مصطفی مافی

Nowadays, Refrigeration systems play a very important and essential role in humans life, so that today's world cannot be imagined without refrigeration equipment. The range of these appliances is increasing daily, ranging from oil and gas equipment to air conditioning systems and health and nutrition. In the food industry, in addition to advances in the field of home refrigerators and cold storages for types of foods, we are seeing a growing expansion of stores and supermarkets that use refrigeration systems to keep food cool. With the increasing number of refrigeration equipment and the fact that they are one of the main consumers of electrical energy, in recent years extensive studies have been conducted to optimize this equipment both in terms of energy consumption and pollution of the environment is caused by the release of refrigerant material used in these devices. This article provides a comprehensive look at the history of refrigeration from a long time ago up to now. In this article, a comprehensive study of the history of refrigeration from the distant past to the present is taken. Also, considering the Futurology in this field and the need to use clean and renewable energies, the result was that it was necessary to supply some of the energy consumed by these systems with renewable energy.

The use of water electrolysis to produce hydrogen gas has received much attention in recent years, because in this method, water is decomposed into hydrogen and oxygen gas without any pollution. In this research, an organic Rankine cycle (ORC) is simulated and analyzed to utilize waste heat to run an electrolyzer. The power generated by ORC is used to produce hydrogen gas in proton exchange membrane electrolyzer (PEME). Model and codes for the electrolyzer is done by EES software, and thermodynamic analyzes are utilized in order to examine the performance of the proposed model. For the evaporator temperature of 67 ℃, the ORC power and thermal efficiency are obtained at 220 kW and 8.5 %, respectively. The production capacity of the electrolyzer considered in this research is 27 kg per hour of hydrogen gas with a temperature of 80 ℃ and a pressure of 101 kPa. Water electrolysis is performed using direct current between two electrodes, anode and cathode, which are separated by a membrane. To validate the simulated model, membrane potential at different values of current density is calculated.

Liquid hydrogen is a solution for storing and transmitting electricity that is produced by renewable energy sources such as geothermal energy. In this paper, a Rankine cycle with a proton exchange membrane electrolyzer, an ammonia absorption refrigeration cycle, and a hydrogen liquefaction cycle are simulated and analyzed for storing geothermal energy as liquid hydrogen. The power generated by the Rankine cycle is used to produce hydrogen gas in the electrolyzer. Additionally, the cooling obtained from the absorption refrigeration cycle is used to pre-cool the hydrogen gas to a temperature of -9.26 ℃, and then the hydrogen is liquefied at -253 ℃ by a mixed refrigeration cycle. The innovation of this study is based on using the cold energy obtained from the absorption refrigeration cycle in the liquid hydrogen production cycle and integrating the liquid hydrogen production process with the geothermal energy system. By using energy, exergy, and economic analysis, the final cycle efficiency was improved compared to the initial system. The special energy consumption of the liquefaction unit is 81.8 kWh per kilogram of hydrogen. In a three-year payback period, using economic analysis, the minimum selling price is calculated to be $2.11, which is lower than a similar liquid hydrogen production cycle presented in the past.

Due to the importance of hydrogen liquefaction and the low efficiency of the existing liquefaction plants, many pieces of research are done to develop a proper liquefaction concept. Utilizing innovative configurations, the use of geothermal and solar energies for absorption pre-cooling systems have been extensively investigated through various studies. In the present study, an innovative concept for hydrogen liquefaction, which utilize absorption pre-cooling supplied by wasted heat contained in gas power-plant’s exhaust flow, is developed and simulated by Aspen HYSYS V. 9. Using two separate equations of state for hydrogen and mixed refrigerant streams and realistic assumption about heat exchangers and turbo-machines have increased the accuracy, besides making it practical. The simulation results show that the developed concept has a better performance in terms of specific energy consumption and coefficient of performance compared to the other proposed concepts, so that the specific energy consumption and coefficient of performance are 4.55 and 27%, respectively. In addition, the suggested concept could be supplied directly by power-plant due to the requirement of being close to the power plant. This removes power distribution losses. Other key feature of the proposed concept, which sets it apart from the other concepts, is its capability to be used for energy storage.

