جستجوی مقالات مرتبط با کلیدواژه « Temperature Distribution » در نشریات گروه « مکانیک »

The purpose of this study is to investigate the conditions governing a flameless combustion furnace with natural gas fuel. In this article, by changing the arrangement and distances of the four symmetrical air inlets from the central fuel inlet, The concept of eddy dissipation model with coefficient correction has been used to model combustion with reduced chemical kinetics DRM22. Two symmetrical cross arrangements "X" and "+" configuration, were determined to minimize the dead space in the furnace for air inlets. Lower limit of the air and fuel inlet distance was assumed to be 12 mm and the upper limit of this distance was 36 mm in the simulation. Most of all, by examining the combustion parameters, the proposed geometry was selected for the construction of the furnace. The recirculation factor (Kv) has been increased by 2.6 times compared to the base furnace. Also, the maximum temperature has decreased by 5% and the difference between the maximum and average temperature by 77 Kelvin compared to the basic furnace, and this indicates better temperature uniformity. Also, the maximum heat of reaction of specified point in the furnace has increased by 63% compared to the base furnace and indicates the higher potential of the furnace in heat treatment. It is possible to extend results of this research to natural gas industrial furnaces.

In this study, the conditions governing a flameless natural gas and air combustion furnace with an internal recirculation system equipped with an arm to increase the recirculation coefficient is numerically investigated on a laboratory scale. The effect of changing its angle on parameters of flameless combustion such as released heat, temperature distribution and internal recirculation coefficient was investigated. The simulation results show that by increasing the angle of the arm and opening the geometry up to 60 degrees, the flow is better directed into the furnace, and the volume of the recirculation area is the largest in the arrangement with an arm angle of 60 degrees. By comparing the value of the recirculation coefficient in the whole furnace, it is observed that its main effect is on the recirculation area, which leads to changes in the uniformity of temperature and released heat. By examining the maximum released heat, it can be concluded that the geometry design with an arm angle of 30 degrees is the best proposed geometry for heat treatment applications. By examining the temperature results, it was concluded that as the angle of the arm of the system is lower (the system becomes more closed) and the accumulation of the combustion flow inside it is greater, The temperature increases from 1727 K (for armless geometry) to 1738 K (for arm angle of 15 degrees).

In some places with hard winters, the heat from sunlight and stored in the soil may not be enough to heat the greenhouse. In such a situation, the additional heat needed must be provided by heating systems. The purpose of this study is to evaluate the effectiveness of the heating system in a glass greenhouse with side air vents and mechanical fans in both night and day periods. In this study, seven different greenhouse designs have been investigated in two periods, day and night. In the daily period, by changing the pressure of the fans, tried to obtain the best condition for providing the appropriate temperature in the greenhouse. Also, in this period, the effect of sunlight on the flow field and temperature changes inside the hall were also investigated. In the night period, the amount of temperature changes by opening and closing the side valves and changing the temperature of the hall floor has been studied. The results of the research show that a greenhouse with a pressure difference of 100 pascal during the day and a greenhouse with a floor temperature of 323.15 K and side vents closed at night have more suitable conditions for growing plants in the off-season.

In the present study, the effects of geometrical properties of gas flow channels on both current density and temperature distributions inside a polymer electrolyte membrane (PEM) fuel cell are investigated. The main purpose here is to clarify the effects of the variation of width, depth, and the ribs of flow channels on the fuel cell performance. To do this, the fuel cell is numerically simulated in two dimensions. The governing equations consist of the conservation of the electrical potential, Darcy’s law as alternative to the momentum equation, Maxwell-Stefan equation for mass transport, energy conservation, and electro-thermal equations along with the Butler–Volmer equation. Numerical results indicate that the width of channels and their ribs have more sensible effects than the depth of flow channels on the current density and temperature distributions and fuel cell performance. While the maximum temperature of the cell is increased by increasing the width of the flow channels, the current density distribution and fuel cell performance can be improved. By decreasing the width of their ribs or depth of channels, the performance of the fuel cell is improved and its maximum temperature is decreased.

Nowadays, the use of lasers in welding titanium alloys has special applications in high-tech industries. This study aims to extract the statistical model showing the effect of changes in the diameter of laser beam diameter and distance in line thickness welding temperature. At first, For establishing this model, the required experiments were designed by the Taguchi method and then evaluated using the finite element method. The surface response method is used to extract the statistical model based on the variation of laser beam diameter and distance through the workpiece thickness. By the analysis of the variance, the statistical model error was evaluated in an acceptable range. According to the evaluated results, the influence percent of the distance along with the workpiece thickness and the laser beam diameter is 76.67 and 97 %, respectively, on the welding temperature. By increasing the diameter of the laser beam, the amount of the welding temperature is significantly reduced. For laser welding of Ti6Al4V, the best laser beam diameter is between 0.2 and 0.24mm.

