Search results

One major challenge in turbulent flow applications is to control the recirculation zone behind the backward‐facing step (BFS). One simple idea to do so is to modify the original BFS geometry, of course, without causing adverse or undesirable impacts on the original characteristics of the primary stream. The main objective of this work is to examine the solidity of the recirculation zone behind several different geometries which are slightly to moderately different from the original BFS geometry.

The implemented modifications cause complicated irregularities at the boundaries of the domain. The experience shows that the mesh distribution around these irregularities plays a critical role in the accuracy of the numerical solutions. To achieve the most accurate solutions with the least computational efforts, we use a robust hybrid strategy to distribute the computational grids in the domain. Additionally, a suitable numerical algorithm capable of handling hybrid grid topologies is properly extended to analyze the flow field. The current fully implicit method utilizes a physical pressure‐based upwinding scheme capable of working on hybrid mesh.

The extended algorithm is very robust and obtains very accurate solutions for the complex flow fields despite utilizing very coarse grid resolutions. Additionally, different proposed geometries revealed very similar separated regions behind the step and performed minor differences in the location of the reattachment points.

The current study is fulfilled two‐dimensionally. However, the measurements in testing regular BFS problems have shown that the separated shear layer behind the step is not affected by 3D influences provided that the width of channel is sufficiently wide. A similar conclusion is anticipated here.

The problem occurs in the pipe and channel expansions, combustion chambers, flow over flying objects with abrupt contraction on their external surfaces, etc.

A novel pressure‐based upwinding strategy is properly employed to solve flow on multiblocked hybrid grid topologies. This strategy takes into account the physics associated with all the transports in the flow field. To study the impact of shape improvement, several modified BFS configurations were suggested and examined. These configurations need only little additional manufacturing cost to be fabricated.

This paper aims to enhance the barrier properties and active protection of a water-based silane coating on mild steel through nanoclay and zinc acetylacetonate simultaneously included into the formulation.

The corrosion protection performance of the silane sol-gel coatings with no additive, zinc acetylacetonate, nanoclay and nanoclay + zinc acetylacetonate was monitored using electrochemical impedance spectroscopy during 5 h of immersion in a sodium chloride solution. Moreover, the surface of coatings was analyzed using a field emission scanning electron microscopy equipped with an energy dispersive X-ray spectrometer (FESEM-EDX) and water contact angle measurements.

In electrochemical impedance spectroscopy analysis, the impedance at low frequencies, coating resistance and charge transfer resistance were the parameters considered which indicated the superiority of silane coating formulated with both nanoclay and zinc acetylacetonate. According to the results of FESEM/EDX and water contact angle measurements, the superiority was linked with the enhancement in the barrier properties in the presence of nanoclay, as well as function of the corrosion inhibitor at coating–substrate interface.

According to the literature, there is no research conducted to study the impact of the simultaneous use of nanoclay and zinc acetylacetonate on the barrier properties and active protection of an eco-friendly silane sol-gel coating including glycidyloxypropyltrimethoxysilane, tetraethoxysilane and methyltriethoxysilane on mild steel in a sodium chloride solution.

In many manufacturing systems, machines are subject to preventive maintenance. This paper aims to schedule the operations of jobs and preventive maintenance tasks in such a way that the completion time of jobs and preventive maintenance tasks is minimized.

An heuristic approach based on artificial immune algorithm is proposed for solving the multiple‐route job shop‐scheduling problem subject to fixed periodic and age‐dependent preventive maintenance tasks. Under fixed periodic assumption, the time between two consecutive preventive maintenance tasks is assumed constant. Under age‐dependent assumption, a preventive maintenance task is triggered if the machine operates for a certain amount of time. The goal is to schedule the jobs and preventive maintenance task subject to makespan minimization.

In addition to presenting mathematical formulation for the multiple‐route job shop‐scheduling problem, this paper proposes a novel approach by which one can tackle the complexity that is raised in scheduling and sequencing the jobs and the preventive maintenance simultaneously and obtain the required schedule in reasonable time.

Integrating preventive maintenance tasks into the scheduling procedure is vital in many manufacturing systems. Using the proposed approach, one can obtain a schedule that defines the production route through which each part is processed, the time each operation must be started, and when preventive maintenance must be carried out on each machine. This, in turn, results in overall manufacturing cost reduction.

Using the approach proposed in this paper, good solutions, if not optimal, can be obtained for scheduling jobs and preventive maintenance task in one of the most complicated job shop configurations, namely, multiple‐route job shop. Thus, the approach can dominate all other simpler configurations.

