Experimental studies on heat transfer augmentation using twisted aluminium taper clips and twisted tapes

Heat exchangers have several industrial and engineering applications. The design procedure of heat exchangers is quite complicated, as it needs exact analysis of heat transfer rate and pressure drop estimations apart from issues such as long-term performance and the economic aspect of the equipment. Whenever inserts are used for the heat transfer enhancement, along with the increase in the heat transfer rate, the pressure drop also increases. This increase in pressure drop increases the pumping cost. Thus it’s highly essential not to allow the pressure drop to go beyond a specified value while going for heat transfer enhancement techniques using inserts. The present paper includes various heat transfer augmentation techniques. A literature review of heat transfer augmentation using twisted tapes has been included. Experimental work on heat transfer augmentation using a new kind of insert called TWISTED ALUMINIUM TAPER CLIP (TATC) is carried out. Inserts when placed in the path of the flow of the liquid, create a high degree of turbulence resulting in an increase in the heat transfer rate and the pressure drop. The work includes the determination of friction factor and heat transfer coefficient for various TATC having different twist ratios. The results are compared with twisted tapes having different twist ratios. Four TATC and two twisted tapes having different twist ratios are used in the study. The performance evaluation criterion R1 is found out to clearly depict the enhancement in the heat transfer rate. The results are aptly supported by observation tables and figures

India’s Trade Partnership with East African Community: Exploratory Results from Trade Indices

Since the initiation of economic reforms in 1991, India adopted an outward-oriented strategy for development. After inception of World Trade Organization (WTO) in 1995, the country initially relied on multilateral trade reforms for export growth, but slow progress of the Doha Round negotiations over the last decade caused it to explore the regional trade agreements (RTAs) route as well from 2003-04 onwards. While in the initial period India focused on deeper trade relationship with Asian partners, namely, Association of Southeast Asian Nations (ASEAN), Japan, South Korea etc. as preferential trade allies, the perceived need to diversify the export markets has led the country to focus on potential trade partners in Africa, Europe, North and Latin America as well in recent times. On the other hand, the economies of East Africa are also embracing the RTA route for their trade promotion and the growing Indian market offers an opportunity for them as well. The present analysis attempts to understand the trade potential between the five East African Community (EAC) countries and India in the sphere of merchandise and services trade by looking through various trade indices. The empirical results indicate that bilateral trade between the two regions have a strong potential, which can be aided further through policy reforms at both ends

A Collective Study on Modeling and Simulation of Resistive Random Access Memory

Abstract In this work, we provide a comprehensive discussion on the various models proposed for the design and description of resistive random access memory (RRAM), being a nascent technology is heavily reliant on accurate models to develop efficient working designs and standardize its implementation across devices. This review provides detailed information regarding the various physical methodologies considered for developing models for RRAM devices. It covers all the important models reported till now and elucidates their features and limitations. Various additional effects and anomalies arising from memristive system have been addressed, and the solutions provided by the models to these problems have been shown as well. All the fundamental concepts of RRAM model development such as device operation, switching dynamics, and current-voltage relationships are covered in detail in this work. Popular models proposed by Chua, HP Labs, Yakopcic, TEAM, Stanford/ASU, Ielmini, Berco-Tseng, and many others have been compared and analyzed extensively on various parameters. The working and implementations of the window functions like Joglekar, Biolek, Prodromakis, etc. has been presented and compared as well. New well-defined modeling concepts have been discussed which increase the applicability and accuracy of the models. The use of these concepts brings forth several improvements in the existing models, which have been enumerated in this work. Following the template presented, highly accurate models would be developed which will vastly help future model developers and the modeling community

Furo[2,3-c]pyrans from a vinyl sulfone modified methyl 2,6-O-anhydro-α-D-hexopyranoside: an experimental and theoretical investigation

A vinyl sulfone modified bicyclic sugar molecule undergoes efficient Michael addition of hetero- and carbon nucleophiles to afford single diastereomers. The same molecule consisting of two other masked functional groups, namely an aldehyde and an oxocarbonium ion, turned out to be a unique synthetic intermediate. The adducts generated from this Michael acceptor and a series of β-dicarbonyl compounds and related reagents after acid treatment afforded a new class of furo[2,3-c]pyrans, forming up to three new bonds and three stereocenters. In-built chirality centers of the sugar derivative controlled the diastereoselectivity of formation of all new bonds without the requirement for any external reagent for asymmetric induction. DFT calculations revealed the formation of furopyrans as the only possible products, which corroborates the experimentally observed results

