جستجوی مقالات مرتبط با کلیدواژه « راندمان » در نشریات گروه « فنی و مهندسی »

A single-switch DC-DC high step-up converter is presented in this paper. There are soft switching conditions in the proposed converter for switching on and off time, which increases efficiency. In order to increase the gain, two coupled inductors have been used, and the leakage inductance of the coupled inductors has been used to create a soft switching condition, and the minimal auxiliary element has been used in the proposed converter. In the proposed converter, only one switch is used, and the condition of the converter is no different from a basic converter in terms of the control circuit. Therefore, the converter does not need to design a new control circuit. The auxiliary circuit added to the converter with a minimal element, provides soft switching conditions for the switch at turn-on, under zero current and at turn-off, under zero voltage, which, in addition to increased efficiency, the circuit has a simple structure. Therefore, the innovation of the paper is to present a switching converter high step-up soft without imposing an additional switch and with a low number of elements. The proposed converter is simulated after full theoretical analysis at 400 W output power, which shows the efficiency of 97.2 percent, in addition to proving the theoretical analysis. Also, the prototype of the converter is made and the experimental results obtained prove the theoretical and simulation results.

Enhancing fog collector efficiency can be achieved by increasing the number of layers in various collectors. This study scrutinized the influence of layers on efficiency for conventional collectors (Raschel and Aluminum mesh) through a meticulous analysis of theoretical relationships and the execution of experimental tests. In the laboratory phase, following the installation of the system, the output flow from the humidifier was directed toward the collecting plate. Subsequently, the efficiency of collectors with 1, 2, 5, and 7 layers was assessed and compared based on the amount of collected water post-fog extraction. The results of the investigation into the theoretical relations governing water extraction from fog revealed a significant trend. As the shade coefficient of the collector increases, aerodynamic efficiency demonstrates an initial increase, peaking at 50-60%, followed by a subsequent decrease. Furthermore, the efficiency of Raschel and Aluminum mesh is intricately linked to the number of layers, with the highest theoretical efficiency observed at 4 and 7 layers, respectively. Experimental findings indicated the highest water collection efficiency for Raschel mesh with 5 layers at 55.3% and for Aluminum mesh with 6 layers at 58.1%. In terms of cost-effectiveness, the optimal number of layers for Raschel and Aluminum mesh is determined to be 2 and 4 layers, respectively.

This paper introduces a novel approach to enhance the performance of a two-phase steam and air ejector through primary supersonic nozzle designs with uncircular cross-sections. Experimental tests evaluated the impact of these novel nozzle designs ،which included a star shape ،a simple square ،a square skewed in the direction of the nozzle axis ،a special sketch ،and a simple circular cross-section as the reference nozzle ،on the ejector's performance. The results indicated that the novel nozzles demonstrated the capability to enhance the ejector's entrainment ratio by up to 12% compared to the conventional circular cross-section reference nozzle. To validate and gain further insights into the novel nozzle designs ،computational fluid dynamics (CFD) simulations were also conducted. The integration of CFD simulations and experimental data showcased the potential of these uncircular cross-section nozzles to improve the ejector's performance. The findings offer promising opportunities for optimizing ejector configurations ، paving the way for more efficient and innovative solutions in various engineering applications.

Nowadays, due to the increase in the amount of environmental pollutants and the electricity production price of energy carriers, the use of renewable energy sources for electricity production is increasing. Among renewable energy systems, photovoltaic systems, due to their stability, long lifetime, and low maintenance costs, are very popular. Utilization of these systems requires an accurate evaluation and understanding of various aspects of their performance, and ignoring this important issue is not only ineffective, but it may also lead to irrecoverable economic costs. To prevent this problem, several simulator applications are available for pre-construction testing of power generation units. In this paper, in order to simulate and assess the possibility of installing a photovoltaic production unit in the study environment, PVsyst application and accurate meteorological data such as annual radiation rate and environmental temperature have been used. Since solar arrays are installed in both movable and fixed forms, in this paper, the performance of both is examined separately and the model that had lower losses in practice and consequently higher efficiency is introduced. The simulation results showed that in the study environment, using the fixed type of solar panel for generating electrical energy is more appropriate than using the mobile type.

