Numerical study of mixed convection heat transfer inside a vertical microchannel with two-phase approach

Journal of Thermal Analysis and Calorimetry - The current study investigates the laminar and two-phase nanofluid flow inside a two-dimensional rectangular microchannel with the ratio of length to...     

Highly Selective Vapor-Phase Acylation of Veratrole over H_3PO_4/TiO_2-ZrO_2: Using Ethyl Acetate as a Green and Efficient Acylating Agent

A simple sol‐gel method with and without surfactant was applied to prepare TiO₂‐ZrO₂ mixed oxides containing Ti and Zr at a molar ratio of 1:1. Several catalysts containing w=15% –35% H₃PO₄ were set up using these mixed oxides. The physical and chemical properties of catalysts were investigated by BET, SEM and pyridine adsorption‐desorption. The catalytic performance of each material was determined for the vapor‐phase acylation of veratrole (1,2‐dimethoxybenzene) to 3,4‐dimethoxyacetophenone (3,4‐DMAP), which was found to be the major product of the reaction of veratrole with ethyl acetate, with alkylated products being the minor products. 2,3‐Dimethoxyacetophenone (2,3‐DMAP) was not detected in the product stream. In the best experimental conditions, the alkylated products were less than 0.7%. This reaction may represent an environmentally friendly alternative to use the ethyl acetate as the acylating reagent. The feed molar ratios of veratrole/ethyl acetate were varied over a wide range of 0.1 to 1, and the optimum feed ratio of veratrole/ethyl acetate was 1:3. Space velocity employed in the veratrole acylation reported as WHSV (veratrole) was 1.2 h^?1. The acylation reactions were carried out in the temperature range of 423 to 673 K and the optimum H₃PO₄ content for acylation was w=15%.     

High‐Throughput Measurement of Binding Kinetics by mRNA Display and Next‐Generation Sequencing

There is great demand for high‐throughput methods to characterize ligand affinity. By combining mRNA display with next‐generation sequencing, we determined the kinetic on‐ and off‐rates for over twenty thousand ligands without the need for synthesis or purification of individual members. Our results are reproducible and as accurate as those obtained with other methods of affinity measurement.     

Substituent effect on structure,electron density,and intramolecular hydrogen bonding in nitroso‐oxime methane

Density functional calculations with Beck's three‐parameter hybrid method using the correlation functional of Lee, Yang, and Parr (B3LYP) were carried out for investigation of the intramolecular hydrogen bond strength in Nitroso‐oxime methane and its derivatives. Also, vibrational frequencies for them were calculated at the same level of theory. The π‐electron delocalization parameter (Q) and as a geometrical indicator of a local aromaticity, the geometry‐based harmonic oscillator measure of aromaticity index has been applied. Additionally, the linear correlation coefficients between substituent constants and selected parameters in R position have calculated. The obtained results show that the hydrogen bond strength is mainly governed by the resonance variations inside the chelate ring induced by the substituent groups. The topological properties of the electron density distributions for O? H ··· O intramolecular bridges have been analyzed in terms of the Bader theory of atoms in molecules (AIM). Correlations between the H‐bond strength and topological parameters have been also studied. The electron density (ρ) and Laplacian (?²ρ) properties, estimated by AIM calculations, show that O ··· H bond have low ρ and negative (?²ρ) values (consistent with covalent character of the HBs), whereas O? H bond have positive (?²ρ) Furthermore, the analysis of hydrogen bond in this molecule and its derivatives by quantum theory of natural bond orbital (NBO) methods fairly support the ab initio results. Natural population analysis data, the electron density, and Laplacian properties as well as υ(O? H) and γ(O? H) were further used for estimation of the hydrogen bonding interactions and the forces driving their formation. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Thermodynamic and heat transfer analysis of heat recovery from engine test cell by Organic Rankine Cycle

During manufacture of engines, evaluation of engine performance is essential. This is accomplished in test cells. During the test, a significant portion of heat energy released by the fuel is wasted. In this study, in order to recover these heat losses, Organic Rankine Cycle (ORC) is recommended. The study has been conducted assuming the diesel oil to be composed of a single hydrocarbon such as C₁₂H₂₆. The composition of exhaust gases (products of combustion) have been computed (and not determined experimentally) from the stoichiometric equation representing the combustion reaction. The test cell heat losses are recovered in three separate heat exchangers (preheater, evaporator and superheater). These heat exchangers are separately designed, and the whole system is analyzed from energy and exergy viewpoints. Finally, a parametric study is performed to investigate the effect of different variables on the system performance characteristics such as the ORC net power, heat exchangers effectiveness, the first law efficiency, exergy destruction and heat transfer surfaces. The results of the study show that by utilizing ORC, heat recovery equivalent to 8.85 % of the engine power is possible. The evaporator has the highest exergy destruction rate, while the pump has the lowest among the system components. Heat transfer surfaces are calculated to be 173.6, 58.7, and 11.87 m² for the preheater, evaporator and superheater, respectively.     

Affordable,entropy-consistent Euler flux functions II: Entropy production at shocks

In this paper, an entropy-consistent flux is developed, continuing from the work of the previous paper. To achieve entropy consistency, a second and third-order differential terms are added to the entropy-conservative flux. This new flux function is tested on several one dimensional problems and compared with the original Roe flux. The new flux function exactly preserves the stationary contact discontinuity and does not capture the unphysical rarefaction shock. For steady shock problems, the new flux predicts a slightly more diffused profile whereas for unsteady cases, the captured shock is very similar to those produced by the Roe- flux. The shock stability is also studied in one dimension. Unlike the original Roe flux, the new flux is completely stable which will provide as a candidate to combat multidimensional shock instability, particularly the carbuncle phenomenon.     

Invariance principles for tempered fractionally integrated processes

We discuss invariance principles for autoregressive tempered fractionally integrated moving averages in $\alpha$-stable $(1<\alpha \le 2)$ i.i.d. innovations and related tempered linear processes with vanishing tempering parameter $\underset{N\to \infty }{lim}\lambda ∕N={\lambda }_1$. We show that the limit of the partial sums process takes a different form in the weakly tempered (${\lambda }_1=0$), strongly tempered (${\lambda }_1=\infty$), and moderately tempered ($0<{\lambda }_1<\infty$) cases. These results are used to derive the limit distribution of the ordinary least squares estimate of AR(1) unit root with weakly, strongly, and moderately tempered moving average errors.     

Modeling vibration behavior of embedded graphene-oxide powder-reinforced nanocomposite plates in thermal environment

Abstract

This article deals with the thermal vibration analysis of the graphene-oxide powder-reinforced (GOPR) nanocomposite plates, once the plate is embedded on the viscoelastic substrate. The structure is subjected to thermal loadings with various temperature rises such as sinusoidal temperature rise (STR), linear temperature rise (LTR), and uniform temperature rise (UTR). Damping behavior of the GOPR nanocomposite plates is investigated based on the variations of the natural frequencies. Four functionally graded (FG) patterns of GOPs’ distribution are taken into account comparatively in order to find out the best model of reinforcing the structure. The homogenization of the materials is carried based on the Halpin-Tsai micromechanical scheme. The governing equations of the motion have been derived through the combination of refined higher-order shear deformation theory and Hamilton’s principle. The accuracy of this modeling is validated with those reported in the open literature. Finally, the influences of different parameters on the natural frequencies of the embedded GOPR nanocomposite plates are investigated based on the damping coefficient of the viscoelastic substrate. The graphical results reveal that the free vibrational behavior of the structure is remarkably affected by the variations of these parameters.