جستجوی مقالات مرتبط با کلیدواژه "کلکتور خورشیدی" در نشریات گروه "مکانیک"

This study investigates the comparative effects of carboxyl-functionalized multi-walled carbon nanotube (MWCNT)/water nanofluids and titanium dioxide (TiO₂) /water nanofluids in direct absorption parabolic solar collectors. To achieve this, a standard testing apparatus was constructed, and the thermal and exergy efficiencies of the collector were calculated using nanofluids at various concentrations. UV/Vis analysis was used to analyze the radiative properties of the nanofluids, and their thermal conductivity was also measured. Experiments were conducted under laminar flow conditions with flow rates of 20, 60, and 100 liters per hour and inlet temperatures of 20, 30, and 40 °C under real conditions with direct solar irradiation. The highest thermal efficiency recorded for the carbon-based nanofluid was 44.96%, while the titanium-based nanofluid achieved a thermal efficiency of 34.98%. Given the substantial improvement in efficiency compared to the base fluid (distilled water), the combined effect of using both nanofluids was also examined, resulting in a maximum thermal efficiency of 48.77%. The exergy efficiency at the highest flow rate and inlet temperature for the base fluid, TiO₂ nanofluid, MWCNT nanofluid, and the hybrid nanofluid were 2.61%, 4.98%, 6.68%, and 7.26%, respectively. The pressure drop of all nanofluids in the absorber tube ranged from 5 to 39.6 Pascals. The studied nanofluids enhance the thermal performance of the system and create low pressure drop, indicating their high efficiency in direct absorption solar collectors.

In this paper, for the first time, to investigate the potential and feasibility of using PVT-ST in relatively hot and moderate weather conditions, it has been studied in four different cities and compared with two common solar systems, PVT and ST. Therefore, the performance of the system is evaluated in terms of the first and second laws of thermodynamics based on the FORTRAN code, and then using the obtained results to analyze the energy consumption of a residential unit in 4 different cities using Carrier software. In addition, the effects of the mass flow rate of the working fluid, in both laminar and turbulent regimes, on the module performance are investigated. Considering the mass flow rate of 0.0304 kg/s (turbulent regime) in July, the thermal efficiency of ST, PVT-ST, and PVT systems are 85.7%, 78%, and 72.9%, respectively. Finally, the investigation of system performance in different cities shows that this system can produce the highest thermal power in Basra. However, the maximum power generation with an average of 77 watts per square meter belongs to Baghdad. Finally, the energy supply of a residential house by combined systems has been investigated. By considering 8 integrated systems, most of the electricity consumption of a residential house can be supplied, but it should be kept in mind that during the peak hours of consumption if this amount of electricity production does not meet the capacity of the house, a fraction of the electricity shortage can be supplied from the stored electricity.

The flat plate solar collector as a heat exchanger is responsible for absorbing the radiant energy of the sun and transferring heat to the working fluid. Water and air are among the most common fluids that flow as the working fluid among these collectors. Considering that efficiency is one of the most important criteria in the evaluation of these collectors, in this study, four fluids from the group of organic liquids and therminol oils were selected and their thermal performance was investigated on the efficiency of a flat plate solar collector. The results obtained in this article show that organic liquids are more efficient compared to therminol oils and have better performance in absorbing heat from the collector and transferring it to the working fluid, and the reason for this is the lower specific heat of organic liquids. It is raised at working temperature. Also, with the increase in the intensity of solar radiation, the energy efficiency and exergy of the collector will decrease and the amount of heat transferred from the working fluid to the collector will increase, and with the increase of the ambient temperature, the exergy efficiency and useful exergy of the collector will decrease. The average values of energy efficiency and exergy due to the choice of working fluid in this design show that organic liquids can be the best working fluid in these type of collectors after water.

