Sharif Digital Repository

In the real engineering problems, the existing materials in the nature or human-made materials, contain different heterogeneities from the view of small scale. Reinforced composite materials and porous media containing grains or micro-cracks are some examples of these materials. Due to the large amount of these heterogeneities as well as the small size, direct modelling of these micro-structures requires extremely high computational and memorial cost. Also, the equivalent models introduced in the literature, have strong limitations and therefore, cannot capture accurate behavior of the material. Hence, multiscale methods have been proposed in order to model these heterogeneous media with... 

Shallow geothermal energy is a renewable and sustainable form of energy that has the potential to help alleviate the growing climate and energy crisis. The most common system used to extract shallow geothermal energy is the ground source heat pump (GSHP) system. The concept of using underground structures in exploiting shallow geothermal energy for space heating and cooling has received increasing attention. This study focuses on the use of geothermal tunnels as a means of extracting shallow geothermal energy.This research examines the effects of different heat transfer mechanisms, and highlights the effects of this phenomenon by focusing on the effects of natural convection around the... 

When the fluid passes through the microchannel, some energy is lost due to drag force and pressure drop. One of the methods used in the last few decades to optimize energy consumption is creating superhydrophobic surfaces in microchannels. These surfaces, with their features such as increasing the contact angle and reducing the contact angle hysteresis, can reduce energy loss, which is due to the presence of unevenness on the surface, and by trapping air and creating a two-phase flow, they reduce the drag force. On the other hand, the air trapped inside these irregularities will also affect the heat transfer of the passing fluid in the microchannel, which by creating resistance in the... 

High temperature modular reactors (HTR) are the most likely next generation reactors that will meet future energy needs. Their inherent safety is the most attractive feature of this type of reactors, and along with that, we can mention the ease of their design, operation and maintenance. Since the reactor is safe in the event of an accident, without activating any external source of security, this reactor is considered intrinsically safe. Despite this inherent property, the reactor is only affected by its physical characteristics, and therefore, many dangerous situations are prevented.The inherent safety feature of this reactor is completely dependent on its proper design. The power density... 

Lithium-ion batteries have the ability to store a significant amount of energy and work at high power, which has led to the wide spread of their use in various industries. In high-power applications, battery heat management increases lifespan, safety, and reduces battery power loss. In this study, the heat management of a very common and widely used 18650 battery using multi-layered phase change material has been investigated. The reason for using multiple layers is that each phase change material has its own weaknesses in addition to its advantages. It is expected that with the proper use of several phase change materials in the thermal management system, the materials will reduce the... 

One of the steps in the production of nuclear fuel pellets used in the core of a nuclear reactor is sintering. Sintering means the consolidation of a pressed powder sample into an integrated solid. This process can be done in different ways, such as traditional sintering, microwave, spark plasma, etc. In the process of fabrication of nuclear fuel pellets, after producing uranium dioxide in powder form and making corrections on the size distribution of powder grains, it would be nolded and then sintered. In this research, the temperature evolution of the green pellets introduced to microwave heating were investigated. In this report, a brief overview of the principles of microwave heating is... 

One of the main components of any solar power plant is the heat storage. Implementing heat storage reduc-es the cost of power generation by increasing the capacity factor of the system. This Thesis aims to analyze the operation of heat storages by modeling latent heat
storage. In this regard, an efficient method named "Method of Characteristics" is utilized. Models developed based on this method are possible to be used for comparison, sensitivity analysis, and optimization due to their low computation time. Sensitivity analysis was carried out based on various parameters such as void fraction, fiUer material size. Results show that using latent heat storage, storage c-apacity is... 

There are different technologies for supplying water from alternative sources that meet different needs. In relation to thermal technologies such as multi-effect distillation, the highest water quality is obtained, there is no limit on the concentration of the incoming water, and there is the least need for maintenance. On the other hand, thermal technologies consume higher energy than membrane technologies. In this process, the better the heat transfer, the number of steps can be increased, and this means the production of more distilled water for the same amount of thermal energy. The distilled water layer on the surface of the heat exchanger has a high thermal resistance compared to the... 

Nowadays, the cooling of electronic equipment has become a challenge for designers and scientists due to their progress. One of the most effective solutions for cooling these devices is using microchannel heat sinks. Researchers conducted so many studies experimentally, numerically, or a combination of them to increase the efficiency of microchannel heat sinks. Several methods have been proposed in previous studies to improve the cooling performance, such as using fins, nanoparticles, porous material, etc. Although increasing the heat exchange surface by using fins is caused to increase heat transfer, it also causes an increase in pressure drop. For this reason, researchers are looking for... 

