Towards the Investigation of Heat Transfer Characteristics in a Viscous Dissipative Shear Driven Flow Through an Annulus: An Analytical Study

In the present study, the laminar forced convective heat transfer of a shear‐driven flow through an annulus in a viscous dissipative environment is investigated. The temperature distribution for different constant heat flux boundary conditions is studied, and so are the heat transfer characteristics of a Newtonian fluid under consideration. Following an analytical methodology, closed‐form expressions of the Nusselt number on both walls of the annulus have been devised. It is shown that the effect of viscous dissipation significantly alters the temperature profile, and the consequential effect is reflected in the variation of the Nusselt number. In most of the cases, variation of the Nusselt number exhibits a discontinuity in behavior at different locations within the annulus where an equilibrium state between the energy is attained due to shear heating and the heat supplied by the wall. However, it has been observed that the greater viscous dissipative heat causes a rise in the temperature and consequently a fall in the rate of heat transfer. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(7): 569–588, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21057     

Economic viability of solar home systems: Case study of Bangladesh

Bangladesh is richly endowed with solar energy. Solar Photovoltaic (PV) system seems to be an appropriate form of renewable energy despite the monsoon type of climate in Bangladesh. The most attractive use of solar home system (SHS) in Bangladesh is the lighting system. People in rural Bangladesh predominantly use kerosene oil based lamps for illuminating their homes at night. Dry cell batteries are used for radio and gradually car batteries are becoming popular for running TV near grid areas where the charging facilities are available. The cost of kerosene and charging cost of battery are quite high and solar home system can compete with them in this particular field. Six cases were analyzed to find out the economic sustainability of the solar home systems at selected villages in Gazipur district, Bangladesh during October 2004–December 2004 and also questionnaire survey method was followed to collect data. This study reveals that the solar home system is financially attractive for small rural business and household lighting with entertainment. Only for household lighting purpose the system is not financially and economically viable without considering social benefits.     

Study of structural evolution during controlled degradation of ultrathin polymer films

The structural aspects of polyacrylamide thin films annealed at degradation threshold temperature have been studied as a function of annealing time using in situ X-ray reflectivity technique in vacuum. We observe significant decrease of thickness and increase of density with annealing time for all the films. The dynamical behavior of the changes was modeled in terms of two distinct exponential decay functions, following our earlier observation of two different time scales for the chemical modification pathways, and was found to be in excellent agreement with the data. The diffusion coefficients of the polymer chains corresponding to the two modes are found to be different by an order of magnitude. It was found that the two dynamical modes correspond to the formation of two degradation products at two different rates. The larger time constants for both the modes in case of thickness reduction compare to the chemical changes was explained in terms of inter-chain entanglement and attachment of the polymer with the substrate.     

Synthesis of polyaniline nanoparticle grafted silica gel and study of its Cr(VI) binding property

Polyaniline nanoparticles have been synthesized through simple micelle technique and then grafted it with silanized silica gel to develop a novel hybrid material. The nanoparticles are characterized by UV‐Vis, TEM, CV, SEM, TGA, DTG, and DSC. Silanization and grafting reactions are evaluated by FTIR and chemical test. The Cr(VI) binding behavior of the composite is studied in various pH of the medium, and both competitive and noncompetitive conditions. The particle size, adsorption capacity, and surface area of the material are found to be 100 nm, 135 mg/g, and 720 m²/g, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental investigations and modeling of drill bit-guided abrasive flow finishing (DBG-AFF) process

Abrasive flow finishing (AFF) is one of the widely used advanced finishing processes in which a small quantity of work material is removed by flowing semisolid abrasive-laden putty over the workpiece surface to be finished. AFF is popular for finishing and deburring of difficult-to-access areas. This process is also used for radiusing, producing compressive residual stresses, and removal of recast layer. In order to enhance productivity of the process, several modifications in AFF process are being tried. In this paper, a concept of rotating the medium along its axis has been introduced to achieve higher rate of finishing and material removal. This process is termed as drill bit-guided abrasive flow finishing (DBG-AFF) process. In order to provide random motion to the abrasives in the medium and to cause frequent reshuffling of the medium, the medium is pushed through a helical fluted drill, which is placed in the finishing zone. The experiments are carried out to compare AFF and DBG-AFF processes with AISI 1040 and AISI 4340 as workpiece materials. The performance of DBG-AFF as compared to AFF is encouraging, specifically with reference to percentage change in average surface roughness (% ΔR _a) and amount of material removed. Modeling using non-linear multi-variable regression analysis and artificial neural networks are carried out to conduct parametric analysis and to understand, in depth, the DBG-AFF process. The simulation data of neural network show a good agreement with experimental results.     

Effects of Different Modes of Hot Cross-Rolling in 7010 Aluminum Alloy: Part I. Evolution of Microstructure and Texture

The current study describes the evolution of microstructure and texture in an Al-Zn-Mg-Cu-Zr-based 7010 aluminum alloy during different modes of hot cross-rolling. Processing of materials involves three different types of cross-rolling. The development of texture in the one-step cross-rolled specimen can be described by a typical β-fiber having the maximum intensity near Copper (Cu) component. However, for the multi-step cross-rolled specimens, the as-rolled texture is mainly characterized by a strong rotated-Brass (Bs) component and a very weak rotated-cube component. Subsequent heat treatment leads to sharpening of the major texture component (i.e., rotated-Bs). Furthermore, the main texture components in all the specimens appear to be significantly rotated in a complex manner away from their ideal positions because of non-symmetric deformations in the two rolling directions. Detailed microstructural study indicates that dynamic recovery is the dominant restoration mechanism operating during the hot rolling. During subsequent heat treatment, static recovery dominates, while a combination of particle-stimulated nucleation (PSN) and strain-induced grain boundary migration (SIBM) causes partial recrystallization of the grain structure. The aforementioned restoration mechanisms play an important role in the development of texture components. The textural development in the current study could be attributed to the combined effects of (a) cross-rolling and inter-pass annealing that reduce the intensity of Cu component after each successive pass, (b) recrystallization resistance of Bs-oriented grains, (c) stability of Bs texture under cross-rolling, and (d) Zener pinning by Al₃Zr dispersoids.     

