نشریه مهندسی مکانیک تبدیل انرژی
سال نهم شماره 2 (پیاپی 31، تابستان 1401)

In this study, modeling, optimization and economic analysis of a multiple generation system based on the use of solar energy using thermoelectric in the Rankin organic cycle. The system under study consists of solar panel subsystems, Rankin organic cycle, absorption chiller and PEM electrolyzer. The fluid used in the Rankin organic cycle contains refrigerant R123. Thermodynamic software for solving EES engineering equations has been used to model the studied system and also to obtain the results of system analysis. In this study, a comparison was made between two systems with the presence of thermoelectric and the system without the presence of thermoelectric and the use of condenser in the Rankin organic cycle and according to the results, the system with thermoelectric presence has better performance. According to the studies performed on the parameters affecting the system outputs, we can name the inlet temperature to the turbine and the area of ​​the solar panel. According to the system exergy degradation study, the solar panel has the most exergy degradation and the least exergy degradation is related to the pump. The NSGA-II genetic multi-objective algorithm is used to optimize the objective functions of the designed system. The two opposite objective functions studied in this study were to increase exergy efficiency and reduce cost rate. The Pareto diagram was obtained in order to determine the best values ​​for the objective functions of the problem, which are the system exergy efficiency and the system cost rate. Finally, the optimum value of the exergy efficiency was 18.25% and the cost rate was $ 1.87 per hour. Also for case study in this study, Khuzestan province and Dezful, Ahvaz and Abadan cities were selected. The results of a case study showed that this system has a high performance in Khuzestan province and the best results were obtained in Abadan.

One of the dangers that always threatens buildings is the risk of fire. Smoke is generated after a fire. In most cases, smoke generated by fire poses a far greater risk to human life than fire. Therefore, by controlling the smoke, the building and the people living in it can be protected and the damages caused by the fire can be reduced. In this study, smoke distribution in the parking lot of a complex was investigated using PyroSim software. Navier-Stokes equations for energy, mass survival were used to solve and large vortex simulation model was used for turbulence. Two scenarios were considered to investigate the fire. In the first scenario, parking without ventilation system was studied and in the second scenario, it was studied with ventilation system. Exhaust fan was used to evacuate the smoke and sapphire 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 visibility is 2 meter. In the second scenario, the smoke concentration is 0/0002 mol / mol, which is 93% better than the first scenario. Also, the visibility was initially reduced to 2 meters and then increased to 20 meters in 600 seconds with the activation of the exhaust fan and smoke evacuation. In fact, visibility improved by 900% compared to the first scenario. Reducing the concentration of smoke and increasing visibility make it easier for people to evacuate during a fire, and people are able to live longer in a fire.

Nowadays, due to the shortage of energy resources, the industries pay more attention to the energy efficiency. in terms of transportation, reducing of energy consumption and increasing the speed of marine vessels and submarines, the surface friction resistance holds an important role. riblets surfaces are a passive method that have ability of surface drag reduction. This study, investigates numearically, the drag reduction of 4 different and new geometries of riblets in different dimensions and velocities. the flow is in the laminar regime range and riblets are aligned perpendicular to the flow direction. Also the distribution of shear stress and static pressure on the riblet surfaces are examined. The Results showed that geometries 1 and 4 have a higher drag reduction (about 10/7% and 10/2%) relative to the geometries 2 and 3 (about 7/7% and 4/4%) Respectively. Unlike geometries 1 and 4, geometries 2 and 3 have a higher viscose force relative to the pressure force on their surfaces. Also the study of speed changes showed that geometries 1 and 4 have a higher drag reduction in each speed respectively.

