نشریه مهندسی مکانیک تبدیل انرژی
سال دهم شماره 2 (پیاپی 36، تابستان 1402)

The aim of the present study was to manufacture porous Si3N4 ceramic through gel-casting of Si powder and RBSN method. The effects of gel solution pH and amount of sintering aids were investigated. Acrylamide  and Methylenebisacrylamide were used as monomers solution (ratio of 15 AM: 1 MBAM). Al2O3, Y2O3, and SiO2 powders (as sintering aids) and Si (as main powder) were added to obtain a slurry with solid loading of 60wt%. Heat treatment and nitridation process were carried out up to 1350ºC and in N2 atmosphere for 22 hr. Results of XRD analysis showed that the final phase in all samples was metallic Si and β-Si3N4 along with some percentages of cristobalite. Analysis of the effects of pH on the final phase of  the samples made of Si powder (pure and without sintering aids) revealed that preparation of the gel solution in acid environment (pH:2~3) led to an increased intensity of β-Si3N4 phase peaks and reduced metallic Si phase in comparison with the alkaline environment (pH:11~12), and the slurry prepared in the acidic environment reacted more effectively with N2 atmosphere. Regarding the effect of sintering aids on the formation of the final phase, the findings suggested that increasing the amount of SiO2 and reducing Al2O3 and Y2O3 did result in the formation of more β- Si3N4 (from 66% to 80%) and decrease in the Si metal (from 18% to 7%). Moreover, increased amount of sintering aids and formation of more liquid phase facilitated the proces of β-Si3N4.

Energy field studies and their calculation for the coming years in buildings show that the effects of climate change, especially the problem of global warming, play an essential role. This research includes two cities of Tabriz and Ahvaz with two different climates and a similar building under scenario A2 and two climatic data periods. It was used. The goal is to evaluate the impact of new and old data on energy consumption in the coming years. To predict climate data such as temperature, radiation, humidity, etc., from the CCWorldWeathergen software and also to prepare the 2TMY file from the TMY Creator software. used. Energy Plus software has been used to simulate energy consumption. The results show that using newer data provides a more accurate estimate than the old data. Due to the increase in temperature in the coming years due to global warming in the two cities of Ahvaz and Tabriz, energy consumption for heating and cooling will decrease. For this purpose, taking into account the hot and cold seasons in the forecast years (2080-2050-2020), it has been proven that for the city of Ahvaz during the year 2080 compared to 2020, a 24% reduction in heating energy consumption and a 5% increase in the cooling part, we will have a 19% decrease in heating energy consumption and a 7% increase in the cooling amount for the city of Tabriz during the year 2080.

The quality of drying in solar dryers depends on the heat transfer inside the dryer and performance parameters such as pressure drop and efficiency factor. Therefore, the purpose of this research is to investigate the effect of dryer geometry, vortex flow generator, radiation intensity and Reynolds number on heat transfer, pressure drop and performance evaluation coefficient of solar dryer. For this purpose, three different geometries were considered, including a channel with a completely smooth surface, a channel with a curved surface, and a channel with a flow perturber, all three of which were exposed to specific and uniform solar heat flux radiation. For each of the above modes and for Reynolds numbers 3000, 4500, 6000 and 7500 and solar radiation intensities of 700, 800, 900, 1000 and 1100 wat/m2, the amount of average Nusselt number, pressure drop inside the channel and performance evaluation coefficient calculated. The results showed that the use of a vortex generating channel and a channel with concave surface compared to a simple channel increases the amount of heat transfer. Also, as the Reynolds number of the flow increases, while the pressure drop increases, the average Nusselt number also increases.

In this research the exergy analysis of a biomass drying system were investigated experimentally by varying some drying parameters and exergy loss, exergy efficiency as the two principal factors in analyzing systems were calculated for this dryer. Exergy is defined as useful work potential of a system in a specified state. Exergy analysis is a powerful tool in design and optimization of energy systems. Biomass, one of the most available renewable energies is defined as organic materials, such as wood, agricultural wastes, and municipal biowastes, especially when used as a source of fuel or energy. The moisture content of fresh woody biomass is typically high and it is beneficial to dry woody biomass before the process of energy yield for better performance and efficiency. In this research Drying experiments were performed in a domestic dryer. In these experiments three different inlet air temperatures, 60, 80 and 100oC and two different particle sizes of fine and coarse were considered. The results showed that the higher inlet air temperatures caused higher values of exergy loss and lower values of exergy efficiency. Also the fine particle size decreased the exergy loss and increased the exergy efficiency. Variation of parameters has changed exergy efficiency from 22 to 47 percent.

The increasing population of the world, the change of style and the limited number of natural resources and energy all make freshwater industrial productions the main contenders for the cost-effective production of freshwater. In this research, the combination of combined cycle power plant (CCPP) using multiple effect distillation (MED) and reverse osmosis (RO) desiccation techniques is investigated through normal and advanced exergy, exergy-economic and exergy-environmental comprehensive analysis. First, CCPP thermodynamic modeling is done using mathematical programming method. Then, a mathematical model is presented to integrate the existing CCPP with MED and RO desalination plants. Finally, the aforementioned normal and advanced analyzes are performed to evaluate the main performance parameters of the integrated CCPP system and MED-RO desalination system, and to identify potential technical, economic, and environmental improvements. A case study is also presented about the Shahid Salimi Neka power plant located in the north of Iran along the Caspian Sea.The mathematical modeling method for this integrated system is solved in "MATLAB" program and its results are validated by "Thermoflex" software. The results show a 3.79% increase in fuel consumption after combining CCPP and water desalination facilities. The exergy efficiency of the advanced system is 42.7% and the highest combustion chamber exergy destruction cost is $1.09 per second. Economic and environmental analyzes of the integrated system also show that gas turbines have the highest investment cost ($0.047 per second). At the same time, the MED system has the highest environmental impact rate, i.e. 0.025 points per second.

In this article, the authors investigate free convection heat transfer in a cavity containing water-copper nanofluid affected by solid wall conduction using numerical methods. The governing equations were solved using a dimensionless numerical method and a simple algorithm. The authors investigated the effect of important parameters, including the volume fraction of nanoparticles and the ratio of the thermal conductivity coefficient of the solid region to the nanofluid, on the flow and heat transfer of the free movement of the chamber. The investigations were carried out at Rayleigh number Ra = 105, volume fractions ϕ=0, ϕ=0.02 and ϕ=0.05 for the ratio of thermal conductivity coefficients Kr =0.1, Kr =1 and Kr =10. The results showed that with an increase in the volume fraction of nanoparticles and the ratio of the conduction coefficient, the speed and power of the flow increased on average. Additionally, an increase in the volume fraction of nanoparticles and the ratio of the conductivity coefficient led to a decrease in the dimensionless temperature of the nanofluid. Moreover, compared to the case of Kr = 1, increasing the volume fraction of nanoparticles and the values of the ratio of the conduction coefficient led to higher Nusselt values along the walls, indicating a higher heat transfer rate passing through the interface of solid and nanofluid. Therefore, a higher ratio of the conduction coefficient can be useful for cooling and reducing the overall temperature of the cavity