Sharif Digital Repository

We conduct an experimental investigation on the pool boiling enhancement in DI water on nanoporous surfaces. The surfaces are modified by anodic oxidation, and cavities with 2 mm diameter and pitches between 2.5 and 5 mm applied on them using EDM method filled with a two-part epoxy with low thermal conductivity properties. The capillary wicking action of the superhydrophilic nanoporous oxide layer enhances the rewetting and spreading of the liquid to dry-spots during boiling. The epoxy disks remain wet and prevent merging bubbles during the pool boiling experiment and a 2-D microflow is induced toward dried regions with synergic effects of nanoporous surface absorption, create a considerable... 

Nowadays, increasing the CO2 emissions are one of the inevitable challenges in the world. In addition, in many industries, fossil fuels are the main source of energy demands which worsen the problem. Since in most applications, the performance and energy loss are highly affected by the drag force, many investigations have been proposed to improve the surface properties to moving surface against the water, and consequently, increasing drag reduction. To this end, one effective way is utilizing superhydrophobic coatings. In this study, we prepare two different superhydrophobic coatings using Al2O3 nanoparticles (NPs) modified by HMDS (1,1,1,3,3,3-Hexamethyldisilazane) and PDMS... 

In the title compound [systematic name: 2-(3,4-dihydroxy-phen-yl) ethanaminium perchlorate], C8H12NO2 +·ClO4 -, the cations and anions are linked into three-dimensional structure via inter-molecular N - H⋯O and O - H⋯O hydrogen bonds. © 2008  

Nano-sized particles of manganese oxides have been prepared by a very simple and cheap process using a decomposing aqueous solution of manganese nitrate at 100 °C. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectrometry have been used to characterize the phase and the morphology of the manganese oxide. The nano-sized manganese oxide shows efficient catalytic activity toward water oxidation and the epoxidation of olefins in the presence of cerium(iv) ammonium nitrate and hydrogen peroxide, respectively  

Oxygen evolution was observed upon mixing solid manganese(III) bidentate Schiff base complexes with aqueous solutions of cerium(IV) ammonium nitrate. However, oxygen evolution was not observed upon mixing solutions of the complexes (in acetonitrile) with Ce(IV). Electron-withdrawing substituents on the Schiff base ligands (NO2, Br) enhanced the reactivity of the manganese complexes toward oxygen evolution. Oxygen evolution was also affected by R groups on the ligands, in the order Me > Et Bz. © 2009 Springer Science+Business Media B.V  

Wind erosion raises mineral dusts from dry and semidry lands and produces dust storms. Such dust masses have created numerous health and economic problems for the residents of southern, southwestern, and central parts of Iran. The main sources, movement, spread, and settlement of dust masses can be determined by solving the governing equations for aerosol transmission. Such information will be certainly useful in managerial decision-making. In this study, the dust event in Tehran on 20–22 February 2016 was studied using numerical model, Moderate Resolution Imaging Spectroradiometer satellite data, and data of ground-based stations. A comparison between the numerical results and in situ... 

In recent years, the city of Tehran, Iran's capital, has encountered numerous dust events so that the dust concentration of PM10 has reached even more than 800 μg m−3. This emphasizes the importance of the statistical study of dust in Tehran and the development of correlations for estimating dust concentration of PM10. In the present study, by evaluating the data measured during dust observations over the years 2013–2016 in Tehran, new statistical models are established for estimating PM10 concentration in terms of horizontal visibility and MODIS AOD. Firstly, simple nonlinear regression models between dust concentration of PM10 and horizontal visibility as well as MODIS AOD are developed.... 

Condensation heat transfer on stainless steel tube utilizing superhydrophobic coatings was investigated. The electrophoretic deposition and spraying methods were employed to coat the tubes’ outer surface. The mixture that was synthesized for spray coating was a hybrid paint. It incorporated polyurethane matrix and a colloidal suspension containing organic nanoparticles. The hybrid paint had a proper adhesion to the substrate which caused more durability compared to the electrophoretic coating. The agglomeration of nanoparticles in the hybrid paint caused the formation of particles with larger size compared to the particles in the electrophoretic coating. Consequently, contact angle... 

Condensation heat transfer on stainless steel tube utilizing superhydrophobic coatings was investigated. The electrophoretic deposition and spraying methods were employed to coat the tubes’ outer surface. The mixture that was synthesized for spray coating was a hybrid paint. It incorporated polyurethane matrix and a colloidal suspension containing organic nanoparticles. The hybrid paint had a proper adhesion to the substrate which caused more durability compared to the electrophoretic coating. The agglomeration of nanoparticles in the hybrid paint caused the formation of particles with larger size compared to the particles in the electrophoretic coating. Consequently, contact angle... 

