Sharif Digital Repository

Porous media have many applications including heat exchangers, single-phase flow and multi-phase flow packed beds and reactors with different flow patterns, aquifers, and oil and gas reservoirs. To evaluate the behavior of porous media there is need to understand transport phenomena. In this work, we focused on metal foam porous media as an advanced porous media. The effective thermal conductivity of solid matrix, heat transfer in the presence of fluid flow, and pressure drop were investigated using CFD techniques in micro-scale supposing that the solid foam structure consisted of connected kelvin cells. The comparison of simulation results with experimental data reported in literature shows... 

Transport phenomena i.e. momentum, heat and mass transfer are occurring inside the eye constantly. Any disturbance in each of these could lead to diseases or ocular problems. Konwledge of transport phenomena can help surgeons and specialists to identify problems more easily and cure the problems effectively. Further more, these phenomena have a great impact on drug delivery inside the eye. Therefore deep understanding of them makes investigation of different therapies easy and convenient. Consequently this understanding could lead to choose the best method and route of administration available. A precise model which is in consistence with the real human eye has been developed and the ocular... 

Flow turbulators have crucial importance in heat transfer and energy harvesting applications. Therefore, in this study, the thermo-hydraulic and vibrational behavior of the floe inside a circular tube with vibrational ball turbulators (VBTs) on an axial elastic wire is experimentally studied for the first time. In this novel design, the elastic wire facilitates turbulence by allowing VBTs to move transversally and rotationally and agitate the flow substantially. The effects of diameter and longitudinal distance (pitch) ratios of VBTs, the Reynolds number, and the axial tension of the wire, on the flow friction factor (f), the Nusselt number (Nu), the thermal performance factor (η), in... 

Laminar forced convection flow through a channel partially filled with a porous material was numerically studied in this thesis. The Navier-Stokes and Brinkman-Forchheimer equations were used to model the fluid flow in the free and porous regions, respectively. Coupling of the pressure and velocity fields was resolved using the SIMPLEC algorithm. The local thermal equilibrium was adopted in the energy equation. The effects of the thermal conductivity ratio, Darcy number, porosity, Reynolds number and height of the porous insert on velocity and temperature field were investigated. The results show that the flow behavior and its associated heat transfer are susceptible to the variation of the... 

Thermoacoustics deals with the conversion of heat energy into sound energy and vice versa. This new and emerging technology has a strong potential towards the development of sustainable and renewable energy systems by utilizing waste heat or solar energy. Although thermoacoustic devices are simple to fabricate; however, the design process is very challenging. The thermoacoustic phenomenon is discovered over a century ago; nevertheless, the rapid advancement in this field occurred during the past three decades when the theoretical understanding of the phenomenon is developed along with the prototype devices. There are several advantages of heat engines and refrigerators based on... 

In this thesis to simulate the behavior of liquid engine Thrust chamber of hot gas from a quasi one dimensional code used when the effects of the heat transfer and friction in those terma. As well as during the regenerative channel is simulated by considering the equation’s of continuity, momentum and energy for one dimensional, effects of increase temperature, pressure drop, change the density of coolant flow resulting from the warming which is visible along the way to increase the accuracy of calculation of the thermal flux output of the engine, use a suitable model for unclear boiling in consideration of heat transfer coefficient used coolant flow it has been. As well as coupling of heat... 

The aim of this thesis is experimentally and numerically investigation of annular flow between the inner rotating smooth surface and the outer stationary grooved surface with or without axial fluid flow. Mounting grooves on the surfaces is important in cooling of rotating machineries such as electric generators and rotating heat pipes. The effect of different parameters such as the air gap between the surfaces, the geometry of the grooves, axial flow and rotation speed are numerically and experimentally investigated. The experimental results with axial grooves show that the entrance length decreases up to 17% with increasing the grooves depth. The reason is enhancement of the mixing and the... 

The good performance in cooling, especially in systems with small dimensions, is one of the critical needs of many industries. Heat transfer around sphere in all systems that contain particles, is important. Many methods have been proposed to improve the heat transfer rate but using nanofluids is one of the ways that has attracted more attention than others. Ferrofluids have magnetic properties in addition to nanofluids properties and this has a significant impact in increasing the heat transfer rate. Controlling heat transfer by magnetic field is one of the unique characteristics of this fluid. The project aim is to investigate the effect of magnetic field on heat transfer around sphere in... 

