مجله مهندسی مکانیک امیرکبیر
سال پنجاه و چهارم شماره 3 (خرداد 1401)

In this paper, the large eddy simulation was used and the one-equation method was adopted as the sub-grid method. In addition, the simulations are performed in three-dimensional, unsteady, and single-phase case and the Froude number is considered 0.000255. To investigate the effect of the combustion model, the combustion model of flamelet generated manifold is used in the simulation of fire in the room and the results of this combustion model are compared with infinite fast chemistry models and eddy dissipation models. Comparing the results, it can be seen that in the fire scenario in the room with a heat release rate of 62.9 kW, the mean temperature in the flame is approximately 1500 Kelvin. Also, the results of the eddy dissipation combustion model and infinite fast chemistry predict the temperature results better than the flamelet generated manifold combustion model; but, all three combustion models are close to experimental results with a relative error of less than 10%, in predicting the velocity. Due to the low computational cost of the flamelet generated manifold model and the ability to use detailed kinetics in this combustion model, as well as its acceptable accuracy, it is appropriate to use this model in the compartment fire simulation.

Brine Concentration is a comprehensive process and has an effective role in reducing environmental pollution due to desalination plant wastewater. In this study, the equations, for feed-forward forced convective falling film brine concentrators, with the desired number of effects and thermal vapor compression have been solved by MATLAB code. Thermodynamic modeling results of a two stage brine concentrator represented that 6.25 ton/hr feed with 90000 ppm concentration produces 5 ton/hr fresh water and 1.25 ton/hr wastewater with 450000 ppm concentration. The gained output ratio of plant is 2.63 and the specific heat transfer area is 74.3 m2s/kg. Also, by thermohydraulic modeling, to control the sediment rate with the limitations of allowable pressure drop and stream velocity in different tube lengths and diameters and evaporator number of passes, heat transfer area and the number of tubes have been calculated. Finally, the effects of design variables on gained output ratio and specific heat transfer area are investigated. The results represented that effects number, feed, and driving steam temperature are the three most important variables since increasing the effects number causes a 17% increase in gained output ratio and 23.5% increase in the specific heat transfer area. Increasing 1 C in feed and motive vapor temperature lead to a 2.5% increase and 3% decrease in the specific heat transfer area. But these two don’t have any effect on gained output ratio.

In this paper, the effect of using three drift eliminators with a different number of waves in a constant total length on compensation water flow rate and cooling efficiency of cooling tower and collection efficiency and air pressure drop of drift eliminator is investigated. These drift eliminators were made of galvanized iron in three models: type A with one wave, type B with two waves, and type C with three waves. The main purpose of this study is to investigate the effect of using drift eliminators on the performance of the cooling tower. Accordingly, experiments were performed on the laboratory cooling tower under constant environmental conditions in terms of temperature and humidity, and parameters including air mass flow rate, water mass flow rate, and inlet water temperature to the tower were assumed as constant. The results of this study show that the use of these types of drift eliminators can increase the cooling efficiency of the cooling tower by 18.5% and reduce the compensatory water flow rate of the cooling tower by 20%. On the other hand, the use of these drift eliminators increases the air pressure drop by 70% per wave and the collection efficiency of the drift eliminator by 48%.

Combined heat and power systems are used for renewable energies and reducing fossil fuels. This work, investigated energy efficiency, exergy, and exergy economic a Brayton cycle and refrigeration cycle with an ejector that used solar energy as a heat source. Inlet pressure turbine, outlet pressure turbine, inlet temperature turbine, and temperature of the evaporator are variable parameters, when one of the parameters changes, the other parameters are kept constant so that the thermodynamic analysis focuses on important parameters. Results showed that inlet pressure of initial flow in ejector and outlet velocity of flow on ejector are increased with increasing outlet pressure of turbine. The storage tank had the most exergy destruction rate among all components for the high-temperature difference that it’s almost 29% from all of the exergy destruction rates. Also, the highest cost per unit of power is related to the combined heat and power cycle that it’s about 53% of the total cost.

