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

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 uniform value of costs 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 desalination of sea water 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 cost The production uniformity in fixed desalination technology is 2000 and in floating desalination technology is 9700 rials per cubic meter. Also, sensitivity analysis tests based on 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.In the present work, a three-effect distillation desalination system is combined with a cascade refrigeration cycle. On the other hand, the effects of various working fluids in the cascade refrigeration cycle were investigated and evaluated on the indicators such as the mass flow rate of potable water, the occupied space of the integrated system, the power consumption of compressors, and the related investment cost. 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 analyzed and 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 intercooler. A combined ORC-VCC 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 a significant reduction in CO2 emission and biomass consumption, as well as an increase in electricity 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 equipment is attributed to the PEM electrolyzer, amounting to 15.44 $/hr, and the total cost of the produced products has reached 0.5627 $/MJ. With intercooling the compressors, 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 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 region 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 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 show 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 finite volume method is used to solve the equations. In this study, 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 indicate that in presence of DBD plasma actuators inside the cyclone, by reducing the velocity of the inlet flow to the cyclone, the particle separation performance of the cyclone is increased. Also, it is obvious 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 greater in the particles with a larger diameter (2 mm). The results indicate that by increasing the applied voltage of the DBD plasma actuators, the maximum tangential velocity and particle separation performance of the cyclone increase. 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 performance of propellers is use of tubercles on blade inspired by nature and basis of passive flow control. In this research, effectiveness of an innovative idea has been investigated from 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 root to tip of blade. Improvement of aerodynamic efficiency has been done by numerical simulation using rotating reference frame method, and improvement of static aeroacoustic efficiency has been done with experimental test resulting from calibration of microphone sensors. Computational fluid analysis using the finite volume method based on finite element and solving Reynolds averaged Navier-Stokes equation with K-Omega-SST model has been validated from reference experimental test. By studying independency of results, 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 main harmonic of propeller, 1.4% in area near rotor plate and 3.8% in area behind plate, shows improvement of aeroacoustic performance.