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In this research, an apparatus was made and utilized to determine the friction coeffi-cient of chickpea grains on steel surfaces. Experiments were carried out on two black and galvanized surfaces and at four sliding velocities of 5, 20, 100 and 500 mm/min, at three moisture content of 7.5%, 15% and 21% wet basis (w.b.) and at three vertical pressure values of 14.28, 100 and 150 kPa. The following results were obtained. 1) For surface conditioning, the steel plates need to be passed through the grains for at least 7 times. 2) At low sliding velocity, by increasing the velocity from 5 to 20 mm/min, the dynamic friction coefficient of chickpea grains increased, and at a sliding velocity of 500 mm/min it was decreased. 3) For the black steel surface, by increasing the moisture content of chickpea grains from 7.5% to 15% w.b., the value of the friction coefficient in-creased; but at a moisture content of 21% w.b., it decreased. For galvanized steel sur-faces, and sliding velocities of 5 and 20 mm/min, increasing the moisture content, the value of friction coefficient was found to decreased, but for sliding velocities of 100 and 500 mm/min it’s behaviour was similar to the black steel surface. 4) Normal pressure has no significant effect on the friction coefficient (at 0.01 level) and the difference between the mean values of the coefficient of friction associated with the normal pressure of 14.28 kPa and 100 kPa, as well as 100 kPa and 150 kPa was not significant at the 0.05 signifi-cance level.

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This paper aims to establish a basic understanding of double bulge tube hydroforming process of stainless steel deep drawn cups. The method is briefly reviewed by carrying outexperimental tests and Finite element analysis. After measuring bulge height in both formed curves by CMM and thickness variation of formed tube by ultrasonic thickness measurement unit, it’s found out that thickness variation in this process is less that other traditional methods such as traditional spinning and rubber pad forming. A finite element model is constructed to simulate the double bulge tube hydroforming process and asses the influence of friction coefficient and tube material properties. It is found that material hardening coefficient had the most significant influence on formability characteristics during double bulge tube hydroforming. As similar as other tube hydroforming processes, increasing friction decrease bulge height and thickness.

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Gears are widely used to transmit power between two parallel shafts. Study on the lubricant film which is formed between the engaged teeth of pinion and gear is of high importance in predicting the performance of the power transmission system as well as surface failure and wear. Gear surfaces in comparison to rolling element bearings have a higher surface roughness and thus considering the surface roughness is important in gear analysis. In this research, the performance of a pinion-gear system operating under mixed-elastohydrodynamic lubrication is being investigated using load-sharing concept. The contacting asperities might experience elastic, elasto-plastic or fully plastic contact. The engagement of pinion and gear for each point along the line of action is replaced with contact of two cylinders. The radii of these cylinders as well as the exerted load vary along the line of action. Using load-sharing concept, the proposed model can predict the lubricant film thickness, friction coefficient, and portion of the total load that is carried by asperities as well as lubricant film. The predicted results are verified by comparison to other available methods which are published in the literature.

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Gears are one of the most important elements of any power transmission system. Among all types of gears, helical gears are more common due to their high capacity in power transmission as well as lower level of noise. The aim of this study is to present a model for analyzing the contact of teeth of helical gears considering thermal effects and surface roughness. In the present model, each helical gear is divided to several narrow spur gears in which each of the spur gears have a small rotation angle relative to the previous one. Also each contact point of gears is replaced with contact of two equivalent cylinders. Considering the fact that the governing regime for gears lubrication is the mixed-elastohydrodynamic regime, the total load is carried by lubricant and asperities' contact. Meshing and lubrication analysis of a pair of helical gears is conducted based on the load-sharing concept and parameters such as film thickness, friction coefficient and temperature rise are predicted. The predictions based on the load-sharing concept are compared to other published results Acceptable accuracy, short execution time along with considering thermal and roughness effects are some of the major characteristics of this study.

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In previous studies, there is no comprehensive experimental study that has evaluated dissimilarity between heat transfer and momentum transfer for all the interactions between effective variables. On the other hand, when a rectangular cylinder is located near a flat plate, skin friction coefficient and heat transfer coefficient are effected some variables that change in an extensive range. Therefore, testing all possible combinations of effective variables will not be reasonable. In this paper, maximum and minimum of skin friction coefficients and heat transfer coefficients were determined using robust Taguchi design. Design of experiments method was applied for decreasing the number of experiments without losing the required information in the first step. Then, experiments were performed in a wind tunnel, the maximum speed of which was 13 m/s. Finally, skin friction coefficient and heat transfer coefficient were optimized using Taguchi method and Minitab software. Results showed that dissimilarity between heat transfer and momentum transfer has occurred for all the possible combinations of the effective variables. Additionally, the gap height between the rectangular cylinder and flat plate was the most effective variable on generating the dissimilarity.

