فهرست مطالب

مهندسی مکانیک مدرس - سال شانزدهم شماره 13 (اسفند 1395)

نشریه مهندسی مکانیک مدرس
سال شانزدهم شماره 13 (اسفند 1395)

  • ویزه نامه مقالات کنفرانس
  • تاریخ انتشار: 1395/11/27
  • تعداد عناوین: 56
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  • Mohsen Khodaee*, Ali Ashrafizadeh, Mostafa Mafi Pages 1-4
    Natural gas is one of the cleanest sources of energy among all fossil fuel resources. The natural gas transfer from the extraction source to the consumption site often poses an expensive and challenging technical problem. In general for the transfer distances less than 4000 kilometers, pipe line is a suitable transfer method. But for longer distances, and places at sea or ocean, it is better to liquefy the natural gas and store it in reservoirs and transport it by ship. To liquefy the gas, its temperature needs to be reduced and considering the economic and safety limitations, the cooling process should be preferably carried out at atmospheric pressure. Therefore, refrigeration systems are required to do so. The required power for the refrigeration in liquefaction plants is notoriously high and contributes greatly in the cost of the final product, i.e. the liquefied natural gas. In this article, an industrial butane liquefaction unit is simplified and then simulated in the HYSYS software. After the validation of the HYSYS results, an optimization problem is defined and solved to minimize the power consumption of the refrigeration system. It is shown that the power consumption can be reduced about 31 percent in this particular case.
    Keywords: butane, lequefaction, optimization, compressor technical limitation, HYSYS
  • Hasan Najafi Khaboshan, Hamid Reza Nazif* Pages 5-8
    Turbulent flow and heat transfer of air are numerically studied for an alternating elliptical axis tube. To reduce computational effort, periodic boundary condition and alternating geometry of tube are considered. Air flow is analysed for 11 different Reynolds numbers in the range of 5,000 to 20,000. In these simulations, the realizable k-ε turbulence model is used. For handling near wall phenomena, enhanced wall treatment that solves equations to the wall is also applied. The results of simulations show that by appearing axial vortices in alternating elliptical axis tubes, the heat transfer rate is improved, however, pressure drop increases. In addition, good agreement is seen between obtained data and ready experimental results for friction coefficient.
    Keywords: Alternating elliptical axis tube, Turbulent flow, Realizable k, model, Nusselt number, Darcy friction coefficient
  • Elahe Norozi Jajarm, Javad Abolfazli Esfehani*, Ahmad Madadi Pages 9-12
    The combustion process in a boiler system is a process with multiple inputs and outputs, time dependent and highly non-linear. So, it’s difficult to set the main parameters using the classic method. The combustion process development with less energy consumption and less pollution is one of the fields of research interest. One method, with this purpose, is using lean premixed combustion in burner of boilers. In this article, the impact of the air injection on the lean premixed flame in stratified burner is studied. Velocity and equivalence ratio are set as variables. In a single flow mode, with increasing equivalence ratio up to stoichiometry ratio, the flame structure sustainability increases. In this mode, by increasing mixture injection velocity from 0.5 to 1 m/s, and decrease in oblique angle, the flow-off flame sustainability improves. By further increase in velocity, beyond 1 m/s, the sustainability comes down. In multiple-flow mode, by air injection from inner duct, no variation in flame structure is noticed. By air injection from outer duct, the flam structure deforms to sustainable conical flame, as in this mode the injected air in outer duct plays insulation role against cool environmental flow. Hence, the outer air injection has a positive effect on flame sustainability.
    Keywords: Boiler, Premixed Combustion, Boltzmann Method, Lean Combustion
  • Shahram Derakhshan*, Ehsan Abdolahnejad, Mohammad Bashiri Pages 13-16
    Nowadays, according to increasing energy consumption especially in HVAC system, the need for optimizing energy consumption and determining energy efficiency class of different devices in HVAC system is essential. Centrifugal pumps, according to the statistical information, are from the high energy consumption devices in HVAC system. So in this paper a centrifugal pump was tested to determine performance curve and class of energy consumption according to standard of Iran (INSO 7817-2, 1st.edition) and new method that was recommended by the authors. Then, it was investigated numerically by using finite volume method and its geometry was optimized by using artificial neural network (ANNs) and Artificial Bee Colony (ABC) algorithm. The optimized parameters were hub diameter, suction diameter, impeller diameter, impeller width and blade angles. The results showed efficiency increase at BEP about 4% and improve the head about 7 m for optimized geometry. Hence, the class of energy consumption according to the Iran standard and the recommended methods in this research was improved from F class to E class and from E class to D class, respectively.
    Keywords: Centrifugal pump, experimental analysis, numerical analysis, optimization, neural network
  • Behzad Firouzeh*, Kourosh Javaherdeh Pages 17-22
    In this study, turbulent mixed convection heat transfer and pressure drop of Al2O3/water nanofluid in helically coiled tube heat exchangers were investigated. Thermo-physical properties of nanofluid and base fluid were considered temperature dependent and analysis for helical coils, with curvature ratios of 0.1, 0.0666 and 0.05, and nanoparticles with volume concentrations in the range of 0-2% in various Reynolds number were carried out. CFD analysis was done by 3D realizable ke turbulent model in ANSYS FLUENT 15. According to the results, it was shown that by increasing the coil curvature ratio and nanoparticles volume concentrations in a same Reynolds number, heat transfer coefficient and pressure drop of helical coils both increased. Using numerical data, a correlation for predicting outer Nusselt number in terms of Rayleigh number in helical coils were proposed. Thermal performance index were compared in various conditions and the maximum value was noticed for coil with a curvature ratio of 0.1 and nanoparticles volume concentrations of 2%. Results showed that using nanofluid and helical coils instead of base fluid and straight pipes, improves thermal performance of the heat exchangers.
    Keywords: Nanofluid, CFD, Heat transfer, Pressure drop, Helical coils
  • Reza Kheiri, Hadi Ghaebi* Pages 23-27
    In this research study, a novel ORC cycle is proposed to improve the efficiency and power generation of the basic ORC cycle. In this proposed new cycle, an ejector, a second stage evaporator and a regenerator are integrated in the basic ORC cycle. Steam from the second stage evaporator enters to the ejector as the primary fluid, after decrease in mixture pressure, it tends to increase the suction of the secondary fluid from the turbine outlet (steam from the turbine). Also steam enters to the regenerator, before the ejector, and by this way supplies a part of required energy for the first stage evaporator and increases the efficiency as well. For thermodynamic modeling a code was developed in the Engineering Equation Solver (EES) software. In addition, different working fluids (R600, R245fa, R236fa, Cis-2-Butene) were examined to evaluate the thermodynamic performance of the basic ORC cycle and new proposed cycle. The results show efficiency increase of the new cycle compared with that of the basic ORC cycle, the value of which depends on the working fluid, as the maximum efficiency increase of 17.5% is noticed.
    Keywords: Organic Rankine Cycle (ORC), ejector, regenerator, thermodynamic performance
  • Hosein Sadeghi٭, Vali Kalantar Pages 28-31
    Since the electricity and the other modern energy sources had not been developed in the past, human being inevitably was trying to find ways to provide comfort of living. One of these cases is Baad-Gir which since a long time ago has been used and appreciated by the general public in hot and dry climate zones dwellers. Now, in addition to growing tendency of researchers to use renewable energy, they are more than willing to improve performance of traditional methods. In the present work, a method has been proposed and investigated to provide room air based on using underground channel. Since the sub- surface soil temperature is much lower than the surface and due to the large volume of soil, it can be considered and used as a heat sink, without any costs and power consumption. In this work, two channels are considered, dry one which is modeled according to soil temperature and the other wet one, via using Ghanat or by adding water manually. Results are compared and it is concluded that this method could be effectively used to decrease temperature of entrance air to the building.
