Sharif Digital Repository

Thermal cracking is the prevalent type of distress experienced by asphalt pavements in cold regions. It is widely assumed that when thermal stresses induced in the pavement exceed the tensile strength of the asphalt surface layer, cracking occurs; however, the role of thermal fatigue should not be ignored. To better describe the low-temperature (LT) performance properties of modified asphalt binders, a new parameter, normalised tensile stress (NTS), was defined in this research. NTS values were compared with bending beam rheometer (BBR), direct tension (DT) and semi-circular bending (SCB) fracture test results. The m-value parameter of the BBR test specifies the type of asphalt binder. This... 

In this paper, oxidation of H2S into elemental sulfur over synthesized aluminabased nanocatalysts was physiochemically investigated and the results were compared with a commercial Claus catalyst. The wet chemical, co-precipitation, and spray pyrolysis techniques were employed to synthesize several alumina nanostructures. Then, the SEM, XRD, and ASAP analysis methods were utilized to characterize in order to choose the best nanocatalyst. The sulfur and H2S contents were determined through the standard UOP techniques. Amongst the synthesized materials, Al2o3-supported sodium oxide prepared through the wet chemical, and Al2o3 nanocatalysts via spray pyrolysis methods were the most active... 

Influences of rare earth (RE) elements addition on thermal fatigue behaviors of AZ91 alloy were studied. Repeated heating and cooling cycles were applied on the samples at 170 and 210 °C to develop thermal fatigue cracks. Crack growth mechanisms and microstructural influences were investigated by optical and scanning electron microscopy (SEM) as well as energy dispersive X-ray spectroscopy (EDS). Thermal fatigue behaviors were observed to improve successively by addition of the RE up to 2wt.%. This improvement was attributed to the consummation of aluminum in melt by precipitation of the needle shaped Al11RE3 phases. This process was attributed to the reduction of Mg17Al12 phase volume... 

Thermal cracking of a vacuum distillation residue of the Abadan refinery in Iran was performed under delayed coking conditions to investigate the effect of operating conditions on the yield and sulfur content of products. At reaction temperatures of 440-500 °C and pressures of 1, 3, and 5 bar, the products included gases, liquids, and coke. The yields of liquid products were higher at 1 bar compared to those for higher pressures. Increasing the reaction temperature at a given reaction pressure led to an increase in the yield of liquid products. Increasing the reaction pressure at a given reaction temperature led to higher yields of coke and gases as well as a decrease in the sulfur content... 

In this work we used the vacuum distillation residue from an Iranian heavy crude oil refinery in a solvent deasphalting (SDA) process using different temperatures (60-120°C), pressures (5-9 bar), solvents (n-pentane and ethyl acetate), and solvent to feed ratios (3 to 1, 5 to 1, and 7 to 1). The resulting products included deasphalted oil (DAO) and residue (PITCH). The DAO yields in SDA when n-pentane was used as solvent were significantly higher than those when ethyl acetate was used as solvent. The DAO was subsequently processed by thermal cracking at 500°C and atmospheric pressure to investigate the effect of solvent deasphalting processing conditions on the yield of coke and liquid... 

The bulk of the worldwide annual commercial production of ethylene is based on thermal cracking of petroleum hydrocarbons with steam. In this research, the effect of coil outlet temperature on the reactor yield has been studied. In order to investigate a reliable mathematical correlation, several data points were obtained by adjusting coil outlet temperature in a real plant. In order to investigate best coil outlet temperature, an objective function was represented. Based on the obtained mathematical correlation and the assumed objective function, it was found that best coil outlet temperature for investigating maximum income is 1,128 K  

Pozzolanic materials, either naturally occurring or artificially made, have long been in practice since the early civilization. In recent years, the utilisation of pozzolanic materials in concrete construction has become increasingly widespread, and this trend is expected to continue in the years ahead because of technological, economical and ecological advantages of the materials. One of the latest additions to the ash family is palm oil fuel ash, a waste material obtained on burning of palm oil husk and palm kernel shell as fuel in palm oil mill boilers, which has been identified as a good pozzolanic material. This paper highlights test results on the performance behavior of palm oil fuel... 