The limitation of fossil fuel sources and environmental damage caused by use of these fuels have made researches on applications of renewable energy, especially solar energy, to be an important issue in recent years. An important issue that arises in the use of photovoltaic panels is the reduction of their efficiency with increasing their temperature. By increase of a degree of Celsius, the efficiency of the photovoltaic panel decreases by 0.45%. The aim of this project is to reduce the temperature of the photovoltaic panel by using porous medium and air. The porous medium used as fins under the panel.Experimental results have shown that by using the medium placed under the photovoltaic... 

Increasing global demand for water, food, energy and the interdependency of these three nexuses increase the necessity of finding suitable solutions and making policies considering the impact of each nexus to the others. The aim of developing greenhouses is to produce high-quality food with high performance while the water consumption decrease. This comes along with huge amount of energy consumption. Solar greenhouse technology utilizes solar energy to decrease heating demand of greenhouse to zero. The greenhouse performance has a direct correlation with climate condition. This research has been conducted to present optimal design for solar greenhouses. Firstly, a solar passive design was... 

Creating sustainable development in today's society is essential, and one of the most important elements to achieve this is the phenomenon of recycling. Lead-acid batteries are one of the sources of environmental pollution, and their separators contain 50% recyclable silica nanoparticles. In this research, impurities in these separators were removed using two methods: washing with water and sandblasting. The purity of recycled nanoparticles was 85.5% in the first method and 98% in the second method. In addition to the importance of recycling, finding a suitable use for recycled materials is also critical. FDM 3D printing is a new method of producing parts, but polypropylene is not commonly... 

The need for cooling and creating thermal comfort conditions for human life is one of today's severe challenges. Therefore, development and innovation to enhance the efficiency of these systems are of great importance. Among the new ideas proposed in this domain, we can mention the M-cycle, which can greatly improve the energy consumption for cooling systems in this sector. In this cycle, the desired cooling is produced by utilizing the latent heat of water evaporation, which is considered a kind of renewable energy. The systems based on this cycle are still under development, and for this reason, there is a necessity to better investigate the heat and mass transfer in the aforementioned... 

Numerical three-dimensional simulation of the entire regions of a gas turbine blade, including hot gas flow over the blade surface, conduction heat transfer within the blade metal, and coolant flow through the Internal cooling System, is highly time-consuming and expensive. Therefore, one-dimensional internal flow simulation is one of the main objectives of this research to address the limitations of commercial software in predicting the temperature distribution along the cooling path. In this study, a one-dimensional in-house simulation code is developed to simulate the coolant flow inside the cooling channels of the internal cooling system of the blade. Additionally, using artificial... 

Electrospray is a process in which the charged liquid is subjected to the effect of an electric field and after passing through an emitter, it will propagate in the form of jets or small droplets. This process is used in applications such as electric thrusters, cooling or mass spectrometry. In the electronics industry, cooling high-temperature microprocessors is a challenge. In this regard, air-based cooling systems are not well able to discharge heat from electrical and electronic components. Electrospray cooling technology is one of the new and promising methods. In this research, the two-dimensional simulation of electrospray cooling is performed by using COMSOL commercial software as a... 

CFD models are accurate but time-consuming for simulation and optimization of steam methane reformer and controlling the tube wall temperature, and syngas production rate and unsuitable for online optimization. Empirical data-driven models are less accurate when there are wide variations in operating conditions. The physics-based model presented in this thesis overcomes these limitations. In this model, the furnace side and the process side are divided into zones with uniform temperature and composition, and for each zone, mass, energy and momentum balances are derived. Radiative heat transfer modeling and calculation of exchange areas are accomplished with the zone method. The system of... 

Today, various industries rely on high-power, high-voltage induction motors for diverse applications. Given the critical role these motors play, any reduction in their lifespan or occurrence of failures can lead to substantial financial losses and even pose risks to lives. One significant factor influencing motor life is the temperature of its components. Manufacturers strive to enhance motor power while minimizing dimensions for economic reasons, but this increases power density and subsequent losses, elevating motor temperature. Consequently, thermal analysis becomes crucial, posing a significant challenge for companies producing high-power induction motors. In this study, a thermal model... 

The unique properties of phase change materials (PCMs), such as high latent heat and nearly constant phase change temperature, have made them a suitable option for use in thermal energy storage systems and thermal management systems. However, the low thermal conductivity of these materials has imposed limitations on their widespread use in industries. In this study, for the first time, the effect of injecting a boiling fluid (BF) into the PCM container to enhance heat transfer and accelerate the solidification process has been experimentally investigated. In this regard, paraffin wax and acetone have been selected as the PCM and the BF, and the effects of parameters such as the initial...