    Keywords: Renewable energy, Baad-Gir, Air conditioning, HVAC, Cooling, Underground channel
  • Danial Hakimirad, Mehdi Maerefat*, Behrouz Mohammad Kari Pages 32-37
    Study of air infiltration in a building is highly important from several aspects, such as energy, air quality, thermal comfort and pollution entrance to the building. In this paper, the effect of new gaskets on air infiltration rate of doors and windows was investigated. To do this, existed gaps between the common doors and windows of Iran were simulated and by installing eight various gaskets, with different material and cross sections, the air infiltration rates at different pressure differences were obtained. The objective of this study was to evaluate the airtight performance of different gaskets, in order to select the right type, as well as providing air infiltration rate data for caulking doors and windows for designer engineers. Results showed different airtight performance for various gaskets, in which, at higher pressures differences could reach up to six times. Data were fitted to the power-law model and the coefficients of the equation were obtained. Based on the results, practical recommendations for calculation of air infiltration rate from doors and windows were also given.
    Keywords: Air infiltration, Experimental simulation, Air sealing, Air tightness, Door, window
  • Javad Amnian, Mehdi Maerefat*, Ghassem Heidarinejad Pages 38-41
    Providing adequate air quality is an important challenge in enclosed parking lots. Hence, increase of ventilation flow is necessary to improve air quality in these places but not sufficient. According to recent researches, the necessary and sufficient conditions for development of good air quality in enclosed parking lots are both adequate ventilation flow and enhancing the heights of exhaust vents. For investigating this claim, in this paper, the change of CO concentration with height in an enclosed parking lot was investigated both numerically and experimentally. The CO concentration in various heights is obtained numerically, using OpenFoam software, and compared with that of measured experimental data Good agreement between numerical and experimental results was obtained. The maximum CO concentration in studied parking lot was obtained within the non-dimensional height range of 0.60.7. Furthermore, the CO variation with height in three different enclosed parking lots was also studied and numerical and experimental results were compared. Based on the results, the maximum CO concentration was also occurred within the non- dimensional height range of 0.60.7.
    Keywords: Enclosed parking lot, carbon monoxide, non- dimensional height, numerical solution, experimental measurement
  • Hosein Khorasanizadeh*, Soroush Sadripour, Alireza Aghaei Pages 42-46
    In this study, the effects of using corrugated absorber plate on heat transfer and turbulent flow in solar air-heater collectors were numerically investigated. The two-dimensional governing equations were solved by utilizing finite volume method and SIMPLE algorithm. The absorber plate with triangle, rectangle and sinuous corrugations in turbulent flow regime and Reynolds number was considered within the range of 2500-4000. Proper geometry was selected based on the best performance evaluation criteria (PEC) and increasing the air temperature from collector inlet to outlet (ITIO). Simulations were performed for two different tilt angles of collector, which are the optimum six month tilts for flat plate solar collectors in Kashan. The results revealed that using corrugated absorber plate has a considerable influence on the flow field and heat transfer. For the whole year the highest PEC was obtained for the sinusoidal corrugated model, however, the highest ITIO was observed for rectangular corrugated model. To achieve best ITIO and the highest PEC, the optimum Reynolds number of 2500 was also noticed.
    Keywords: Solar collector, Corrugated absorber plate, Turbulent regime, Performance evaluation criteria
  • Hadi Ramin*, Pedram Hanafizadeh, Mohammad Ali Akhavan Behabadi Pages 47-50
    There is a gap between the design performance and the actual energy consumption of buildings. The previous results showed tha t energy consumption may change considerably even in identical buildings. Occupants in the buildings are responsible for these variations, therefore, understanding their behavior may help to bridge the gap between design and actual energy consumption of buildings. In this paper, occupants’ behavior as an important factor in energy saving have been considered. The recent advances in this filed are reviewed in order to understand its current situation.
    Keywords: Occupant's behavior, Energy consumption, Building design, operation
  • Omid Ghanbari Asli*, Koroush Javaherde Pages 51-55
    In this study, a double-pipe heat exchanger under turbulent flow conditions was numerically simulated. The simulations aimed for the effect of nanofluid and circular fins on the outer wall of the inner pipe. Fins with different heights (1mm, 2mm, 3mm) and pitches (0.05, 0.1, 0.2) are considered as simulation variables. Furthermore, the effect of the water-Al2O3 (with the varied volume concentration of 1-2%) was studied. The range of Reynolds number for turbulent flow is changed between 5000 and 100000. The results revealed that the use of circular fins on the inner pipe yield 4-12% increase in the heat transfer rate. Moreover, adding the nanofluid of Al2O3 to water increases the Nusselt number, in which the Nusselt number increases with nanoparticles concentration. Increase of fin height as well as decrease of pin pitch improves heat transfer and increases pressure drop. Pressure drop found to be more sensitive to fin geometry variation, which has negative effect on thermal performance efficiency of heat exchanger. Subsequently, it was noticed that, using nanofluid slightly affects the pressure drop but it drastically increases the efficiency of fin equipped heat exchanger.
    Keywords: Double pipe heat exchanger, Circular fins, Nanofluid, Turbulent flow
  • Kourosh Javaherdeh*, Mahdi Amin Fard, Mohammad Zoghi Pages 56-63
    Organic Rankine Cycles are appropriate technology for the conversion of low quality thermal energy to electrical power. In this research the organic Rankine cycle was studied from energy, exergy and exergo-economic points of view, and it was simulated with hybrid solar and geothermal heat source in order to produce electricity and hot water. In this configuration, 90℃ geothermal brine was used to preheat the organic fluid and 150℃ solar fliud was used for organic fluid evaporation. Waste heat in condenser was also used to produce hot water. Simulation results show that power energy and exergy efficiency of combined heating are 0.566 and 0.156 and electrical energy and exergy efficiency are 0.057 and 0.065, respectively. Moreover, the amount of work output and total irreversibility are 50 and 671.1, respectively. Solar collector, the evaporator and condenser are the most important components from the exergo-economic point of view, due to the high initial cost rate and Exergy destruction. Parametric analysis result shows that the temperature increase in evaporator has positive effect on cycle operation and causes the increase in electricity efficiency and decrease in irreversibility. Also, the increase in pinch point temperature difference of evaporator has a negative effect on cycle operation. From economic point of view, the increase in evaporator and pinch point temperature difference of evaporator causes the decrease in capital coast rate. Also, the solar radiation change find to have positive effect on system operation, based on exergo-economic point of view, which causes the increase in energy and exergy efficiency.
    Keywords: Exergo-economic, CHP cycle, Organic Rankine cycle, Parametric study, Renewable energy
  • Farzin Davoodi, Hasan Hasanzadeh, Alireza Zolfaghari*, Mehdi Marefat Pages 64-68
    Comprehensive evaluation of individual thermal sensation could help engineers to optimum design heating and cooling systems, in order to reduce energy consumption. Differences in the persons’ individual parameters such as age, gender, weight, height and basal metabolic rate have a significant effect on the human body thermoregulation and thermal sensation. Since the individual parameters have not been considered in standard thermal comfort models, they don’t lead to accurate results for specific individuals. In this study, the impact of individual characteristics, including weight, height and gender, on thermal sensation have been evaluated separately and discussed to improve the prediction of thermal comfort for different persons. Individual three-node model has been accurately estimated thermal sensation of the bare and clothed parts of the body by considering individual physiological differences in human thermoregulation. The model has been verified against the analytical and experimental results where a good agreement was found. Sensitivity analysis revealed that the differences in BMI’s persons could result in a variance of 1.5 unit in calculation of thermal sensation. Thermal sensation results show that females, compared with males, are more sensitive at 15℃ (as operative temperature) and the difference, depending on BMI’s subjects, is within the range of 0.27-0.9 units.