A fire accident of a passenger train from Tehran to Ahvaz has been numerically simulated. In this study, emission patterns, temperature distribution and the other parameters have been investigated after the start of the fire. The transient governing equations have been solved by Pyrosim software for different scenario based on mass fraction of products, unused fuel and other fire parameters. The results are compared with an actual case. The results showed that less than two minutes after the start of the fire, the conditions inside the wagon reached a critical situation in terms of temperature, smoke and visibility. To prevent the fire from spreading to other parts of the wagon, firefighting operations must be performed in less than four minutes.

Extensive research has been done to improve the quality and reduce the propulsion weight of aircraft, which has led to the invention of new technologies and the construction of new engines. In all these studies, the study of temperature distribution and heat transfer in the body of the combustion engine in order to evaluate the characteristics and performance of the engine is considered important and necessary. One of the most innovative designs is the vane rotary motor design, which is considered to be a revolution in the motor industry. In this article, initial design of the seals of this engine is discussed based on thermal analysis. The method of increasing the air temperature in the combustion chamber has been investigated and the temperature distribution has been calculated by two methods of engineering estimation and numerical analysis. In engineering estimation, the basic relations of heat transfer, radiative, conduction, and energy balance equation are used, and the energy survival equations are satisfied, and the combustion process is modeled as a diesel cycle. Combustion is considered as a heat source and heat transfer coefficients are calculated in the form of computer code. The results of numerical analysis of this issue are compared and validated with the results of the estimation program and the appropriate cover and material for the components of the combustion chamber as well as the appropriate material and location of the seals are selected according to the temperature distribution

High heat transfer rate as one of the important advantages of fluidized bed reactors is attributed to hydrodynamic mechanisms. In this research the important hydrodynamic parameters such as minimum fluidization velocity, pressure drop, bed height, bubble formation and flow regime were investigated experimentally and numerically. The two-fluid model coupled with the kinetic theory of granular flow and two different drag models of Gidaspow and Syamlal-O'Brien were applied in the present simulation. The results showed that by using the Gidaspow drag model in numerical solution, the minimum fluidization velocity with an approximate error of 13.8% and the bed height with an average error of 9% are predictable in comparison with the experiments. In order to investigate the effects of particles properties on temperature distribution of a bubbling fluidized bed, several solid particles with different densities and thermal diffusivities were investigated. Finally, to demonstrate the advantages of fluidized beds to receive the required hot air in industrial units, temperature distribution and required height of a bubbling fluidized bed reactor were compared with a similar constant surface temperature simple channel. The results showed that the outlet air temperature of a bubbling fluidized bed is about 28 degrees Celsius higher than a similar simple channel.

Due to wide application of conical sandwich shells in the modern industries, it is nessesary to investigate the mechanical behavior of theses structures. In this paper, for the first time, by considering the flexibility of the core in the high order theory of sandwich shells, the the buckling behavior of the truncated conical sandwich shells which include a temperature dependent porous FG core and two temperature dependent homogeneous face sheets are investigated in various thermal conditions. The power law rule which modified by considering the two types of porosity volume fractions are applied to model the gradually variation of functionally graded materials. By applying the principle of minimum potential energy, considering the in-plane stresses in the core and faces, and nonlinear von-karman strains for both mechanical and thermal stresses, the governing equations are obtained under the axial in-plane compressive loads. A Galerkin procedure are used to solve the equations in a simply supported boundary condition. Uniform, linear and nonlinear temperature distributions are used to model the effect of the temperature changing in the sandwich shell. To verify the results of these work, they are compared with FEM results obtained by Abaqus software and for special cases with the results in literature. Critical load variations are surveyed versus the temperature changing, geometrical effects, porosities, and some others in the numerical examples.

Combustion chamber has a crucial role in gas turbines and has a significant effect on the pollution and efficiency of them. Due to the complicated flow in combustion chambers because of high turbulence intensity, flow mixing, and flame behavior, prediction of the performance of such chambers is very complicated. There is a vital need for experimental investigations to study and understand the flame behavior in combustors. This experimental study was performed using a can type combustion chamber and LPG fuel at atmospheric conditions. First, stability curve, temperature distribution in the combustion chamber, and its exit plane in 6 flow conditions and then flow behavior were evaluated. The pollution at the outlet was obtained in different conditions and equivalence ratios. The results show that the flame tends to go downstream of the combustion chamber when the fuel mass flow rate increases (or in other words, by increasing the equivalence ratio) in constant air mass flow rate and finally exits from the chamber. By increasing the air mass flow rate in constant fuel mass flow rate, CO pollution is increased, and NOx pollution is decreased.