Effects of Thermal Annealing Upon the Morphology of Polymer–Fullerene Blends

Grazing incidence X‐ray scattering (GIXS) is used to characterize the morphology of poly(3‐hexylthiophene) (P3HT)–phenyl‐C61‐butyric acid methyl ester (PCBM) thin film bulk heterojunction (BHJ) blends as a function of thermal annealing temperature, from room temperature to 220 °C. A custom‐built heating chamber for in situ GIXS studies allows for the morphological characterization of thin films at elevated temperatures. Films annealed with a thermal gradient allow for the rapid investigation of the morphology over a range of temperatures that corroborate the results of the in situ experiments. Using these techniques the following are observed: the melting points of each component; an increase in the P3HT coherence length with annealing below the P3HT melting temperature; the formation of well‐oriented P3HT crystallites with the (100) plane parallel to the substrate, when cooled from the melt; and the cold crystallization of PCBM associated with the PCBM glass transition temperature. The incorporation of these materials into BHJ blends affects the nature of these transitions as a function of blend ratio. These results provide a deeper understanding of the physics of how thermal annealing affects the morphology of polymer–fullerene BHJ blends and provides tools to manipulate the blend morphology in order to develop high‐performance organic solar cell devices.     

Variation in Fatty Acid Composition in Indian Germplasm of Sesame

A germplasm collection of 33 entries comprising 22 sesame (Sesamum indicum L.) cultivars, 4 landraces of S. mulayanum and 7 other accessions of 4 wild species were analyzed for the fatty acid compositions of their seed oil. The entries varied widely in their fatty acid compositions. The percentage content of oleic, linoleic, palmitic and erucic acids ranged between 36.7–52.4, 30.4–51.6, 9.1–14.8 and 0.0–8.0, respectively. Linolenic and arachidonic acids were the minor constituents but varied widely in wild species. Oleic and linoleic were the major fatty acids with mean values of 45.9 and 40.5%, respectively and the mean of their combined values was 86.4%. The polyunsaturated fatty acid (PUFA) compositions ranged from 30.9 to 52.5% showing high variation in PUFA in the germplasm. Linoleic acid content was very high in one landrace (47.8) and one accession each of three wild species, S. mulayanum (49.3), S. malabaricum (48.2) and S. radiatum (51.6%). Use of fatty acid ratios to estimate the efficiency of biosynthetic pathways resulted in high oleic and low linoleic desaturation ratios and consequently high linoleic and very low linolenic acid contents in seed oil. The results of this study provided useful background information on the germplasm and also identified a few accessions having high linoleic acid which can be used for developing cultivars with desirable fatty acid compositions.     

Removal of Pb(II) from aqueous solution by adsorption using activated tea waste

A basic investigation on the removal of Pb(II) ions from aqueous solutions by using activated tea waste was conducted in batch conditions. An inexpensive and effective adsorbent was developed from waste tea leaves for the uptake of Pb(II) from aqueous solution. The influence of different experimental parameters—shaking time, particle size, adsorbent dose, initial pH, temperature, etc.—on lead uptake was evaluated. Lead is adsorbed by the developed adsorbent up to maximum of 99.7%. The initial Pb(II) concentrations were 5, 10, 15 and 20 mg/l in the experiment. The adsorption was found to be exothermic in nature. The Langmuir, Freundlich and Tempkin isotherm models were tried to represent the equilibrium data of Pb(II) adsorption. The adsorption data was fitted very well to the Langmuir isotherm model in the studied concentration range of Pb(II) adsorption. Isotherms have been used to determine thermodynamic parameters of the process: free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°). Column experiments were performed to study the practical applicability of the system. The kinetics and the factors controlling the adsorption process were also discussed. Activated tea waste is a better adsorbent compared to other adsorbents available in literature.     

Performance estimation of sub-30 nm junctionless tunnel FET (JLTFET)

In this paper we examined the short channel behavior of junction less tunnel field effect transistor (JLTFET) and a comparison was made with the conventional MOSFET on the basis of variability of device parameter. The JLTFET is a heavily doped junctionless transistor which uses the concept of tunneling, by narrowing the barrier between source and channel of the device, to turn the device ON and OFF. The JLTFET exhibits an improved subthreshold slope (SS) of 24 mV/decade and drain-induced barrier lowering (DIBL) of 38 mV/V as compared to SS of 73 mV/decade and DIBL of 98 mV/V for the conventional MOSFET. The simulation result shows that the impact of length scaling on threshold voltage for JLTFET is very less as compared to MOSFET. Even a JLTFET with gate length of 10 nm has better SS than MOSFET with gate length of 25 nm, which enlightens the superior electrostatic integrity and better scalability of JLTFET over MOSFET.