مجله مهندسی مکانیک امیرکبیر
سال پنجاه و چهارم شماره 5 (امرداد 1401)

Petrochemical industry effluents are one of the most hazardous effluents available, which contain toxic and biodegradable compounds, and their release into nature carries serious environmental risks. In this way, it is necessary to purify them. In this research, the Fenton method was used as one of the efficient advanced oxidation methods for Abadan petrochemical wastewater treatment. The effect of three parameters of ,  concentration and  ratio, and their interference on the dye removal efficiency of this effluent was performed using the design method of the Box-Bonken statistical test with the help of Design Expert software. In order to achieve the maximum amount of dye removal as an indicator of pollution, the optimal conditions were Selected by the software as , the amount of oxidizing , and the molar ratio . In these conditions, the highest rate of dye removal was predicted to be 79.5%, which in real conditions showed a yield of 72.5%, which is acceptable due to laboratory error (). The electro-Fenton method was also used to increase the removal efficiency. In the electro-Fenton method, under optimal conditions of Fenton process ( and ) and current density of , the maximum dye removal efficiency of 100% was obtained.

A Downburst can produce divergent outflow wind on the ground surface, which is different from the behavior of atmospheric boundary layer flows. In this research, the effects of downburst on a cube-shaped structure in two different directions of flow (α), four different ground surface angels relative to the downburst direction (θ), and different radial distances (X/D) relative to the downdraft center were investigated by a simulator that was made for this thunderstorm. Simulation of this flow is created by a blower whose task is to uniformize the flow created by the fan embedded behind it. The velocity and turbulence intensity of flow was measured at different X/Ds. also, the distribution of pressure coefficient on the sides of the model was measured at the X/D locations. In addition, a good agreement has been observed between the data comparison of this study and previous studies. It was observed that at the center of the downburst for all θs, the structure has a positive pressure coefficient along its sides. By moving away from the center of the storm, the flow behavior is similar to the boundary layer flows. By increasing θ, it was found that the difference of pressure coefficient between the windward side relative to the roof and the backward sides, increased, which in the worst case has changed by about 80%. By examining the direction of flow to the model, it was found that the force coefficients when the model is at α=45°, are about 35% less than when the model is at α=0°. Finally, it was found that at X/D=1, the maximum force coefficient is applied to the structure.

Complex flow separation in thrust optimized parabolic nozzles in the over-expanded condition is one of the challenging issues of many numerical investigations. The correct estimation of a thrust optimized parabolic nozzle performance extremely depends upon the accurate estimation of the onset of flow separation. Literature review indicates that conventional Reynolds-averaged Navier–Stokes turbulence models have a significant error in predicting the onset of flow separation in these types of nozzles due to the overestimating of turbulent kinetic energy production. Recently proposed generalized k-omega has made it possible to rectify numerical simulations based on governing physics and using limited experimental results. In the present study, the flow physics in the LEA_TOC nozzle has been investigated with the numerical simulation approach. At the first, the significant error of conventional Reynolds-averaged Navier–Stokes turbulence models is shown to simulate flow separation in this type of problem. Then, the generalized k-omega parameters are modified based on the limited experimental result of the LEA_TOC nozzle, and the ability of this model has been evaluated to estimate the flow physics under different pressure ratios. Numerical investigations show that generalized k-omega has a high capability for accurately estimating the onset of flow separation at a wide range of nozzle pressure ratios. Applying the corrected generalized k-omega has resulted in an improvement of about 30% in the estimation of the onset of separation in the over-expanded LEA_TOC nozzle compared to the k-ω-SST model.

In this research, a new type of add-on flap is presented and the effect of adding it to the blade of a horizontal axis wind turbine and optimizing its location and length is investigated. The use of an add-on flap is more cost-effective than other conventional methods since it does not need major modifications to the existing blades. For increasing the accuracy of the blade element momentum algorithm, the aerodynamic coefficients of the blade section are obtained by numerical solution of the governing equations, while in most similar studies, methods based on airfoil linear theory were used. The results showed that the modification made in the blade momentum element algorithm increased the accuracy of the solver while maintaining its computational speed. The results show that using this type of flap arrangement, the value of the base turbine power coefficient was increased from 0.29 to 0.41, which shows a significant increase compared to other methods.