In this paper, air gasification of Tehran’s refinery Mazut is investigated. First, Mazut gasification is modeled by the equilibrium method and then, the thermal operating of an entrained flow gasifier is studied experimentally. An entrained flow gasifier is designed and manufactured for 7 kg/h flow rate of heavy fuel oil. The physical/chemical properties of this heavy fuel oil are determined via standard laboratory experiments. In Aspen plus, a parametric study is conducted by the equilibrium model in order to investigate the effects of equivalence ratio on syngas composition, gasification temperature, and higher heating value for the steady-state condition. Temperature distribution along the gasifier and the solid carbon consumption are effective parameters on syngas composition and gasification performance. In an experiment, the gasification temperature is measured at different locations of a gasifier. The modeling results show that the values of H2, CO, and HHV have a maximum which is accompanied with complete consumption of solid carbon at equivalence ratio 0.39. By increasing equivalence ratio, gasification temperature increases which are supported by experimental results. The comparison of modeling and experimental result shows that difference between model and experimental temperature increases by increasing equivalence ratio. Also, after a short distance from the injector, the temperature is decreased along the gasifier with a constant rate. Finally, in order to provide the optimum gasification operation, the proportion between an appropriate gasifier length and operating equivalence ratio is presented based on one of the gasification reaction.

The fuel cell is an electrochemical energy exchanger that directly converts the chemical energy into direct current and heat. Thermal management and water management are two major challenges in designing and efficiency of polymer fuel cells, which are inherent in each other. In this paper, by manufacture PEM fuel cell and test under different conditions, an analysis will be made of how the temperature is distributed in the full cell. By studding this temperature distribution, the relationship between power generation and heat distribution, thermal parameters (temperature distribution, maximum and minimum temperature) are extracted. The innovation aspect of this paper is to achieve an understanding of the distribution of temperature in polymeric fuel cell under different operating conditions. Also, the temperature distribution has been investigated in open-end and dead-end operating modes in different pressures and stoichiometries. When the fuel cell is changed from the open-end to the dead end mode, the maximum temperature changed from the outlet section in to the input section. By increasing pressure, the importance of maldistribution control and design of a suitable cooling system will increase.

In this paper, the pressure and temperature distributions over the ramp of an Aerospike nozzle in different pressure ratios are presented. Governing equations of the turbulent flow have been solved using the finite volume method and different turbulence models. By comparing the obtained results with available experimental data, SST k-ω model has been selected for numerical simulations. In this study, the length of the recirculation zone, the temperature, and pressure variations within the recirculation zone and locations of the separation and reattachment points have been investigated in detail. Results show that the increase in the pressure ratio can move separation, reattachment points, and recirculation zone to downstream of the flow and also increase the length of the recirculation zone simultaneously. The maximum and minimum temperatures did not change but the maximum and minimum pressures reduced. Also, the results show that the reattachment point has the maximum temperature of the flow and this maximum temperature point can be adopted as the reattachment point.

In the present study, using the ABAQUS 2017 finite element code and using the DFLUX subroutine, a 3D numerical analysis of laser welding in the lap joint of AA6061 and AA5086 aluminum alloys was carried out. The effect of the position of a harder and softer alloy on the upper and lower parts of the weld in two different thicknesses of the two parts was studied on such cases as: thermal distribution, the width of the different welding regions and the residual stress caused by laser welding. In total, and based on the input conditions of the problem, 8 states were prepared for simulation. Based on the results, the A4 sample has the lowest maximum temperature difference between the upper and lower parts in all of these states, which is due to the presence of harder metal with lower thickness in the upper part of the joint. In all cases, regardless of the position of the upper or lower parts, the higher longitudinal residual stresses will occur in the harder part, the AA6061 alloy, and in all states the maximum longitudinal residual stress formed over the yield stress of the harder alloy. Regarding the level of σzz in the workpiece, the best conditions are, respectively, A1 and B1, because they also experience lower residual stresses levels, and the difference in residual stress between the two upper and lower regions of these specimens is lower.

In addition to variable properties of fluids, heat interaction with ambient, and axial wall conduction, the temperature distribution of a three-fluid heat exchanger, is strongly affected by Geometric and design parameters. Geometric parameters such as exchanger length and tube diameter and design parameters are fluid flow rate and ambient temperature. In this study, the effect of geometric and design parameters on the temperature distribution and effectiveness of a three-fluid heat exchanger with three thermal communication have been investigated. The governing equations on the flow, are simulated considering heat-in-leak to the cold fluid and variable properties of the fluids, and are solved based on the first law of thermodynamics and analytical methods. Cooling the hot fluid and heating the cold fluid, have been considered as the objective of the three-flow heat exchanger, in order to effectiveness investigation. The effect of ambient heat in leak is to increase the cold fluid temperature, leading to a little lift on hot fluid temperature profile, will result in an enhancement in the cold effectiveness and a reduction on hot effectiveness. Increasing ambient temperature, enhances the effects of heat in leak from ambient. An increase in the diameter of outer tube, Where the cold fluid is flowing and is in contact with the ambient, makes the hot and cold temperatures become farther apart in each cross-section, and decreases the hot and cold effectiveness. An increase in the flow rate of the cold fluid, results in a higher hot effectiveness and reduces the cold effectiveness. Due to An increase in the hot flow rate, both the hot and cold effectiveness are enhanced.