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In this paper, the effect of gas and liquid inlet superficial velocities and distance from upstream on slug frequency is studied experimentally. Empirical correlations are also presented based on the obtained results. The tests are conducted for liquid holdup αl= 0.75 and three distances from inlet in a long horizontal channel made of Plexiglas with dimensions of 510 cm2 and 36m length in Multiphase Flow Lab. of Tarbiat Modares University. The superficial liquid and air velocities rated as to 0.11-0.56 m/s and 1.88-13 m/s, respectively. The obtained results show that slug frequency is dependent to superficial liquid velocity directly. Slug frequency decreases with slip ratio increase. Slug frequency has strong dependency on superficial liquid velocity and increases monotonically with it. However, superficial gas velocity has damping effect on slug frequency. As slug moves towards downstream, slug frequency will be decreased but slug velocity will be increased.

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Abstract- In this paper, the effect of gas and liquid inlet velocities and for the first time the effect of liquid hold up on slug initiation position are studied experimentally. Empirical correlations are also presented based on the obtained results. The tests are conducted for three liquid hold ups (0.25, 0.50 and 0.75) in a long horizontal channel made of Plexiglas with dimensions of 510 cm2 and 36m length in Multiphase Flow Lab. of Tarbiat Modares University. The superficial liquid and air velocities rated as to 0.11-0.56 m/s and 1.88-13 m/s, respectively. The obtained results show that as αl=0.25, slug initiation position is increasing monotonically with Usl and Usg. During αl=0.50, slug initiation position is increasing with Usl and Usg but the slope is smoother than αl=0.25. For αl=0.75, slug initiation position is decreasing monotonically with Usl and Usg. In the case of equal void fraction of phases, slugs are generated weakly (low pressure). However, for the unequal void fraction of phases strong slugs (high pressure) are formed.

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In this article, two-phase slug flow is simulated numerically in a horizontal duct with rectangular cross-section using Volume Of Fluid (VOF) method. Conservation equations of mass, momentum and advection equation are solved in open source OpenFOAM code accompanying k-ω SST turbulence equations. Simulation is conducted based on the experimental results in the duct with rectangular cross-section. The results shows, due to Kelvin-Helmholtz (K-H) instability criteria slug initiation forms in the air-water interface during three dimensional turbulence modeling. Water level was increased slightly at interface in both numerical simulation and experiment. This level increase satisfies the K-H instability to generate a slug at interface. During slug initiation, the pressure behind slug is increased significantly. Big pressure gradient at the beginning of the slug in compare to the end of it causes the slug length to be increased as propagate along the duct. The numerical simulation of present research is capable of predicting the slug length accurately in accordance with experiment; however, the slug position with 22% inaccuracy was obtained. Comparison of the results with the numerical and experimental results of other researchers confirms higher accuracy of flow prediction in the present work.

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In the present article, velocity and deformation of an air bubble have been considered in quiescent liquid at different consecutive slopes from 5 to 90 degrees in respect to horizontal condition. To establish these purposes, air-water two-phase flow has been simulated numerically by using volume of fluid method. The two-phase flow interface has been traced by using Piecewise Linear Interface Calculation (PLIC) method. Surface tension force was estimated by Continuum Surface Force (CSF) model. The simulation results show that maximum bubble velocity occurred at 45 degrees which is in agreement with the previous researchers result. Simulation of bubble movement was also continued to two consecutive slopes at different angles. At slope deviation location, a vortex was generated due to liquid movement governed by gravity forces. This vortex changes the bubble velocity as well as bubble shape. This vortex also reduces the bubble velocity and changes the bubble nose shape from sharp to flatten at deviation from low to high slope values. However, at deviations from high to low slope values, the bubble nose becomes more sharpened in addition to bubble velocity increase. The maximum average velocity of bubble movement at two consecutive slopes was obtained during the condition that the first and second slopes were set to 60 and 30 degrees, respectively.

