Showing 13 results for Das
Babaei R., Shahinfar S., Homayonifar P., Dadashzadeh M., Davami P.,
Volume 3, Issue 3 (Jul 2006)
Abstract
In the present study a Finite Difference Method has been developed to model the transient incompressible turbulent free surface fluid flow. A single fluid has been selected for modeling of mold filling and The SOLA VOF 3D technique was modified to increase the accuracy of simulation of filling phenomena for shape castings. For modeling the turbulence phenomena k-e standard model was used. In order to achieve an accurate model, solving domain was discrete to three regions includes: laminar sub layer, boundary layer and internal region. This model was applied to experimental models such as a driven cavity, Campbell benchmark [1] and top filled cavity. The results show that the suggested model yield favorable predictions of turbulence flow and have a good consistency in comparing with experimental results.
M. Pirhadi Tavandashti, M. Zandrahimi, B. Akbari,
Volume 6, Issue 1 (winter 2009 2009)
Abstract
Abstract: Nanoparticles exhibit a high reactivity and strong tendency towards agglomeration. In this study, aluminum
oxide (alumina) nanoparticles were characterized by gas adsorption (BET), transmition electron microscopy (TEM)
and photon correlation spectroscopy (PCS) techniques to assess the agglomeration of the particles. There is a good
correlation between the BET and TEM measurements but PCS was larger in the mean and median size and with a
degree of agglomerates being detected. Some agglomeration was evident, but most of the particles existed as discrete
objects as observed in the (HR) TEM images which were in good agreement with the agglomeration factor.
B. Akbari, M. Pirhadi Tavandashti, M. Zandrahimi,
Volume 8, Issue 2 (spring 2011 2011)
Abstract
Abstract: Most properties of nanoparticles are size-dependent. In fact, the novel properties of nanoaprticles do not prevail until the size has been reduced to the nanometer scale. The particle size and size distribution of alumina nanoparticle, as a critical properties, have been determined by transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), surface area analysis (BET) and x-ray diffraction peak broadening analysis. The particle size was found to be in the range of 5-95nm. Cumulative percentage frequency plot of the data extracted form TEM images indicates that particle size distribution obeys the log-normal function. The TEM images also reveal that particles are spherical in shape and loosely agglomerated. Comparing of the XRD and TEM results shows that the particles are single-crystal. The HRTEM images also verify that the particles have a single-crystal nature. In comparison, there is a good correlation between the BET, XRD and TEM measurements other than PCS that is sensitive to the presence of the agglomerates.
A. Khakzadshahandashti, N.varahram, P. Davami,
Volume 11, Issue 2 (June 2014)
Abstract
This article examines the Weibull statistical analysis that was used for investigating the effect of melt
filtration on tensile properties and defects formed inside the casting. Forming and entrapping of double oxide films
have been explained by using the context of critical velocity of melt in the runner. SutCast software results were used
to examine the amounts of the velocity of melt as such. SEM/EDX analysis is used to observe the presence of double
oxide films in the fracture surfaces of the tensile specimens. The article goes on to propose that castings made with
foam filters with smaller pores show higher mechanical properties and reliability due to higher Weibull modulus and
fewer defects
R. Hasanzadeh, T. Azdast, R. Eungkee Lee, A. Afsari Ghazi,
Volume 14, Issue 3 (September 2017)
Abstract
Material selection is a main purpose in design process and plays an important role in desired performance of the products for diverse engineering applications. In order to solve material selection problem, multi criteria decision making (MCDM) methods can be used as an applicable tool. Bumper beam is one of the most important components of bumper system in absorbing energy. Therefore, selecting the best material that has the highest degree of satisfaction is necessary. In the present study, six polymeric nanocomposite materials were injection molded and considered as material alternatives. Criteria weighting was carried out through analytical hierarchy process (AHP) and Entropy methods. Selecting the most appropriate material was applied using technique for order preference by similarity to ideal solution (TOPSIS) and the multi-objective optimization on the basis of ratio analysis (MOORA) methods respect to the considered criteria. Criteria weighting results illustrated that impact and tensile strengths are the most important criteria using AHP and Entropy methods, respectively. Results of ranking alternatives indicated that polycarbonate containing 0.5 wt% nano Al2O3 is the most appropriate material for automotive bumper beam due to its high impact and tensile strengths in addition to its low cost of raw material. Also, the sensitivity analysis was performed to verify the selection criteria and the results as well.
