IRANIAN JOURNAL OF MECHANICAL ENGINEERING (ENGLISH)
Year:2019 | Volume:21 | Issue:2 |Papers Count:12

The optimization is done by changing geometric and hydrodynamic parameters of the micro-channel flow. The governing equations are solved numerically by finite volume method. Results show that the number of channels, the width of the ribs and the coolant velocity in bottom channel will have considerable impact on cooling performance of the straight micro-channel. Also, since spiral geometry has not been studied in the literature until now, the spiral geometry in the micro-channel cooling performance has also been studied in this study. In this case, the results also show that the lower the curvature radius, the cooling will improve. The optimization is done by changing geometric and hydrodynamic parameters of the micro-channel flow. The governing equations are solved numerically by finite volume method. Results show that the number of channels, the width of the ribs and the coolant velocity in bottom channel will have considerable impact on cooling performance of the straight micro-channel. Also, since spiral geometry has not been studied in the literature until now, the spiral geometry in the micro-channel cooling performance has also been studied in this study. In this case, the results also show that the lower the curvature radius, the cooling will improve.

In this study, a novel model of thermoelectric-photovoltaic hybrid system installed in cubical solar cavity receiver is presented and the heat transfer equations included radiant heat transfer inside the cavity, conduction heat transfer from photovoltaic modules and thermoelectric generators, and the electric power generation equations are solved numerically. In this cavity structure the re-radiation from the photovoltaic modules is absorbed in different directions and by reducing re-radiation loss, the power generation efficiency increases. The radiation heat transfer analysis depicts the re-radiation in solar cavity receiver is lower than 8%, while the re-radiation from flat plate photovoltaic module is near 60%. The results show that generated power in this cavity hybrid system is two times more than generated power by flat plate hybrid system under different irradiation levels. Heat transfer analysis of cavity hybrid system shows the maximum irradiation is on downside surface of the cavity, and so the downside surface is the more efficient surface for installing the photovoltaic-thermoelectric hybrid system. Consequently, the cost of produced energy by applying Photovoltaic-Thermoelectric hybrid module in one side and thermoelectric generators in other sides is 40% less than all side hybrid cavity. The results show that increasing the heat convection coefficient from 5 to 10, increase the generated power 114. 8 mW to 352. 5 mW.

In this research, heat sink microchannel will be investigated. In order to improve the efficiency of heat transfer should be increased the fluid thermal conductivity. in this study, Numerical Investigation of the forced convective heat transfer in Serpentine heat sink microchannel with water-AL2O3 and Water-CuO has been studied, and the influence of hydraulic diameter, the Reynolds number and volume fraction of nanoparticles on heat transfer is discussed. The results of this study show that with the increase of Reynolds from 97. 3 to 97. 98, the pressure drop for nanoparticles of CuO increased from 1. 7 kPa to 31. 4 kPa and with the increase of Reynolds from 91. 80 to 1121. 35 Nuselt number will be multiplied by 3. 2. Two different volume fractions of 1% and 3% and distinctive nanoparticle diameters were employed. Increasing the nanoparticles volume fraction together with decreasing the nanoparticles diameter enhances the Nusselt number value. The pressure drop coefficient did not change significantly by using nanofluid with various volume fractions and varied nanoparticle diameters.

An experimental study has been conducted to show the effect of aspect ratio on pressure drag of a cam-shaped tube in cross-flow of air. The aspect ratio varies between 1. 35 ≤ L/D ≤ 3. 13 and Reynolds number based on equivalent diameter changes in the range of 2. 5×103 to 5. 5×103. Studies were carried out at the angles of attack of 0 and 180 degrees. Results show that by increasing the aspect ratio, the drag coefficient decreases. The drag coefficient at the angle of attack zero degrees is about 54 to 82 percent lower than the circular tube with the same equivalent diameter. Also, the drag coefficient at the angle of attack 180 was about 42 to 82 percent lower than the circular tube with the same equivalent diameter. It was found that the cam-shaped tube with L/D=3. 13 has a minimum drag coefficient which is about 82% lower than a circular tube with equivalent diameter.

In this paper, for the first time, natural convection heat transfer of a nanofluid in the presence of a uniform magnetic field inside a parallelogram shaped cavity with two triangular obstacles with different boundary conditions is simulated by using lattice Boltzmann method. The right vertical wall of the cavity is assumed to be adiabatic and the inclined walls are kept at constant cold temperature, while the left vertical walls are kept at constant hot temperature. The flow and temperature field is calculated by solving lattice Boltzmann equations for velocity and temperature distribution functions simultaneously. D2Q9 lattice arrangement for each distribution function is used. The results have been validated with available results in the literature. The effects of different parameters such as Rayleigh number (103-105), Hartmann number (0-90), nanoparticle volume fraction (0-0. 05) and different boundary conditions at triangular obstacles on natural heat convective heat transfer are investigated. The results show that, at a constant Rayleigh and Hartmann number, the average Nusselt number takes its maximum and minimum value when the triangular obstacles are kept at constant cold and hot temperatures, respectively. For all cases, it is found that the average Nusselt number increases with enhancement of Rayleigh number. Also, increasing of Hartman number decreases the flow velocity and heat transfer rate. Furthermore, increase of volume fraction of nano particles enhances heat transfer rate, however its changes for different Rayleigh and Hartman numbers are not the same.

