Sharif Digital Repository

A thermodynamically-consistent phase field approach for crack propagation which includes the following novel features is presented. (1) Scale dependency was included by relating the length scale to the number of cohesive interatomic planes at the crack tip. Because of this, the developed theory is applicable from the atomistic to the macroscopic scales. (2) The surface stresses (tension) are introduced by employing some geometrical nonlinearities even in small strain theory. They produce multiple contributions to the Ginzburg-Landau equation for crack propagation. (3) Crack propagation in the region with compressive closing stresses is eliminated by employing a stress-state-dependent kinetic... 

Electrospray cooling is experimentally examined for high volumetric flow rates (80 mL/h) stabilized by a novel hemispherical nozzle. Stability of the Taylor cone-jet mode of this nozzle is increased by interaction of the discharging liquid with the outer wall of a hemispherical cap, installed at the tip of a simple nozzle. The liquid can then be discharged at high flow rates at the same mode. The liquid is ethanol and the test surface temperature as well as the cooling heat flux are measured. The results of the surface temperature, the heat flux and the heat transfer coefficient are compared between the three cases. The first and main case is the electrospray using the novel hemispherical... 

Kinetics and isotherms of adsorption behavior of nanoscale Zr-based metal-organic framework for the removal of three organic dyes including acidic, direct and basic ones from aqueous solutions were studied by sorption models. Nanocube-shaped UiO-66 particles with an average edge length of 215 nm, specific surface area of 1215 m2/g, total pore volume of 0.58 cm3/g, and average pore diameter of 1.8 nm were prepared by solvothermal methods. Analyzing of the equilibrium isotherms indicates that direct dye removal is best fitted with the Langmuir isotherm. Study of the adsorption kinetics also determines that direct dye adsorption follows pseudo-first-order model (R2=0.99). The kinetics of basic... 

A complete cycle of droplet nucleation, growth, coalescence and jumping on different textured hydrophobic and superhydrophobic surfaces is studied for the first time, using a 2-D double distribution function thermal lattice Boltzmann method. First, droplet nucleation mechanism on smooth and rough surfaces is studied in detail. The results reveal the presence of cooled vapor layer instability in the condensation on completely smooth surfaces. However, on the rough surfaces and near the roughness a completely different mechanism is observed and the nucleation occurs on the roughness wedges. Also, the condensation on different textured surfaces with nominal contact angles θa=90°,120°,155° is... 

In this paper, a comprehensive three-dimensional model of photovoltaic thermal system integrated with phase change material (PVT/PCM) is developed and simulated. The effect of some key parameters using parametric analysis on performance of PVT/PCM system with water as working fluid is investigated. Parameters considered in this study include the properties of PCM (i.e. melting temperature, enthalpy of fusion and thermal conductivity), solar radiation and mass flow rate. The parametric analysis ranges are selected according to the properties of the most of available PCMs on the market, which shows the practical application of the numerical research. Furthermore, a three-dimensional model of... 

This paper presents an investigation of the effects of tool rake angle and nose radius on the surface quality of ultraprecision diamond-turned porous silicon. The results showed that as rake angle decreases, the high-stress field induced by the tool edge increases, causing microcracks to propagate extensively near the pore walls. As a result, the ductile-machined areas shrank under a negative tool rake angle. On the other hand, brittle fracture occurred around pores released cutting pressure significantly. These trends of rake angle effects are distinctly different from those in the cutting of non-porous silicon. Finite element simulation of stress in the cutting area agreed with the... 

This paper presents an investigation of the effects of tool rake angle and nose radius on the surface quality of ultraprecision diamond-turned porous silicon. The results showed that as rake angle decreases, the high-stress field induced by the tool edge increases, causing microcracks to propagate extensively near the pore walls. As a result, the ductile-machined areas shrank under a negative tool rake angle. On the other hand, brittle fracture occurred around pores released cutting pressure significantly. These trends of rake angle effects are distinctly different from those in the cutting of non-porous silicon. Finite element simulation of stress in the cutting area agreed with the... 