M. Abbasalizadeh, R. Hasanzadeh, Z. Mohamadian, T. Azdast, M. Rostami,
Volume 15, Issue 4 (December 2018)
Abstract
Shrinkage is one of the most important defects of injection molded plastic parts. Injection molding processing parameters have a significant effect on shrinkage of the produced parts. In the present study, the effect of different injection parameters on volumetric shrinkage of two polymers (high-density polyethylene (HDPE) semi-crystalline thermoplastics and polycarbonate (PC) as a representative of amorphous thermoplastics) was studied. Samples under different processing conditions according to a L27 orthogonal array of Taguchi experimental design approach were injected. Effect of material crystallinity on the shrinkage of injected samples was investigated. Obtained results revealed that semi-crystalline thermoplastics have larger shrinkage values in comparison with amorphous thermoplastics. Shrinkages of injected samples were also studied along and across the flow directions. Results showed that the flow path can dramatically affect the shrinkage of semi-crystalline thermoplastics. However for amorphous thermoplastics, results showed an independency of obtained shrinkage to flow direction. Analysis of variance (ANOVA) results illustrated that cooling time was the most effective parameter on shrinkage for both PE and PC injected samples; followed by injection temperature as the second important parameter. The optimum conditions to minimize shrinkage of injection molded samples are also achieved using signal to noise ratio (S/N) analysis.
A. Khakzadshahandashti, N. Varahram, P. Davami, M. Pirmohammadi,
Volume 16, Issue 3 (September 2019)
Abstract
The combined influence of both melt filtration and cooling rate on the microstructure features and mechanical properties of A356 cast alloy was studied. A step casting model with five different thicknesses was used to obtain different cooling rates. The effect of melt filtration was studied by using of 10 and 20 ppi ceramic foam filters in the runner. Results showed that secondary dendrite arm spacing decreased from 80 μm to 34 μm with increasing cooling rate. Use of ceramic foam filters in the runner led to the reduction of melt velocity and surface turbulence, which prevented incorporation of oxide films and air in the melt, and consequently had an overall beneficial effect on the quality of the castings. A matrix index, which is the representative of both SDAS and microporosity content, was defined to consider the simultaneous effect of melt filtration and cooling rates on UTS variations. Also, the fracture surface study of test bars cast using 10 and 20 ppi ceramic foam filters showed features associated with ductile fracture.
R. Hasanzadeh, S. Fathi, T. Azdast, M. Rostami,
Volume 17, Issue 2 (June 2020)
Abstract
Heat transfer in foams consists of conduction through solid and gaseous phases, convection within the cells as well as radiation through the whole medium. Radiation thermal conduction affects the overall thermal conductivity by 40% in a high porosity. Therefore, the investigation of that term seems to be necessary. Radiation thermal conduction depends on the extinction coefficient which its determination is experimentally complex. In this study, this coefficient is theoretically estimated using Glicksman model for polyolefin foams and is verified in comparison with the experimental data. Extinction coefficient which plays an effective role in the radiation thermal conduction depends on the morphological properties including foam and solid densities, cell and strut diameters. The results demonstrate that the radiation thermal conduction decreases by reducing cell size and increasing foam density and strut diameter. An L25 orthogonal array of Taguchi approach is used for optimization of radiation thermal conduction respect to foam density, cell and strut diameters as variable parameters. The analysis of variance results illuminate that foam density and cell diameter with 58 and 32% contribution are the most effective parameters on the radiation thermal conduction, respectively. At optimum conditions according to the prediction tool of Taguchi approach, the radiation thermal conduction significantly decreases to 1.0908 mW/mK.