The air humidification-dehumidification method is a good option for decentralized freshwater production because of no need for high temperature operation. The main disadvantage of these systems is their dependence on direct sunlight. to solve this problem, using the sun's thermal energy storage during the day and using this energy during the night can be a very good option that can be achieved using phase change materials. In the present work, it is also possible to continue the desalination process after sunset, by equipping the solar collector with phase change material from two different types of paraffin wax. MATLAB software has been used to solve the equations governing the components of the desalination system. According to the results, the temperature of the output water from the solar collector plays a significant role in the amount of fresh water produced. The results also confirm that the use of phase change material leads to more than 9% increase in fresh water production. Another important result is that in the phase change materials the melting process speed is substantially higher than the freezing process speed.

In this paper, the thermodynamic performance of a solar assisted high temperature heat pump with water heating application is investigated. The comprehensive simulation and analysis of energy and exergy was done by Haysis and MATLAB software. This analyzes produce some convincing results due to the use of environmentally friendly and environmentally friendly energy sources. Thermodynamic analysis in thermal energy systems is very important due to the identification of high-consumption equipment and determining the location and level of inefficiency of the system equipment. According to the results of the system energy, among the equipment of the P100 pump system and the HX1 heat exchanger, it has the lowest and the highest energy consumption, respectively. 2.09 and 22669.11 kW. Also, the exergy analysis shows that the highest amount of exergy of currents with 367092 kW is related to the input flow of the tank and the highest exergy destruction of the equipment is 15563 kW related to the solar collector. This exergy destruction of the solar collector with temperature changes throughout the year with the lowest destruction in July at the rate of 14342 kW and the highest exergy destruction of 15678 kW relates to the month of June. Among the rotating equipment, the most exergy destruction is related to the k101 compressor of the water heat transfer cycle.

The purpose of this study is to evaluate the potential of solar nanofluids (liquid with dispersed nanoparticles) for direct absorption of solar radiation and steam production. At present, solar thermal energy systems suffer great losses due to heat transfer processes, therefore, the development of nanotechnology and its achievements such as various nanoparticles, has created high hopes to increase the efficiency of solar collectors through direct absorption of sunlight. In order to make optimal use of solar nanofluid systems, it is necessary to identify and study them. In this research, four different nanofluids have been synthesized, identified and evaluated. Two of them were water-based nanofluids and the other two were thermal oil-based nanofluids. Also, the optical properties of nanofluids were measured at room temperature with a spectrophotometer and compared with the base fluid. The optical properties, in addition to being measured at room temperature, have also been evaluated after heat treatment on nanofluids at high temperatures. This temperature increase is intended to recreate operating conditions for those closer to the actual applications. DLS measurements show a similar hydrodynamic average of 138 nm for the sample containing SDS and 135 nm for the sample containing SDS and PVP.

One of the applications of solar energy is solar absorption cooling system in air conditioning systems. Energy for these systems is supplied using a solar system. In this research, two different problems have been investigated by changing the conditions of an absorption system. So, the pressure in the low pressure region in one of the problems and the pressure in the high pressure region in the other problems is constant. Therefore, the best operating mode can be investigated for the selected system. According to the conditions of this problem, the best operation conditions for this selected solar absorption system were evaporator temperature of 7°C and heat flux of 530W/m2. Finally, some important parameters of the solar collector (glass cover thickness, distance between the absorber pipes, distance between the absorber plate and the glass cover, specific heat capacity of the fluid, heat transfer coefficient of air, heat transfer coefficient of fluid) are optimized to supply the required load of the absorption system. According to the results, the glass cover thickness, the distance between the absorber plate and the glass cover, and the heat transfer coefficient of the fluid are in the optimal conditions. But, the heat absorbed in the collector can be increased by about 10% by changing the distance between the absorber pipes, the specific heat capacity of the fluid, and the heat transfer coefficient of the air. Also, the present results error were about 1% and 1.5% for modeling of the solar collector and the absorption system, respectively.

