An improved lumped analysis for transient heat conduction by using the polynomial approximation method

In this study, unsteady state one-dimensional heat conduction is analyzed using a polynomial approximation method. As a classical lumped model is only applicable for use with Biot numbers of less than 0.1, and additionally, it cannot be used for high-temperature gradients within the region, an improved lumped model is implemented for a typical long slab, long cylinder and sphere. It has been shown that in comparison to a finite difference solution, the improved model is able to calculate average temperature as a function of time for higher value of Biot numbers. The comparison also shows that the presented model has better accuracy when compared with others recently developed models. The simplified relations obtained in this study can be used for engineering calculations in many conditions.     

Improving the efficiency of an exhaust thermoelectric generator based on changes in the baffle distribution of the heat exchanger

Journal of Thermal Analysis and Calorimetry - A significant amount of the heat is lost in the vehicle exhaust and simply transferred to the environment. Using a thermoelectric generator (TEG), it...     

Unique substituted 3-oxo-1,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole-1-carboxamides generated by Ugi 3CC using bifunctional starting material

2-(2-Formyl-1H-benzimidazol-1-yl)acetic acid, as a bifunctional formyl-acid was prepared in four steps. This compound underwent one-pot reaction with primary amines, and alkyl isocyanides under Ugi conditions. A series of novel 3-oxo-1,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole-1-carboxamides were obtained in moderate to excellent yields.     

The efficient synthesis of 14-alkyl or aryl 14H-dibenzo[a,j]xanthenes catalyzed by bismuth(Ⅲ)chloride under solvent-free conditions

An efficient method for the synthesis of 14-alkyl or aryl 14H-dibenzo[a,j]xanthene derivatives by the reaction of β-naphthol,and aldehydes in the presence of a catalytic amount of bismuth（Ⅲ） chloride（BiCl₃） under solvent-free conditions at 110℃is described.Aliphatic and aromatic aldehydes were used in the reaction and in all cases the desired products were synthesized successfully.This reaction was studied under different temperatures;the maximum yield was obtained in a short reaction period at 110℃.The method offers the advantages of high yields,short reaction times,simplicity and easy workup compared to the conventional method of syntheses.     

Synthesis,crystal structures and antibacterial studies of oxidovanadium(IV) complexes of salen-type Schiff base ligands derived from meso-1,2-diphenyl-1,2-ethylenediamine

A series of new derivatives and previously reported Schiff base ligands and their oxidovanadium(IV) complexes were synthesized, characterized and tested as potential antibacterial agents against four human pathogenic bacteria. These N₂O₂ type Schiff base ligands were derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with different salicylaldehyde derivatives, and their metal complexes were obtained from the reaction of these ligands with bis(acetylacetonato)oxidovanadium(IV). Our studies showed that the metal complexes had moderate antibacterial activity, and this activity was higher than that of the free ligands against both Gram-positive and Gram-negative bacteria. Besides, it was found that the presence of more substituents on the ligands increases the antibacterial activities of both the free ligands and their complexes. The crystal structures of H₂L⁴ and its corresponding complex VOL⁴ were determined by X-ray crystallography.     

An improved isogeometrical analysis approach to functionally graded plane elasticity problems

The isogeometric analysis method is extended for addressing the plane elasticity problems with functionally graded materials. The proposed method which employs an improved form of the isogeometric analysis approach allows gradation of material properties through the patches and is given the name Generalized Iso-Geometrical Analysis (GIGA). The gradations of materials, which are considered as imaginary surfaces over the computational domain, are defined in a fully isoparametric formulation by using the same NURBS basis functions employed for the construction of the geometry and the approximation of the solution. The basic concept of the developed approach is concisely explained and its relation to the standard isogeometric analysis method is pointed out. It is shown that the difficulties encountered in the finite element analysis of the functionally graded materials are alleviated to a large degree by employing the mentioned method. Different numerical examples are presented and compared with available analytical solutions as well as the conventional and graded finite element methods to demonstrate the performance and accuracy of the proposed approach. The presented procedure can also be employed for solving other partial differential equations with non-constant coefficients.     

Preparation of highly flexible cellulose acetate membranes modified by hyperbranched poly(amine ester)-epoxidized soybean oil and evaluation of its filtration properties

Cellulose acetate (CA) is considered as one of the first materials used in membrane technology. However, CA membranes suffered finding their way for widespread commercial applications due to low mechanical stability and sensitivity to bio-fouling. In this study a green procedure was developed to overcome some of CA drawbacks in membrane applications. For this purpose 2nd generation of hyperbranched poly(amine ester) (HBPAE-G2), was synthesized using methyl 3-[bis(2-hydroxyethyl)amino]propanoate and triethanolamine through a pseudo one-pot polycondensation, reacted with soybean oil fatty acid, and then double bonds epoxidized by H₂O₂/formic acid to acquire hyperbranched poly(amine ester)-epoxidized soybean oil (HBPAE-ESBOFA). Finally, this reactive additive was blended with CA membrane dope solution to obtain simultaneously plasticized and cross-linked structure. Synthesis procedures were monitored by FTIR and NMR techniques, and membrane samples were investigated using ATR-FTIR, FE-SEM (top and cross-sectional), TGA and DSC. Filtration properties were studied by determining pure water flux, water contact angle, bio-fouling, water content, mean pore size and solute rejection tests. Permeability tests showed decline in water flux, but fouling resistance, salt rejection and thermal properties improved. Moreover, modified samples showed fascinating flexibility and mechanical stability enhanced dramatically.