In this study a hot filament chemical vapour deposition (HFCVD) technique was used to prepare Fe-Cr films on Si substrate as catalysts for thermal CVD (TCVD) growing of carbon nanotubes (CNTs) from liquid petroleum gas (LPG) at 800 °C. To characterize the catalysts or CNTs, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy were used. The XPS spectra obtained at different stages of Ar+ sputtering revealed that in the depth of catalyst layers, the relative Fe-Cr concentrations are higher than the top-surface. SEM images of samples after TCVD indicate a significant CNT growing at the backside of catalyst... 

Sefid-rud concrete buttress dam with a height of 106m was damaged during the devastating 1990 Manjil earthquake. The dam was repaired and strengthened using epoxy grouting of cracks and the installation of post-tensioned anchors. In a previous study, nonlinear seismic response of the highest monolith with empty reservoir was investigated experimentally through model testing. A geometric-scaled model of 1:30 was tested on a shaking table to study dynamic cracking of the model. As a result of the similarity between model and prototype cracking pattern, the model was retrofitted according to prototype retrofitting plan after the Manjil earthquake and re-tested on shaking table to estimate the... 

Thermal cracking is the prevalent type of distress experienced by asphalt pavements in cold regions. It is widely assumed that when thermal stresses induced in the pavement exceed the tensile strength of the asphalt surface layer, cracking occurs; however, the role of thermal fatigue should not be ignored. To better describe the low-temperature (LT) performance properties of modified asphalt binders, a new parameter, normalised tensile stress (NTS), was defined in this research. NTS values were compared with bending beam rheometer (BBR), direct tension (DT) and semi-circular bending (SCB) fracture test results. The m-value parameter of the BBR test specifies the type of asphalt binder. This... 

Thermal cracking of hydrocarbons converts them into valuable materials in the petrochemical industries. Multiplicity of the reaction routes and complexity of the mathematical approach has led us use a kind of black-box modelingsartificial neural networks. Reactor feed type plays an essential role on the product qualities. Feed type is a qualitative character. In this paper, a method is presented to introduce a range of petroleum fractions to the neural network. To introduce petroleum cuts with final boiling points of 865 °F maximum to the neural network, a real component substitute mixture is made from the original mixture. Such substitute mixture is fully defined, it has a chemical... 

This article presents a routine for prediction of the crack growth path in gears. Crack simulation helps in determining failure modes and crack detecting by vibration monitoring. To simulate crack propagation an effective method is developed by which the meshing force is calculated based on the compliance of meshing teeth in every stage of crack growth. In this method the compliance matrix of the tooth is calculated using three-dimensional boundary element analysis without the need for simultaneously modelling two meshing gears. The force distribution on the contact area is then calculated using Hertz theory and compliance matrices of meshing teeth. The method is used in prediction of the... 

In this paper, an adaptive finite element analysis is presented for 3D modeling of non-planar curved crack growth. The fracture mechanical evaluation is performed based on a general technique for non-planar curved cracks. The Schollmann's crack kinking criterion is used for the process of crack propagation in 3D problems. The Zienkiewicz-Zhu error estimator is employed in conjunction with a weighted SPR technique at each patch to improve the accuracy of error estimation. Applying the proposed technique to 3D non-planar curved crack growth problems shows significant improvements particularly at the boundaries and near crack tip regions. Several numerical examples are presented to illustrate... 

A computer-controlled pilot plant has been constructed to study the dynamical behavior and control of the thermal cracking furnace. The governing equations that describe the furnace dynamics are presented, and, based on these equations and a kinetic model, software that simulates the steady-state behavior of the system has been developed. The furnace is divided into eight zones that can be heated independently, and, therefore, any desired temperature profile can be applied. The variables to be measured are the furnace zone temperature, coil outlet temperature (COT), and product yield. Two different control strategies (namely, COT control and furnace wall temperature control) are applied...