R.s Krishna, J. Mishra, A. Adeniji, Sh. Das, S. Mohammed Mustakim,
Volume 17, Issue 4 (December 2020)
Abstract
The field of nanomaterial has greatly advanced in the last decade following a wider range of applications in the fields of electronics, automobiles, construction, and healthcare due to its extraordinary and ever-evolving properties. Synthesis of the nanomaterial plays a crucial role in redefining the current engineering and science field. At the same time, procuring an environment-friendly end product through eco-friendly solutions and sustainable processes is the key to many global problems. Green synthesis of nanomaterials like graphene and its derivatives involves mild reaction conditions and nontoxic precursors because it is simple, cost-effective, relatively reproducible, and often results in more stable materials. This paper primarily focuses on the green synthesis of graphene and its derivatives (graphene oxide & reduced graphene oxide) and geopolymers; a green technology for preparing graphene reinforced geopolymer composites. Various methods used globally for green synthesis of graphene and geopolymer are briefly discussed and this paper tries to integrate these two areas for a green end product. Possible applications of these green composites are also discussed to provide insights on the current growth and developments.
S. Das, R. Ghadai, A. Krishna, A. Trivedi, R. Bhujel, S. Rai, Sh. Ishwer, K. Kalita,
Volume 17, Issue 4 (December 2020)
Abstract
Graphene oxide (GO) and reduced graphene oxide (rGO) is a semiconductor device which finds its many applications in the various electronic devices. In the present study GO and rGO thin sheets have been grown over Si wafers using Hummer’s and modified Hummer’s method and a comparison in the properties of the coatings have been carried out. The morphology of the sheets characterized by SEM revealed similar transparent sheet like structure for both the chemical synthesis. The diffraction pattern of GO and rGO prepared with modified Hummer’s method showed peak shift to lower diffraction angle from 9.96 o to 9.63 o and 26.4 o to 26.3 o respectively. The diffraction peaks were observed at diffraction phase of 001 and 002 crystal plane. FTIR spectra revealed presence of oxygen functional groups in GO thin sheets whereas peaks for oxygen functionalities are absent in rGO. The polarization curve indicated similar corrosion resistance of GO and rGO thin sheets grown under Hummer’s and modified Hummer’s. Capacitive property of rGO is better than GO as observed by the electrochemical analysis of GO and rGO..Graphene oxide (GO) and reduced graphene oxide (rGO) is a semiconductor device which finds its many applications in the various electronic devices. In the present study GO and rGO thin sheets have been grown over Si wafers using Hummer’s and modified Hummer’s method and a comparison in the properties of the coatings have been carried out. The morphology of the sheets characterized by SEM revealed similar transparent sheet like structure for both the chemical synthesis. The diffraction pattern of GO and rGO prepared with modified Hummer’s method showed peak shift to lower diffraction angle from 9.96 o to 9.63 o and 26.4 o to 26.3 o respectively. The diffraction peaks were observed at diffraction phase of 001 and 002 crystal plane. FTIR spectra revealed presence of oxygen functional groups in GO thin sheets whereas peaks for oxygen functionalities are absent in rGO. The polarization curve indicated similar corrosion resistance of GO and rGO thin sheets grown under Hummer’s and modified Hummer’s. Capacitive property of rGO is better than GO as observed by the electrochemical analysis of GO and rGO.
Maryam Salehi, Milad Dadashi, S. Parsa Kashani Sani,
Volume 20, Issue 2 (June 2023)
Abstract
In the present study, bulk refined-structured Al 5083 alloy with high mechanical properties was successfully fabricated by hot consolidation process of nanostructured melt- spun flakes. The influence of cooling rate and pressing conditions on the microstructure and mechanical properties of the alloy were investigated using X-ray diffractometer (XRD), optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), microhardness, and compression tests. Rapid solidification combined with the hot consolidation at T=753 K (480 °C) and P= 800 MPa for 20 min produced a bulk sample with the desirable bonding, good microhardness (184.2±12.4 HV), and high strength (273±8 MPa) combined with 7 pct. fracture strain. These amounts are 78.6±5.1 HV, 148 ±9 MPa and about 5 pct. for the as-cast sample. Microstructural refinement during the controlled consolidation of nanostructure rapidly- solidified flakes contributes to such high mechanical properties of the bulk sample.