Following the scarcity of non-renewable resources such as oil, gas and coal, more research is focused on the issue of high energy consumption and society's dependence on fossil fuels. The use of renewable energy and the development of microgrids can be necessary to reduce dependence on fossil fuels. Photovoltaic systems play a key role in microgrids as a source of renewable energy supply. In these systems, the output voltage of the cell is usually much lower than the voltage required by the DC bus, and as the output current increases, the amount of this voltage decreases significantly. Therefore, the presence of a step-up DC-DC converter with a wide input voltage range is necessary to connect the low-voltage cell source and the high-voltage DC bus connected to the inverter. In this paper, a new structure is presented for non-insulated DC-DC boost converters based on voltage lift technique. The proposed converter has a proper voltage gain at output and an acceptable voltage stress on switch and diodes in comparison with recent references. The proposed converter has a switch with easier control and high reliability due to the input source common point and the output load of the converter. Analysis of the voltage stress as well as selection of suitable elements along with converter analysis in continuous mode are performed and calculation validity is confirmed by presented laboratory results.

The main purpose of this article is thermodynamic modeling and performance analysis of solar gas turbine hybrid system equipped with a solid oxide fuel cell. Double and triple hybrid cycles have been studied by researchers in recent years. In this research, it has been tried to investigate the hybrid cycle of gas turbine and solid oxide fuel cell by being equipped with a solar receiver as a new triple cycle (SOFC-Solar GT) and to compare its results with the double cycle gas turbine and fuel cell (SOFC-GT). In this research, two different configurations have been considered for this triple hybrid system. Compressor pressure ratio, gas temperature entering the turbine, solar radiation intensity, and fuel cell temperature have been evaluated as important and effective parameters in the cycle performance. Examining the results of this research shows that the use of solar receiver will reduce the fuel consumption in the hybrid system and increase the overall efficiency by 8-9%. On the other hand, the results show that the net production power in solar hybrid cycles is 45- 50% more than the basic cycle.

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.

A high step-up two-inputs DC-DC converter is presented in this paper. The soft switching condition is provided for switch in turn on instant, so the converter efficiency is high. Due to the fact that only the capacitor is used to increase the voltage gain and there are no coupled inductors in the converter, the input current of the converter is continuous. The technique used to increase gain can be used with more stages to achieve higher voltage gain. The converter can also be used as a single input intertwined instead of two inputs, which in this case the input current ripple is reduced. The voltage stress on the switches is lower than the output voltage, so lower voltage switches can be used, which reduces the converter cost. The proposed converter is completely analyzed and in order to prove the theoretical results, a simulation is performed on the converter at 500 watts. The results of the simulation at full load show an efficiency of about 95.5%.

Nowadays, the use of thermoelectric as one of the methods of recovering waste heat energy has received much attention. In this research, while presenting a new thermal energy recovery system in the molten slag of steel Industry, thermodynamic analysis of the proposed system from the perspective of energy and exergy is also presented. Then the effect of various parameters including Seebeck coefficient on the performance of the proposed system is investigated. The results of modeling in both power cycle and thermoelectric cycles have been validated by previous research. The results of thermodynamic analysis show that the largest contribution to the exergy destruction of the proposed system is related to the heat recovery system. According to the results, the production capacity of the heat recovery system from the total production capacity is about 49% and the efficiency of the first law of thermodynamics for the proposed system is 24.7% and the efficiency of the second law of thermodynamics is 32.88%. Economic analysis indicates that with thermoelectric generator cost of 1 $/W the payback rate of investment is less than 2 years.

Sedimentation in dam reservoirs is known as an effective factor of reducing dams’ life-time and reservoir capacity, disruption of dam operation, blockage and corrosion in intake structures, drain valves and other sediment venting structures and consequently increase costs of maintenance and other related damages. This proves the importance of understanding the hydraulic behavior of density current in dam reservoirs. In this study, the trend of density current moving in Lorestan Roudbar reservoir has been investigated by Mike 3 model. The aim of this study is to withdraw maximum gravity current concentration in flood time period from bottom outlets in order to decrease sedimentation in reservoirs active volume. Therefore, three-dimensional hydrodynamics simulation of density current in this reservoir has been done. The modeling scenarios have been designed to calculate how much mass can be vented from bottom outlet to save more capacity in reservoir when flood with various return time period occur. The results show that increasing the return period of the flood the sediment discharge efficiency, increases. Sediment venting efficiency is increasing with a two-year return period and reaches a maximum in floods with a 20-year return period when the maximum efficiency of sediment venting is roughly 17%.