    Keywords: Thermal individual characteristic, Individual thermal sensation, Human body thermoregulation, Three-node model
  • Amir Omidvar* Pages 69-72
    A substantial portion of heat loss in buildings occurs through the exterior envelope. When the floor heating system is used in buildings with poor thermal insulation, in order to provide the heating load, more heat flux must be entered through the floor. It would disrupt occupant's thermal sensation or cause local thermal discomfort. So, thermal transmittance of the building envelope has significant effect on thermal comfort performance of floor heating system. Hence, it is necessary to establish a thermal design criteria for the building envelope. In this research, according to the standards of thermal comfort (i.e., ISO7730, ASHRAE 55) and by following Iran national building regulations (section 19), the required heat transfer coefficient is calculated for the external envelope of buildings with floor heating system. Then, the functional method reported in section 19 of the national building regulations has been developed for designing exterior envelope of buildings with radiant underfloor heating systems. Results showed that, in residential buildings that the occupants are free to choose their favorite clothing, in order to use floor heating system, thermal characteristics of the building envelope should be designed with stricter conditions. In adaptive clothing situation, the required heat transfer coefficient of the exterior building envelope would be 20 – 30% smaller, depending on climatic conditions.
    Keywords: Floor Heating, Thermal Comfort, Building Envelope, Functional Method
  • Asgar Minaei, Mehdi Maerefat* Pages 73-77
    The direct utilization of the borehole as a heat sink of the building in several cities with cold climates is studied in the present article. Cities of Ardebil, Tabriz, Urmia, Zanjan, Shahr-e-Kord and Hamadan is considered for investigation. Both residential and office buildings are investigated. The water circulates through the U- shaped tubes in borehole and cools down. Then, the cooled water lowers down the air temperature entering to building in a fan coil. The borehole heat exchanger and fan coil is simulated in Matlab software and the building is simulated in the Energy Plus software. Using MlE GUI code, Matlab software is coupled to the Energy Plus software. The potential of the ground sink direct cooling in residential and office sample buildings is investigated for aforementioned cities. The results show that for all envisaged cities, by utilization of ground sink direct cooling system with borehole heat exchanger, the thermal comfort is satisfied in almost all of the cooling hours in both residential and office building.
    Keywords: Borehole heat exchanger, Ground sink direct cooling system, Iranian cold cities
  • Hamed Moslehi, Hamid Niazmand*, Mohammad Moghiman Pages 78-81
    Air conditioning systems are from the top energy consuming appliances in buildings. Under Floor Air Distribution (UFAD) is a displacement ventilation system that works by dividing the occupied space of a building into two zones: Lower section and the upper section. In UFAD system, low temperature air delivers through underfloor inlets and heated up by existing people and electrical equipment, in which, makes thermal stratification in the zone. In this study, based on Fanger's model, simulation results on air supply inlet locations in four cases indicate that thermal comfort index (TCI) is between -0.5 and 0, which is suitable for summer. Moreover, Predict Percentage of Dissatisfied People (PPD) is predicted within the range of 6-10% in all cases.
    Keywords: Air conditioning, Under floor air distribution (UFAD), Energy, Thermal comfort
  • Omid Pedram*, Hossein Tafrishi Pages 82-86
    Importance of energy saving, increasing prices of energy and using non-renewable fossil fuels, make scientists and industrialists to use less power in economic cycles. Among variety of available combined cycles, the one which is a combination of a vapor compression cycle and ejector cycle, is used extensively in food industry and transportation. The energy of this cycle can be provided by solar panels, waste heat in other processes and the heat comes out of car exhaust. In this study, the combined cycle is analyzed in terms of performance, COP, optimization and exergy in the same boundary conditions and for two refrigerant fluids: Propane and R134a. The effect of area ratio (diffuser inlet to the nozzle outlet) on the performance coefficient is investigated. Also, exergy losses of this cycle are compared with the vapor compression cycle. These comparisons are studied for different components of the cycle. Results show that energy losses in this cycle are less than vapor compression cycle, due to the less exergy losses in the parts. The COP values of the ejector-compression cycle are higher than that of the vapor compression cycle. Propane with less global warming potential value than CFCs is more efficient to apply in order to get higher relevant cooling.
    Keywords: Optimum Energy, Ejector Cycle, Compression Cycle, Combined Cycles, Exergy Analysis
  • Naghmeh Jamshidi *, Nasibeh Sadafi Pages 87-91
    In this paper, phase change material (PCM) was utilized in the hydronic floor heating system for house heating in the winter. The outdoor temperature was considered moderate and humid, as the climate in North of Iran. The effect of hot water temperature in tubes, transition temperature, latent heat and finally thermal conductivity of PCMs are investigated and the operating characteristics of the system were compared with that of the non- phase change energy storage system. The results showed that the PCM stabilized temperature within the room and decreased energy consumption. Latent heat of PCM found to have a minor effect on room temperature, whereas increase in the transition temperature of PCM caused increase of the lagging time between outside and inside room temperatures. Increasing the thermal conductivity of the PCM, the rise of room temperature per unit time was accelerated, in addition, increasing the weight fraction of Nano particles in PCM was dampened the amplitude of room temperature variation during the day. Therefore, using Nano-PCM was found to be of great significance for house heating and comfort condition of occupants.
    Keywords: CFD simulation, Nano-PCM, hydronic floor heating system, moderate, humid climate
  • Moein Manghalsaz, Seyed Mojtaba Mousavi Nainiyan*, Mostafa Mafi Pages 92-95
    The choice of the correct liquefaction cycle is the most important factor in improving the used processes in natural gas liquefied units. From thermoeconomic viewpoints, the selected process should present the highest exergy efficiency and lowest production cost of LNG. There are many processes for liquefying of natural gas. In this paper, the expander-nitrogen processes type is selected because of their advantages such as enough knowledge about equipment and given design parameters. The results of the exergy analysis show that the exergitic efficiency of the cycle is over 3% in the two expander-nitrogen process rather than simple expander. In the next step, to do an economic analysis, the total annual cost of the cycles is calculated with 15% interest rate and 10 life cycle process. The results of the economic analysis also show that the total annual cost of two-expander- nitrogen process is 28% less than a simple expander process. Therefore, two-expander cycle is introduced for liquefying natural gas because of its better economic and exergetic efficiency parameters.
    Keywords: Expander-nitrogen process, Economic analysis, Exergy analysis
  • Mehran Saadati Nasab, Alireza Zolfaghari, Morteza Anbarsooz *, Elaheh Norouzi Jajarm Pages 96-99
    One of the most effective methods for reducing the energy consumption of high-rise buildings, besides using appropriate building aspect ratios, is employing double skin facades. Double skin facades always show desirable performance in cold seasons, however, in hot seasons, their performance strongly depends on the facade components design and the climate of the building location. In hot climates, using double skin facades might increase the energy consumption of the building. In order to solve this issue, the researchers suggested using smart glasses. In this paper, the performance of a double skin façade with smart electro-chromic glasses was investigated in terms of the monthly and annual energy consumption in Tehran climate. Results showed the superior performance of the selected double skin façade with electro-chromic glasses, with respect to the regular single and double skin facades. It was also found that employing double skin facades with electro-chromic glasses would result in a 25% reduction of the building energy consumption in cold months and a 26% reduction in hot months, which have significant effects on the annual energy consumption of the building.