A large part of Iran is located in a hot and dry climate and due to it, has a high amount of sun absorption. Indoor temperature comfort systems play a major role in energy consumption in various parts of the building, and by applying passive design methods such as solar chimneys can help maintain comfortable thermal conditions in buildings and reduce energy consumption. In this study, a thermal performance evaluation of the temperature distribution was performed by Design Builder simulation program in a building with office use in Kerman. Is. Then, by applying the chimney form variables, temperature changes and thermal comfort were studied at different angles to improve the effectiveness of solar chimneys at angles of 40 to 90 degrees in 10 degree steps relative to the horizon by solving the parameters of average air velocity and The volumetric flow rate of the flow was determined and finally, using the fluid dynamics (CFD) method of Design Builder software, the temperature distribution and the flow of air were investigated. Percentage can optimize the total energy consumption by about 16% and increase the thermal comfort index from its average value in July from 2.97 units to 2.25 units. Meanwhile, the average value of thermal comfort index in January has risen from -2.93 to -2.24 and its values ​​are closer to the standard range of Ashrae 55 and ISO 7730. However, an independent solar chimney is not able to meet the thermal comfort significantly in extreme hot weather,, and other solutions are needed to provide proper ventilation.

Using Hydrogen instead of fossil fuels has grown significantly due to its high energy density and zero carbon emission during consumption. The most economical method of storing hydrogen is liquefaction. In this study, after pre-cooling by the cold energy of the PRICO and liquefied natural gas (LNG) regasification systems, hydrogen gas enters the next stage and it liquefies by a mixed refrigeration cycle. The novelty of this cycle is based on the new design of a high-efficiency hydrogen liquefaction cycle which is using the cold energy of a LNG regasification process, in turn, results in less power consumption in the compression part and also less cost of power consuming for one kilogram of liquid hydrogen compared to that for a similar cycle. Energy, exergy, and economy analyses are implemented to investigate the proposed cycle. In the proposed hydrogen liquefaction cycle with the capacity of 14 tons per hour, the specific energy consumption (SEC) 15 % and payback period 20% decreased in comparison to the similar cycle.

Constructing peak-shaving liquefaction units with 600 times reduction in volume of natural gas, is the most desirable way to store surplus natural gas in the warm seasons and using it in cold seasons of the year. In this research, along with selecting Shahid Rajaee power plant in Qazvin as case study, the natural gas liquefaction cycle with mixed refrigerant with the purpose of supplying the fuel of total unit of this power plant for 60 days was established; and subjected to technical analysis. Then the amount of initial investment and current costs of the natural gas liquefaction unit is calculated. The economic evaluation of the project based on the net present value method and 12 percent discount rate assumption indicates the payback period is 4.3 years. Sensitivity analysis about variation in discount rate and initial investment cost is another consideration in this study. The results show that even with an increase in the discount rate up to 40% or 50% increase in the initial investment cost, the construction of liquefaction unit is economically justified, but by considering that the life cycle of project is 20 years, such a payback period is not much desirable.

In recent decades, the use of natural energy sources such as light and solar energy in the field of construction and architecture has been very useful. The aim of this study was to investigate the effect of the location of openings on indoor air flow distribution for thermal comfort of users and natural ventilation, in addition to the distribution of daylight factor and pmv in space. Air circulation, wind speed, air temperature and daylight factor in 16 scenarios of placement of openings in a cube-shaped residential architecture was studied in the hot and dry climate of Yazd as a case study. In addition, in the present article, computer modeling method, library studies and field measurement were used. The analyses of air circulation, wind speed, air temperature and user satisfaction (PMV) were carried out using CFD method in Design Builder software and the amount of daylight factor (DF) distribution, uniformity rate (Uo) were analysed using Relux Software. The results indicated that the placement of one opening in the direction of the prevailing wind and the other two openings in its lateral directions provided the desired air flow and turbulence with appropriate speed and air circulation creating thermal comfort conditions for users in space. The amount of ventilation and air circulation in space, speed, temperature and distribution were balanced. In this scenario, the user satisfaction index (PMV) was 5% higher than other scenarios and the amount of daylight distribution and visual comfort (uniformity rate = 0.6) were in the appropriate range.

