Theoretical modeling of suspended grain-size distribution in fluvial environment by stratification and secondary current approaches

Here we propose a theoretical model to compute the suspended grain-size distribution in fluvial environment. We derive the model based on the Reynolds averaged Navier–Stokes equation and the continuity equation of sediment phase. The model includes the effects of secondary current and stratification which are the cause of complex interaction between turbulence and grain-size distribution in the sediment-laden flow. Due to an immense importance of particle–particle and particle-turbulence interactions near the channel bed, we include their impacts in the boundary condition of the model. The present model has noteworthy contribution to demonstrate the phenomena of suspended grain-size distribution in the real world. Reported experimental data in literature shows well agreement with the numerical solution computed from the suggested model. The better computational accuracy of the present model is ascertained when the upper bound of calculated error between observed experimental data and computed values is found to be lowest for our model in comparison to a large number of existing models developed from different mathematical viewpoints.     

Removal of Volatile Organic Compounds from polluted air

Volatile Organic Compounds (VOCs) are among the most common air pollutants emitted from chemical, petrochemical, and allied industries. VOCs are one of the main sources of photochemical reaction in the atmosphere leading to various environmental hazards; on the other hand, these VOCs have good commercial value. Growing environmental awareness has put up stringent regulations to control the VOCs emissions. In such circumstances, it becomes mandatory for each VOCs emitting industry or facility to opt for proper VOCs control measures. There are many techniques available to control VOCs emission (destruction based and recovery based) with many advantages and limitations. Therefore, deciding on a particular technique becomes a difficult task. This article illustrates various available options for VOCs control. It further details the merits, demerits and applicability of each option. The authors hope that this article will help in critically analysing the requirements and accordingly decide on the appropriate strategy to control VOCs.     

Three-dimensional visualization and quantification of non-aqueous phase liquid volumes in natural porous media using a medical X-ray Computed Tomography scanner

This study demonstrates the capabilities of a typical medical X-ray Computed Tomography (CT) scanner to non-destructively quantify non-aqueous phase liquid (NAPL) volumes, saturation levels, and three-dimensional spatial distributions in packed soil columns. Columns packed with homogeneous sand, heterogeneous sand, or natural soil, were saturated with water and injected with known quantities of gasoline or tetrachloroethene and scanned. A methodology based on image subtraction was implemented for computing soil porosity and NAPL volumes in each 0.35 mm x 0.35 mm x 1 mm voxel of the columns. Elimination of sample positioning errors and instrument drift artifacts was essential for obtaining reliable estimates of above parameters. The CT data-derived total NAPL volume was in agreement with the measured NAPL volumes injected into the columns. CT data-derived NAPL volume is subject to a 2.6% error for PCE and a 15.5% error for gasoline, at average NAPL saturations as low as 5%, and is mainly due to instrument noise. Non-uniform distributions of NAPL due to preferential flow, and accumulation of NAPL above finer-grained layers could be observed from the data on 3-D distributions of NAPL volume fractions.     

Study on the Thermo-Mechanical and Biodegradable Properties of Shellac Films Grafted with Acrylic Monomers by Gamma Radiation

Shellac (SL) films were prepared by casting and were grafted with various acrylic monomers of different functionalities using gamma radiation. Different formulations of shellac with varying concentrations (3, 5 and 7%) of these acrylic monomers such as 2-hydroxyethyl methacrylate (HEMA), 2-ethylhexyl acrylate (EHA) and 1,4-butanediol diacrylate (BDDA) in methanol were prepared. The pure shellac and other treated films were then irradiated under gamma radiation (Co-60) at different doses (0.5–5 kGy) at a dose rate of 3.5 kGy/h where 1 Gy = 1 J/kg = 100 rads. The mechanical properties like tensile strength (TS) and elongation at break (Eb) of the prepared films were studied. The mechanical properties of the irradiated shellac films demonstrated superior values. Among the formulations, shellac grafted with BDDA (SL-g-BDDA) showed the highest TS and Eb values which were 543 and 168% higher than those of raw shellac films, respectively. The water uptake behavior of raw and treated films was also studied. The raw film showed 11% water uptake but HEMA containing film showed 67%. In the soil burial test, HEMA containing shellac film was rapidly degraded than other raw, EHA and BDDA grafted films. Thermal properties indicated that grafting of acrylic monomers decreased the melting temperature of the pure shellac films.     