This paper aims to compare the electrical and thermal performance of different designs of hybrid photovoltaic-thermal collectors. The main advantage of photovoltaic-thermal collectors in comparison to common photovoltaic modules is decreased cell temperature and an associated increase in their electrical efficiency. In addition, the combination of photovoltaic module and solar thermal collector makes it possible to produce both heat and electricity in a single device and reduces the area required for collector and module installation. In this research, the electrical and thermal efficiency of different designs of photovoltaic-thermal collectors is investigated. The heat transfer fluid considered for heat dissipation is water. A theoretical analysis of eight types of different photovoltaic-thermal collectors, including sheet and tube with spiral (circular cross-section) and parallel tube (circular, square and rectangular cross-sections) designs were implemented based on thermal modeling. These include collectors with different flow paths and different cross-section geometries. According to the results, sheet and tube design with circular cross-section has minimum and sheet and tube design with rectangular cross-section has maximum thermal and total efficiency. Also, glass cover reduces the electrical efficiency and increases the thermal efficiency and total thermal energy.

The compressor inlet air cooling, especially in hot climates, has significant effect on the power output augmentation of the gas turbines. The typical methods of inlet air cooling mainly consist of evaporative cooling and fogging systems and chillers. The water consumption in evaporative cooling and fogging systems and power consumption and investment cost in vapor absorption and compression refrigeration systems are high. So, the purpose of this article is to investigate the possibility of using the night sky radiative cooling system for cooling the intake air of the gas turbine compressor. This mode of refrigeration is among the renewable and passive cooling technologies. In this method, the circulating water used to cool the intake air of the compressor, at night and in the exchange of radiation with the sky, is cooled using flat plate solar collectors without glass and then returns to the storage tank for reuse on the next day. The effect of parameters such as the number of collectors and their arrangement in series or in parallel on the cooling capacity of system is investigated. Also, the required storage tank volume for returned water from collectors is calculated. The results show that, the compressor’s intake air cooling for six hours a day needs a water storage tank with a minimum capacity of 1000 cubic meters. Also, by using 400 parallel collectors and a 1000 cubic meter storage tank, the amount of power produced increases by an average of 2 MWh.

The aim of this paper is to compare the electric power output of the photovoltaic Module (PV) and photovoltaic-thermal water collector (PV/T). The electrical efficiency of photovoltaic Modules is greatly reduced by increasing their surface temperature. The hybrid photovoltaic-thermal collector consists of a PV Module with a thermal collector attached behind it. The circulating fluid in the collector removes heat from the module and increases its electrical efficiency. In the first part of this paper, a theoretical analysis of a liquid PV/T collector is made based on thermal modeling using the first law of thermodynamics. An unglazed hybrid photovoltaic-thermal collector with serpentine tubes has been designed and manufactured to validate the theoretical results. Then the collector has been tested for three days and results have been compared with a sample photovoltaic module. The theoretical calculations were performed using Matlab software and its results showed good agreement with experimental results. Our finding shows a maximum increase of 6% in the electrical efficiency of PV/T in comparison to the PV module. At the same time, the water temperature has increased by 5°C.

In this paper, an exergoeconomic analysis of a cogeneration system of heating, cooling and power has been done for the needs of a 100-bed hospital. The electricity required for the hospital is produced by an organic Rankine cycle. Using the heat exchanger in the cycle, the heating load of the hospital is provided. The steam output of the turbine has also been used to launch a cascade refrigeration cycle and to provide a cooling load for the hospital. The combination of absorption and compression refrigeration cycles provides for the preservation of some of the drug items that should be stored at very low temperatures. To supply heat in the boiler of this plant, three types of collectors including linear parabolic, Fresnel Linear Collector and Dish Collector have been used and compared. The results showed that collectors are more critical than the other parts of the economy due to the high initial investment cost. Also, the LFR collector from the economic point of view showed better system performance than others. The system was tested for performance in 9 different provinces of Iran with different radiation intensity levels. The results showed that Bushehr and Golestan provinces had the highest and lowest potential, respectively. Also, the effect of radiation intensity and operating fluid on the system was investigated.

This paper examines the design, manufacture, and analysis a Gamma-type Stirling engine using the solar parabolic collector. The calculation base for designing is so that the size of the solar parabolic collector needed to start the engine is not too large. After finishing the design and manufacturing of the parts, the assembled Stirling engine was initially initiated by a 550W electric heater tested in two non-insulated and insulated conditions for different input power. In the non-insulated state, the Stirling engine has a maximum power of about 68.69W with an output of 12.66%; and insulated mode of Stirling engine maximum watts with an output of 15.72% was obtained. Then we constructed a solar parabolic collector based on the power of the heater used. Designing the collector is such that it has the ability to reflect around 550W. Thus, the diameter of the collector is 1m and its depth is 12cm. This solar parabolic collector provides the power needed by the engine to work during the day. The maximum output power of the solar Stirling engine is about 30W.