Changes in the ambient temperature and feed gas flowrate are among the parameters that should be taken into account when designing peak-shaving single mixed refrigerant liquefaction processes. In this investigation, a liquefying system for storing the required gas energy for a typical 332 MW power plant during a 60-days cold season peak period was designed and its function under varying ambient temperature and also feed gas flowrate was studied. The results indicate that in minimum temperature condition, the minimum temperature difference in the multiflow heat exchanger will decrease with a slight slope, while with in maximum temperature condition, the minimum temperature difference in the multiflow heat exchanger will drop with a steep slope that show the risk of temperature cross during maximum temperature condition. Also, the study of changes in the flowrate of feedgas indicates that in the environmental conditions below the design point (base state), increasing the feed gas flowrate occasion increase the minimum temperature difference in the heat exchanger. But in the environmental conditions above the design point (base state), the increase in feed gas flowrate will result in a sharp decrease in the minimum temperature difference.

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 choice of glass has continuously played an important role in the physical structure of Islamic architecture and this selection has a direct impact on energy consumption. Meanwhile, azure blue as one of the most common colors in Islamic architecture, has received special attention. The present study seeks to study the type of indoor skylights in commercial complexes of Mashhad due to its importance in the amount of cooling load; heating; lighting, ventilation and indoor temperature. Due to this prominence, in the present study, by using a comparative research method; the most suitable type of glass in commercial complexes with indoor skylights is simulated using Builder Design software. For this purpose, primarily, the Almas Sharq Complex of Mashhad was simulated in software and then in order to determine the most appropriate type of interior skylight in commercial complexes, in terms of the effect on heating load, cooling, lighting, ventilation and temperature in the commercial complex; five types of glass were selected in two Hvac states, on and off. It was found that in the Almas Sharq complex of Mashhad in regard to the type of glass applied, the Thermochromics glass is the most suitable type of glass in order to reduce the temperature by 10%, and increase the entry of natural light in the cold and dry climate commercial complexes of Mashhad in both modes of ventilation system on and off.

The major share of energy consumption in the building sector includes cooling and heating systems. However, today the need for thermal comfort of users is met by using mechanical equipment. Passive design method can help maintain comfortable thermal conditions in buildings and reduce energy consumption by minimizing the use of mechanical or electromechanical air conditioning systems. In particular, the implementation of solar chimneys to ventilate the interior of the building reduces energy efficiency. Solar chimney is a passive and innovative design. In this article, an evaluation of thermal comfort performance in a government building with and without solar chimney integration in Kerman is presented, which is modeled by Design Builder simulation program and using fluid dynamics method. (CFD) The temperature distribution and airflow were studied. The results of this study showed that the integration of solar chimneys can reduce the PMV (predicted average vote) by 55% compared to the base building and its values ​​to The standard range of Ashri 55 and ISO 7730 is approaching. In the continuation of the research, experiments were performed on creating the lower cavity of the solar chimney. So that the PMV thermal comfort criterion from 4.63 units to 2.56 units and the average room temperature in the hottest month of the year (July) from 36.21 degrees Celsius to 33.61 degrees

In recent decades, atriums have been installed in public buildings to optimize energy consumption and provide thermal comfort, and therefore have always been of interest to mechanical engineers, architects and designers. Atrium also created different microclimates with different thermal layers in its lower space, which affected the cooling load and thermal comfort inside the building.Therefore,the purpose of this research, is to find the most suitable form and height of atrium for reducing energy consumption and heat stratification in commercial buildings of Mashhad city with cold and dry climate.

