Mahmoud Baghbanian; shaban ghavami jolandan; Seyed Mohammad Safieddin Ardebili; Seyed Majid Sajadiye
Abstract
Introduction In recent years, Underground heating systems are one of the cleanest and best types of heating systems which these techniques have been used in many greenhouses. In this method, a source of thermal energy, which is often a gas or diesel, is used to heat the fluid. Then, the heated fluid ...
Read More
Introduction In recent years, Underground heating systems are one of the cleanest and best types of heating systems which these techniques have been used in many greenhouses. In this method, a source of thermal energy, which is often a gas or diesel, is used to heat the fluid. Then, the heated fluid is transferred to the entire greenhouse through the pipe networks that are placed on the floor of the greenhouses and under the soil, and creates a pleasant heat. During the cold months of the year, having a proper heating system for the greenhouse is essential. A standard greenhouse heating system could improve the temperature inside the greenhouse and spread it evenly on the entire surface of the greenhouse and finally, it is very effective in the growth and quality of plants and products in all months of the year. Today, fluids play a very important role in industry, especially in heating systems. Common fluids such as water, ethylene glycol and motor oil have a limited conductivity coefficient. Therefore, using the above-mentioned fluids at high temperatures causes heat transfer problems. Nanofluids consist of very small particles (usually less than 400 nm) dispersed in a base fluid. The conducted research shows that due to the high thermal conductivity of nanofluids compared to common fluids, in the future nanofluids will become a new type of fluid used in advanced heat transfer for engineering applications. Therefore, according to the importance of this topic, in this research, the heating system of the greenhouse floor is simulated and analyzed using CFD technique.Materials and Methods In this research, in order to simplify the process of simulation, the inhomogeneity in the fluid flow is ignored and the single-phase flow is considered. In order to investigate the effect of each of the nanofluids on the fluid behavior and heat transfer of the pyramidal greenhouse, analysis and simulation of the greenhouse was performed based on three-dimensional computational fluid dynamics. First, the geometry of the control volume of a greenhouse was designed in Solidwork software, and in order to check the simulation, a pyramidal geometry was considered. The boundary conditions for the coldest day and night temperature in the year were extracted according to the environmental conditions by measuring the data of temperature, humidity and air flow. Two parameters of pressure drop value and Nusselt number were selected as target parameters in this research. The flow friction coefficient in the floor heating section was calculated through the pressure drop along the section and its hydraulic diameter. Single-phase fluid pressure drop in all pipes inside the thermal cycle was modeled in this section. Finally, the parametric analysis of the results and the comparison of the heating efficiency of the greenhouse floor for two types of nanofluid alumina and titanium dioxide in volume percentages of 1%, 2% and 3% were used. Besides, the effect of the mentioned parameters on the Nusselt number and in the flow of floor heating was investigated.Results and DiscussionBased on the obtained results, it was concluded that an increase in Reynolds number in all volume percentages leads to an increase in Nusselt number and alumina nanofluid has a higher Nusselt number than titanium dioxide nanofluid. Also, in both nanofluids assuming a constant inlet temperature of 40℃ and a diameter of nanoparticles of 5 nm, the Nusselt number also increased with an increase in the volume percentage of particles at a constant Reynolds number. According to the results obtained with the increase in the diameter of nanoparticles, the Nusselt number decreased for both alumina and titanium dioxide nanofluids, which is greater for titanium dioxide nanofluids. Considering the findings related to the pressure drop, with the increase in the volume percentage of nanoparticles in both nanofluids, the pressure drop increased, and this drop is more severe in the alumina nanofluid, and it could be attributed to the higher density and viscosity of the alumina nanofluid compared to the titanium dioxide nanofluid. The results related to the pressure drop showed that, with the increase in the volume percentage of nanoparticles in both nanofluids, the pressure drop increased, and this drop is more intense in the alumina nanofluid and this factor is attributed to the higher density and viscosity of alumina nanofluid compared to titanium dioxide nanofluid. On the other hand, the increase in Reynolds number in both nanofluids has resulted in an increase in pressure drop. The results related to the changes in the friction coefficient in terms of Reynolds number in different volume percentages show that the coefficient decreases with the increase in Reynolds number, and these changes are more intense at lower Reynolds numbers. By comparing the performance coefficient between alumina nanofluid and titanium dioxide nanofluid, it can be concluded that the average value of this coefficient is 14% higher than other nanofluids for alumina nanofluid. But, the sensitivity of the performance coefficient of titanium dioxide nanofluid compared to alumina nanofluid is more intense to the changes of Reynolds number.Conclusion Due to the production of greenhouse products in all seasons and the necessity of precise greenhouse control, it can be concluded that dealing with new and advanced methods in the management and optimization of the country's greenhouses is importance. The results of the present research show the fact that the simulation of heating from the greenhouse floor and its various aspects can be a suitable measure to check the uniformity and proper distribution of heat inside the greenhouse. In order to improve the efficiency of thermal equipment, using nanofluids with higher thermal ability is essential. Besides, comparing the performance coefficient of the system due to the use of nanofluids indicated the high efficiency of the use of nanofluids in comparison with pure water in the greenhouse floor heating system.