In this study, energy and exergy efficiency of residential-type direct absorption solar collector using PVP-coated silver nanofluid has been evaluated experimentally. First, stability and thermophysical and optical properties of nanofluid have been considered using the theoretical and experimental methods. Then, outdoor thermal performance of collector is investigated using the experimental setup based on EN12975-2. Results of energy analysis show that the collector efficiency is increased by increase of flowrate and concentration of nanofluid asymptotically. It is observed that exergy efficiency is firstly increased by nanofluid concentration and then, decreased after reaching the optimum value. The optimum concentration was 500 ppm for all flowrates. The variation of exergy efficiency by reduced temperature difference is similar to volume fraction. The optimum exergy efficiency is obtained at 0.01 m2K/W. The decrease of exergy efficiency by flowrate indicated that exergy losses due to pressure drop have the significant effect on the collector performance.

It is the aim of this paper to determine the parameters affecting thermal performance of flat plate solar collectors. As a first step, theoretical models for different configurations of a flat plate collector are introduced. These include riser tubes below the absorber plate, tubes above the absorber and tube in between.
A comparison is then made between the theoretical results and real experiments which were implemented in solar energy laboratory at South Tehran Branch of Islamic Azad University.
According to the results, the maximum absorbed energy is for the case where tubes are below the absorber plate. Decreasing the distance between the riser tubes , applying low emissivity glass and increasing insulation thickness are among the parameters which increase collector thermal efficiency. In addition, decreasing the pressure of the gas between the absorber plate and collector glazing increase collector efficiency. Insulation material and working fluid also affect the collector thermal efficiency.

In this study, the performance of direct absorption solar collector is experimentally investigated using Fe3O4/Silica hybrid nanofluid based on deionized water. First, stability of prepared nanofluids is considered using spectral absorbency method. Then, spectrophotometry method is used for measuring optical properties of nanofluids. A prototype of this new type of collector was built with applicability for solar water heating systems. The procedure of EN 12975-2 standard was used for testing the thermal performance of the collector. Results show that collector efficiency is enhanced by nanofluid concentration, so that collector maximum efficiency is 73.9%, 79.8% and 83.7%using nanofluid with concentration of 500 ppm, 1000 ppm and 2000 ppm, respec/tively. This vaule is 63% using the base fluid as working fluid. Regarding very low volume fractions of nanofluids used in direct absorption solar collectors, the viscosity of the base fluid experience insignificant increase, therefore, pumping power will not increase significsantly. Such increase in efficiency show that direct absorption solar collector performance using hybrid nanofluid is much better than that of using the water at the same operating conditions. Application of stable hybrid nanofluid results in higher conversion efficiency of solar energy to useful energy.

The Aquifers are underground porous formations containing water. Confined aquifers are surrounded by impermeable layers on top and bottom, called cap rocks and bed rocks. These aquifers are suitable for seasonal thermal energy storage.A confined aquifer with a very low groundwater flow velocity was considered to meet the annual cooling and heating energy needs of a residential complex located in Tehran, Iran.Three different alternatives of aquifer thermal energy storage (ATES) were employed to meet the heating/cooling demands of the complex. These alternatives were: using ATES for cooling alone, employing flat plate solar energy collectors for heating alone and employing a heat pump for cooling and heating. For the economical evaluation of the alternatives, a life cycle cost analysis was employed. For the environmental evaluation, Ret Screen software was employed. For the three considered operational alternatives, using ATES for cooling alone had the minimum payback period time of 2.41 year and life cycle cost of $16000. In the environmental consideration of the three alternatives, coupling of ATES with heat pump for cooling and heating had the minimum of CO2 generation, corresponding to 359 tons/year.