    Keywords: Double skin façade, Electro-chromic glass, Optimization, Natural ventilation
  • Ghanbar Ali Sheikhzadeh*, Soroush Sadripour, Alireza Aghaei, Mohammad Bagher Shahrezaee, Mohammad Reza Babaei Pages 100-103
    In this paper, forced turbulent convection flow and heat transfer of air inside a desert helicopter cabin was studied. The main goal was to provide human thermal comfort, by using cooling system, for a desert helicopter pilot in summer. A body subdomain was considered around the pilot that includes the pilot's using area in the cabin. The governing equations were numerically solved by the control volume approach based on the SIMPLE technique and standard k-ε turbulent model. The effects of air supply parameters velocity and temperature on pilot's thermal comfort are presented and the optimization was carried out to find the best case with the minimum predicted percentage dissatisfied (PPD). It was found that temperature and velocity of supply air have a remarkable influence on thermal comfort characteristics. The air temperature and air velocity in pilot's body subdomain decreased and increased respectively, by increasing supply air velocity. Finally, the predicted mean vote (PMV) and PPD indexes were calculated for different supply air performances and the minimum PPD was obtained for the case with supply air temperature and velocity of Tin=10 °C and Vin=0.4 m/s, respectively.
    Keywords: Thermal comfort, Predicted mean vote, Heat transfer, Forced convection, Turbulent flow
  • Ali Sohani*, Hoseyn Sayyaadi, Yaghoob Khosravanifard Pages 104-108
    A direct evaporative cooler utilizes evaporative pads to improve heat and mass transfer process. In this study, previous published models for prediction of temperature of the cooled air and pad pressure drop were employed and a simple and accurate method for determination of pad’s specification was developed. This method calculates the specification of cellulose evaporative cooling pad system in seven stages. As a case study, a benchmark residential unit with the floor area of 97.1 square meters was selected in Tabriz, Tehran and Zahedan as representing cities of diverse climatic conditions of Iran. The proposed method was applied to characterize the proper cooling system parameters, including pad frontal velocity, specific area and pad thickness. According to the results, 6.9, 13.8 and 11.9 cm were the suitable pad thicknesses with specific area of 680 m2.m-3 for Tabriz, Tehran and Zahedan, respectively.
    Keywords: Direct evaporative cooler (DEC), cellulosic pad, the method of determination of characteristics, Diverse climatic conditions of Iran
  • Ehsan Bagheri*, Mehdi Maerefat, Asgar Minaei Pages 109-112
    In the present research, the effect of ambient temperature on a distributed generation (D.G.) gas engine generator performance in hot and dry climate of Yazd province is studied. The gas engine is an internal combustion engine which is coupled with a 1 MW generator and engine cooling system is performed by a fan cooler. Ambient conditions such as altitude above the sea level, temperature and humidity are strongly effective on the gas engine performance and as a result affect the system electrical power output. In this paper, the effect of changes in ambient temperature on gas engine performance and heat and electricity generation in summer and winter weather conditions is studied. Results show that in summer the ambient temperature highly affects the system performance such that, in the ambient temperatures higher than 40 ºC, the electrical power output decreases approximately 12% for every 5℃ increase in ambient temperature. In winter and ambient temperatures lower than 15℃, the effect of ambient temperature on the system output is less significant than summer season. In combined heat and power (CHP) cases, these changes are effective on generated heat rate. According to results, in economic and technical evaluation of these systems the effect of ambient temperature on power and heat generation must be considered and backup must be provided if needed.
    Keywords: Distributed generation (D.G.), Gas engine, Combined heat, power (CHP)
  • Ahmad Alipoor*, Reza Nasiri Pages 113-118
    Most of energy sources have some disadvantages such as environmental problems and being expensive, so using solar energy for greenhouse heating in cold seasons is a very important issue. Solar energy is a periodic source, so using of energy storage systems is inevitable. In this paper, phase change materials was used in heating system of a solar greenhouse built in Dezful and its influence on temperature gradient of bed soil is experimentally investigated. A model greenhouse with a ground area of 3 m2 was coupled with a heating system consisting of a water tank contained 18 kg paraffin wax (latent heat 190 kj/kg and melting point 55ºC) as phase change material. During the daytime, temperature of the paraffin wax reaches to melting point, with energy of solar radiation absorbed by tow collectors, and daily available energy stored as thermal energy (sensible heat and latent heat). This stored energy is released during the night to heat bed soil of greenhouse. Temperature gradient of soil were evaluated to figure out thermal performance of this energy storage system. Results of this study indicates that about 10 ºC increase in minimum nighttime temperature and average temperature of soil in different depths was achieved.
    Keywords: Solar energy, Greenhouse heating, Energy storage systems, Phase change materials, Temperature gradient
  • Ali Sohani*, Parisa Hajialigol, Hoseyn Sayyaadi, Yaghoob Khosravanifard Pages 119-122
    A combined cooling, heating and power (CCHP) system which provides power and heat demands of a five story benchmark residential building was considered. After calculation of power demand, cooling and heating loads, the best alternative for the prime mover and sizing strategy was selected. The selection was made by analytic hierarchy process (AHP). The decision making criteria were the life cycle cost, annual carbon dioxide emission and annual average of efficiencies. Limitations in available equipment and their specific capacities were considered in this research. According to the results, the national motor with the efficiency of 37.60%, sized based on the maximum electrical load, and with the score of 44.4/ 100 found to be the best alternative.
    Keywords: Combined cooling, heating, power (CCHP), Decision making, National motor (EF7), Fuel cell, Strategy of sizing the prime mover
  • Seyede Bahare Mousavi, Mohammad Mahdi Heyhat Pages 123-126
    One of the ways to increase the efficiency of tube heat exchangers is using nanofluid as working fluid. The heat transfer and exerted forces of flow over a cylindrical tube have been studied widely. In this paper, the convective heat transfer characteristics and fluid flow through a heated circular cylinder, for low Reynolds numbers of water-based nanofluid in the steady cross-flow regime have been investigated numerically. The governing equations include: continuity, momentum and thermal energy have been solved by the standard finite volume method. Two-dimensional steady flow filed computation were carried out for an uniform velocity and volume fractions range of 0.01≤φ≤0.05 over a range of Reynolds number from 10 to 30 and flow and heat transfer characteristic have been studied for Alumina/water nanofluid. The results indicate that the nanoparticles volume fraction, Reynolds number and effective physical properties of nanofluid can significantly affect the heat transfer characteristics. Adding nanoparticles to the base fluid lead to reduce the mean Nusselt number values while the heat transfer rate enhances.
    Keywords: Stationary cylinder, nanofluid, heat transfer coefficient, Static, Dynamic models, Heat exchanger
  • Hamid Mohseni, Khosro Lari*, Saber Sadeghi Pages 127-130
    Solar collectors compared to standard heating systems can provide significant savings in energy consumption. This paper concerns with analyzing the coupled radiative and natural convective heat transfer in solar flat-plate collectors, when the collector cavity is considered as a radiative participating media. First, an appropriate model for analysis of the thermal behavior of the collector is validated using reliable results in the literature. The discrete ordinates method is used for the radiative analysis and thermal analysis of a flat-plat solar collector, with real specifications and by considering water channel under the absorber, in summer solar conditions and for a wide range of air absorption coefficients are performed. According to the results, by increasing the absorption coefficient of the air, the temperature of absorber plate is decreased while the temperature of the air is increased. The effect of the absorption coefficient on the air temperature is higher than the temperature of the absorber plate. Also, by decrease in the absorber temperature, the outlet water temperature, that is approximately equal to the temperature of the absorber plate, is decreased.