Two-phase systems are important tools for droplet formation that have received much attention in recent decades due to their vast applications. In the present work, the process of water-in-oil droplet formation, in a coaxial geometry using the fluid volume method, and the impact of effective parameters such as dispersed phase velocity and density and also interfacial tension are investigated. The results are used to produce spherical γ-alumina particles by the oil drop method. In this study, using a laboratory setup, the factors affecting the droplet formation process are investigated. Results are validated against laboratory data. The measurement error is about 5% for droplet size and about 4% for sphericity. Studies show that although the mentioned parameters have a great effect on droplet size and separation time, the dependency of droplets diameter on interfacial tension and dispersed phase density is higher. Increasing the interfacial tension causes increasing droplets size and separation time. Also increasing the density of the dispersed phase reduces the diameter of the droplets and increases separation time. Increasing the velocity also had a small effect, but lead to an increase in size and reduced droplets separation time.

In recent years, actuator methods in aerodynamic simulations have been favored by researchers. These methods can significantly reduce the computational effort compared to full-scale body resolving simulations. They are also more accurate than conventional methods that use simplified models. In this study, an actuator surface model is used to simulate flow around an airfoil in a steady two-dimensional incompressible flow. In these models, the geometry of the airfoil is represented by volume forces distributed along the airfoil chord. For this purpose, the collocated method of mass corrected interpolation method is coupled with the Actuator Surface Model. To determine the accuracy of the results, the actuator surface method is compared with the full- computational fluid dynamics simulation method. Besides, a new study is presented to investigate the effect of changing different parameters of the actuator surface model on the accuracy of results. Finally, pressure and vorticity contours are plotted, and obtained results are compared with full- computational fluid dynamics results. The obtained results show that although the actuator surface has a moderate accuracy in calculating parameters such as velocity and pressure, it can predict aerodynamic forces and flow structures with acceptable accuracy. The method presented in this article can be used as an efficient tool in studying more complex cases.

Nowadays, population growth and energy consumption, especially non-renewables, are growing significantly. It is expected that by increasing public awareness about the necessity of optimal energy consumption, the choice of methods and equipment that will lead to less energy consumption of the building, will be more welcomed. Among heating systems, the underfloor heating systems can reduce fuel consumption due to lower operating temperatures, despite creating uniform heat in all zones of the building. On the other hand, In Iran, which has a high potential for solar energy, it is possible that by combining underfloor heating and solar heating systems, despite the reduction of fossil fuel consumption, the desired heat in the building can be provided. In the present study, a combined floor heating system including a solar underfloor heating system and a hot water boiler is designed and simulated to heat a building in the cold climate of Iran to reduce fossil fuel consumption. The simulation results show that the solar heating system designed in this study can provide 98.5 % of the total energy required for domestic hot water and 17.3 % of the total energy required for underfloor heating. These results show that the heating system provided for building energy supply in the cold climate of Iran is very useful and can significantly reduce fossil fuel consumption.

The solar radiation absorption efficiency is one of the challenges for engineers in solar energy systems. Using the hybrid nanofluids, which are obtained by dispersing two or more types of nanoparticles in the base fluid, can be effective in better absorption of solar energy. In this study, the effect of type, concentration, and mixing percentage of nanoparticles on optical properties and solar thermal utilization efficiency has been tested. First, magnesium oxide nanofluids and multi-walled carbon nanotubes with water-based fluid were fabricated by a two-step method in volumetric concentrations of 0/01%%Vol, 0.02% Vol, and 0.04%Vol, and then the optical properties of single and hybrid forms were measured by spectrophotometer and have been compared by existing relations. Then, to obtain the solar thermal utilization efficiency, a solar simulator has been used. The results show that increasing the concentration of nanofluid, improves the optical properties and solar radiation absorption efficiency. Magnesium oxide nanofluid, multi-walled carbon nanotubes, and hybrid nanofluid have the values of extinction coefficient about 38, 40, and 50 times higher than pure water, respectively. The hybrid nanofluid absorbs more than 90% of the sun's energy at the highest concentration (0.04% Vol) and at a penetration depth of 0.3 cm. Solar energy absorption increases by increasing the concentration, hybridizing the nanofluid, and increasing the penetration distance.

Improving the performance of a tri-generation organic Rankine cycle for the production of power, fresh water and heat using solar energy to respond to the needs in remote areas is very important. One of the effective factors in the performance of such a cycle is the thermodynamic behavior of its working fluid. Finding a suitable working fluid that has a good behavior on power generation, freshwater production and heat are of particular importance. This study aims to find an appropriate working fluid by analyzing, simulating, and optimizing a tri-generation Rankine cycle powered by solar parabolic trough collectors for simultaneous production of power, fresh water, and heat. The performance of this cycle is investigated with various mixtures of organic fluids R152a, R600a, and R1234yf which are categorized as wet, dry, and isotropic fluids, respectively. Therefore, first, a parametric study is conducted and followed by a multi-objective optimization for which power, fresh water, and heat are the objective functions. While the various mixture of these three working fluids are considered to be optimized. The results show that three-component mixture is more suitable for achieving three goals simultaneously, while if one of the objectives is considered, only one of these fluids should be used.