Rising fossil fuel prices, global warming concerns, advancements in the field of technology, and so on, caused the Trigeneration energy systems to be an attractive option to supply consumer energy demands in recent years. Therefore, in this article, these energy systems are introduced, and their main advantages are presented. In addition, different types of Power Generation Unit used in these systems described, and the advantages and disadvantages of each one are listed. Furthermore, a procedure for designing a trigeneration energy system to utilize in tropical areas proposed, that is based on providing maximum cooling demands. As well as, a procedure for extracting the optimal operation pattern of these energy production systems on different days of the year proposed which is based on an optimization problem. Moreover, a sample numerical study conducted to find out how to determine the optimal size of different devices in a trigeneration power system for use in a tropical residential campus. Electrical, heating and cooling demands of the residential campus are in accordance with the consumption pattern of consumers located in the metropolitan area of Ahwaz with frequent warm weather conditions. The study is codified in the MATLAB program, and its results are derived in the form of economic analysis. It is worth mentioning that, the possibility of selling electrical energy to the main grid is considered in the extraction of optimal operation pattern for a typical summer and winter days.

In this work, the effect of emitter electrode arrangement on the Electrohydrodynamic effectiveness is studied using micropolar fluid model through a smooth channel. Finite volume method by the open source CFD code OpenFOAM is used to solve governing equations. The effects of longitudinal position and the gap between emitter electrode and collector electrode, as well as, longitudinal arrangements are investigated. The computed results of micropolar approach are compared with obtained from the fully turbulent k-ε model. The results of each type of the EHD flow with certain conditions show that the adequate material parameter(κ _ω ⁄ μ ) is constant for the longitudinal electrode arrangements for single electrode and multiple electrodes because this parameter completely depends on the flow and the high magnitude of electric body force. Also, this parameter is increased with decrease of the gap between emitter electrode and collector electrode. In addition, the heat transfer enhancement and also the flow pattern has the same efficiency for both the micropolar and the k-ε models.

In this paper, three-dimentional numerical analysis of mutual effects of free oscillations of an inherent unstable body with flexible stabilizer attached to it, is performed in subsonic viscous flow. For solving fluid dynamics, finite volume method using a computational fluid dynamics software is done and for analysis of structure deformation, Euler-Bernouli cantilever beam theory is implemented in the computer code. For analyzing the fluid-structure interaction, iterative partitioned coupling algorithm is used for interrelation and data exchange between structure and fluid sections. With inserting the equations of body dynamic motion into the simulation code and coupling these solvers, the ultimate computational framework is formed that can be implemened to capture Body-Fluid-Structure Interactions. The results of different simulations shows that without the flexible stabilizer, the oscillations of free flying body will grow towards instability. Morover, if the center of mass goes rearward with respect to the nose, and with increasing the flow speed, the oscillations intensity of body will grow. The obtained results are useful for the stabilization of the free flying bodies that need to be stable during flight stages or must be oriented specially in landing phase e. g. reentry vehicles.

In this paper, modeling of ammonia-water absorption refrigeration system has been carried out by EES software with mass and energy balances in all system components. Then, a computer program has been developed to examine the system's performance by coupling the MATLAB and EES softwares. The effect of low pressure on performance and operating parameters of the system under two different conditions are investigated. These conditions include operation at a constant generator temperature and operation at optimum obtained values for generator temperature proportional to low pressure variations. The investigated parameters are concentration of weak and strong solutions, mass flow rates of weak solution and refrigerant, enthalpy variations at different points of the system, generator temperature, thermal loads of all components, coefficient of performance and absorption cycle efficiency. Also, the variations of saturation quality at inlet-outlet the evaporator and inlet the absorber are considered in terms of low pressure. The optimal value of low pressure is determined by focusing on the performance of system and refrigerant saturation quality at mentioned points. As obtained results, coefficient of performance, optimal value of low pressure and generator temperature are evaluated equal to 0. 473, 2. 28 bar and 139. 3 ° C, respectively at temperatures of 35, 35 and-15 ° C for absorber, condenser and evaporator, and also it was shown that in determining the optimal value of the parameters, it is necessary to consider the refrigerant saturation quality at mentioned points as well as performance investigation as essential constraints of simulation and optimization process.

Air-conditioning is used in many commercial buildings and houses today and the energy required for the air conditioning system can be very high in extreme conditions. In this paper, for the purpose of intensifying heat and mass transfer and reducing the pressure drop, new structures for the membrane of these converters have been used; these structures include a curved membrane with a semicircular profile and a curved membrane with convex surfaces. This paper analyzes the numerical study of new membrane such as curvature and circular, using COMSOL Multiphysics. Modeling involves the transfer of heat and mass for turbulent flow. The pressure drop, the average Nsult number and Sherwood calculated and correlated with different reynolds. The results of this study show that the curved membrane with a semicircular profile increases the heat and mass transfer by about 7% and 6%, and the curved membrane improves the pressure drop by about 50% compared to the triangular heat exchanger.