For study of the effect of planting dates and irrigation intervals on quality and quantity performance of Nutrifeed Millet, an experiment was conducted as split plot in a randomized complete block design with three replications on four planting dates (22nd May, 2nd June, 13th June, 24th June) and three levels of irrigation (8, 11 and 14 days) in Neyshabour Agricultural College fields in 2019. Forage crop in the first and second harvest were assessed according to quantity characteristics (fresh and dry forage, leaf to stem ratio, number of tillers per plant, number of tillers in m2) and quality characteristics (total protein content, ash percent). The results indicated that by reducing the irrigation period time distance, fresh forage yield increased per unit area. With any delay in planting date, performance of fresh forage yield per unit area decreased. A decrease in the number of tillers at the second harvest caused an increase in protein and ash percentage because of the increase in leaf to stem ratio. Total dry matter, protein percentage, number of tillers in plant, weight of fresh stem decreased when time distance of irrigation periods increased. In addition, total dry matter, fresh leaf weight, protein performance value and fresh leaf weight decreased with delays in planting date.

Water pumping stations usually use fixed speed pumps that have a good efficiency over a small range of pressure and flows. If different flows and pressures are required, unsuitable pump speeds will yield excessive energy losses. This imposes additional costs, especially on pressurized irrigation systems, which are constantly changing their irrigation needs, sometimes monthly. In pressurized water distribution systems, a constant speed pump is often used because of its simplicity. However, constant speed pipes are not easily able to deal with changing demands in water flows. When the demand for the discharge differs from the design discharge, the required demand (discharge and head) could be met by changing the pump speed without making any special changes in the system. Using an electronic drive circuit, the electrical frequency can be changed and the rotation speed of the pump motor can thus be modified. In this study, the application of variable speed pumps in pressurized irrigation systems is investigated. Two pumping station scenarios including a fixed speed pump and a variable speed pump are considered. The results show that using a variable speed pump increases the average pump efficiency by 18.7%. In addition, the variable speed pump system reduces the electrical consumption 57.6 % compared to a fixed speed pump. Therefore, the use of variable speed pumps in pressurized systems is recommended.

The task of pressure reducing stations is to regulate the gas pressure in the standard range for different uses. The indirect water bath heater is used as part of the gas pressure transfer station to heat the gas before the pressure drops so that the condensate temperature in the gas does not reach the point of hydration formation during breaking and reducing the gas pressure. In this study, according to the characteristics of natural gas and heat transfer relations and mass survival and energy equations, an acceptable analysis of the thermal behavior of heaters has been done and the heater is modeled with appropriate accuracy and the effect of geometric parameters on the heat performance of the heater is investigated. By changing the heater geometry from cylindrical to cubic geometry, acceptable results were obtained by increasing efficiency and reducing fuel consumption.

To improve the performance of photovoltaic-thermal (PV/T) system through thermal management, the effects of four different ‎geometry of cooling pipes including circular direct pipe (CDP), circular sinusoidal pipe (CSP), rectangular zigzag duct (RZD), ‎and rectangular step duct (RSD), type of refrigerant, and flow rate are investigated on the temperature distribution, thermal, and ‎electrical efficiencies through numerical modeling in this paper. The results show that RSD has the best performance, so that the ‎thermal and electrical efficiencies have been improved by 15.2% and 2.2%, respectively. On the other hand, the fluid head loss ‎in RSD is increased by about 2.6 times compared to that of CDP. The results also indicate that microencapsulated phase change ‎material (MPCM) fluid leads to an increase in the thermal efficiency of about 40% respect to the water, however, Ag nano-fluid ‎just improves the thermal efficiency by 28%. Increasing the flow rate of refrigerant also caused to enhance the heat transfer ‎coefficient and leads to a decrease in the average surface temperature of the PV panel by 6.4oC and 7.5oC in CDP and RSD, ‎respectively.‎