Industrial and research use of thermal plasma technology for a wide range of applications such as material processing, gasification, and disposing of hazardous waste. In this research, we have designed and manufactured a plasma torch for the gasification of liquid carbon-based materials. In particular, these materials must be sprayed at a certain angle into the plasma. The plasma torch is one of the components of a liquid waste gasification device, in this research, we have only studied the thermodynamic and electrical characteristics of the plasma torch. The plasma torch has been tested in two cases Finally, the electrical and thermodynamic characteristics of the plasma torch were measured and compared to each other. According to the results, the plasma torch has a maximum electrical voltage of 210 V and thermal efficiency of 86.2%. The maximum plasma enthalpy value is 21.5 MJ/kg and the maximum plasma jet temperature at the nozzle outlet is 3400 K. Plasma torch at a distance of 20 mm from the nozzle outlet has a temperature above 3000 degrees Celsius, which can be completely gasified the organic compounds and carbonaceous materials.

In this paper, a numerical study is presented on the investigation of heat transfer and melting process of phase change material in a finned triplex tube. The non-Newtonian Power-Law model is used to simulate the non-Newtonian fluid and the enthalpy-porosity method is used to simulate the melting process. The results show that the melting process in the case of using Newtonian fluid is more than in the case of using non-Newtonian fluid. Thus, the average value of the melting fraction of the phase change material in 5000 seconds is about 3.03% higher for the Newtonian phase change material. The effect of the two-layer composition of the Newtonian & non-Newtonian phase change material and how they are placed in the middle and outer tubes on the melting process has been investigated. For this purpose, two arrangements have been considered according to the way the fluids are placed in the middle-outer tube: 1. Newtonian & non-Newtonian fluid and 2. Non-Newtonian fluid - Newtonian. The melting process for the Newton-non-Newtonian fluid state is faster than for the non-Newtonian-Newtonian fluid state. The melting fraction in the Newtonian & non-Newtonian fluid states is about 10.32% higher than in the other state. The amount of melting fraction decreases with increasing Consistency index and decreasing Power-law index. The Nusselt number changes are similar to the melting fraction changes.

This paper investigates the local temperature difference between the phase change material and porous medium during the two-dimensional melting process by considering natural convection and applying sinusoidal boundary condition. Hence, the density distribution function is used to solve momentum equations and two separate distribution functions are used to solve energy equations to calculate the local temperature difference and liquid fraction of the phase change material. Also, the effect of parameters such as amplitude and frequency of oscillation and Sparrow number on the percentage of local temperature difference and comparison of liquid fraction in the presence and absence of natural convection, are studied. Results show that with increasing frequency from 1 to 3, the percentage of local temperature difference increased from 41.44% to 67.53%, and with increasing oscillation amplitude from 1 to 3, the percentage of local temperature difference is reduced from 41.44% to 20.56%. Also, by increasing the Sparrow number from 322 to 6000, the percentage of local temperature difference decreases from 41.44% to 4.21%. Also, it is observed that by changing oscillation frequency, liquid fraction does not change much compared to the conditions of pure conduction; however, as the amplitude of oscillation increases, the percentage of deviation of liquid fraction from the pure conduction increases.

In this research for the aim of optimizing the gas consumption, increasing the thermal efficiency of a household gas water heater has been investigated numerically. The optimal design and configuration of the baffles in the middle tube of the gas water heater prevents the quick exit of the exhaust gases and consequently increases the retention time of the hot gases inside the middle tube and reduces the wasting of their thermal energy. The combustion process in the gas water heater is a chain process and completing this process occurs along its path in the middle tube. Therefore for obtaining the maximum thermal efficiency, the numerical analysis of the combustion process and designing and configuration of the baffles inside the middle tube have been carried out and conducted simultaneously. The Ansys Fluent computational fluid dynamics code has been employed for the computational simulation of the combustion of the gas, the heat transfer from the contents of the middle tube into the water tank and distribution of the velocity of the exhaust gases along their path inside the middle tube and around the baffles. Computational simulation of the problem under investigation has been carried out by considering different geometries and configurations of the baffles along the path of the exhaust gases. Numerical results show that the mass fraction of the methane gas and the carbon dioxide in the exhaust gases is negligible and consequently all of the methane gas has been consumed. The numerical results have been verified by the experimental results.