    Keywords: Flat plate solar collector, Radiative heat transfer, Natural convection heat transfer, Absorption coefficient
  • Ali Sohani*, Sahar Rezapour, Hoseyn Sayyaadi, Yaghoob Khosravanifard Pages 131-134
    Using the combined cooling, heating and power generation (CCHP) systems is one of the most efficient ways to improve the performance of the systems which operate by combustion of fossil fuels. One of the first and important steps in implementation of CCHP system is the sizing of its prime mover. It is usually done based on the maximum power demand. Considering life cycle costs (LCC), annual carbon dioxide emission (ACDE) and annual average of efficiency (AAE) as the objective functions, a novel strategy for sizing the prime mover of a CCHP system was introduced for a residential complex including 72 same buildings each consisting of 7 same units. Pareto optimal frontier (POF) and final optimum solution were found by Non-dominated sorting genetic algorithm II (NSGA-II) method and TOPSIS. The results showed that the best strategy for sizing the prime mover was based on 86.6% of maximum required electrical power, which in this case, the ACDE and AAE improved up to 14.3 and 0.37%, respectively, while LCC increased 15.4%.
    Keywords: Combined cooling, heating, power generation (CCHP) systems, Novel strategy for sizing the prime mover, Multi-objective optimization, Total life cycle costs
  • Mahdi Kouhestani, Roohollah Ahmadi* Pages 135-140
    With increase of population and modernization of the cities, energy demand for heating, ventilation and air conditioning systems increases rapidly to improve the satisfaction factor of buildings. Therefore, nowadays the importance of implementation of energy storage systems is significant. Latent heat thermal energy storage (LHTES) systems have many advantages due to their high-energy storage densities and small temperature variation during storage. In this paper, cooling load of a room in Tabriz was calculated by Career software. Then a numerical analysis of a free cooling system using commercial paraffin RT24, as phase change material (PCM), was performed and effect of inlet air temperature and flow rate of storage tank during charging and discharging processes was investigated. Cold energy storage simulation shows that air flow with the temeperature 19°C during night, lead the paraffin to solidify in 4 hours. Stored cold enrgy with the amount of 1.2 kW in PCM liberates energy, via free cooling system, in the room during 2.5 hours of July afternoon.
    Keywords: Latent heat thermal energy storage, Phase change material, Free cooling, Numerical analysis
  • Alireza Zolfaghari*, Haneyhe Bijari, Mojgan Chaji Pages 141-144
    Thermal comfort prediction of patient and surgical team has an important effect on the quality of surgery. Evaluation of thermal comfort at the top of the operating table is an important issue especially when the patient has thermal sensation in surgery under local anesthesia. This study was conducted to explore the influence of the inlet air temperature of the operating room (OR) on the thermal comfort of surgical team and patient. This was performed by applying a numerical calculation to map the air flow and energy field. In this regard, the AIRPAK software was employed to perform the numerical simulation. The results were reported in tree critical area: above the patient, the left and right side of operating table. Results revealed that due to increment of inlet temperature, Predicted percentage of dissatisfied of surgical team and patient increased by 0.1156 and 0.1868, respectively. Therefore, thermal sensitivity of patient to temperature variation is much higher than operation staff.
    Keywords: Sensitivity, Operating room, Temperature, Thermal comfort
  • Mehdi Nasrabadi*, Donal Finn Pages 145-148
    The growth in the use of mechanical vapour compression based air conditioning systems for office cooling in temperate climates has led to increased interest in alternative low energy active cooling systems. Cooling towers as a means for producing chilled water, in conjunction with radiant and displacement cooling systems, offer a possible alternative approach for space conditioning of office spaces in temperate climates. The current research hypothesis is based on assessing an integrated cooling tower and radiant/displacement ventilation cooling system for office conditioning in temperate climate. The concept is capable of producing chilled water between 14-18°C with low approach temperatures (1-3K) and using this water for building sensible cooling by radiant surfaces (floors or ceilings) and building latent cooling by displacement ventilation. A mathematical model of the cooling tower system was developed using MATLAB. The cooling tower was validated against experimental data and integrated with an EnergyPlus model of an office building model incorporating radiant cooling and displacement ventilation systems. Using the overall simulation model, assessment was carried out based on ASHRAE design day specifications for Paris as representative of warm and humid climate. The results indicated that although the COP of the integrated cooling system was fluctuated between 2 and 8, this system can provide thermal comfort condition during 67% of working hours in Paris design day.
    Keywords: Cooling tower, radiant cooling, thermal comfort, system performance
  • Mohammad Sayyahi, Mojtaba Mamourian*, Hosein Sabeghi Pages 149-152
    Modern air conditioning systems, thermal management of electronic components and progress towards miniaturizing parts have attracted the attention of engineers towards using thermal transfer instruments with high-performance. One of these tools is pulsating heat pipes with low cost and high efficiency for transferring heat from the source with high temperature to low temperature source. In this paper, design and manufacture of a prototype pulsating heat pipe were analyzed . The designed model consists of 6 loops of copper pipes with 2.2 mm inner diameter and 4 mm external diameter. The height of the loop is 280 mm, length of the evaporator and condenser is 100 mm and the adiabatic section is 80 mm. One of the most important parameters in pulsating heat pipes is working fluid and filling ratio. In this paper, the gas R-22 and distilled water is used in four of filling ratio. The results showed that the evaporator temperature has increased with increasing input power and thermal performance of distilled water is better than gas. Also, the filling ratio of 60 percent of distilled water has the best performance among the other fillings ratio.
    Keywords: Heat pipe, pulsating, working fluid, filling ratio
  • Ghanbar Ali Sheikhzadeh*, Alireza Aghaei, Narges Ahmadi Pages 153-156
    Common fluids such as water, ethylene glycol and oil have low thermal conductivity compared to metals and metal oxides. Hence, in recent decades, use of nanofluids has received significant interest. These fluids are colloidal of a base fluid (such as water or oil) with metal, ceramic or polymer nanoparticles. In this study, multi walled carbon nanotubes/water nanofluid in a forced convection heat transfer was investigated numerically in turbulent flow through a curved tube (180°) with constant wall temperature. Effects of Reynolds number and nanoparticles volume fraction on convection heat transfer were considered. Results showed that with increase in Reynolds number from 4000 to 6000, convection heat transfer coefficient was enhanced by 24%. Also, with increasing the volume friction of nanoparticles up to 0.01, convection heat transfer coefficient increased by 21% compared to the base flow.
    Keywords: nanofluid, multi walled carbon nanotubes, turbulent flow, Numerical analysis
  • Mohammad Mehdi Keshtkar*, Maryam Nafteh Pages 157-161
    The air quality in operating rooms has always been so important because of the harmful and undesirable gases and particles. As the air ventilation in surgery room is so crucial, a system must be used in the room to lead the dirt air to outside and replace it with fresh and filtered air. In this work, laminar air flow conditioning by linear slot diffuser and air curtain in the surgery room was investigated. For modeling of the problem, Computational Fluid Dynamic (CFD) was used. In this paper, it was tried to find the best procedure in order to overcome the undesirable factors in surgery room, such as pollution and velocity of the room. The purpose of this research is to find the optimized circumstances for the people inside the surgery room. The aforementioned factors were changed at deferent levels and then simulations were performed using FLUENT software to understand air curtain and linear slot diffuser conditioning effect in a surgery room.
