Vibrations of rotating blades have been a subject of constant research interest due to their practical significance. There have been numerous linear and nonlinear models with different levels of complexity reported in the literature. The present study is concerned with the in plane largeamplitude vibrations of a rotating Euler-Bernoulli beam following the model developed by Turhan and Bulut [1]. A reduced-order model has been derived to simulate the dynamic behavior of the rotating blades and the fixed points and their stability have been investigated. It is shown that some key parameters, such as the effective blade length and the hub rotational speed, affect the system stability. The analytical results obtained using the method of multiple scales and the numerical results are in good agreement.
Industrial epoxy coating based on epoxy, amine curing agent and organic solvent were prepared, their mechanical property, curing kinetics were discussed in terms of solvent addition. The curing degree of epoxy coating was characterized by employing FTIR, the mechanical properties were studied by using tensile testing, the nonisothermal curing kinetics and glass transition temperature of the prepared epoxy coating were also investigated by differential scanning calorimetry (DSC). The results indicated that the addition of solvent could lower the curing degree which affect the formation of crosslinked structure, the tensile strength and modulus of elasticity were also weakened by the increasing amount of solvent, while the flexibility was highly improved in the presence of solvent. An lower curing rate was observed with solvent addition in comparison with that of pure epoxy, it also indicated that activation energy of curing reaction increases with rising conversion where crosslinking is regarded as diffusion controlled.
In this study, a facile way was developed to fabricate flexible carbon (CNT)/graphene foam by dipcoating graphene oxide and carbon nanotube mixed solution on the polyurethane foam templated, followed by pyrolysis at 900? for 30 min. The experimental results show that addition of CNT can significantly increase the flexibility of graphene foam, which makes it a promising candidate into flexible energy device.
Curing is considered as the major factor in deciding the final mechanical performance of laminated Kevlar/epoxy composites. The parameters such as curing time, temperature and applied pressure during the hot pressing will affect the chemistry of crosslinking of the epoxy matrix and interaction of epoxy with the Kevlar fiber. The present study is carried out to evaluate the optimal curing conditions of the Kevlar/epoxy nanocomposites. DSC and TGA tests are carried out to determine the thermal stability and optimal curing conditions. Mechanical performance is investigated by drop weight tests. The results show that the optimal curing temperature for maximizing the mechanical properties is at 170oC. Peeling off the Kevlar layers are observed for nanocomposite samples cured under 100oC.
Highly hydrophobic composite membranes were prepared by electrospinning a suspension of teflon oligomers (OTFE) in poly(vinylidenefluoride-co-hexafluoropropylene) (PH) solution and were designated as PH-x%OTFE. Two sets of membranes with OTFE concentration of 39 and 64 wt.% were prepared. The composite membranes were hot-pressed to improve their structural integrity, mechanical strength, and the liquid entry pressure (LEP). The effect of OTFE addition as well as hot-pressing on the properties of the membranes were studied. Contact angle and LEP values of 135o and 33 psi, 138o and 19 psi, and 146o and 13 psi were obtained for the as-prepared membranes containing 0 wt.%, 39 wt.%, and 64 wt.% OTFE respectively, while contact angle and LEP values of 130o and 44 psi, 137o and 44 psi, and 138o and 25 psi were obtained for the hot-pressed membranes containing 0 wt.%, 39 wt.%, and 64 wt.% OTFE respectively. The fabricated membranes showed stable flux and a salt rejection of about 100% for 42h of continuous flow when tested in direct contact membrane distillation. The composite membrane containing 64wt% OTFE had an average vapor flux of 10 kgm^(-2) h^(-1) which was comparable to that of the control PH membrane, while the composite membrane containing 39 wt.% OTFE had a lower average vapor flux of 5 kgm^(-2) h^(-1).
The proposed research method involves spray coating a polymer composite followed by plasma etching the surface to generate the necessary roughness. Different etching gasses and conditions are explored to tailor our generated coating to the desired optimum conditions. However, this process is still under research to improve its effectiveness and mainly its efficiency.
An integrated biorefinery process based on acidic leaching, alkaline treatment and concentrated sulfuric acid hydrolysis was developed for the simultaneous recovery of lignin, hemicelluloses, bleached cellulose from date palm lignocellulosic biomass waste. These fractions can serve as viable source of bio-chemicals with potential high-value applications. Thermogravimetric, Scanning Electron Microscopic and FTIR characterization results demonstrated that a combined acidic-alkaline treatment enhanced the degradation of lignin-carbohydrates complexes releasing lignin, cellulose and hemicellulose in higher yield than many traditional methods. Moreover, cellulose, lignin and hemicellulose components, 47.26, 17.92 and 2.35 %, yield was obtained, respectively. In terms of total mass balance, it was possible to refine the investigated biomass for production of lignin, hemicellulose and cellulose to about 67.53% of the feed.
In order to address the increasing demand for fresh water due to accelerated social and economic growth in the UAE and the rest of the world, water treatment technologies, such as desalination, have been rapidly developed in attempts to safeguard water security. Electromembrane desalination processes, such as electrodialysis, belong to a category of desalination technologies which involve the removal of ions from ionic solutions with the use of electrically charged membranes termed ion exchange membranes (IEMs). The challenges associated with IEMs have drawn the attention of many researchers, who have investigated various approaches to enhance their properties. The incorporation of nanomaterials (NMs) is one of the popular approaches employed. This work investigates the incorporation of graphene-based NMs into the polymer matrices of IEMs with the aim of improving the desalination capabilities of IEMs.
In this study, natural sand particles were characterized and tested for oil in water emulsion separation. The sand particles were characterized using standard instruments and based on which the separation mechanisms were proposed. Wettability of the natural sands was checked through WCA (water contact angle) and underwater OCA (oil contact angle) measurements. The top surface morphology of was characterized with SEM (scanning electron microscope). Separation efficiency was evaluated by testing reduction of turbidity and rejection of TOC (total organic carbon). Experimental results revealed that: 1) The naturally available cleaned sands show superhydrophilicity and underwater superoleophobicity; 2) Porous Sands bed could realize even higher separation efficiency than commercial PES and Nitrocellulose microfiltration membranes, with rejection of total organic carbon higher than 90% for Dodecane in water Emulsion, higher than 99% for Hexane in water emulsions.
Microbial desalination cell offers great promise of high salinity removal with zero energy input. Moreover, membrane bioreactors are of great reliability in treating wastewater. The objective is to introduce a hybrid system of membrane bioreactor and microbial desalination cell for simultaneous wastewater treatment, seawater desalination and electricity production. Synthetic wastewater,seawater, potassium hexacyanoferrate III, yeast and glucose are used as the anode feed, saline water feed, cathode oxidizing agent, microorganisms and substrate, respectively. The system is studied under open and closed circuit modes. A smaller scale system of 350 ml capacity with a side stream MBR is more efficient than its alternative of 4.5 L capacity with an immersed MBR. A reduced middle chamber size of 250 ml capacity achieved higher desalination percentage by 5.97%. Three external resistances are used, namely 10.2, 3833 and 302200 ohms. Highest total desalination rate, but lowest power density are obtained using 302200 ? external resistance.