Sandesh Jirage, Kishor Gaikwad, Prakash Chavan, Sadashiv Kamble,
Volume 21, Issue 1 (March - Special Issue 2024)
Abstract
The Cu2ZnSnS4 (CZTS) thin film is newly emerging semiconductor material in thin film solar cell industry. The CZTS composed of economical, common earth abundant elements. It has advantageous properties like high absorption coefficient and best band gap. Here we have applied low cost chemical bath deposition technique for synthesis of CZTS at low temperature, acidic medium and it’s characterization. The films were characterized by different techaniques like X-Ray diffraction, Raman, SEM, Optical absorbance, electrical conductivity and PEC study. The X-Ray diffraction, Raman scattering techniques utilized for structural study. The XRD revels kasterite phase and nanocrystalline nature of CZTS thin films. These results and its purity confirmed further by advanced Raman spectroscopy with 335 cm-1 major peak. The crystallite size which was found to be 50.19 nm. The optical absorbance study carried by use of UV-Visible spectroscopy analyses its band gap near about 1.5 eV and its direct type of absorption. The electrical conductivity technique gives p-type of conductivity. The scanning electron microscopy (SEM) study finds it’s rock like unique morphology. The EDS technique confirms its elemental composition and it’s fair stoichiometry. The analysis of PEC data revealed power conversion efficiency-PCE to 0.90%.
The Cu2ZnSnS4 (CZTS) thin film is newly emerging semiconductor material in thin film solar cell industry. The CZTS composed of economical, common earth abundant elements. It has advantageous properties like high absorption coefficient and best band gap. Here we have applied low cost chemical bath deposition technique for synthesis of CZTS at low temperature, acidic medium and it’s characterization. The films were characterized by different techaniques like X-Ray diffraction, Raman, SEM, Optical absorbance, electrical conductivity and PEC study. The X-Ray diffraction, Raman scattering techniques utilized for structural study. The XRD revels kasterite phase and nanocrystalline nature of CZTS thin films. These results and its purity confirmed further by advanced Raman spectroscopy with 335 cm-1 major peak. The crystallite size which was found to be 50.19 nm. The optical absorbance study carried by use of UV-Visible spectroscopy analyses its band gap near about 1.5 eV and its direct type of absorption. The electrical conductivity technique gives p-type of conductivity. The scanning electron microscopy (SEM) study finds it’s rock like unique morphology. The EDS technique confirms its elemental composition and it’s fair stoichiometry. The analysis of PEC data revealed power conversion efficiency-PCE to 0.90%.
Mahnaz Dashti, Saeid Baghshahi, Arman Sedghi, Hoda Nourmohammadi,
Volume 21, Issue 3 (September 2024)
Abstract
Abstract
The power line insulators are permanently exposed to various environmental pollutants such as dust and fine particles. This may lead to flashovers and therefore widespread power blackouts and heavy economic damage. One way to overcome this problem is to make the insulator surface superhydrophobic. In this research, the superhydrophobic properties of the insulators were improved by applying room-temperature cured composite coatings consisting of epoxy and hydrophobic nano-silica particles. Either octadecyl trichlorosilane (ODTS) or hexamethyldisilazane (HMDS) was used to coat the silica nanoparticles and make them hydrophobic. Then, the hydrophobic silica was added to a mixture of epoxy resin and hardener. The suspension was applied on the surfaces of a commercial porcelain insulator and cold cured at ambient temperature. The coating increased the water contact angle from 50° to 149°. Even after 244 h exposure to the UV light, the samples preserved their hydrophobic properties. The adhesion of the coating was rated as 4B according to the ASTM D3359 standard. The coating decreased the leakage current by 40% and increased the breakdown voltage by 86% compared to the uncoated sample and showed promise for making power line insulators self-cleaning.