    Keywords: Surgery Room Conditioning, Computational Fluid Dynamics, Air Curtain, Pollution, Linear Slot Diffuser
  • Mohammad Sayyahi, Mojtaba Mamourian*, Matin Ghadiri Pages 162-165
    One of the challenges facing engineers in the industry is high performance cooling systems. Pulsating heat pipe is suitable method for eliminating this concern. Besides, Nanofluid has attracted attention due to higher thermal conductivity and high thermal transfer properties in recent years. The performance of Pulsating heat pipes is based on the fluid phase change. In this paper, we analyze a prototype of pulsating heat pipe. The designed model is consist of 6 loops copper pipes with 2.2 mm inner diameter and 4 mm external diameter .Each loop is 280 mm that lengths of the evaporator and condenser are both 100 mm and height of adiabatic section is 80 mm. A two-step method of making nanoparticles and nano fluids with fill ratio of 60% is used and Fero fluids Fe3O4 mass concentration was varied at four levels (0.1, 0.3, 1, and 3).It was shown that the thermal resistance decreases with increasing input power, The results showed that thermal performance of nano fluid is better than pure water and the best performance is noticed in case of 1% mass concentration of nanofluid.
    Keywords: Pulsating heat pipe, nano fluid, ferro, fluid, working fluid
  • Javad Vaziri Naeen Nejad, Fathollah Ommi*, Seyed Hossein Moosavy Pages 166-170
    In water treatment plants, after collecting millimeter-sized particles by filters, cyclone separator are being used to deposit and remove micron-sized particles. In this study, a numerical simulation is carried out by applying two-phase Eulerian-Lagrangian and RSM turbulence model and grid independency test is performed. Then results are validated by comparison with experimental data. Continuously, by embedding an acoustic stimulator with specific frequency and amplitude, the collection efficiency of fine particles is investigated. Results show an increase in particles’ separation efficiency as the injection diameter and velocity increase. It has been shown that by applying an acoustic excitation, the separation of fine particles noticeably increased but this increase has no tangible effect on separation of large particles. Wake formation in a conventional and an acoustic cyclone is also compared. An optimized frequency and pressure level are introduced for better separation efficiency of sand particles. Finally, the effect of an acoustic excitation in different injection velocities has been studied and compared with a conventional cyclone.
    Keywords: Cyclone, Separation, Acoustic excitation, Frequency
  • Masoud Nazari *, Ali Ghaffari Pages 171-174
    The purpose of this study is to design a method for analyzing dynamic behavior of Heating Ventilation and Air Conditioning system (HVAC) to employ in online simulations. Essential data as input-output of neural network is provided using energy and mass conservation equations. An implicit numerical method is used to solve dynamic equations of coil. The results of mathematical methods are applied in the output of neural network to design an online model. The proposed model is based on an active system used in HVAC system of clean rooms in Iran Pasteur Institute. Since in active air handlers input and outputs are not measured, here air conditioning systems is modeled generally. The results in comparison with real system data indicate an acceptable performance of the proposed method, so that combination of numerical results with a nonlinear autoregressive exogenous model (NARX) makes it possible to control the system effectively besides saving a significant amount of time.
    Keywords: HVAC, online modeling, gray box, artificial neural network
  • Seyed Alireza Zolfaghari*, Hassan Hassanzadeh, Morteza Taheri Pages 175-179
    Investigation on thermal comfort in a public transport has a significant impact on the satisfaction of this environment. Therefore, in this study, the thermal comfort conditions in a bus was investigated and among the different factors affecting on the thermal comfort in this space, the shape and the location of the inlet valves are studied in order to achieve optimum thermal comfort index for seated people. Hence, three different inlet valves with the same area and the same inlet air velocity was considered; circular cross-sections under each seat, rectangular valves on the floor and rectangular valves on the body and at the height of 0.2 meters from the floor. The results show that in order to achieve the optimal thermal comfort index, temperatures for circular air inlet must be 24.0
    ̊ C, for rectangular valves on the floor must be 20.1
    ̊ C and for the rectangular valve of the body must be 21.6
    ̊ C. These results suggest that the use of circular air inlet in the cooling system is more economical. To evaluate the effect of height on the thermal comfort index, the difference of the index was calculated with the height of 0.1 and 1.1 meters for three different inlet valves. The results show that by the use of rectangular valve on the body, the distribution of thermal conditions on the body of the passengers will be more uniform.
    Keywords: Ventilation system, Bus, Thermal comfort
  • Rahim Sohrabi, Mohsen Ghazikhani*, Hamid Niazmand Pages 180-184
    Adsorption cycle has become one of most popular technologies in recent years which operates based upon the adsorption and desorption of an adsorptive material in an adsorbent material which is usually a porous solid. Thus, a four-bed adsorption cycle with silica gel-water as working pair is modeled by means of a computer code written in MATLAB software, and thermodynamic properties are obtained from REFPROP software. In this article, in order to consider the heat transfer process more accurately and the heat transfer to the environment from the tubes, the passing flow in the adsorbent beds, evaporator, condenser and the connecting pipes between the master and slave beds are discretized. The next step directs to investigate the effect of entrance flow temperature to the adsorbent bed during cooling and heating processes on the operating parameters of system and energy lost. The obtained results indicate that increasing the temperature of hot water and decreasing the temperature of cooling water will lead to the increase of COP and cooling capacity of system. Hence, the best choice based on the maximum available temperature for hot water and normal temperature range for cooling water are 75ᵒC and 25ᵒC, respectively. In these conditions, COP and cooling capacity of system will be 0.37 and 17.2Kw, respectively.
    Keywords: Adsorption, adsorbent bed, silica gel, COP, cooling capacity
  • Karim Jafarian, Alireza Zolfaghari*, Azim Nazari Pages 185-188
    In this study, a standard building has been simulated with carrier software. Energy saving and economic issues, arising from insulation, were discussed. By modeling the sample space ASHRAE Standard No. 600 in Tehran weather, the heating and cooling load of the building annual consumption is calculated by using proposed external wall materials. Besides, the amount of Heating and cooling energy savings, achieved with this insulation, was obtained. Wall insulation costs including labor, transportation and other expenses were also calculated. Finally, the break-even time to the spending costs were calculated and for insulation of external walls found to be about 1.5 years after investment. Also for the most frugal insulation, Western Wall with Heblex suggested insulation, the payback period is 13 months which is reasonable.
    Keywords: Heating, cooling load, economic feasibility, energy savings, break, insulation
  • Ehsan Bagheri Fahraji*, Mehdi Maerefat Pages 189-193
    Heat pumps are under variable loads in heating and cooling mode and their capacity must be controlled with respect to load. One of the best methods for heat pump control capacity is variable refrigerant flow (VRF) system. VRF heat pumps face complex dynamic conditions because of variable loads and interaction between heat pump and building, thus an appropriate heat pump modeling is essential for performance evaluation and utilization in control strategy fields. In the present paper, a study and comparison of VRF heat pump dynamic models to find an appropriate model for utilization in control strategy fields is performed. Among the available models, moving boundary model has high computation speed but lower accuracy and is not applicable sometimes such as start time. Finite difference model computation speed is low but its accuracy and stability is high. A combination of moving boundary and finite difference method (hybrid model) provides advantages in terms of model speed and accuracy as well as possibility to utilize in all dynamic and steady conditions. Besides, using this model in control strategy fields will result in appropriate performance, less building temperature fluctuations and less system energy consumption.