This research has used fluent software and Mathematical equations. Initially, Almase Shargh commercial building in Mashhad with central atrium in a spherical form of 5 m height was selected and after field measurements and data recording by dataloggers, the common atrium forms (spherical, prismatic, parabolic and flat at 3 m, 5 m, 7 m and 10 m) were replaced and in order to measure the heat stratification, the Mathematical formulas was used.

According to field observations and data measurements, the fifth floor and attic of the indoor skylight due to the influence of sunlight and lack of air conditioning, are critical areas of heat stratification and are out of range of thermal comfort throughout the year. Therefore, the amount of energy consumption during the year to provide thermal comfort in these floors is high, which can be reduced by reducing the levels of light-absorbing interior walls and using materials with high thermal capacity.

The results show that the flat form with a height of 3 meters, due to the reduction of light levels in the interior wall and the temperature difference between the floors is the most appropriate form of atrium for reducing energy consumption and cooling load up to 7% and reducing heat stratification in commercial complex in cold and dry climate of Mashhad city.

In this study, two types of dual-purpose compression refrigeration systems including single-compressor and dual-compressor (cascade) with different eco-friendly refrigerants to achieve two temperature ranges above zero and below zero have been investigated. The purpose of this study is to investigate the annual energy consumption of dual-purpose refrigeration systems with eco-friendly refrigerants and also to investigate the parameters affecting the efficiency of these systems. Studies have shown that the cascade system has a higher efficiency than single-compressor system and the best refrigerant in terms of performance in this system is R290. It was also found that in the single-compressor system only R134a refrigerant is applicable and the other refrigerants in the evaporator create pressure under atmospheric pressure. Also, this system is only applicable in hot and humid climates for all seasons of the year, while the cascade system is applicable in all seasons of the year and in all climates. Comparison of these two systems shows that assuming the total load capacity of the refrigerator is constant, increasing the cooling load in the low temperature range leads to increased energy consumption of the cascade system. Also founded that the annual energy consumption of cascade system is 7% lower than single compressor in the case of equal distribution of cooling load between two temperature ranges.

Iran is using natural gas as the main energy carrier in many sectors. Establishing peak-shaving liquefaction units due to reduction in volume of natural gas, is the most desirable way to store surplus natural gas in the warm seasons and using it in cold seasons of the year. Due to the high cost of operating and maintenance of liquefaction cycles, inventing solutions aimed at reducing energy consumption and improving the economy of these units, is really important. In this research, along with selecting Shahid Rajaee power plant in Qazvin as case study, the natural gas liquefaction cycle with mixed refrigerant and absorption refrigeration pre-cooling with the purpose of supplying the fuel of total unit of this power plant for 60 days was established. Then, it was subjected to technical and economic analysis and in terms of operational parameters was compared with common single mixed refrigerant cycle (without precooling). Results show that in comparison to common single mixed refrigerant cycle the specific power consumption %43, the cost of liquefaction plant equipment %15, the flow rate of mixed refrigerant %69 decreased and the figure of merit %28.36 increased.

In the last decade, renewable energy sources have been proposed as an appropriate alternative to meet the energy needs of remote rural areas. The present work focuses on the feasibility of locally available renewable energy production systems development (including solar systems and biomass resulted from manure dung). The studied rural area, Eastern Alamut, located in Qazvin province and consists of three cold and impassable villages of Pichebon, Narmelat and Dinheroud. In order to fulfill energy supply of the rural region, three scenarios have been presented and related techno-economic analyses have been done. Firstly, all heating (cooking and hot water are included) and electricity demands have been met solely by photovoltaic system. In the second scenario, heating and electricity have been supplied by biogas as well as CHP system. Moreover, the heat loss of CHP has been used to warm up the digester. In the last survey, the electricity need has been supplied by photovoltaic system along with covering heating demand through biogas. In this scenario, the required heat to operate digester is provided using the photovoltaic system. In each scenario, volume of digester and equipment of solar system have been calculated. The techno-economic analysis shows that the second scenario that has a positive Net Present Value in each discount rate (5%, 10% and 15%) and Internal Rate of Return is 24.24% 23.26% and 38.6% for Pichebon, Narmelat and Dinehroud villages, respectively, is as a practical design and economic option.

