نشریه مهندسی مکانیک تبدیل انرژی
سال نهم شماره 5 (پیاپی 34، زمستان 1401)

Nowadays, the issue of increasing efficiency and improving energy consumption in industry has become more and more important to researchers. For this reason, in this study, a numerical analysis of heat transfer and fluid flow inside a tube containing a porous medium and the use of nanofluids were performed. Simultaneous use of porous structure and nanofluid as a fluid is one of the innovations of this research that significantly increases heat transfer in the pipe. The modeling was performed in two dimensions with the assumption of slow flow, at a constant temperature and with the presence of water-silver nanofluid to improve heat transfer. The main purpose of this study was to achieve the minimum coefficient of friction and the maximum Nusselt number at the same time as two opposing objectives to reduce the flow resistance in the pipe and increase heat transfer. Speed ​​profiles; Two-dimensional tube pressure and temperature were obtained in volume fraction, porosity coefficient and different Darcy numbers. Then the Nusselt number and the coefficient of friction were investigated. The results of this study showed that by decreasing the Darcy number, the value of the Nusselt number increases. Also, the amount of coefficient of friction has increased somewhat. The reason for the increase in heat transfer can be related to the increased interaction between the nanofluid and the porous material. In fact, larger Darcy numbers have lower energy recovery rates than wasted energy. Another reason for the increase in Nusselt number is the decrease in temperature. The reason for the increase in the coefficient of friction can also be related to the increase in speed, pressure and Reynolds number along the pipe.

Due to the importance of pipelines as vital arteries for fuel and energy supply in the world, maintenance, stability, continuity of transmission, supply of refinery feeds and fuel supply to various industries is very important and necessary. The present study was conducted to analyze the performance of pigs and to investigate the effect of factors affecting pigging operation in oil pipelines. In this research, by performing experiments in real and operational conditions, the results of pigging operation in product pipelines in different diameters and lengths have been investigated, so that the effect of fouling of the inner wall of the pipeline on the flow rate, pump required power in pump house and pressure drop in different products with different physical conditions as well as calculation and evaluation of pigging speed in each operation and the effect of pig weight on pigging speed and power required in pump houses are presented. The results of this study show that pigging in a 14-inch oil pipeline with a length of 109 km and a flow rate of 360 cubic meters per hour, equivalent to 54,330 barrels per day, which has 0.4 cm of fouling, prevents a reduction in volumetric flow rate of 23 cubic meters per hour, equivalent to 3460 barrels per day, increases the required power of the pump in the pump house by 35.79 kW and increases the pressure drop by 8.9%. Also, by examining the effect of pipeline slope on the pressure behind the pig, knowing that the pump power in the pump house does not change and the pig speed is the same along the route, it is determined that increasing the height of the pipeline causes the static pressure head converted to a height head, and if the pig enters downhill areas, it will cause the height head converted to pressure behind the pig.

Accurate determination of the thermophysical properties of nanofluids and the parameters affecting them are of particular importance in the industrialization of nanofluids. One of the most important parameters affecting properties such as viscosity and thermal conductivity is the pH of the nanofluid. In this research, the pH levels of three metal oxide nanoparticles including aluminum oxide (AL2O3), magnesium oxide (MgO) and zinc oxide (ZnO) dispersed in distilled water were measured in the temperature range between 303 K to 333 K and concentration range between 0.01 to 1% volumetric concentration. For more accuracy, pH measurements were performed twice for each sample and the mean value for the final pH was recorded. The results showed that with increasing the temperature by about 10%, the pH values ​​of aluminum oxide, magnesium oxide and zinc oxide nanofluids decreased by 37, 11 and 9%, respectively. Also, the addition of aluminum oxide nanoparticles has given acidic properties to distilled water, but the addition of magnesium oxide and zinc oxide nanoparticles to distilled water have given alkaline properties to the suspension. Finally, using the experimental results obtained for three metal oxide nanofluids, an equation for predicting pH as a function of concentration and temperature was proposed.

One of the main problems of human beings today is the use of fossil fuels. To solve this problem and worry about the energy crisis due to lack of these resources, renewable energy can be replaced. One of the largest sources of clean energy is solar energy, which can be used in solar thermal power plants. In this study, aluminum oxide nanofluid with water has been used in the linear parabolic solar thermal combined heat and power plant with Rankin cycle and the energy and exergy efficiency of this power plant has been used by the nanofluid and the storage tank has been investigated. The plant also has an energy storage tank with molten salt to provide the amount of energy needed at night in the absence of sunlight. The energy analysis and exergy equations of this power plant have been done with the help of EES software. The result of this analysis demonstrate that the exergy efficiency of the solar system is 16/27% and the energy efficiency is 59/72%.

In this experimental study, the effect of using a heat exchanger with louvered strip inserts louvered strip inserts on flow and heat transfer utilizing various types of nanofluids is studied numerically. The continuity, momentum and energy equations are solved by means of a finite volume method (FVM). The top and the bottom walls of the pipe are heated with a uniform heat flux boundary condition. Two different louvered strip insert arrangements (forward and backward) are used in this study with a Reynolds number range of 10,000, 15,000, 20,000, 25,000, 30,000. The effects of various louvered strip slant angles and pitches are also investigated. Three different types of nanoparticles, Al2O3, CuO and ZnO with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 20 nm to 50 nm, dispersed in a base fluid (water) are used. The numerical results indicate that the forward louvered strip arrangement can promote the heat transfer by approximately 77 % at the lowest slant angle of α=10° and largest pitch of S=50 mm. The maximal skin friction coefficient of the enhanced tube is around 5.7 times than that of the smooth tube and the value of performance evaluation criterion (PEC) lies in the range of 1.34–1.57. It is found that Al2O3 nanofluid has the highest Nusselt number value, followed by ZnO, and CuO while pure water has the lowest Nusselt number. The results show that the Nusselt number increases with decreasing the nanoparticle diameter and it increases slightly with increasing the volume fraction of nanoparticles. The results reveal that there is a slight change in the skin friction coefficient when nanoparticle diameters of Al2O3 nanofluid are varied.

It is impossible to develop the application of solar energy over the country and, particularly, to develop the establishment of solar power stations without solar radiation potentiometry, accurate identification of regions with appropriate radiation, or extraction of credible data that can specify the amount and distribution of this energy. This paper investigated the optimal design and feasibility of establishing a two-hundred-kilowatt power station in the city of Sanandaj, Iran considering the relevant economic examinations. In this paper, the PVsyst software was used for calculation of received solar energy and optimal design of the power station, and RETScreen was used for examination of the economic feasibility. For this purpose, the photovoltaic array layout was designed and optimized to prevent shadows cast by modules and occupy the smallest possible area given the geographic location of the site in Sanandaj where the power station was to be established. This would mitigate system costs and raise the productivity of the power station using the available solar potentials. Next, the output curve, involving annual energy production, loss, and cast shadow, were extracted, analyzed, and used as an input to the economic feasibility study. The results also demonstrated that the return of capital exhibited a favorable rate given the high capacity of energy production in the area under investigation.