    Keywords: Heat pump, Dynamic model, Variable refrigerant flow (VRF)
  • Alireza Zolfaghari*, Mahdi Afzalian Pages 194-198
    In the present study, the effect of velocity of inlet air from raised floor plenum supply on thermal environment and performance in a data center has been investigated. Inlet air temperature is considered fixed at 12 ºC and the air velocity is varied at four levels (0.6, 0.8, 1.0 and 1.2 m/s). To evaluate these para,eters effect, three non-dimensional indexes such as Return Temperature Index (RTI), Return Heat Index (RHI) and Supply Heat Index (SHI) are used. Computational fluid dynamics (CFD) and AirPak are used to predict the effect of the inlet air velocity on thermal environment. Based on the results, with increase in inlet air velocity, Return Temperature Index and Return Heat Index are both increased while Supply Heat Index is decreased. This can be explained by increase in bypass airflow. Bypass airflow is caused by the air that leaves the CRAC (Computer Room Air conditioning) unit and return to it directly without passing through the servers. This causes the lower efficiency, lower lifetime for equipment and more energy consumption for data center. Moreover, mixing the cool air and hot outgoing air from racks is increased and performance of data center is decreased.
    Keywords: Data center, Thermal environment, Cooling system
  • Zahra Tahmasbi Abdar, Khosro Lari *, Morteza Abdolzade Pages 199-202
    Greenhouse cultivation offers more product than traditional manufacturing. Air conditioning is one of the most important tools for climate control inside the greenhouse. In this study, HVAC in a greenhouse through the thermal and fluid flow analysis of a cavity containing air under greenhouse conditions have been carried out using computational fluid dynamics techniques. In this cavity, coupled natural convection and radiation heat transfer occurs. The medium inside the cavity is considered as a gray participating medium without scattering. The upper wall of the cavity is semi-transparent that is affected by direct and diffuse solar radiation. To analyze the two dimensional and steady state flow, Navier-Stokes equations are used by taking constant viscosity. Discretization of governing equations is done using finite volume method and the discrete ordinates method is used to model the radiative transfer equation. Results for temperature and streamline distributions, the velocity at the centerlines and the Nusselt numbers at the walls are provided. The results show that with increasing Rayleigh number, the increase in radiation heat transfer is more significant than convection.
    Keywords: Computational fluid dynamics, Participating media, Discrete ordinates method, Solar radiation
  • Mahtab Aminzadeh, Ali Safavinejad, Alireza Zolfaghari * Pages 203-208
    In the present study, the performance of three arrangements of high temperature radiant heaters (single radiant heater, couple radiant heaters with the same powers and couple radiant heaters with the different powers) in presence of asymmetric flow field has been investigated. The aim is to evaluate their performance in providing uniform thermal conditions, energy consumption and contaminant distribution. For this reason, a sample industrial environment with one inlet and outlet opening has been considered. For the mentioned conditions, continuity equation, momentum equations, energy equation, radiative transfer equations and species concentration equation have been solved by OpenFoam numerical solver. Also, energy consumption has been evaluated. The results show 13% decrease in energy consumption and minimum amount of contaminant concentration while using single radiant heater. However, maximum floor temperature distribution deviation is noticed in this case. Furthemore, results indicate that the best arrangement is utilizing couple radiant heaters with different powers, sincethe temperature drop (due of asymmetric flow field) compensates and it has the minimum floor temperature distribution deviation Moreover, In terms of energy consumption and average of contaminant concentration, it is similar to couple radiant heaters with the same powers.
    Keywords: Radiant heater, Industrial environment, Contaminant distribution, Uniform thermal conditions
  • Jalal Ghandehari *, Ali Kianifar Pages 209-212
    Nowadays, considering the limitations of fossil fuels, using optimization methods such as nanofluids for increasing the efficiency of solar water heaters has received a significant attention. In this study, the effects of nanofluid iron oxide with a mixture of 50% water volume and propylene glycol base fluid, as the working fluid in the solar flat plate collectors, were experimentally investigated. Nanofluid iron oxide nanoparticles at three different mass concentrations and in three volumetric flow rate have been experimented. All tests were done on cloudless, clear days in summer, and in Hav ā khurshid Research Institute at Ferdowsi University of Mashhad. Results indicate the proper potential of nanofluid iron oxide (magnetite) in enhancing the thermal efficiency of solar flat plate collector, as the most important component of solar water heaters, as the maximum efficiency increase of 12% was noticed.
    Keywords: Flat- plate solar collector, Fe-3 O-4 nanofluids, Thermal efficiency
  • Payam Rahim Mashaei *, Seyed Mostafa Hosseinalipour, Hamid Fazeli, Mohsen Taheri Ghazvini, Sajede Madani, Kazem Esmailpour Pages 213-216
    An analytical-numerical study on the thermal behavior of nanofluid in a cylindrical heat pipe is performed to investigate the nanofluid application in air conditioning systems. Pure water and Al2O3-water nanofluid are used as working fluids. A mathematical modeling is developed to predict the heat transferred by the heat pipe between precooling and reheating sections of the air conditioning system. The obtained results by proposed model are validated against experimental data and a good agreement between them is observed. The effect of nanoparticle concentration and size on the amount of energy required in precooling and reheating sections are evaluated. The results reveal that using nanofluid can dramatically decreases the temperature difference between condenser and evaporator sections of a cylindrical heat pipe under constant transferred thermal energy condition. Enhanced condition for precooling and reheating processes is provided for higher concentration and lower size of nanoparticles. Also, not a significant variation in heat transfer is observed by increasing nanoparticles size beyond 40 nm. The findings of this study prove the potential of nanofluid application for air conditioning of buildings located in regions with hot and humid climate.
    Keywords: Air conditioning systems, Nanoparticle, Precooling, Dehumidification, Reheating
  • Jalal Ghandehari, Ali Kianifar* Pages 217-221
    Using nanofluids is one of the new methods to improve the thermal performance of solar collector, that is the most important component of solar water heaters. Exergy optimization or increase Exergy efficiency are the most important issues in thermodynamic systems. In this research, the effects of iron oxide nanofluids, with a base fluid consist of mixture of 50% water and propylene glycol as an agent fluid, in solar flat plate collectors was studied experimentally. Iron oxide nanofluid concentration was varied up to 0.3%, and discharge rate was also changed at three levels. All tests were performed on summer clear days and without cloud in Havakhorshid institute in Ferdowsi university of Mashhad. Results indicate iron oxide nanofluids has good potential to improve Exergy efficiency of solar flat plate collectors, as an increase of 1.2 % was noticed.
    Keywords: Flat- plate solar collector, Fe3O4 nanofluids, Exergy efficiency
  • Peyman Asad Ayoubi *, Mahmoud Ebrahimi Pages 222-225
    One method to maximize the generated power of wind turbines is to improve the performance of the rotor's blade. This is possible through optimizing their geometry design by maximizing the ratio of the lift to drag coefficients C_l⁄C_d of the airfoils. The airfoils used in the tip section of the rotor blade are thinner compared with other sections of the blade, which makes the tip lighter, thus inducing less amounts of momentum to the turbine hub. In the present study, after examination of 150 airfoils, those that met the criteria for the thickness of the blade tips were chosen. Then, using appropriate aerodynamic analyses, the airfoil featuring the highest value of C_l⁄C_d was selected for further geometrical design optimization. The geometrical design of the selected airfoil was optimized using Xflr software, so that the value of C_l ⁄(C_d )parameter was maximized. For the optimized blade geometry, the maximum increase of about 7.8 % in C_l⁄C_d parameter was noticed compared to that of initial blade.
