نشریه یافته های نوین کاربردی و محاسباتی در سیستم های مکانیکی
سال یکم شماره 4 (زمستان 1400)

The purpose of this study is to evaluate the potential of solar nanofluids (liquid with dispersed nanoparticles) for direct absorption of solar radiation and steam production. At present, solar thermal energy systems suffer great losses due to heat transfer processes, therefore, the development of nanotechnology and its achievements such as various nanoparticles, has created high hopes to increase the efficiency of solar collectors through direct absorption of sunlight. In order to make optimal use of solar nanofluid systems, it is necessary to identify and study them. In this research, four different nanofluids have been synthesized, identified and evaluated. Two of them were water-based nanofluids and the other two were thermal oil-based nanofluids. Also, the optical properties of nanofluids were measured at room temperature with a spectrophotometer and compared with the base fluid. The optical properties, in addition to being measured at room temperature, have also been evaluated after heat treatment on nanofluids at high temperatures. This temperature increase is intended to recreate operating conditions for those closer to the actual applications. DLS measurements show a similar hydrodynamic average of 138 nm for the sample containing SDS and 135 nm for the sample containing SDS and PVP.

In this paper, the robust convergence of iterative learning control (ILC) in a linear rehabilitation robot with parametric uncertainty is obtained. Today, rehabilitation robots have an essential role in assisting physiotherapists in repairing muscle injuries. Since the uncertainties in rehabilitation robots change with practice in iteration, it is crucial to eliminate the effect of variable parametric uncertainty with iteration. Also, parametric uncertainty in the input and output matrices of a rehabilitation robot model directly affects the convergence of the ILC algorithm, and a small effect on each of these matrices may lead to algorithm divergence. In this paper, first, the law of the ILC algorithm without uncertainty is obtained. Then the robust convergence of this algorithm with a fixed learning gain in the presence of parametric uncertainty is proved. Finally, validation of the results obtained on a rehabilitation robot model is analyzed and evaluated.

In this paper, using computational fluid dynamics, the dynamic properties of the flow in the two-way grooves of a centrifugal compressor gas seal are simulated. The computational area consists of a gas film between two fixed and rotating rings and the space inside the grooves. Leak performance is tested at thicknesses of 3.08 and 5.08 μm. In order to perform the numerical solution, the continuity and Navier-Stokes equations are solved assuming complete gas using disorganized cells. The flow regime is considered layered. The results obtained include the pressure distribution. The results of numerical solution of the geometric model with bidirectional C-shaped groove were evaluated with Gabriel experimental results. Geometry discussed in this dissertation is the geometry of dry gas compressor C-14200 alkylation unit of Abadan Oil Company. The results show that the rotation speed of the Dry Gas Seal, or DGS for short, has a significant effect on the hydrodynamic effect, while the pressure of the outer radius and the thickness of the gas film both reduce the hydrodynamic effect.

Saving energy is one of the most important challenges in the world today. In recent years, growing concerns about the environmental consequences of energy consumption and global warming have doubled in importance. On the other hand, the share of the construction sector in the energy consumption of countries is significant and for this reason, in recent decades, in most industrialized countries, basic measures have been taken to improve consumption patterns, using various tools such as regulations. One of the most important energy consumed is electrical energy, which is one of the most basic energy sources of buildings and plays an important role. The complex problems and processes of electricity generation and transmission, the pollution generated by the production of fossil fuels, and other cases have prompted researchers to seek solutions to reduce energy consumption or, in other words, optimize energy consumption. In this study, some practical solutions to move towards energy saving have been investigated and the effect of using materials with different heat transfer coefficients in external walls according to Semnan weather conditions on the modeled building and to analyze the cooling and heating load of the building. Compared with renewable materials. Finally, the external wall, using a 20 cm straw block, has reduced the annual energy consumption compared to perforated pottery, autoclaved concrete, and Article 19 of the National Regulations has resulted in 3%, 0.6%, and 2.76%, respectively.

This article which deals with the application of interdisciplinary phenomena,New methods of improving heat transfer of heat exchangers in mechanical engineering have been studied It then applies these methods to chemical reactors.Because in a chemical reactor, in addition to heat transfer and pressure drop, which are two important categories in heat exchangers, a chemical reaction is also added.Therefore, the use of heat transfer improvement methods are examined with more sensitivity so that they have the least pressure drop and the highest heat transfer.In this study, the use of straight and helical longitudinal fins in thermal cracking reactors was investigated And it was found that each of these types of fins increase the pressure drop due to friction or drag force Which have a negative effect on the chemical reaction.Then, by calculating the thickness of the viscous sub lary layer for the gaseous fluid by presenting a new method in converting the flow regime along the wall from laminar to turbulent By performing CFD simulation of peripheral grooves in a pipe Then a conclusion was suggested By using small grooves in the reactor wall can be in addition to reducing the pressure drop caused by drag force,By increasing the radial component of the velocity by more than 3 times the smooth tube, the heat transfer from the pipe wall to the fluid in the boundary layer was improved.

In recent years, the use of parking space in large buildings has become popular. One of the dangers that always threatens buildings is the risk of fire. Smoke is generated after a fire. Smoke from fire poses a greater risk to life than fire. By controlling the smoke, the building and its occupants can be protected and the damage caused by the fire can be reduced. In this study, smoke distribution and temperature profiles in the parking lot of a commercial complex were investigated using Pyrosim software. Navier-Stokes equations for energy, Conservation of mass were used to solve, and Large Eddy Simulation model was used for turbulence. Two scenarios were considered to investigate the fire. In the first scenario, parking without a ventilation system was studied and in the second scenario, it was studied with the ventilation system. Exhaust fan was used to evacuate the smoke and a supply fan was used to supply fresh air. The results of these two simulations were compared with each other. The fire power was 4 MW. The results showed that in the first scenario, the smoke concentration is 0.003 mol / mol and the temperature is 80 ° C. In the second scenario, the smoke concentration is 0.0002 mol / mol, which is 93% better than the first scenario. The temperature also dropped to 28 ° C by evaporating the smoke in 1200 seconds. In fact, the temperature improved by 65% compared to the first scenario. Reducing the concentration of smoke and lowering the temperature make it easier for people to evacuate during a fire.