We investigate heat transfer between parallel plates separated by liquid argon using three-dimensional molecular dynamics (MD) simulations incorporating with 6-12 Lennard-Jones potential between molecule pairs. We use thermal walls constructed from the oscillating molecules, which are connected to their original positions using linear spring forces. Channel walls are maintained at specific temperatures using a recently developed interactive thermal wall model. This approach is much more effective than the one which uses a fixed lattice wall modeling to simulate the heat transfer between wall and fluid. Heat flux and temperature distribution in nanochannels are calculated for channel height... 

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... 

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... 

The numerical modeling of engineering contact problems is one of the most difficult and demanding tasks in computational mechanics. Frictional contact can be observed in many problems; such as: crack propagation, metal forming operation, drilling pile etc. The thermodynamic coupling problems arise naturally in many industrial processes, such as thermal protection structures ,nuclear fuel elements, layerd structures , heat exchanger as well as metal forming. In these situations predicting temperature field as well as the stress field is of considerable applied importance. When two or more bodies are forced to contact whit each other as a result of thermal or/and mechanical load thermodynamic... 

The main idea of this investigation is to increase heat transfer rate by increasing flow circulation of working fluid. By placing additional branches in the evaporator section, secondary bubble pumps were created which improved the circulation of fluid inside PHP. This research was implemented in two distinct phases. In the first phase, the novelty was implemented on a single turn PHP and in the second phase, the same procedure was implemented on a 4-turn PHP. In order to investigate the impact of these additional branches, two similar heat pipes were fabricated. One of them was the conventional PHP and the other had additional branches and is named additional branch PHP (AB-PHP). Thermal... 

Multistream plate-fin heat exchangers are used to supply the energy required by process units in the oil and gas industry. improving their performance is very important to reduce operating costs. In many applications, mixed refrigerants have replaced to improve the performance of plate-fin heat ecxhangers; Because the greater adaptability of the mixed refrigerant to the required refrigeration conditions that reduces the exergy losses. The Prico liquefaction cycle is one of the most commercial and commonly used liquefaction cycles. One of the most important parameters in designing a Prico liquefaction cycle is the molar percentage of the mixed refrigerant components. Proper determination of... 

The present work illustrates the results of an experimental study of ferrofluid flow in a tube subjected to a constant heat flux on its wall and filled with permeable material under the effect of magnetic field. The aim of this project is investigating the enhancement of heat transfer and obtaining a uniform temperature distribution inside the pipe. In order to achieve this, a porous medium with a porosity of 0.39 and ferrofluid with volume fractions of 0.6, 1.0 and 1.5 are used simultaneously, in the presence of magnetic field. The experiments are held for four different Reynolds numbers of 147.1, 167.3, 184.3 and 205.1. Also, four various modes of the oscillatory magnetic field are applied... 

In recent years, different of nanoparticles as oil additives has been investigated in many studies . These research show that nanoparticles are deposited on the surface friction and improve tribology properties of base oil and also significant reduction of wear and friction caused by the nanoparticles. Compared with metal and metal oxide nanoparticles , carbon nanotubes (CNT) due to the high thermal conductivity and high aspect ratio , is an excellent candidate as the nanoparticle is dispersed . For preparing useful oil it is essential to stabilize nanoparticles in fluid that will not settle over long time . Oils containing nanoparticles by increasing the heat transfer coefficient... 

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... 

Some researches have been carried out in the last 20 years in order to increase the present IC engines thermal efficiency and their optimum performance. (HCCI) engine is viewed as a combination of spark-ignition (SI) and compression-ignition (CI) engines. This is because HCCI engines use premixed fuel/air mixture like SI engines and have auto ignition combustion after the mixture is compressed like CI engines. Control of combustion and ignition timing are the main challenges of these engines. Ignition delay, compression ratio, fuel air equivalence ratio and intake temperature and pressure are considered to be the most effective parameters on HCCI combustion.HCCI engines have great potentials... 

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... 

In this study, heat transfer and fluid flow inside a rectangular microchannel with partial porous media is simulated numerically. Darcy-Brinkman-Forchheimer equations are used to model the porous media. The effect of height of porous media, permeability (Darcy number), porosity and inlet velocity (Reynolds number) on Hydrodynamic and heat transfer performance are examined. At different values of height of porous media 0.2, 0.4, 0.6, 0.8, and 1 mm the Nusselt number of microchannel are 1.72, 1.78, 1.86, 1.94, and 2.02 compared to the microchannel without porous media. And the porous drop are 1.09, 1.2, 1.49, 1.76, and 2.15 compared to the microchannel without porous media. And FOM are 1.78,...