    Keywords: Wind turbine, geometrical design optimization, rotor's blade, airfoil
  • Ali Edalati Nejad, Seyyed Abouzar Fanaei*, Javad Khadem Pages 226-229
    It is necessary to study the flame structure from the approach of its temperature, species consumption rate and pollutants emission. In this paper, the combustion of Methane/Air was investigated with the counterflow diffusion flame model using OpenFoam software. In order to model the problem, Multi-step GRI3.0 mechanism in 324 steps and 53 radical species was used. In this solution, the convergence of unsteady states was considered 10-6 for each time step and residual physical parameters. With the maximum error of 21%, it is an acceptable agreement in the comparison between numerical model and experimental data in the similar state. The results show that in this type of heating system, the amount of the production of carbon emissions that are harmful to human's health are almost critical.
    Keywords: Counterflow, Diffusion flame, Combustion of methane-air
  • Shahrooz Motaghian, Hadi Pasdarshahri* Pages 230-234
    Air curtain devices are widely being used as thermal sealing in environments with heavy human traffic from outer zones. One of these applications is isolating and sealing of cold rooms. In addition, these devices are used in order to keep wildfires and chemical pollutions from spreading. In this study, performance of vertical air curtains, which have more applications, are investigated in both aforementioned usage areas. Analysis of air curtain performance are investigated through two case studies: in the first one, Air curtain isolating performance in heat transfer reduction from a cold room to a warmer zone with 25ᵒC temperature difference is evaluated, in which the device is installed in warmer room. In the second case study, an ongoing fire in a room with presence of air curtain to control toxic CO from spreading to neutral room is simulated. The fire room is filled with CO at the temperature of 300ᵒC. the two case studies were conducted with identical geometries. . Sensitivity analysis is carried out on air curtain device efficiency in different jet velocities and velocity angles. Computational fluid dynamics (CFD) method by mean of commercial software ANSYS FLUENT 16.2 is used to evaluate air curtain effect.
    Keywords: Air curtain device, Cold room, Heat Transfer, Mass transfer, CFD
  • Alireza Zolfaghari, Hamed Bayazi, Mahtab Aminzadeh*, Ali Foadaddini Pages 235-239
    In this research, the effects of flow rate and temperature of supply air on the performance of a bed-based task/ambient air conditioning system (TAC) for heating have been investigated. A bed-based task/ambient air conditioning system including a bed, a supply air inlet on the top of the occupant's head and a return air outlet under the bed have been considered and for this system, the equations of flow, energy and thermal comfort have been solved by OpenFoam numerical solver. Furthermore, the thermal comfort conditions, local thermal discomfort and energy utilization coefficient have been evaluated in the present study. The results show that the performance of the mentioned system significantly depends on the supply air temperature and flow rate. So that, the low flow rates of supply air may cause non-uniform temperature and velocity distributions and this leads to unpleasant thermal comfort conditions. Also, in order to achieve the benefits of TAC systems, using of high supply air flow rates must be avoided, since high flow rates affect a wide area of the room instead of the bed zone. The results also indicate that the energy utilization coefficient increases with supply air flow rate increment that it shows the high advantage of using TAC systems for energy consumption in high supply air flow rates.
    Keywords: Task, ambient air conditioning system, thermal comfort, sleep conditions, energy utilization coefficient
  • Morteza Adibkia *, Abbas Salemi Tajjarod, Mohammad Adibkia Pages 240-244
    Limitations of energy resources and the essence of energy saving necessitate the use of the suitable paint to prevent energy waste in various buildings and industries. Ceramic insulations are of particular importance due to high thermal resistance, low absorption coefficient, and easy operation and implementation, caused by existed micro-particles in their compositions. In this study, a three-dimensional chamber is considered with real dimensions and boundary conditions are varied. Using Boussinesq approximation and due to the low Reynolds number, modeling and simulation were done using k-ε turbulence model (LRN), Do radiation model and Piso algorithm. Methods such as LCA technique, Exergoeconomic calculations, and exergy rate are also used for economic calculations and exergoenvironmntal factor is used for environmental impacts. The results indicate that exergoeconomic factor varies in the range of 45% to 85% and average exergy ratio of about 1.5 kw and the efficiency value of 90% are noticed. Finally, it is shown that the use of ceramic microparticles in the external wall of buildings saves energy up to 18%.
    Keywords: Optimization, exergoeconomic, exergoenvironmntal, ecological assessment, ceramic microparticles, energy saving
  • Alireza Zolfaghari*, Abdolazim Zarei, Abolfazl Farsad Pages 245-247
    This research deals with the thermal performance of a building with and without, a sunspace as a passive element of the building structure, in two different climate types of Tehran and Tabriz. For this purpose, DesignBuilder software is utilized to simulate and analyze the test case. Results indicate that using a double window sunspace with a schedule in summer time can enhance the thermal performance of the building and leads to decrease of about 16.2% in heating load for Tabriz and 15.2% for Tehran. During the summer, this results in lower cooling loads of about 15.1% and 14.2% for Tabriz and Tehran, respectively.
    Keywords: Passive solar systems, sunspace, energy consumption
  • Seyad Kazem Mousavi, Seyed Mohammad Hojjat Mohammadi *, Ebrahim Jahanshahi Javaranehran, Mehran Ameri Pages 248-251
    Small-scale cogeneration systems, by using the micro-turbines, have provided required electricity and heat in Hotels and residential complexes over the years. Hotels with CCHP system has higher energy efficiency compared to other energy systems, since usescogeneration waste heat for heating and cooling applications. The main advantages of cogeneration systems are reduction in fuel consumption, lower greenhouse gas emissions and environmental pollutions. In this study, it was tried to further introduce these systems, their function and economic analysis at the national level, in order to extend their usage in different places such as office, industrial, commercial and residential complexes. One method is to use solar radiation to provide part of energy required for water heating. Energy consumption pattern in a large hotel over the years was considered and economic analysis was performed for different energy consumption scenarios. Payback period were computed of each scenario, in order to make a positive attitude towards the use of cogeneration systems utilizing solar energy.
    Keywords: Co-generation, Micro-turbine, Flat plate collector, Economic analysis
  • Hadi Ramin*, Pedram Hanafizadeh, Mohammad Ali Akhavan Behabadi Pages 252-255
    In this study, dynamic transient model (Exact model) rather than annual heating and cooling degree-days method (crude and approximate one) was applied to calculate the annual heating and cooling loads in order to optimize the insulation wall thickness. Concrete and Expanded polystyrene (EPS) were considered as the main wall and insulation material respectively. One dimensional transient heat transfer problem for multilayer walls was solved to obtain the temperature distribution within the wall. In order to determine the optimum thickness, which minimizes the total cost of insulation and energy dissipation, the economic analysis was carried out for the lifetime of 25 years. Both heating and cooling loads are taken into account in the optimization process. Time lag and Decrement factor are also calculated for the un-insulated and insulated wall. Environmental aspects of energy consumption including fuel consumption and pollutant emissions are also investigated. Annual total fuel consumption and pollutant emissions were obtained for a wall with optimum insulation thickness and the results were compared with an un-insulated wall. The results demonstrated that the application of insulation materials in the optimum thickness decreases the total heating and cooling demands significantly. It is also found that using the insulation in buildings decreases annual fuel consumption and pollutant emissions considerably.
    Keywords: thermal, environmental optimization, insulation thickness, time lag, decrement factor