This paper aims to access the protective function of hybrid sol-gel coatings deposited on 304L stainless steel substrate in silane solutions containing a mixture of tetraethoxysilane, methyltriethoxysilane and glycidyloxypropyltrimethoxysilane with different pH values during various immersion periods.

The 304L stainless steels coated through 10 and 30 s of immersion in the silane solutions with pH values of 2.1 and 2.8 were exposed to NaCl solution. The corrosion resistance of the coated substrates was studied through taking advantage of electrochemical noise method as well as atomic force microscopy (AFM), water contact angle and field emission-type scanning electron microscopy (FESEM) surface analysis.

The electrochemical current noise, PSD (I) plot, noise resistance and characteristic charge as parameters extracted from electrochemical noise method indicated the superiority of eco-friendly silane coating deposited on the substrate surface during 10 s exposure to the solution, due to the film uniformity and homogeneity as confirmed by FESEM and AFM. Moreover, immersion of the stainless steel in the silane solution with pH 2.1, characterized by higher hydrolysis ratio, led to more effective corrosion control in the NaCl electrolyte according to the results of electrochemical noise and FTIR measurements.

The noise resistance and characteristic charge as electrochemical noise parameters were only used in this research to evaluate the protective behavior of the water-based silane sol-gel coatings. Future studies should examine the correlation between electrochemical noise data and the parameters extracted from other electrochemical methods, e.g. electrochemical impedance spectroscopy.

The data obtained in this research may provide an effective approach based on electrochemical noise method to screen the silane sol-gel coatings for protection of metallic substrates against corrosion.

According to the literature, no report can be found studying the effect of immersion time on a silane solution, including glycidyloxypropyltrimethoxysilane, tetraethoxysilane and methyltriethoxysilane, as well as the silane solution pH on the corrosion resistance of 304L stainless steel in NaCl solution through electrochemical noise method.

The exploration of performance determinants in social enterprises has gained increasing relevance among researchers and practitioners, particularly in rural tourism. The purpose of this paper is to analyze the contributions of transformational leadership and social entrepreneurship to the performance of social enterprises in the context of rural tourism. Further, the mediating roles of social capital, creativity and social value were investigated.

Data were gathered through a survey of 168 employees of social enterprises operating in the rural tourism setting. Eight surveyors were sent out to conduct the survey. Data were analyzed by structural equation modeling (SEM) using AMOS 18.0.

The results of the SEM suggested that transformational leadership is positively associated with social value, social capital and performance of social enterprise. In addition, social entrepreneurship had a significant influence on social value, social capital and performance of social enterprise. Creativity and social value predicts the performance of social enterprise. Further, social capital was found to have a positive relationship with creativity. Finally, the mediating roles of social capital, creativity and social value were also confirmed. The findings thus highlight the power of the social value creation and social capital in the social enterprises operating in the rural destinations.

The findings assert that social entrepreneurship and transformational leadership are key sources of social value creation, social capital and creativity in rural tourism context indicating the need for additional efforts on this kind of entrepreneurial activity. The findings can motivate policymakers to promote social entrepreneurship in rural tourism destinations as a means of stimulating bottom-up social capital and social value creation.

This study is among the first to examine the hypothesized relationships focusing on tourism social enterprises.

Electronic components’ efficiency is the cornerstone of technology progress. The cooling process used for electronic components plays a main role in their performance. Embedded high-conductivity material and provided microchannel heat sink are two common cooling methods. The former is expensive to implement while the latter needs micro-pump, which consumes energy to circulate the flow. The aim of this study is providing a new configuration and method for improving the performance of electronic components.

To manage these challenges and improve the cooling efficiency, a novel method named Hybrid is presented here. Each method's performance has been investigated, and the results are widely compared with others. Considering the micro-pump power, the supply of the microchannel flow and the thermal conductivity ratio (thermal conductivity ratio is defined as the ratio of thermal conductivity of high thermal conductivity material to the thermal conductivity of base solid), the maximum disk temperature of each method was evaluated and compared to others.

The results indicated that the Hybrid method can reduce the maximum disk temperature up to 90 per cent compared to the embedded high thermal conductivity at the same thermal conductivity ratio. Moreover, the Hybrid method further reduces the maximum disk temperature up to 75 per cent compared to the microchannel, at equivalent power consumption.

The information in this research is presented in such a way that designers can choose the desired composition, the limited amount of consumed energy and the high temperature of the component. According to the study of radial-hybrid configuration, the different ratio of microchannel and materials with a high thermal conductivity coefficient in the constant cooling volume was investigated. The goal of the investigation was to decrease the maximum temperature of a plate on constant energy consumption. This aim has been obtained in the radial-hybrid configuration.