In this study, a severe dust storm has been simulated using the WRF-Chem model to investigate the accuracy of different dust emission schemes in estimating dust concentration in Tehran, the capital of Iran. First, by comparing the results of the GOCART, AFWA, UOC-2001, UOC-2004, and UOC-2011 dust emission schemes in WRF-Chem model, it is observed that the GOCART and AFWA schemes have the best performance compared to the in-situ measurements. The GOCART scheme with a better prediction of the trend of the dust concentration profile, and the AFWA scheme with a better prediction of the dust concentration peak value, are selected as the preferred schemes for this region. In the following, by... 

Two new silver(I) complexes ((tptz)Ag2(NO3) 2 and [Ag5(tptz)4](NO3)5) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) have been synthesized and characterized by X-ray diffraction, elemental analysis, 1H NMR, IR, fluorescence, UV-Vis spectroscopy and electrochemistry. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted with one of the Ag complexes as a catalyst, soluble enough in organic solvent, using oxone (2KHSO5·KHSO4·K2SO4) as an oxidant under biphasic reaction conditions (CH2Cl 2/H2O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature  

In this study, numerical computations are performed with the main purpose of shedding light on the mixing characteristics in an innovative T-shaped micromixer equipped with a twisted structure. A 3-D model is presented and verified to mix two miscible fluids in a single phase. By considering different geometrical cases, the proposed T-mixer is compared using the standard T-mixer (Base case) running in the same operational conditions. Furthermore, the impacts of variation in the geometry of twisted design are scrutinized for Re (Reynolds number) in the extent of 1≤Re≤500 with the focus of obtaining a significant mixing quality for flow through the micromixer. MI (Mixing index), PI... 

A polymeric phenolato-bridged potassium compound, K(2-bromo-4,6 dinitrophenolate) (H2O), was obtained by reaction of methylammonium 2-bromo-4,6-dinitrophenolate and potassium chloride in water. 2-bromo-4,6 dinitrophenolate co-ordinates to the metal ion by phenolic O atom, Br, and O atoms of the nitro groups. K+ ion is eleven-coordinate in the compound. Single-crystal X-ray diffraction for methylammonium 2-bromo-4,6-dinitrophenolate and single-crystal X-ray diffraction, elemental analysis, IR, UV-Vis spectra, and fluorescence emission spectra for the complex have also been determined. Methylammonium 2-bromo-4,6-dinitrophenolate was solved in the monoclinic system, space group P21/c, with the... 

The density jump on an inclined surface is analyzed using an integral method by applying mass and momentum conservation equations. The jump occurs in a two-layered fluid flow in which the upper layer is stagnant and very deep. A relation is derived, which gives the conjugate depth ratio as a function of inlet densimetric Froude number, inlet concentration ratio, bed slope and entrainment. A set of experiments are performed to verify the relation. The theory and the measurements are in good agreement. The analysis reveals that increasing the surface inclination results in a decrease in the conjugate depth ratio. This analysis also shows that the densimetric Froude number just after the jump... 

The title complex [Mn(tptz)(CH3COO)(OH2) 2]NO3 was synthesized through the reaction of tptz (2,4,6-tris(2-pyridyl)-1,3,5-triazine), nitric acid and manganese(II) acetate. The molecular structure was characterized by X-ray diffraction, elemental analysis, electrochemistry, EPR, IR, fluorescence and UV-Vis spectroscopy and its oxygen evolving activity has been studied. X-ray structure analysis shows that each Mn(II) ion is seven coordinated by a bidentate acetate, three nitrogen atoms of tptz and two oxygen atoms from two water ligands, which are coordinated in axial positions. The complex acts as an oxygen evolving complex with oxone (2KHSO5·KHSO4·K 2SO4) as primary oxidant in aqueous... 

A new manganese complex of the formula [Mn(tptz)(OH 2) 3](CF 3SO 3) 2·EtOH, (1, where tptz = (2,4,6-tris(2-pyridyl)-1,3,5-triazine) is presented, exhibiting an excellent catalytic activity and selectivity in oxidation of various sulfides to the corresponding sulfoxides with UHP (urea hydrogen peroxide) as oxidant under air at room temperature. A modified preparation procedure produces another new manganese complex of the formula [Mn(tptz)(CH 3COO)(OH 2) 2](CF 3SO 3)·3H 2O (2). X-ray structures of both Mn(II) complexes, properties (elemental analysis, electrochemistry, EPR, IR, Raman, and UV-Vis spectra), as well as DFT studies results are reported  

The mononuclear complex [Mn(tptz)(CH3COO)(OH2)2]NO3 (1) was investigated by electrospray ionization mass spectrometry in aqueous solution at pH 4.5. Electrospray ionization mass spectrometry shows that mononuclear and dinuclear manganese cationic species are present in solution, probably in equilibrium with neutral 1. An experiment showed that the most important reaction in the presence of oxone (2KHSO5·KHSO4·K2SO4) is decoordination