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In this paper, the variation of coefficient of friction, which is one of the main and important parameters in fretting fatigue, has been investigated experimentally. Measuring of coefficient of friction has been performed with the designed device by the researchers. The advantage of using the above device is that it can almost accurately measure the contact pressure and friction force and thus the coefficient of friction. Al alloy 2024-T3 has been used as it is the frequently used alloy in aerospace structures. The coefficient of friction is considered here as a parameter which is a function of normal and cyclic axial load. Another important point in performing the test is the variation of frictional stress at different normal and axial loads which is measured. Results show that as the normal load increases, the coefficient of friction reduces but the frictional stress increases. Changing the frictional stress is the main parameter in investigating wear between interfaces. The above results can be applied in numerical analyses such as life prediction and/or predicting joints fracture section such as double shear lap joints which experience fretting fatigue.

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The usages of stirling engine in many industry such as aerospace, submarines and combined heat and power systems, requires more and detailed analysis in such engines. This type of engine is an external combustion which may use almost any type of fuel. In this article the Nusselt number and friction coefficient of a Stirling engine heat exchanger is investigated numerically. The geometry of this heat exchanger is an arc shape pipe with reciprocating flow. Various parameters such as angular frequencies, type of fluids, working gas pressures, flow regime and heater geometry impact on the Nusselt number and friction coefficient of the heater were investigated. By increasing the angular frequency and the working gas pressure the Nusselt number increases but the friction coefficient decreases. The influences of different working fluids indicated that the Carbon dioxide has the highest Nusselt number. The results also show that the friction coefficient is highly dependent on the flow regime. The comparison between the two different geometry type heaters show that the arc-type geometry led to higher Nusselt number. The friction coefficients of both geometries are almost similar to each other at high frequencies.

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Oscillating flow is one of the most important characteristics of flow in stirling engine heat exchangers. In this study reciprocating flow in stirling engine cooler is investigated numerically. Numerical solution is based on finite volume and pressure based algorithm by using the commercial CFD code fluent. A Shell and tube type heat exchanger used as cooler. The working fluid, gas flows inside the tubes while the cooling fluid, water flows around the tubes. The heat transfer coefficient, temperature difference between tube walls and working fluid, Nusselt number and friction coefficient are calculated for Helium, Carbon‌ dioxide and Nitrogen at different operating pressure and oscillating frequency. The Nusselt number, heat transfer coefficient and temperature difference between tube walls and working fluid increase with increase of operating pressure or oscillating frequency while Friction coefficient decreases. Helium has the highest heat transfer coefficient and friction coefficient and the lowest temperature difference between tube walls and working fluid. At the highest operating pressure and oscillating frequency, Carbon dioxide has the highest Nusselt number and the lowest Friction coefficient. Finally empirical equations for Nusselt number and friction coefficient are proposed for Helium, Carbon dioxide and Nitrogen, the error of the equations are within 0.23-8.07% when the range of kinetic Reynolds number is 2.96-212.50.

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Superhydrophobic surfaces have gained significant attention as a promising approach for drag reduction of submerged objects. Accurate evaluation and prediction of drag reduction induced by these surfaces require expensive experimental measurements, numerical simulations, or the development of reliable models and correlations. In this paper, a model is proposed for calculating the skin friction coefficient and drag reduction of superhydrophobic flat surfaces. Utilizing previous data on the skin friction coefficient of flat surfaces under no-slip boundary conditions, a model is developed to estimate the skin friction reduction and skin friction coefficient of these surfaces after applying superhydrophobic coatings. The validity of the model is verified by comparing its results with those of computational fluid dynamics (CFD) simulations of flow over a flat plate at different velocities. The results of the model and simulations indicate that for inlet velocities of 1, 5, and 25 m/s and a slip length of 50 μm, drag reductions of 15%, 41%, and 77%, respectively, are expected. Additionally, the skin friction reduction increases with increasing flow Reynolds number. The developed model is validated for flat surfaces and its ability to accurately estimate the skin friction coefficient and drag force of these surfaces is thoroughly examined. However, further investigations are required to assess the model's validity for curved surfaces and variable slip lengths.

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By studying the physical properties of oilseed rape, the obtained data have a practical application when constructing machines for sowing, harvesting, transporting, warehouse design, and seed processing. During oilseed rape harvest, seed moisture can be different, and it is imperative to understand the physical properties of the seeds to correctly adjust the equipment. Depending on the climate conditions, oilseed rape can have different seed moisture content. This investigation included three winter varieties of oilseed rape widely grown in European countries. The effect of different degrees of seed moisture (6, 11, 16, and 21%) on the physical properties of oilseed rape, seeds were investigated by using standard methods in three growing seasons (2015/17). When moisture content in the kernels increased, 1000-grain weight, seed volume and porosity, static and dynamic angles of repose also increased in the tested varieties. Increased seed moisture reduced the true density and bulk density of the three tested varieties. The highest coefficient of friction was found on plywood and the lowest on stainless steel sheet. Oil and protein contents of the tested varieties ranged between 39.38 and 43.90%, and 17.65 and 23.12%, respectively. Oleic, linoleic, α-linolenic, and palmitic acids were the most representative fatty acids. Knowing the physical and chemical properties of oilseed rape seeds, it would be possible to significantly contribute to the breeding process in order to identify high-quality genotypes.