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Experimental investigation conducted on Taylor bubble characteristics in a large bend including three consecutive inclinations. For this purposes, flow maps were obtained for the bend and horizontal section of upstream of the bend to define the area of this regime and mechanism of Taylor bubble formation. The effect of superficial gas-liquid velocities and the duct slope were studied on average velocity, length and frequency of bubbles. The results show, the bubble velocity and length increase as gas superficial velocity increases and the duct slope decreases. However, liquid velocity increase has decreasing effect on this characteristics. Bubble frequency is independent of slope change and reduces as gas superficial velocity increase. However, bubble frequency reduces at first and then increase as liquid superficial velocity increases. Regarding the safety regulation for industry, the minimum of the bubble frequency should be generated for the required liquid mass flow rate. Meanwhile, for the gas velocity, some optimization is required between frequency reductions with Taylor bubble velocity increase in addition to bubble length reduction. Regarding the background of the present field with shortage of results on Taylor bubbles frequency, some correlations based on the superficial Reynolds number of phases were presented for each inclination.

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Experimental investigation of two-phase air-water flow was conducted at consecutive inclinations of a large bend (with three equal slopes in respect to each other) and including the horizontal sections of the inlet and outlet of the bend. The results show that the elongated bubble regime flows without any effect of duct inclination change and consistent for all three zones of horizontal sections of before and after the bend and the bend itself. It was also noticed, as the duct inclination decreases along the route, vortex misty flow transmits to misty annular flow at higher gas flow rates. The annular flow regime was noticed only at the first slop of the bend. Slug flow was observed at the horizontal sections upstream and downstream of the bend. The slug flow at the upstream generated by the interfacial instabilities but at the downstream formed by Taylor bubbles. Slug flow area in the flow diagram increases as liquid flow rate increase at both horizontal sections. In addition, the void fraction change rate with phases mass flow rate was considered at the duct inlet.

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In this paper, two-phase air–water flow was investigated experimentally and simulated numerically using VOF method. The tests are conducted in Multiphase Flow Lab. of Tarbiat Modares University. In order to evaluate the rib effect on flow regimes, experimental investigation was conducted with ribs of different width and pitch where assembled on front and back side walls (side walls) of the duct during different test runs. The rib width and pitch were held constant during each test. The experimental work considered for different regimes of wavy, plug and slug which generated in the ducts with and without rib applying various phase velocities. The effects of using ribs on regime boundaries are presented in the flow diagrams and discussed in details. Compared to the smooth duct, the ribbed duct affects the different regime boundary positions noticeabily. The results showed that in the duct with small sizes ribs, the first slug initiates at longer time and distance in compare to the duct equipped with bigger size ribs. The results show that for normal operational flow velocities, the ribbed duct decreases the slug area on flow diagram map in compare to smooth duct. However, ribs facilitate the slug regime initiation for phase velocities in accordance with slug generation, which is not benefit of operational condition.

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Objective: In this study we introduced an RGD-containing peptide of collagen IV origin that possesses potent cell adhesion and proliferation properties. This peptide was immobilized on a nanofibrous polycaprolactone/gelatin scaffold after which we analyzed human bone marrow-derived mesenchymal stem cells (hBMSCs) adhesion and proliferation on this peptide-modified scaffold. Methods: Nanofibrous scaffold was prepared by electrospinning. The peptide was synthesized by solid-phase peptide synthesis and immobilized on electrospun nanofibrous a polycaprolactone/gelatin scaffold by chemical bonding. Native and modified scaffolds were characterized with Scanning Electron Microscope (SEM) and Fourier-Transform Infra-red Spectroscopy (FTIR). Adhesion and proliferation of hBMSCs on native and modified scaffolds were analyzed by the Methylthiazol Tetrazolium (MTT) assay. Results: SEM images showed that electrospun scaffolds had homogenous morphology and were 312±89 nm in diameter. There was no significant difference in scaffold morphology before and after peptide immobilization. FTIR results showed that the peptide was successfully immobilized on the scaffold. Based on MTT assay, cell adhesion studies indicated that peptide immobilization improved cell adhesion on RGD-modified scaffolds at all corresponding time points (pConclusion: This novel peptide and modified nanofibrous scaffold, having improved cell adhesion and proliferation properties, can be used for tissue engineering and regenerative medicine by using hBMSCs.