The goal of this research is to design and build a solar adsorption chiller operated by activated carbon / methanol. Continuous refrigeration systems are able to produce cooling continuously. This paper examines the effect of activated carbon particles on the performance of a continuous adsorption chiller device. The source of this chiller is through sunlight and supplied by a parabolic collector that does not need to track sunlight. The system operates with two adsorbent beds that, when one is adsorbed, the other is desorbed. The experiments were carried out in Yasuj during three different days in the month of Bahman for three hot water input to the chiller 38℃, 34℃ and 30℃. The average ambient temperature during the experiment is 18℃. Experimental results shows that for the total energy input, 13MJm-2, the average performance factor of the chiller is when the inlet temperature of the hot water of the chiller is 38℃, 34℃ and 30℃, respectively, of 0.123, 0.103 and 0.10. For Previous temperatures the average specific cooling power of the device was obtained at 88Wkg-1, 65Wkg-1 and 50Wkg-1 respectively.

Present paper has investigated the performance assessment of a humidificationdehumidification (HDH) desalination system connected to photovoltaic thermal (PV/T) collectors. The main components of the system include humidification, dehumidification and PV/T collectors. Problem governing equations are obtained by writing the energy balance for the system various components and solved numerically. The simulation results of the present study are in fair agreement with the experimental data of previous literatures. Paper results show that at least three PV/T collectors with total area 2.3 m2 is needed to supply the minimum solar energy for the startup of system. Also, there is a desired mass flow rate for brackish water and air which maximize the system energy efficiency. The desired values of mass flow rate of brackish water and air and the maximum energy efficiency are 0.025 kg/s, 0.03 kg/s and 65%, respectively. Furthermore, the increase of PV/T collectors number increases freshwater productivity and output electrical power and decreases the energy efficiency due to the increase of consumed pumping power. Due to the negative influence of the temperature increase of inlet brackish water on the performance of dehumidifier and PV/T collectors, it causes the decrease of freshwater productivity, electrical power and energy efficiency.

Unglazed transpired solar air heater collectors are relatively new solar technologies that can be used for air heating or pre-heating ventilation air and drying agricultural and industrial products. Passing air through the perforated plate, which is usually metallic is the main mechanism of heat transfer. The cost of buying and preparing the absorber plate is the dominant share of costs allocated to this type of collector. In the present study, performance of non-metallic absorber plates available in the Iranian market, as an alternative to metal absorber plates are examined experimentally and theoretically. Therefore, three collectors with Metallic, Polycarbonate and Compressed-Plastic are designed, fobricated and tested in real conditions. In addition, a thermal modelbased on the first law of thermodynamic is developed for these collectors. In this model, all mood of heat transfer (including conduction, convection and radiation) are considered. Results show that there is a good agreement between experimental and theorical results (For most test condition, average relative error in estimation of the outlet temperature of the collectors is less than 5%). The results showed that the performance of three collector’s, espisially for low mass flow rates, was not too different. However, for considered condition Steel (metallic) collector has the best performance and the polycarbonate collector the worse performance. The performance of the Compress plastic was close to the Steel collector and given the low cost of non-metallic collectors, it can be used as a convenient alternative to metal collectors.

Optimal design of combined renewable energy systems for supplying heat load of greenhouses is studied. It is tried to analyze the system technically and economically so that it would be optimal from both viewpoints. Optimal design is done from technical point of view using TRNSYS software by setting different parts of the system so that besides preheating of the fluid entering the evaporator of the heat pump for increasing the temperature, heat recovery of the ground in maximum heat extraction periods and heat recovery during summer time is occurred. The optimized system is then studied from economical point of view and the final optimized design is then selected by trade-off between economical and technical considerations. Selected model has mean seasonal coefficient of performance of 4.14 for heat pump, borehole length of 150 meters and total solar collector area around 9.42 square meters and the temperature of the fluid in ground cycle would increase up to 0.5 or 1 degrees centigrade. Optimal amounts gained are compared with those obtained from and TRNSYS and MATLAB relation. Finally to supply electrical load homer software is used and the optimum system is chosen considering design conditions.