مجله مهندسی مکانیک امیرکبیر
سال پنجاه و پنجم شماره 9 (آذر 1402)

Water plays an important role in human life and is one of the first human needs for survival. Therefore, due to population growth and industrialization and therefore the lack of water resources in the world especially in Iran, its supply needs special attention. Currently, 97.5% of the water resources on the planet cannot be used. The main purpose of this study is the economic study of the use of fixed and floating freshwater in Makran beaches. One of the most important methods in this field is the desalination and desalination processes of seawater. Given that for government projects, only the final price or in other words the cost price is considered, the method of levelized cost of production over the useful life has been chosen. According to the information of the Electricity and Energy Master Planning Office of the Ministry of Energy, the results show that the desalination of seawater in the form of building a factory (fixed desalination plant) is more economical compared to the floating desalination plant, in such a way that the levelized cost of production in fixed desalination technology is 2000 and in floating desalination technology is 9700 rials per cubic meter. Also, sensitivity analysis tests based on the discount rate, production capacity coefficient, and escalation rate of fuel cost show that on one hand, floating desalination technology is more sensitive to the above variables than fixed desalination, and on the other hand, the change of this variable has no effect on changing the economic priority. The results show that seawater desalination in the form of a factory (fixed desalination) is economical compared to floating desalination.

Regarding the energy and potable water crisis and many environmental problems due to the use of fossil fuels, it is necessary to utilize the waste heat of industrial equipment to produce potable water without using another energy source. The cascade refrigeration cycle is one of the widely used industrial equipment, which has valuable waste heat at a high temperature. In this research, the mentioned waste energy is used as an independent energy source to produce potable water in the thermal desalination system. The present work combines a three-effect distillation desalination system with a cascade refrigeration cycle. Along with comparing the 28 working fluid pairs, a scoring method was used to determine the best working fluid pair due to the different scenarios and priorities. The results showed that the lowest power consumption of compressors belongs to R600-R717 working fluid pair. Moreover, the highest mass flow rate of produced potable water, the lowest occupied space and the lowest related investment cost happen when R744-R600A is considered. Using the scoring method, it was determined that when all indicators are considered for selecting the working fluid pair, even in different scenarios with different priorities, the best choice is R600-R717.

In this research, a novel trigeneration system driven by biomass-solar energies has been investigated from energy exergy, economic and environmental viewpoints. The solar energy is used to produce hydrogen (by a PEM electrolyzer powered by thermal photovoltaic panels). To meet the intermittent nature of solar energy, it is used for hydrogen production. The hydrogen is used as fuel in the combustion chamber. The proposed gas turbine cycle consists of two high and low-pressure turbines and two compressors with an intercooler. A combined organic Rankine-vapor compression refrigeration cycle that uses the recovered heat from the gas turbine is used to produce refrigeration and air cooling in the interstage compressor. The obtained results provide that the combination of solar-based hydrogen production and biomass-based gas turbine leads to an increase in power production capacity. The proposed combined system provides an energy and exergy efficiency of 21% and 17% and the emission of 0.00884 kg/s of CO2. The highest capital cost rate among the components is attributed to the PEM electrolyzer, amounting to 15.44 $/hr, and the total cost of the products has reached 0.5627 $/MJ. Using an intercooler, the energy and exergy efficiencies of the system have increased by 6% and 4%, respectively.

In this paper, the numerical solution of compressible, transonic, unsteady, inviscid, and two-phase of moist-air flow in converging-diverging nozzles is studied. To do so, both equilibrium and non-equilibrium thermodynamic models with Roe's scheme are considered and the results are compared. In the equilibrium thermodynamic model, the solver is spatially third-order and temporally second-order accurate, but in non-equilibrium thermodynamic model, the solver is spatially first-order and temporally second-order accurate. For the moist air in dry regions the pressure, temperature, and velocity are extrapolated while in wet regions the steam quality has been used instead of pressure. In this study, the influence of the geometry expansion rate and inlet total temperature and pressure on nucleation rate and the wetness fraction at the nozzle exit are investigated. The results show that by increasing the expansion rate of the nozzle the condensation onset occurs earlier; also, the nucleation rate and wetness fraction at the nozzle exit is increased. Comparing the results of equilibrium and non-equilibrium thermodynamic models shows that the non-equilibrium thermodynamic model has better agreement with the experimental data.

In this paper, the effect of secondary flow induced by the DBD plasma actuators on the flow and separation performance of solid particles in a cyclone is numerically investigated. The effect of the effective parameters such as the applied voltage of the DBD plasma actuator, the arrangement of plasma actuators, the velocity of the incoming flow of the cyclone, and the size of solid particles are evaluated. The results show that the separation performance of the cyclone in the presence of the DBD plasma actuators increases in all particles with different diameters between 1 and 2 mm, compared to the cyclone without the presence of plasma actuator, and the performance enhancement is higher in the particles with a larger diameter (2 mm). The arrangement of plasma actuators has a significant effect on the particle separation performance of the cyclone, and the uniform installation of plasma actuators in the entire height of the cylindrical part of the cyclone (type one arrangement) improves the particle separation performance compared to other arrangements. The results show that the use of the DBD plasma actuators inside the cyclone can increase the cyclone separation performance by 26.5% compared to the cyclone without the DBD plasma actuator.

One of the effective methods in improving the performance of propellers is the use of tubercles on blades inspired by nature and the basis of passive flow control. In this research, the effectiveness of an innovative idea has been investigated from an aerodynamic aspect with computational fluid dynamics analysis and from aeroacoustic aspect with experimental testing. This idea has been studied by creating wavy simultaneous tubercles on leading and trailing edges with a wavelength of 6 mm and an amplitude range of 3 degrees in pitch direction from near the root to tip of the blade. Improvement of aerodynamic efficiency has been done by numerical simulation using the rotating reference frame method, and improvement of static aeroacoustic efficiency has been done with experimental tests resulting from the calibration of microphone sensors. Computational fluid analysis using the finite volume method based on finite elements and solving Reynolds averaged Navier-Stokes equation with K-Omega-SST model has been validated from reference experimental test. By studying the independence of results, the appropriate computing domain and grid for numerical simulation of flow has been determined. Results show an increase in aerodynamic efficiency of 7.5% in advance ratio equivalent to maximum efficiency and an increase of 22% in others. Reduction of maximum sound intensity in frequency equivalent to the main harmonic of the propeller, 1.4% in the area near the rotor plate and 3.8% in the area behind the plate, shows improvement of aeroacoustic performance.