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The aim of this study, design and fabrication a prototype of double-tube magnetorheological damper (MR damper) involving micron sized and soft ferro magnetic of carbonyl iron (CI) particles and stabilizer nanoparticles of silicone (SiO2). Whiles initially magnetorheological fluid as its application and required, designed and fabricated. Then sedimentation and magnetorheometry tests (in mode of shear) was done. That the resulting of sedimentation test, illustrated that after 10 days, the value of sedimentation just was 15% and maximum of shear stress in maximum current was about 20kpa, that was desired. Then the magnetic section of the research, was conducted using the existing relationships and Maxwell software, at the end, using this data, the geometric dimensions of the MR damper, designed and fabricated. appropriate damper, was double tube type damper and at the combination of two valve and shear modes. After fabrication of appropriate damper, damping test was carried out on appropriate damper by damping test machine, that with regard to the receive graphs from test, at currents of 0 ,1 and 2 amps and speed of 0.05m/s, the magnitude of damping force aspect zero current(conventional damper), at saturate magnetic intensity (H_mr) was 5 times conventional damper. That was desired.

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Ceramic matrix composites (CMCs) are a new class of high technology materials which can be utilized as a replacement for metallic super-alloys. CMCs have a vast array of applications in modern industries due to their upstanding properties, including low density, relatively high hardness and fracture toughness, and high corrosion and wear resistance. Extremely high hardness and inhomogeneous structure of CMCs cause unstable process and high grinding forces and temperature. This research was conducted in order to overcome the grinding challenges of these composites by recognizing and analyzing the effects of main process parameters comprising cutting speed, feed speed, and depth of cut on the grinding forces, specific energy, and grinding force ratio in three different environments including dry, wet and MQL grinding. To evaluate the significance of input parameters and their influence on the responses and also to derive predicting equations, Analysis of Variance (ANOVA) was employed. It was concluded that MQL technique is the most efficient cooling-lubrication method where implementation of this process reduces the tangential grinding force by 38.88% and normal grinding force by 31.16%, relative to dry grinding; however, the amount of force reduction in wet grinding is 34.22% for tangential grinding force and 24.81% for normal grinding force, relative to dry grinding. In addition, increase of cutting speed leads to reduced grinding forces and force ratio and higher amounts of specific energy, and also increase of feed speed and depth of cut cause higher grinding forces and force ratio and lower amounts of specific energy.

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Titanium is currently widely used as dental implant, but it may cause allergic problems. For this reason, the use of partially stabilized zirconia (PSZ) in dental applications has increased in recent years. Because of extreme hardness and brittleness of ceramic (PSZ) and in order to achieve dimensional and geometrical accuracy, grinding is necessary. In this research, a comprehensive study was carried out to investigate the effect of the grinding parameters of PSZ on surface roughness, grinding cost and PSZ phase transformation. It was observed that, increasing both depth of cut and feed rate results in an increase on tetragonal to monoclinic phase transformation. It was also observed that using a metal bond grinding wheel with higher concentration and larger abrasive size results in lower grinding cost. It was observed that using resin bond grinding wheels instead of metal bond grinding wheels, results in average 8% lower surface roughness. However, an increase in grinding wheel concentration results in a decrease in the surface roughness. Response surface method (RSM) was used to find an optimum condition and create a mathematical model between inputs and outputs and it was shown that the average R-square of the model was more than 0.90. PSZ microstructure and surface roughness could be controlled by controlling the grinding parameters. Using a metal bond grinding wheel with higher concentration and larger abrasive size results in lower grinding cost.

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In this research, the abrasion resistance of components made by Additive Manufacturing (AM) has been modeled. AM is widely used in various industries today and the Fused Deposition Modelling (FDM) process is one of the most popular methods of fabrication in this field. Although many researches have been done with the aim of modeling mechanical behavior in this field, but limited studies have been done in the field of wear and modeling of this phenomenon. In this research, in order to create an exact mathematical relationship between the input variables (layer thickness, raster angle and air gap) and the response variable (wear rate), the experimental design using the Central Composite Design (CCD) method has been done. Twenty systematic experiments were performed to determine the response and provide a proportional regression model. Using analyze of variance (ANOVA), a mathematical model corresponding to the actual process was obtained, and the validity of the proposed model was confirmed by statistical methods. The result show that the proposed model predicts the wear rate of Acrylonitrile Butadiene Styrene (ABS) parts made by FDM method with a coefficient of determination of 95.62%. The result of the experimental study and model analysis showed that the variable of air gap and the effect of its interaction with raster angle, creates the highest wear rate and also the second-order effect of layer thickness has the most negative effect on wear rate.