In the past few years, a significant body of research has been devoted to designing magnetic micron scale robotic systems for minimally invasive medicine. The motion of different microorganisms is the nature's solution for efficient propulsion of these swimmers. So far, there has been a considerable effort in designing micro swimmers based on the propulsion of bacteria while the motion of numerous other microorganisms has not been a source of inspiration for designing micro swimmers yet. Inspired by propulsion of Paramecium which is a ciliate microorganism, a novel micro swimmer is proposed in this article which is capable of cargo transport. This novel swimmer is composed of multiple... 

In this study, biodiesel (FAME) was prepared using a novel heterogeneous catalyst of phosphomolybdic acid (H3PMo12O40, HPMo)/support graphene oxide (GO). The characterization of the catalyst was evaluated by SEM, EDX, Map analysis, TEM, FT-IR, and Raman analyses. The production of biodiesel from waste cooking oil (WCO) was carried out by the electrolysis method. The process of the trans-esterification reaction was optimized by applying the response surface methodology (RSM) based on the central composite design (CCD) approach. The effects of four independent variables of methanol to oil molar ratio (6–12 mol:mol), catalyst weight (0.5–1.5 wt%), time (8–24 h), and voltage (30–70 V) were... 

In the current research, a three-dimensional photovoltaic thermal system integrated with phase change material system with nanofluids is investigated. The working fluids involved in this study include nano-magnesium oxide, multiwall carbon nano tube and hybrid (mixture of nano-magnesium oxide and nano-multiwall carbon nano tube) nanofluids dispersed in pure water. After comparing single-phase model and mixture model, the mixture model is used in the study and fluid flow regime in the collector is assumed to be laminar, fully develop, uniform and incompressible, to model the nanofluid in the system. A parametric analysis is conducted to examine the effect of various parameters such as working... 

Radial forging is an open forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, as well as for creating internal profiles for tubes such as rifling the gun barrels. The radial forging of tubes is usually performed over a mandrel to create an internal profile and/or size the internal diameter; but the process can also be used without a mandrel when workpiece geometry does not allow it or the internal surface quality is not critical. In some industrial applications, it may not be possible to use a mandrel inside the tubular workpiece, e.g., due to geometrical limitations of the workpiece. In this study, finite element modelling is applied to model the... 

Nutrient pollution has become a global environmental issue. Innovative biological nutrient removal (BNR) processes are needed to overcome the drawbacks of conventional technologies. This study evaluates the potential of a hybrid 5-stage Bardenpho - moving bed biofilm reactor (MBBR) process for organic carbon and nutrient removal from municipal wastewater at different hydraulic retention time (HRT) and nitrate recycle ratio (R). Response surface methodology (RSM) based on a central composite design (CCD) of thirteen experiments was applied to optimize the nitrogen and phosphorus conversion of the treatment system. High removal efficiencies of about 98.20%, 92.54%, 94.70% and 96.50% for total... 

Enzymatic removal of Bisphenol A (BPA), acknowledged as an environmentally friendly approach, is a promising method to deal with hard degradable contaminants. However, the application of “enzymatic treatment” has been limited due to lower operational stability and practical difficulties associated with recovery and recycling. Enzyme immobilization is an innovative approach which circumvents these drawbacks. In this study, laccase from Trametes hirsuta was used for BPA removal. Amino-functionalized magnetic Fe3O4 nanoparticles were synthesized via the co-precipitation method followed by surface modification with (3-aminopropyl)trimethoxysilane (APTMS). The as-prepared nanoparticles were... 