Graphene, Graphene-Derivatives and Composites: Fundamentals, Synthesis Approaches to Applications

Graphene has accomplished huge notoriety and interest from the universe of science considering its exceptional mechanical physical and thermal properties. Graphene is an allotrope of carbon having one atom thick size and planar sheets thickly stuffed in a lattice structure resembling a honeycomb structure. Numerous methods to prepare graphene have been created throughout a limited span of time. Due to its fascinating properties, it has found some extensive applications to a wide variety of fields. So, we believe there is a necessity to produce a document of the outstanding methods and some of the novel applications of graphene. This article centres around the strategies to orchestrate graphene and its applications in an attempt to sum up the advancements that has taken place in the research of graphene

In Silico Studies toward Understanding the Interactions of DNA Base Pairs with Protonated Linear/Cyclic Diamines

Protonated amino groups are ubiquitous in nature and important in the fields of chemistry and biology. In search of efficient polyamine analogues, we have performed DFT calculations on the interactions of some simple cyclic and constrained protonated diamines with the DNA base pairs and compared the results with those obtained for the corresponding interactions involving linear diamines, which mimic biogenic polyamines such as spermine. The interactions are mainly governed by the strong hydrogen bonding between the ligand and the DNA base pairs. The DFT calculations suggest that the major-groove N7 interaction (GC base pair) with linear diamine is energetically more favored than other possible interactions, as reported with spermine. The cyclic diamines exhibited better interactions with the N7 site of the AT and GC base pairs of DNA than the linear diamines. The net atomic charges calculated for the protonated amine hydrogens were higher for the cyclic systems than for the linear diamines, inducing better binding affinity with the DNA base pairs. The stable conformers of cyclic diamines were predicted using the MP2/aug-cc-pVDZ level of theory. The positions of the protonated diamine groups in these cyclic systems are crucial for effective binding with the DNA base pairs. The DFT-calculated results show that diequatorial (ee) 1,2-cyclohexadiamine (CHDA) is a promising candidate as a polyamine analogue for biogenic polyamines. Molecular dynamics simulations were performed using explicit water molecules for the interaction of representative ligands with the DNA base pairs to examine the influence of solvent molecules on such interactions

Regioselectivity of Vinyl Sulfone Based 1,3-Dipolar Cycloaddition Reactions with Sugar Azides by Computational and Experimental Studies

DFT (M06-L) calculations on the transition state for the 1,3-dipolar cycloadditions between substituted vinyl sulfones with sugar azide have been reported in conjunction with new experimental results, and the origin of reversal of regioselectivity has been revealed using a distortion/interaction model. This study provides the scientific justification for combining organic azides with two different types of vinyl sulfones for the preparation of 1,5-disubstituted 1,2,3-triazoles and 1,4-disubstituted triazolyl esters under metal-free conditions

Experimental and Computational Study of the (Z)-Selective Formation of Trisubstituted Olefins and Benzo-Fused Oxacycles from the Ruthenium-Catalyzed Dehydrative C-H Coupling of Phenols with Ketones

The cationic Ru-H complex was found to be an effective catalyst for the dehydrative C-H coupling of phenols with ketones to form the trisubstituted olefin products. The coupling of phenol with linear ketones led to highly stereoselective formation of the (Z)-olefin products. The dehydrative coupling of phenol with enones and diones efficiently formed the benzopyrene and related oxacyclic derivatives. The reaction of 3,5-dimethoxyphenol with cyclohexanone-2,2,6,6-d(4) showed a significant H/D exchange to both vinyl and alpha-CH2 positions on the olefin product (72-75% D). A significant carbon isotope effect was observed on the ortho-arene carbon of the olefin product. The free energies of intermediate species for the entire catalytic cycle were successfully computed by using the DFT method. The DFT study revealed that the E/Z stereoselectivity is a result of the energy difference in the insertion step of ortho-metalated phenol to an enol form of the ketone substrate (Delta Delta E = 9.6 kcal/mol). The coupling method provides a direct catalytic C-H olefination method for ketones to form trisubstituted olefins without employing any reactive reagents or forming any wasteful byproducts © 2018 American Chemical Societ