Among desalination systems, the use of reverse osmosis has become very widespread due to its advantages. One of the challenges in desalination systems especially in the reverse osmosis method is the existence of a control algorithm to overcome the uncertainties and disturbances. Another challenge of such systems is their power supply. A high-pressure pump supplies the pressure behind the membrane in the reverse osmosis system. The use of renewable energy not only does not have any environmental effects but also provides sustainable energy for such systems. In this paper, to answer these two challenges, at first, the integrated model of the reverse osmosis desalination system with the solar photovoltaic system has been examined; then for each part, a control algorithm is designed and simulated. An optimized fuzzy controller has been designed to track the maximum power point at different temperatures and radiation conditions in the photovoltaic solar system. The fuzzy controller has been optimized with the invasive weed optimization algorithm. The electric motor has been controlled using a fuzzy proportional–integral–derivative algorithm. The super-twisting sliding mode control has been used for the reverse osmosis system. The simulation results show that the proposed algorithm for the combined reverse osmosis-photovoltaic system has a good performance in different operating conditions and can remove and eliminate disturbances on the system.

The main important roles of bipolar plates in solid oxide fuel cells are the uniform distribution of reactants to the reaction sites, the collection of current, and the separation of each cell from another. Therefore, the performance of a solid oxide fuel cell is highly dependent on air and fuel flow channel design. In order to investigate how the geometry of air and fuel flow channels affects performance, current, and power density, simulation results are discussed to evaluate the performance of two types of fuel cells with direct ducts and converging-diverging ducts. In this research, a three-dimensional model of an anode-supported hydrocarbon fueled solid oxide fuel cell is presented. The results show that the pressure difference between the converging diverging channels produces a transverse flow in the channels and ribs which is in favor of better distribution of the reactants in the fuel cell with the converging diverging channels. This transverse velocity causes a 6% increase in fuel consumption in the cell with converging diverging channels than the cell with direct channels at a voltage of 0.7V, but due to the reduction of the reaction area of this cell compared to the usual cell, the current density is 10% lower. At voltages above 0.55V, fuel cells with converging diverging channels have a higher fuel consumption than fuel cells with direct channels due to the presence of transverse flows.

Today, due to the growing importance of polymer electrolyte membrane fuel cells in the production of clean energy, the diagnosis of this energy converter has become very important. Diagnosis can significantly increase the useful life and reliability of the fuel cell. A major part of the defects related to the polymer electrolyte membrane fuel cells is due to the disturbance of the moisture balance in them. Flooding is one of the most common defects associated with fuel cell imbalance, which is possible in both the cathode and the anode side of the cell. In previous works, the cathode has been considered as the only possible place for flooding, mainly because it is the source of water production. In this article, the anode is also considered as a possible place for this phenomenon. The method of this research is based on taking data from the stack under healthy operating conditions and trying to estimate the output parameters of stack voltage, cathode pressure drop, and anode pressure drop using related inputs using the adaptive neuro-fuzzy method. In conditions of uncertain operation in which the healthy or flooding operation of the stack is not known, comparing the deviation of the actual values of the outputs from the model with the allowable values of these deviations (0.735 [V], 0.0092 [bar] and 0.0047 [bar], respectively) can lead to determining flooding or normal conditions.

In this paper, graphene nanoplate was stabilized in a water-based fluid by sodium dodecyl sulfate as a surfactant. The prepared nanofluid in weight percentages of 0.01 -0.145 was placed in a gasket plate heat exchanger in the presence of cold fluid (deionized water). All experiments were performed for laminar flow in the range of Reynolds numbers of 500-1500. The effect of flow rate and concentration of nanofluid was investigated on the overall coefficient of heat transfer and pressure drop. The concentration increase causes both to increase at the same time. As a result, heat exchange efficiency and thermal effectiveness of the nanofluid were also analyzed. The highest thermal effectiveness (89%) and efficiency (1.244) occur at a minimum flow rate (2 liters per minute) and maximum weight percentage (0.145) Taguchi method was used to find the optimal conditions and confirm the validity of the experiments. It was also found that the decrease in the flow rate (98.56%) has a greater effect on the results of thermal effectiveness than the increase in concentration (0.404%). The error rate was 0.018%, which shows the accuracy of the results.