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The grinding process is one of the most important and widely used machining processes to achieve the desired surface quality and dimensional accuracy. Since the undeformed chip thickness is not a constant value in the grinding process and is changing independently and momentarily for each abrasive, the determination of the undeformed chip thickness accurately is essential to determine the grinding forces and surface topography of the grinding wheel. Previous studies on grinding forces were mainly regardless of the micro-mechanisms between the abrasive and the workpiece. On the other hand, only the average values ​​of forces could be calculated by determining the average value for undeformed chip thickness. In this study, a new analytical model with the approach of kinematic-geometric analysis of abrasive grain trajectory is presented to determine the undeformed chip thickness and subsequent grinding forces. This model predicts the components of normal and tangential grinding forces (including sliding, plowing, and cutting forces) accurately and in detail based on the instantaneous undeformed chip thickness obtained from the kinematic analysis of abrasive movement and micro-mechanisms between abrasive and the workpiece. In the end, experimental tests were performed to validate the theoretical model.

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Given the current demand for surfaces with non-polished morphology like structured surface that enhance its tribological properties, providing a method with minimal production cost and high performance has attracted attention. The present study focuses on presenting a new method for producing structured surfaces with hydrophobic performance. In this method, using the grinding process with a special grinding wheel, an attempt has been made to produce these widely used surfaces. By modifying the topography of the wheel surface and changing the arrangement of abrasive particles from random to arranged distribution with the diamond particles in predefined locations, an attempt was made to design and manufacture a special grinding wheel for the production of structured surfaces. A segment with 1*1 cm2 including diamond particles with mesh size of 40/50 were manufactured during the electroplating process in a nickel bath medium and by installing the segment on the wheel hub and performing the grinding process with this developed wheel, surfaces containing continuous and discontinuous scratches with the same geometry were produced. Static contact angle test for the unstructured surface was about 37 degrees that improved to 141 degrees with the structured surface, which is an impressive improvement.

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Application of vertical air curtain refrigerators in commercial stores has gained popularity due to easy access of products by the customers. However, energy consumption of these refrigerators is approximately %50 higher than that of refrigerators with doors. This paper experimentally investigates the effect of ambient temperature variation on the performance of these refrigerators. Experimental measurements include parameters such as temperature, pressure, relative humidity, velocity, and power consumption in both air cycle and refrigeration cycle. Moreover, parameters such as compressor power, refrigeration effect, total load, coefficient of performance, pressure ratio, thermal entrainment coefficient, refrigeration capacity, volumetric and mass flow rates of air in the evaporator and condenser, refrigerant mass flow rate, condenser heat, air curtain thermal efficiency, Richardson number, Reynolds number, and deviation modulus under different ambient conditions were calculated. The experimental results show that the refrigeration performance is affected by ambient air temperature, which directly influence on the infiltration rate of ambient air into the refrigerator compartment and on the return air temperature to the evaporator. Therefore, the return air temperature is crucial indicator for assessing the efficiency of the refrigerator. With increasing ambient temperature, compressor power increases, while the refrigeration effect and COP decrease. The results also indicate that as ambient temperature rises, air curtain efficiency decreases somehow that temperature difference between front and rear of the shelves may reach up to 4.6°C. For every 1°C increase in ambient temperature, compressor power consumption increases by approximately %0.64, while refrigeration effect and COP decrease by %0.06 and %1.77, respectively

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This study evaluated the quantitative and qualitative traits of 13 local summer squash populations. The experiment was carried out in a randomized block design with 3 replications for two years (2019 to 2020). The following traits were considered in this study: number, weight, length, width, and length/width ratio of fruits, seed yield, seed yield/fruit yield ratio, 1000 seeds weight, percentage of empty seeds, seed length, seed width, seed kernel/whole seed ratio, and seed oil percent. Also, quality tests were conducted including ease of separation of skin from the kernel, taste quality, and desirability of seed shape and size from the consumer's point of view. The analysis of variance showed significant differences in most of the studied traits. Based on the results of the mean comparison of traits, the highest seed yield was observed in Ghalami-Kalaleh#1 and Mashhady-Azadshahr and then Mashhady-Khoy populations. The highest taste quality from the consumer point of view belonged to the Goushti-Kalaleh population. The results represent a positive and highly significant correlation between seed yield and fruit number. No significant correlation was observed between seed yield and other related traits. It is recommended that fruit number trait be considered in selecting programs and modifying high-yielding populations.