one floor to upper floors. FDS analysis involves burning of two different stacks of polyester jacket of six feet height and with a maximum heat release rate per unit area of 1500kw/m2 over a storage area 50m2 and 150m2, respectively. The resulting CO generation and removal rates from FDS are used in CONTAM to predict fire-borne CO propagation in different zones of the garment building. Findings of the study exhibit that the contaminant flow rate is a strong function of the position of building geometry, location of initiation of fire, amount of burnt material, presence of AHU and contaminant generation and removal rate of CO from the source location etc. The transport of fire-smoke in the building Hallways, stairways and lifts are also investigated in detail to examine the safe egress of the occupants in case of fire.

This work is aimed at developing a way to harvest energy from a fluid stream with the application of piezoelectric transducers in a small channel. In this COMSOL Multiphysics based simulation study, it is attempted to harvest energy from the abundant renewable source of energy available in the form of kinetic energy of naturally occurring flow of fluids. The strategy involves harnessing energy from a fluid-actuator through generation of couples, eddies and vortices, resulting from the stagnation and separation of flow around a semi-circular bluff-body attached to a cantilever beam containing a piezoceramic layer. Fluctuation of fluidic pressure impulse on the beam due to vortex shedding and varying lift forces causes the flexible cantilever beam to oscillate in the direction normal to the fluid flow in a periodic manner. The periodic application and release of a mechanical strain upon the beam effected a generation of electric potential within the piezoelectric layer, thus enabling extraction of electrica...

Understanding the relationship between surface roughness and wetting state is essential in designing microstructured surfaces with tunable wetting properties. In this work, an analytical model for predicting the wetting state on microgroove geometry is developed and applied to intrinsically hydrophilic brass surfaces with a wide range of groove geometry. To enhance the scope and applicability of the developed model, it is implemented on a number of other aluminum microgrooved surfaces. Before applying any surface minimization algorithm to obtain equilibrium droplet shape, the stable wetting state is determined by comparing the total surface energy of the liquid droplet in Cassie and Wenzel wetting state. It is found that hybridization of the microgrooved surface (PDMS coating on the groove base) reduces the critical microgroove dimensions for exhibiting a Cassie wetting state. The unusual spreading of water droplets, observed experimentally on certain microgrooved surfaces, is predicted more accurately when slightly inclined pillars (with a 7° inclination from vertical) instead of vertical wall are assumed. These results corroborate our earlier claim that the shape and the slope of the pillar edge are responsible for the unusual spreading exhibited by certain surfaces. Moreover, implementation of the experimentally obtained values of droplet elongation ratio in the numerical model further enhances the accuracy of the obtained results. The present mathematical model offers an excellent tool for predicting the wetting state of the rough hydrophilic surface using its roughness geometry, and the numerical approach of implementing inclined pillar and droplet elongation ratio can improve the accuracy of drop shape simulation while predicting the wetting states accurately.

Frost formation on heat exchangers is an undesirable phenomenon often encountered in different applications where the cold surface with a temperature below freezing point of water is exposed to humid air. The formation of frost on the heat transfer surface results in an increase in pressure drop and reduction in heat transfer, resulting in a reduction of the system efficiency. Many factors, including the temperature and moisture content of air, cold plate temperature, surface wettability etc., are known to affect frost formation and growth. In our present study, a model for frost growth on rectangular, periodic microgroove surfaces for a range of microgroove dimension (ten to hundreds of micron) is presented. The mathematical model is developed analytically by solving the governing heat and mass transfer equations with appropriate boundary conditions using the EES (Engineering Equation Solver) software. For temperature, a convective boundary condition at frost-air interface and a fixed cold plate surface temperature is used. Instead of considering the saturation or super-saturation models, density gradient at the surface is obtained by considering experimentally-found specified heat flux. The effect of surface wettability is incorporated by considering the distribution of condensed water droplets at the early stage of frost formation. Thickness, density and thermal conductivity of frost layer on the micro-grooved surfaces are found to vary with the dimension of the grooves. The variation of density and thickness of the frost layer on these micro-grooved surfaces under natural convection is numerally determined for a range of plate temperature and air temperature conditions and is compared with experimental results found in the open literature.