The present study aimed to introduce two novel power-refrigeration combined cycles into optimal usage of LNG cryogenic energy and reducing exergy losses due to high-temperature difference in the heat transfer process. The combined cycles include a compression-ejector refrigeration cycle and two low and high-pressure Rankine cycles in which the power required to operate the compression-ejector refrigeration cycle’s compressor is provided by the power generated by the two-cycle Rankin turbines. Increasing the cooling energy compared to direct LNG evaporation is considered as the benefits of the novel combined cycles. A thermodynamic analysis, along with optimizing both novel combined power-refrigeration cycles, was performed through the first and second thermodynamics laws and the fixed surface model assumption for the ejector. Analyzing the design parameters demonstrated that the maximum thermal and exergy efficiency and maximum refrigeration increasing ratio in both novel combined power-refrigeration cycles increase as the pump discharge pressure increases and the output pressure of Rankine cycle turbine reduces. The maximum thermal and exergy efficiency in cycle (І) were 77.31% and 23.69%, and 87.49% and 23.95% in cycle (ІІ), respectively through performing optimization in the boundaries set for the design parameters. Finally, the highest refrigeration increasing ratio to direct evaporation of LNG for cycle І and ІІ was 63.37% and 73.9%, respectively.

The production of clean electricity is one of the most basic human needs today. Therefore, the use of power plants that use renewable and environmentally friendly fuels (new energy) as their base fuel, has been highly appreciated. However, the output voltage level of local power plants based on new energies is as low as the input voltage of the next floors (inverters, etc.). Therefore, researchers have tried to solve this defect by using DC / DC boost converters. The structures related to these converters are different based on the designer's expectations such as voltage gain, output power, efficiency, input voltage specifications, etc. Boost converters are responsible for increasing the DC voltage by switching and storing energy in their inductor. But the same simple structure can be created with the help of new tricks such as using magnetic coupling, adding passive incremental circuits to the converter structure, creating more complete structures by using several active switches and even combining several structures together to the desired point in terms of voltage gain. On the other hand, with soft switching methods (resonance, snubber, etc.), the efficiency of boost converters is in the acceptable range. In this paper, the types of power plants based on new energy and then boost converters, which are the most basic elements of a power plant based on new energy, it is categorized in terms of incremental structures and applied methods for optimizing these converters, especially in terms of reducing losses and increasing efficiency.

Cyclone separators are used to separate the solid particles from the gas streams in industrial applications. A strong swirling turbulent flow inside the aero-cyclone causes the particle separation due to their inertia. Two important parameters for cyclone design are the pressure drop and separation efficiency. The cyclone geometry strongly affects the efficiency and pressure drop. Therefore, in this article, different new geometries for the vortex finder of the cyclone are considered and tested experimentally. The efficiency and pressure drop have been measured and compared for different fabricated vortex finders. A typical high-efficiency Stairmand cyclone was considered and the guide vanes with an angle of 10 and 20 degrees to the horizontal plane were added to the original vortex finder. Experimental results show that for the guide vanes with 20 degrees angle, and at the gas velocities between 10 and 20 m/s, the pressure drop is reduced by 58% and the efficiency is increased by 2.3%.

It’s known that equalizing inductive reactance (caused by winding inductance) with capacitive reactance (caused by resonance capacitor) and creating resonant frequency is imperative to produce heat in metal pan located on induction cookers’ coil fed by classic resonant convertor. Moreover, the magnetic field induced by the currency passing through the induction cooker coil (with an active component and high frequency), produces Eddy currents in the pan and the Ohmic losses resulted from these currents (Req×I2 ) causes heat in the pan. Thus, in order to produce higher heat and cook faster, there is a need to increase the transitional active power to the cookers’ coils of these types and this in turn, raises the system efficiency. Increasing the transitional active power to the induction cookers’ coil means increasing the Ohmic losses caused by Eddy currents produced in the pan. To achieve this, by changing the circuit structure in classic resonant converter (using a voltage amplifying inductor in the converter input) as well as changing the switching system, a converter named “proposal converter” is developed and studied in this dissertation. This proposal converter increases the system efficiency by about 20 percent.

Due to the increasing use of data centers, especially in the telecommunications industry, it is necessary to consider optimal cooling systems for these systems. One of the important factors in this regard is the effect of the diameter of the copper banks of the ice bank. Due to the lack of similar empirical work in this field, a small-scale ice bank system was built to measure the performance of the designed system empirically. The investigated storage system is static and indirect, which involves the formation and melting of ice on the outer surface of the pipe. The required cooling energy is stored in ice, stored and used as needed. The ice bank system is tested under the actual operating conditions to determine the effect of copper tube diameter on its performance. Acceptable repeatability of the tested results confirms the accuracy of the information provided. The results indicate that, at a uniform thermal surface of the tubes, the rate of ice formation increased by 4% by decreasing the diameter of the copper tube diameter.