Effect of Urea on the Mechanical Properties of Gelatin Films Photocured with 2-Ethylhexyl Acrylate

Thin films of gelatin were prepared by casting. Then the films were photocured and the mechanical properties were studied. The tensile strength of UV cured gelatin films showed about 10% enhancement than that of raw gelatin films. Minor amount of urea (1–5%) was used as additive in aqueous gelatin solution and films were prepared using same technique. Four formulations were prepared in methanol with 2-ethylhexyl acrylate in the presence of photoinitiator (darocur-1664). The films were soaked in the prepared formulations and then cured under UV radiation at different intensities (5–25 passes). Percentage of urea, monomer concentration, soaking time and radiation intensities were optimized with the extent of polymer loading, TS and elongation at break of the photocured film. The films containing 2% urea, cured with 3% EHA for 3 min at 15th UV pass showed the highest mechanical properties. A significant improvement of TS (31%) occurred when EHA (3%) was incorporated.     

Selection of appropriate adsorption technique for recovery of VOCs: an analysis

Realization of the adverse effects of volatile organic compounds (VOCs) in the environment and the consequent enforcement of stringent regulations, accelerated the research and developmental activities across the world for achieving economic solutions. As a result, several advanced concepts of adsorption, a commercialized separation technology, have emerged. The availability of so many options means the industrialists, consultants and researchers experience problems in selecting the appropriate one. The present paper, through analysis of the type and concentration of VOCs, VOCs vs adsorbent suitability, the extent of separation required, and different adsorption techniques based on traditional and new advanced concepts, is an attempt to establish a qualitative guideline for the selection of the appropriate technique for recovery of VOCs.     

Study on the Physico-mechanical Properties of Photo-cured Chitosan Films with Oligomer and Acrylate Monomer

Chitosan films were prepared from dried prawn shell via chitin and then tensile properties like tensile strength (TS) and elongation at break (Eb) of the films were evaluated. Six formulations were developed using methyl methacylate (MMA) monomer and aliphatic urethane diacrylate oligomer (M-1200) in methanol along with photoinitator (Darocur-1664). Then the films were soaked in the formulations and irradiated under UV radiation at different doses for the improvement of physico-mechanical properties of chitosan films. The cured films were characterized by measuring TS, Eb, polymer loading (PL), water absorption and gel content properties. The formulation containing 43% MMA and 15% oligomer in methanol solution showed the best performance at 20th UV pass for 4 min soaking time.     

Temperature-dependent pyrolytic product evolution profile for low-density polyethylene from gas chromatographic study

In this work, a product distribution study from thermal degradation of low-density polyethylene (LDPE) is presented. Thermal degradation of the polymer was investigated under dynamic condition in an inert environment using a thermo-gravimetric analyzer (TGA) coupled with evolved products’ analysis using a gas chromatograph (GC). Fractions evolved at nine different temperatures from 200 to 600 °C were injected into GC for a detailed product analysis. The main objective of the present investigation is to highlight the species-specific evolution profiles of LDPE pyrolyzates (C5–C44) at different stages of its degradation under an inert environment. Pyrograms have been analyzed in terms of amount of different products evolved at various pyrolysis temperatures. Volatile pyrolyzates essentially remain low at low decomposition temperature (200–300 °C) of the polymer, which gradually increase to attain a maximum at maximum decomposition temperature (470 °C) and finally level off at 600 °C. In the mechanistic approach adopted to understand the decomposition mechanism of LDPE, the following reaction types were considered: (a) main chain cleavage to form chain-terminus radicals; (b) intramolecular hydrogen transfer to generate internal radicals; (c) intermolecular hydrogen transfer to form both volatile products and radicals; and (d) β-scission to form both volatiles and terminally unsaturated polymer.