نشریه مهندسی مکانیک تبدیل انرژی
سال هشتم شماره 3 (پیاپی 28، پاییز 1400)

This study investigated the effect of an omnidirectional magnetic field on the heat transfer performance of a saline water-Al2O3 magnetic nanofluid (MNF) cavity. The cavity was a quarter-circle with a cold left wall and a heated right wall, whereas other surfaces were insulated (adiabatic). All surfaces were assumed constant. The governing equations were solved numerically based on control volume and SIMPLE algorithm. The nanoparticle concentration ranged from 0 to 0.04 percent, the Hartmann number (Ha) was between 0 and 9, and the Rayleigh number (Ra) was 105. Findings indicated that increased nanoparticle concentration and magnetic field intensity enhance the reductive effect of the Lorentz force. Increasing the magnetic field intensity has an insignificant effect on the thermal performance of the fluid with zero nanoparticle concentration. As the nanoparticle concentration increases, the electrical conductivity of the fluid increases too which leads to a significant increase in the reductive effect of the magnetic field so that a 2% increase in nanoparticle concentration at Ha = 4.5 reduces heat transfer by more than 45%, whereas this reduction is higher than 65% at a nanoparticle concentration of 4% and Ha = 9.

Replacing clean and renewable energy with energy from fossil fuels is critical today, and more efficient energy systems and more efficient use of renewable resources are needed to sustain energy systems in the future. In multiple power generation systems, proper selection of energy supply sources is one of the most important issues. Solar energy, which according to the potential of the implementation site, which is the implementation site of this project in Khuzestan province, was determined as a suitable source to provide the necessary energy for the system studied in this dissertation. In the present study, we investigated a renewable system and the use of solar energy with suitable and close to reasonable conditions with high solar potential. The main components of the system consist of a solar tower system, a heat storage source, a Brighton cycle, a steam Rankin cycle, Reverse Osmosis and a single-effect absorption refrigeration cycle. The main outputs of this system include fresh water, generated electricity and cooling. These systems are a receiver system where heat is transferred to the mirrors and hot air is given to the turbine and then the power generation process is performed. Fresh water produces cooling absorption through RO desalination and chiller. In this system, there is a Brighton cycle that uses a solar system instead of a combustion chamber, which is an innovation. EES software has been used as an engineering tool to model the system and obtain thermodynamic results.The city of Ahvaz was analyzed by examining the potential of solar radiation as a case study. The most important effective and practical parameters in these studies are solar intensity (DNI), number of heliostat (N_hel), turbine inlet pressure (P8) and compressor pressure ratio (r_p).

In this study, a three-dimensional steady state simulation of the coil containing hot oil in the radiation section of the vertical cylindrical furnace of an industrial unit was investigated. This coil has nine U-shaped bends with an angle of 180 degrees. Using computational fluid dynamics, flow velocity and pressure, fluid outlet temperature, and coil wall temperature in different parts of the system were calculated. To validate the model, comparison of the simulation results of the coil wall temperature at the end of the fluid path and the fluid temperature at the outlet with industrial values ​​has been performed. Comparison of the computed wall temperature and fluid temperature at the coil outlet with the industrial values showed deviations of about 6% and 0.44%, respectively. The presence of bends in the coil caused some fluctuations in the parameters along the coil. Centrifugal force due to the curved geometry of the coil changed the pressure distribution, and this pressure change caused the fluid velocity and temperature, and wall temperature to fluctuate, so that in the bend, the pressure fluctuated about 4952 Pa, fluid velocity changed up to 2.83 m/s, the fluid temperature varied to about 2 K, and the wall temperature difference was about 10 K.

In this study, the energy consumption of NGL plants was assessed using two methods of retrofit pinch analysis and grass-root design based on actual experiments. Energy consumption is increasing very rapidly, especially in high-energy consuming industries such as oil, gas, and Natural Gas liquid refineries. Pinch analysis as a well-established and successful technique is used to improve the energy efficiency of the above-mentioned plants. As a real case study, a natural gas liquids(NGL) plant 800, from National Iranian South Oil Company located in southwest of Iran was considered. According to retrofit analysis results, all of the main pinch rules are met in the current state, and there is no need for any correction in retrofit Pinch Analysis. In the following, considering the ΔTmin of similar plants, the high value of ΔTmin reflects the plantchr('39')s significant potential for reducing energy consumption by the grass-root method. The results of the grass-root method shows that 19% of the plantchr('39')s energy consumption can be saved.

The use of limited reserves and pollution problems related to fossil fuels, the need for storage options as well as the use of renewable energy is felt. Solving environmental problems also requires a clean and efficient method. Today, fuel cells for energy efficient conversion, along with by-products of heat and water, known as efficient electrochemical converters and electricity, have been considered as a new production technology due to the need for clean energy and fossil constraints. . These include the ability of fuel cells to generate electricity without creating any mechanical movement, as well as their technologies, which have also received much attention in commerce. Polymer Electrolyte Membrane Fuel Cells (PEMFC), Solid Oxide Fuel Cell (SOFC), Direct Methanol Fuel Cell (DMFC), Phosphoric Acid Fuel Cell (PAFC), Alkaline Fuel Cell (AFC) and Molten Carbonate Fuel Cell (MCFC) Fuels are discussed in this study. Membranes and improved cell efficiency as well as durability and reliability allow us to use them in competition with traditional combustion engines. Also, the performance of fuel cells causes a significant reduction in costs. In this review, we will analyze recent developments in fuel cells and compare them.

Among the methods of heat transfer, the bubble boiling phenomenon as a method with high heat transfer coefficient is considered by many researchers. On the other hand, natural convection and nucleate boiling have interactions on each other which lead to strengthening and weakening each other in different situations. In the present numerical study, a three-dimensional tall cavity filled with incompatible fluids of water, vapor, and air with a uniform heat flux on the main wall has been investigated.  At first in this study, the range of the critical heat flux for nucleate boiling has been predicted and then, the interaction between the natural convection and nucleate boiling and the effective parameters on heat transfer have been studied.The results show that increase in the Raleigh number due to increase in the dimensionless height of fluid in the tall cavity  has improved the enhance of separation of gas bubbles due to boiling pheromone on the wall surface and as a result,  has delayed the film boiling regime.  However, in lower dimensionless heights of fluid in the cavity  (lower Rayleigh number), streams of fluid due to natural convection haven’t got enough strength to separate bubbles from the surface and bubbles slip on the surface instead of separating from it. In addition, vortexes of fluid caused by natural convection, first form in the down parts of the cavity and then they gradually develop and be active in other parts of the fluid. Also in this paper is well shown that the production and separation of the gas bubbles cause turbulence in the fluid flows.