Atherosclerosis as a common cardiovascular disease is a result of both adverse hemodynamics conditions and monocyte deposition within coronary arteries. It is known that the adhesion of monocytes on the arterial wall and their interaction with the vascular surface are one of the main parameters in the initiation and progression of atherosclerosis. In this work, hemodynamic parameters and monocyte deposition have been investigated in a 3D computational model of the Left Anterior Descending coronary artery (LAD) and its first diagonal branch (D1) under the heart motion. A one-way Lagrangian approach is performed to trace the monocyte particles under different blood flow regimes and heart motion... 

The boiling of a fluid dripping on the surface of molten phase-change materials provides an efficient means for heat exchange or cooling of the melt. For the first time, in this study, the impact of acetone drops onto molten paraffin as a direct-contact solidification method is experimentally investigated to get a better insight into the interaction between the drop boiling and the heat extraction process from the phase change materials during impact. As the acetone drop impacts the molten paraffin surface, acetone starts to boil, and a portion of molten paraffin is solidified. Four impact Weber numbers (corresponding to heights of 10, 20, 30, and 40 cm) for the acetone drop and six surface... 

This study aims to investigate, optimize, and simulate the dispersed phase holdup at flooding conditions for the standard physical systems in a pulsed extraction column with the disc-doughnut configuration. The interaction impacts for operational parameters (pulse intensity and organic and aqueous phase velocities) and interfacial tension (systems type) were examined using the response surface approach. A novel correlation for the dependent parameter, namely holdup at flooding based on the quadratic model, was developed with the central composition design methodology. A desirable agreement between actual data and calculated data from the proposed model was observed because of the high... 

In this study, biodiesel (FAME) was prepared using a novel heterogeneous catalyst of phosphomolybdic acid (H3PMo12O40, HPMo)/support graphene oxide (GO). The characterization of the catalyst was evaluated by SEM, EDX, Map analysis, TEM, FT-IR, and Raman analyses. The production of biodiesel from waste cooking oil (WCO) was carried out by the electrolysis method. The process of the trans-esterification reaction was optimized by applying the response surface methodology (RSM) based on the central composite design (CCD) approach. The effects of four independent variables of methanol to oil molar ratio (6–12 mol:mol), catalyst weight (0.5–1.5 wt%), time (8–24 h), and voltage (30–70 V) were... 

The thermal energy received by each surface of an Earth-orbiting satellite strongly depends on its position and orientation. In this sense, simultaneous orbit and attitude estimation (SOAE) using the surface temperature data has been focused in the present study. The Earth infrared (IR) radiation and the Earth's top-of-atmosphere (TOA) albedo are two key sources of radiation affecting the satellite surface temperature rate. The Earth's radiation information has been monitored for the past two decades by the Clouds and the Earth's Radiant Energy System (CERES) project, producing a comprehensive set of Earth radiation budget (ERB) data for climate, weather and applied science research. The... 

In this research, a green solid catalyst of phosphomolybdic acid (HPA) prated on Chitosan was synthesized to produce biodiesel. The prepared catalyst was characterized using Fourier Transform Infrared spectroscopy (FTIR), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray (EDX), X-ray diffraction (XRD), and XRF analyses. The catalyst was applied in microwave-assisted trans-esterification of Pomegranate oil, and the biodiesel production process was optimized by response surface methodology based on central composite design (RSM-CCD). The effect of influential reaction parameters, including time (33–142 min), catalyst weight (0.15–5.6 wt%), and methanol to oil molar... 

Herein, we demonstrated a facile method for the fabrication of magnetic and superhydrophobic polyurethane sponge with water contact angle of 159° as an adsorbent for cleanup the marine oil spill pollution. For this aim, a polyurethane sponge was coated with carbon black (CB), hexagonal boron nitride (h-BN)@Fe3O4, and acrylic resin and then characterized by different techniques. Owing to the chemical and thermal stability of h-BN and CB, the modified sponge was stable under corrosive conditions (pH = 1–14 and salt solutions) and at different temperatures (−12 °C–105 °C). In addition to common oils and organic solvents, we also used the real spilled oils containing monoaromatics and...