This paper aims to propose a new nonlinear function estimation fuzzy system as a novel statistical approach to estimate nanofluids’ thermal conductivity.

A fuzzy system having a product inference engine, a singleton fuzzifier, a center average defuzzifier and Gaussian membership functions is proposed for this purpose.

Results indicate that the proposed fuzzy system can predict the thermal conductivity of Al₂O₃/paraffin nanofluid with appropriate precision and generalization and it also outperforms the classic interpolation methods.

A new nonlinear function estimation fuzzy system was introduced as a novel statistical approach to estimate nanofluids’ thermal conductivity for the first time.

Education is a human right and access to high quality education is key to sustainable socioeconomic development. Improving the quality of higher education institutes is essential for generating the productive human resources. Assessing the quality of higher education from the students’ perspective can be considered a crucial factor in the monitoring of service quality in universities. The purpose of this paper is to evaluate the quality of educational services in a higher education institute, the Kermanshah University of Medical Sciences (KUMS), in the west of Iran.

A multistage sampling method was used to select 346 students from the KUMS, who were enrolled in the second semester of the academic year 2015-2016. The SERVQUAL questionnaire was used to gather data on students’ perceptions and their expectations about the quality of educational services. The authors used a statistical significance level of 0.05 to examine the gap between the students’ expectations and their perceptions of service quality in five dimensions, namely tangibles, responsiveness, reliability, empathy and assurance.

The results showed that there was a negative service quality gap in all five dimensions. The overall mean score of students’ expectations and their perceptions was 3.19±0.44 and 2.4±0.45, respectively. The score gap between the overall mean score of perceptions and expectations of students was −0.79, which was statistically significant (p<0.0001). The highest and lowest quality gaps were related to the assurance (−0.84) and tangible (−0.70) dimensions, respectively.

The study indicated that the quality of educational services provided in the KUMS did not meet students’ expectations in five dimensions of service quality. Thus, it warrants further investigations to determine how to improve the quality of educational services in higher education institutes such as the KUMS.

The purpose of this paper is to carry out a numerical study on the dynamic and thermal behavior of a fluid with a constant property and flowing turbulently through a two-dimensional horizontal rectangular channel. The upper surface was put in a constant temperature condition, while the lower one was thermally insulated. Two transverse, solid-type obstacles, having different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel and fixed to the top and bottom walls of the channel, in a periodically staggered manner to force vortices to improve the mixing, and consequently the heat transfer. The flat rectangular obstacle was put in the first position and was placed on the hot top wall of the channel. However, the second V-shaped obstacle was placed on the insulated bottom wall, at an attack angle of 45°; its position was varied to find the optimum configuration for optimal heat transfer.

The fluid is considered Newtonian, incompressible with constant properties. The Reynolds averaged Navier–Stokes equations, along with the standard k-epsilon turbulence model and the energy equation, are used to control the channel flow model. The finite volume method is used to integrate all the equations in two-dimensions; the commercial CFD software FLUENT along with the SIMPLE-algorithm is used for pressure-velocity coupling. Various values of the Reynolds number and obstacle spacing were selected to perform the numerical runs, using air as the working medium.

The channel containing the flat fin and the 45° V-shaped baffle with a large Reynolds number gave higher heat transfer and friction loss than the one with a smaller Reynolds number. Also, short separation distances between obstacles provided higher values of the ratios Nu/Nu₀ and f/f₀ and a larger thermal enhancement factor (TEF) than do larger distances.

This is an original work, as it uses a novel method for the improvement of heat transfer in completely new flow geometry.

The concentration of women entrepreneurs on influential events such as the development of green entrepreneurship, which lead to the coordination and dynamic balance between economic and environmental goals, can create a bright future for businesses with sustainable and environmentally friendly architecture. The main purpose of this study is to provide a framework for the successful entry of women entrepreneurs into green entrepreneurship.

The present qualitative applied descriptive-analytical study was conducted on a population of women entrepreneurs working in green businesses. This population was obtained by the non-probability chain sampling method and an exploratory interview with the saturation of 12 individuals. Thematic analysis was used to analyze the findings.

The results revealed that creating shared value, inclusive social acceptance, multifaceted interactions and green dynamic bedding are effective in the entry of women entrepreneurs into green entrepreneurship in the form of “competitive empowerment” and “multiplied green synergy”. Thus, managers and planners should consider some factors, including shared value, social acceptance, inclusive acceptance, building green culture, knowledge flows, multiple participation, networking dimension, green marketing, competitiveness, creating platforms, green technologies and risk management.

This research tries to present a framework for the entry of women entrepreneurs into green entrepreneurship area.