Positron Emission Tomography is one of the most efficient cancer diagnosis methods. In this method a radioactive (positron emitting) substance called Tracer is injected to the patient and the positron emission tomography scanner produces images by capturing the positrons emitted from the tracer existing inside the body. The qualified methods has mistaken in cancer diagnostics. In this paper, a mathematical method is used for diagnosis of cancerous region based on image obtained from positron emission tomography. A compartmental model based on ordinary differential equation is used for this reason. The fludeoxyglucose tracer which is one of most famous tracer for cancer diagnostic is used for modeling and the three compartments model is applied. To verify the applied mathematical methods, the experimental results of real case (positron emission tomography imaging of a mouse) is investigated and activity curve of tracer for different region of real case are plotted for diagnosis of cancerous tissue. The results indicated that reviewing time activity curves alongside positron emission tomography images can help enhancing the accuracy of cancer diagnosis.

In this investigation, performance enhancement of direct evaporative cooling system using storage reservoir of cold water has been studied. The water in the reservoir is aimed to store the cold energy overnight and use it during daytime to reduce the temperature of exhaust air from cooler. In this paper, at first stage, the governing equation of above mentioned hybrid direct evaporative cooler is extracted and then, the effect of water storage reservoir mass on the temperature of exhaust air from cooler is investigated. Take a typical summer day in Tehran for example; the results indicate that the use of storage reservoir containing water with a mass of three times larger than the mass of dry air passed through cooler per hour decreases the temperature of the cooled air by 2.02℃ at 14:00 clock. The major advantages of this system are shifting the hours for the maximum and minimum cooled air temperatures towards other hours of a day (e.g., from 05:00 and 14:00 to 06:00 and 18:00, respectively) as well as reducing the cooled air temperature range from 6 to 3.5℃.

In this article, the leakage of the refrigerant in a two stage liquefaction system with multi component refrigerant is studied. Leakage is occurred due to various factors, including the existence of cavity in high pressure area and affects the performance of the process. Due to the absence of a specific method to handle leakage of refrigerant an innovative method is performed and validated by comparing experimental data. The results show the leakage at high-pressure points, causes a little reduction of specific work, but the product (liquefied natural gas) is significantly reduced. Additionally, it is shown that leakage increases the risk of temperature interference in heat exchangers, which should cause malfunctions in system operation.

Early diagnosis of hypertensive diseases such as cancer plays an essential role in preventing disease progression. The main cause of death from cancer is the reappearance of the disease due to the release of tumor cells in the blood of the patient. Among the various methods that have been devised for monitoring blood in recent years, the techniques based on micro-scale flow have specially been considered. The development of these methods has led to the emergence of microfluidics laboratories on the chips, which their main advantages are low prices and simplicity. Since the particles’ sizes are different in the flow of blood, the direction of these particles in the micro-channels will vary due to the different forces, and therefore they can be analyzed to the design of bio-microchips. In the present study, a two-phase flow containing spherical particles with the dimensions of blood cells was considered, and the forces affecting the particles of this current, including the lift forces and drag forces, were studied using COMSOL software. For this purpose, a micro divergent channel was designed and the effect of ratio of the outlet width to the inlet width (Aspect Ratio) as an effective geometric parameter in the biological particle separation was analyzed. The study of the effect of particle dimensions and various geometric parameters of the channel on bio-particles separation are the main goals of this research. The results show that by increasing the Aspect ratio, focusing of the larger particles would increase at the outlet of micro-channel.