Hypersonic glide vehicles have been considered as untraceable systems with high maneuverability in recent years. On the other hand, flying in the range of maximum aerodynamic efficiency is important due to its effect on increasing range and improving air maneuverability. In this research, the hypersonic glider flight parameters including position and instantaneous velocity relative to the body profile and the amount of climb angle have been investigated using the point mass flight path determination method. The type of body profile has been selected due to the significant increase in aerodynamic efficiency and simplicity of redesign of other components, elliptic cross section. The study of aerodynamic coefficients in Mach 6.7 shows the high accuracy of the modified Newtonian method as the basis of calculations, which is then, corrected according to the flight conditions by the computational fluid dynamics. Due to the instantaneous changes in aerodynamic coefficients at each time step, depending on the altitude and Mach number, a two-way coupling between aerodynamic analysis and point mass flight is used. The results show a 54% increase in range and a 29% increase in incident speed with a decrease in body height. These values are 16% and 74% in the studies related to the radius of nose curvature and 44%, 25% in the study of the initial climb angle

In this paper, a device based on wearable sensors is introduced to describe quantitative body movements in different sports. This device can be an alternative to Image processing techniques. Image processing devices have always been used to describe quantitative body movements, which in addition to being costly, have to be used in specific conditions. The device is built from a number of wireless modules that are easy to use in real-world environments with no limitations. In this method, a quantitative description of movement is made by wireless modules and is performed by the data collected from these modules. In order to analyze the data that was extracted from an athlete's body movements with these wearable sensors, the outputs are simulated in Matlab, and some of its kinematic and kinetic parameters have been studied. Then, at the end of this paper, the quality of movement of a professional athlete and a beginner athlete are compared, and the result is shown. Kinematic and dynamic analyzes on the above activities showed the following The movements are generally correctly recorded. The kinematic analyzes performed for the various movements are consistent with the facts. For example, the kinematic analysis of the recorded motions showed that the coaching movement was more beautifully performed, and this was evident qualitatively during the movement.

Intraperitoneal injection of chemotherapy has been proposed as a promising method for the treatment of peritoneal metastasis, and its use in conjunction with cytoreductive surgery has shown interesting results in the treatment of patients. However, drug penetration into the tumor is limited in this method, and a better understanding of the factors influencing this low penetration depth is necessary. For this purpose, in the present study, a numerical model has been developed to investigate drug transport during intraperitoneal chemotherapy. Using this model, first, the Spatio-temporal distribution of free, bound and internalized drug concentrations are calculated. Then, by calculating the drug penetration depth and the fraction of killed cells, the effectiveness of the treatment is evaluated. Results of a 10mm tumor after 60 minutes of treatment showed that the drug is available only in a limited area of the outer region of the tumor. The values of fraction of killed cells and drug penetration depth were 1.2% and 11.4%, respectively, which indicates a poor treatment efficiency. The findings of this paper can be used in future numerical and experimental studies to gain a deeper insight into the mechanisms of drug delivery to the tumor by intraperitoneal injection.

In this paper, the active flow control of flow-induced vibration of a circular cylinder placed in the isothermal channel affected by jet injection is studied. The effect of flow injection on heat transfer inside the channel has also been examined. For this purpose, three slots are placed symmetrically in the upper and lower walls of the channel at distances 0, D, and 4D where D is the diameter of the cylinder from the side surface. The main innovation of the present study is to evaluate the effectiveness of the proposed flow control method in terms of channel height. For this purpose, 6 channels with heights of 5.5D, 6D, 7D, 8D, 9D, and 10D are considered to perform fluid-solid interaction simulations. The finite element method has been used to solve the flow and energy equations. For coupling the movement of the cylinder with the flow field, the dynamic mesh method is used. Numerical results show that for all channels with different heights, jet injection, either unilaterally or bilaterally, from slot 3, has no effect on displacement because the distance of the jet from the cylinder is large. By increasing the height of the channel, the injection velocity must be increased to completely reduce the oscillations of the cylinder.