M.J. Malekzadeh; M. Kiani Dehkiani; M. Sajadiyeh
Abstract
Introduction The limitation of fossil fuels and environmental pollution by using them have encouraged researchers toward renewable fuels. The most important renewable fuels are bioethanol, biodiesel and biogas. Biogas is a gas that is produced from biodegradable fermentation, agricultural products ...
Read More
Introduction The limitation of fossil fuels and environmental pollution by using them have encouraged researchers toward renewable fuels. The most important renewable fuels are bioethanol, biodiesel and biogas. Biogas is a gas that is produced from biodegradable fermentation, agricultural products and wastes, animal waste and urban waste by anaerobic digestion. One of the products that has a significant amount of waste is sugar cane. This plant is widely cultivated in Khuzestan Province and annually produces a lot of waste which is currently not useful. One of the most important wastes is bagasse. Bagasse is the solid residues after crushing sugar cane and extracting it. Bagasse is composed of cellulose (45%), humiculus (27%), lignin (21%), extract (5%) and a small amount of inorganic salts (2%). A lot of bagasse is produced in sugar cane production process (about 240 kg with a moisture content of 50% per ton of sugar cane). Every year, a lot of bagasse is wasted. One of the most useful ways is to convert it into biogas and provide the percentage of the required thermal and electrical energy of the plant. Therefore, in this study, the effect of temperature and percentage of cow manure as an additive on biogas production from bagasse sugar cane was investigated. Materials and Methods The used bagasse in this research was provided from Farabi industry and Cultivation, located 48 km from Ahwaz, and a cow manure was provided from a livestock farm in Hamidieh, Ahwaz. In order to increasing the production efficiency of biogas, sugar cane bagasse was milled. Batch reactors of 4 liters was used to produce biogas from sugar cane bagasse. To control and maintain the working temperature, the reactors were placed in a water bath and the temperature of the bath was kept constant by using the thermal element and the thermostat. Cow manure was used to provide source of microorganisms. Cow manure with 5, 10, 15 and 20% weight percentages (B5, B10, B15 and B20) was blended with bagasse (numeric index of B indicates the percentage of cow manure in the blends). Sodium bicarbonate was used to control the pH of the reactors. Stirring was carried out manually in order to homogenize the materials and prevent the formation of hard layer at the top of the reactors. The amount of produced biogas was daily measured by water displacement method. Another measured parameter was the total Solid Index (TS), which represents the percentage of organic and inorganic matter for materials of the reactors. The experiments were carried out by using eight reactors for 30 days and the results were analyzed by completely randomized factorial design. Results and Discussion The results of variance analysis of biogas production in terms of bagasse to cow manure ratio and temperature changes showed that they had a significant effect at 1% level on biogas production. Considering the interaction effects of temperature and bagasse to cow manure ratios have a significant effect on the produced biogas at a 1% level. The results showed that with increasing in the percentage of cow manure in the materials, the amount of biogas production increased at both temperatures, so that by increasing the ratio of cow manure in the blends from 5 to 20% at 35 and 45 ° C, the produced biogas increased by 27.78% and 81.83%, respectively. By increasing the percentage of cow manure in the blends, the number of microorganisms in the digestion increased, and as a result of their activity, the amount of produced biogas increased. It was also observed that with increasing the temperature of digestion from 35 ° C to 45 ° C, the biogas production for B5, B10, B15 and B20 blends increased by 19.82%, 22.5%, 15.85% and 80.8%, respectively. The highest amount of cumulative production of biogas was obtained 0.3 m3.kg.VS-1 for 45 ° C and 20% cow manure to bagasse ratio. Conclusion In this research, the effect of cow manure in blend of sugar cane bagasse and temperature on produced biogas was investigated. The experiments were carried out at two temperatures of 35 and 45 ° C, and four blends with different weight percentages from cow manure to bagasse (5, 10, 15 and 20 percent). The results showed that with increasing the percentage of cow manure in blends, the amount of biogas production increased. Also, with increasing temperatures from 35 ° C to 45 ° C, the production of biogas in all blends increased.
N. Hafezi; M. J. Sheikhdavoodi; S. M. Sajadiye; M. E. Khorasani Ferdavani
