Pool boiling heat transfer characteristics of graphene-based aqueous nanofluids

Journal of Thermal Analysis and Calorimetry - In the present study, experiments on pool boiling heat transfer of graphene nanofluids on a flat heater surface (40 mm diameter) were...     

A catalytic multicomponent protocol to dihydropyridine-3-carboxylate from terminal alkynes,isocyanates, and malonates

Monatshefte für Chemie - Chemical Monthly - A domino catalytic reaction between terminal alkynes, isocyanates, and malonates has been developed. Copper acetylides attack on isocyanates to form...     

Ammonia modification of activated carbon to enhance carbon dioxide adsorption: Effect of pre-oxidation

A commercial granular activated carbon (GAC) was subjected to thermal treatment with ammonia for obtaining an efficient carbon dioxide (CO₂) adsorbent. In general, CO₂ adsorption capacity of activated carbon can be increased by introduction of basic nitrogen functionalities onto the carbon surface. In this work, the effect of oxygen surface groups before introduction of basic nitrogen functionalities to the carbon surface on CO₂ adsorption capacity was investigated. For this purpose two different approaches of ammonia treatment without preliminary oxidation and amination of oxidized samples were studied. Modified carbons were characterized by elemental analysis and Fourier Transform Infrared spectroscopy (FT-IR) to study the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties. The texture of the samples was characterized by conducting N₂ adsorption/desorption at −196 °C. CO₂ capture performance of the samples was investigated using a thermogravimetric analysis (TGA). It was found that in both modification techniques, the presence of nitrogen functionalities on carbon surface generally increased the CO₂ adsorption capacity. The results indicated that oxidation followed by high temperature ammonia treatment (800 °C) considerably enhanced the CO₂ uptake at higher temperatures.     

On the generating function e xt+yϕ(t) and its fractional calculus

In this article, we derive the coefficient set {H _m (x,y)} _m=1 ^∞ using the generating function e ^xt+y?(t). When the complex function ?(t) is entire, using the inverse Mellin transform, and when ?(t) has singular points, using the inverse Laplace transform, the coefficient set is obtained. Also, bi-orthogonality of this set with its associated functions and its applications in the explicit solutions of partial fractional differential equations is discussed.     

Experimental investigation of forced convective heat transfer coefficient in nanofluids of Al2O3/EG and CuO/EG in a double pipe and plate heat exchangers under turbulent flow

Nanofluid is the term applied to a suspension of solid, nanometer-sized particles in conventional fluids; the most prominent features of such fluids include enhanced heat characteristics, such as convective heat transfer coefficient, in comparison to the base fluid without considerable alterations in physical and chemical properties. In this study, nanofluids of aluminum oxide and copper oxide were prepared in ethylene glycol separately. The effect of forced convective heat transfer coefficient in turbulent flow was calculated using a double pipe and plate heat exchangers. Furthermore, we calculated the forced convective heat transfer coefficient of the nanofluids using theoretical correlations in order to compare the results with the experimental data. We also evaluated the effects of particle concentration and operating temperature on the forced convective heat transfer coefficient of the nanofluids. The findings indicate considerable enhancement in convective heat transfer coefficient of the nanofluids as compared to the base fluid, ranging from 2% to 50%. Moreover, the results indicate that with increasing nanoparticles concentration and nanofluid temperature, the convective heat transfer coefficient of nanofluid increases. Our experiments revealed that in lower temperatures, the theoretical and experimental findings coincide; however, in higher temperatures and with increased concentrations of the nanoparticles in ethylene glycol, the two set of results tend to have growing discrepancies.     

A novel double-recessed 4H-SiC MESFET with partly undoped space region

In this paper, a novel double-recessed 4H-SiC metal semiconductor field effect transistor (MESFET) with partly undoped space region (DRUS-MESFET) is introduced. The key idea in this work is to improve the DC and RF characteristics of the device by introducing an undoped space region. Using two-dimensional and two-carrier device simulation, we demonstrate that breakdown voltage (V_BR) increases from 109 V in conventional double recessed MESFET (DR-MESFET) structure to 144.5 V in the DRUS-MESFET structure due to the modified channel electric field distribution of the proposed structure. The maximum output power density of the DRUS-MESFET structure is about 25.4% larger than that of the DR-MESFET structure. Furthermore, lower gate-drain capacitance (C_GD), higher cut-off frequency (f_T), larger maximum available gain (MAG), and higher maximum oscillation frequency (f_max) are achieved for the DRUS-MESFET structure. The results show that the f_max and f_T of the proposed structure improve 95.6% and 13.07% respectively, compared with that of the DR-MESFET structure. Also, the MAG of the DRUS-MESET is 4.5 dB higher than that of the DR-MESFET structure at 40 GHz. The results show that the DRUS-MESFET structure has superior electrical characteristics and performances in comparison with the DR-MESFET structure.     

Solvation thermodynamics of neutral and charged solutes using the solvation-layer interface condition continuum dielectric model

We demonstrate that the solvation-layer interface condition (SLIC) continuum dielectric model for molecular electrostatics, combined with a simple solvent-accessible-surface-area (SASA)-proportional model for nonpolar solvent effects, accurately predicts solvation entropies of neutral and charged small molecules. The SLIC/SASA model has only seven fitting parameters in total and achieves this accuracy using a training set with only 20 compounds. Despite this simplicity, solvation free energies and entropies are nearly as accurate as those predicted by the more sophisticated Langevin dipoles solvation model. Surprisingly, the model automatically reproduces the negligible contribution of electrostatics to the solvation of hydrophobic compounds. Opportunities for improvement include nonpolar solvation, anion solvation entropies, and heat capacities. More molecular realism may be needed for these quantities. To enable a future, explicit-solvent-based assessment of the SLIC/SASA implicit-solvent model, we predict solvation entropies for the Mobley test set, which are available as Supporting Information.