This article has been investigated the effect of natural light and appropriate skylights on improving daylight performance and reducing energy consumption in classrooms.In order to implement the country’s general environmental policies and reduce school costs with the optimal use of energy, daylighting is a factor for participation in reducing energy consumption and a step towards achieving the goal of 1404. This article’s purpose is to evaluate daylighting performance and provide solutions to improve visual comfort. In order to achieve this goal, Shahid Mahdavi preschool in the northwest of Tehran was selected as a case study due to its special physical characteristics such as light shelf, trombe wall, light shelves, geometric designs on the roof and diagonal atrium. Based on the quantitative research method, a case sample was selected and light metering was performed using light measuring instruments in the two southern classes of Mahdavi preschool with and without light shelves on January 12, 2021 with sunny sky conditions and at specific times. Climate Studio software was used to simulate and analyze the results. Brightness rating was used by the rating indicator in green buildings (4.1 LEED). The qualitative method is also based on inductive reasoning and using extensive library studies. Finally, the results of field information and software analysis were reviewed and the useful daylight illuminance factor was evaluated in all 4 models, which was in the acceptable range. Therefore, a combination of south windows and light shelves, along with semi-transparent moving curtains, causes a uniform distribution of daylight. Using atrium in the north side of the classroom will increase lighting performance and its uniformity. Suggestions for improving visual comfort are presented in this study.

Using solar dryers in areas with high solar intensities is an economical way to dry food. Drying performance factors depend on factors such as the geometry of the dryer, the drying material and the climate of the area. Therefore, the aim is to simulate fluid flow and heat transfer in a solar dryer to dry the mint plant in Kerman region, which was done using computational fluid dynamics (CFD). In this study, by adding a ventilation fan above the dryer chamber, the dryer temperature was controlled and improved during the hot seasons of the year. This simulation is done as much as possible by considering the actual operating conditions and even the material and materials used in the construction of the dryer so that the results are as close to reality as possible. By validating the results obtained from the numerical simulation method with the data presented experimentally in other articles, it was proved that by using the dynamic method of computational fluids, the behavior of real dryers can be simulated with high accuracy. The advantage of using the simulation method over making a laboratory sample is that in this method it is possible to observe the pattern of air flow through the inner and outer part of the dryer, evaluate the pattern of temperature changes and also the amount of radiation received by the dryer for a full day and generalization. It exists for a year with much lower time and cost. Due to the fact that the performance of the system can be predicted for one year, as a result, it is possible to determine the appropriate or inappropriate time periods of this device for drying mint. It was also stated in this study that by installing a fan to suck the air currents of the dryer, the drying performance of mint can be improved and the heat transfer in the dryer can be improved, especially in the hot months of the year. It is also shown that using the installed fans, the air temperature of the dryer can be reduced to 18 degrees Kelvin, and as a result, a more desirable dried sample can be achieved.

In the present research, the behavior and flow pattern of a Counter current Gas-Liquid Two-Phase Flow in different Transparent Vertical pipes made from Plexiglas with inner diameters of 26 mm and 44 mm were experimentally investigated. The considered fluids included the water and the air, and the results were obtained for a total of 304 select cases differing in the apparent velocities of the water and the air. The air and the water were flown from separate inlets upward and downward, respectively. The apparent velocities of the air and water in the 26 mm pipe were investigated in the ranges of 10.47 – 26.17 m/s and 0.06 – 0.36 m/s, respectively. The corresponding ranges for the 44 mm pipe were  3.56 – 9.14 m/s and 0.02 – 0.12 m/s, respectively. The liquid film thickness in the annular flow was measured by the Quick shut valve technique. The Entrainment fraction was measured Isokinetic-sampling technique. Provision of the Counter current Gas-Liquid Two-Phase Flow conditions in terms of initial flow orientation and the investigation of the effect of this design on the flow patterns, liquid film thickness, and the Entrainment fraction are the major innovations of the present research.In contrast to previous research works, the present study sets the scene for a more accurate evaluation of the annular flow pattern for calculating the liquid film thickness and the Entrainment fraction by designing the initial inlet orientation. Based on a comparison, as far as the calculation of the Entrainment was concerned, the results of the present research exhibited good agreement with the Oliemans model in the 26 mm pipe and the Wallis model in the 44 mm pipe, and when it came to obtaining the liquid film thickness, the results were consistented to those of the Schubring model.It is shown that the predictions of this new correlation outperform those from previously reported studies.