Sharif Digital Repository

In this paper, a one-dimensional and two-dimensional numerical approach is used to study the effect of various parameters such as micro combustor height, mass flow rate and external convection heat transfer coefficient on the temperature and species mass fraction profiles. A premixed mixture of H2-Air with a multi-step chemistry (9 species and 19 reactions) is used. The transient gas phase energy and species conservation equations result in an Advection-Diffusion-Reaction system (A-D-R) that leads to two stiff systems of PDEs, which can not be solved by conventional Computational Fluid Dynamics (CFD) methods. In the present work, Strang splitting method, which is suitable for nonlinear stiff... 

Developing of electric instruments with high performance needs high capacity heat transfer equipments. Pulsating heat pipes have better performance compared with normal heat pipes and can be used for cooling electronic instruments in near future. Also, one specific kind of heat pipes, which is called rotating pulsating heat pipe, can be used in cooling the turbine blades. Rotating pulsating heat pipe is a mechanism in which the pipes can rotate around the axis perpendicular to the plane of pipes. In this research one rotating heat pipe was built and the effects of heat input, filling ratio and rotational acceleration were examined experimentally. The Innovation in the research was to obtain... 

Application of nanotechnology in the field of heat transfer has increased recently. The need to increase heat transfer rate yet decrease the size of cooling equipment, brought about lots of attention to thermal properties of Nanofluids. Nanofluid is the suspension of nanometer-sized solid particles in base liquid. Research on convective heat transfer of nanofluids which is only two decades old, shows great potential in increasing heat transfer rate. Although there is a remarkable research on thermal conductivity of Nanofluids, negligible research was conducted on combined Nanofluids . Developed Theory for thermal conductivity of combined nanofluid can be used to modeling the thermal... 

This research study presents an experimental investigation on forced convection heat transfer of an aqueous ferrofluid flow passing through a circular copper tube in the presence of an alternating magnetic field. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated convection regimes caused by interactions between magnetic nanoparticles under various conditions were studied. The process of heat transfer was examined with different volume concentrations... 

Nowadays, there is rapid development of practical engineeringsolutions to a multitude ofheating problems. Heat generated inmicro-devices used in manufacturing and electronics require specialsolutions. Pulsating Heat Pipes (PHPs) are novel and efficient technology in the field of heat transfer and previous researches show that using ferrofluid (magnetic nanofluid) in Pulsating Heat Pipes (PHPs) enhances the thermal performance in comparison with the case of distilled water under certain conditions by applying magnetic fields and the performance is dramatically improved at horizontal heating mode. In this research an experimental setup for visualizing two phase flows in a flat-plate Pulsating... 

Developing of electric instruments with high performance needs high capacity heat transfer equipments. Pulsating heat pipes have better performance compared with normal heat pipes and can be used for cooling electronic instruments in near future. Also, one specific kind of heat pipes, which is called rotating pulsating heat pipe, can be used in cooling the turbine blades and every rotating device. Rotating pulsating heat pipe is a cooling device in which the pipes can rotate around the axis perpendicular to the plane of pipes. In this research one rotating heat pipe was built and the effects of heat input, filling ratio, working fluid and rotational acceleration were examined experimentally,... 

Considering problems related to energy, including high fuel prices, increasing demand, constraints, and environmental pollution, makes it clear that efficiency is one of the major problems in all over the world. Iran’s southern parts and those countries around Persian Gulf face serious shortage of drinking water. Moreover, on top of the other three types of energy production the need for drinking water is highly sensible. Therefore, the use of CCHPW System is the best solution in these areas. The purpose of this design is to empower the control capability of the combined systems over all factors and apply the necessary changes under different conditions. This endeavor requires a program to... 

This research study presents an experimental investigation on forced convection heat transfer of an aqueous ferrofluid flow passing through a circular copper tube in the presence of a magnetic field. Both constant magnetic field and alternating magnetic field was examined. Moreover magnetic field layout and strength and modes of alternating magnetic field was investigated. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated convection regimes caused by... 

Thermopneumatic micropump is one type of positive displacement micropumps, which has many applications due to its relatively large stroke volume, low working voltage, and simple fabrication in microscale. In this paper, a numerical study of heat transfer and fluid flow in a valveless thermopneumatically driven micropump is presented. For rectifying the bidirectional flow, a nozzle and a diffuser are used as the inlet and outlet of the chamber. Since the fluid flow is induced by the motion of a diaphragm, the numerical simulation includes fluid structure interaction, which requires applying a dynamic mesh. The domain of solution is divided into two sections; the actuator unit, which contains... 

Loop heat pipe (LHP) is a two phase heat transfer device that is mostly used in cooling spacecrafts facilities. In this research a novel LHP is studied analytically and its steady state operating characteristics is analyzed in a one dimensional approach with heat transfer and pressure drop correlations. The novel LHP has a new arrangement in evaporator and reservoir configuration in comparison with conventional LHPs, which results in a different energy and fluid flow. In addition, the novel LHP has a new mechanism for acive control of working temperature. In modeling the proposed LHP the fluid and energy flows are first determined, then proper correltaions for calculationg each energy flow... 

A Loop heat pipe (LHP) is an efficient two phase heat transfer device that is widely used in cooling applications. In this research a novel LHP was designed, fabricated and its performance was investigated through various experiments. The novel LHP has a new arrangement in evaporator and reservoir configuration in comparison with conventional LHPs, which results in a different energy and fluid flow. In addition, the novel LHP has a new mechanism for active control of working temperature which was not already used. Aside from its good performance, this LHP has easier and lower cost manufacturing process compared with the conventional ones. Also the proposed temperature control method is... 

In this Study, experimental tests were carried out to investigate the effects of adding water-based ferrofluid to diesel fuel in a diesel engine. These effects included the combustion performance and exhaust emission characteristics of the diesel engine. To this end, emulsified diesel fuels of 0, 0.4, and 0.8 ferrofluid/Diesel ratios by volume were used in a four stroke diesel engine. The results indicate that adding ferrofluid to diesel fuel has a perceptible effect on engine performance, increasing the brake thermal efficiency and decreasing the brake specific fuel consumption as compared to diesel fuel. Furthermore, adding ferrofluid to diesel fuel increased the exhaust gaseous... 

A desired circulatory flow in flat-plate pulsating heat-pipes may improve electronic thermal management. This desired flow can be achieved by fabricating connecting channels (CCs) to increase flow resistance in one direction. In addition, connecting channels may increase the freedom degree of fluid. In order to investigate the effect of CC, two aluminum flat plate thermal spreaders with overall size 320mm×220mm×5mm - one with CC (CC-FPHP) and one without it- were fabricated. Both of the speaders have square channels with crosssection 2mm×2.8mm. The FPHPs were charged with ethanol as working fluid with filling ratios of 35%, 50%, 65%, and 80% by volume. Performance of connecting-channels in... 

On track to achieve heat transfer methods for small-scale, this research describes the design process of fabrication and experimental analysis of micro heat pipes with a rectangular section. First, the overview of micro-fluid systems and conventional mechanisms of heat transfer in these systems is discussed. Then, in order to describe the research theory and principles of heat pipe, various types of heat pipes micro scale and macro scaled are analyzed. After that, the method used for fabrication of a micro heat pipe without grooves is described. A new method for fabrication of MHP is investigated in this study. By using this method, one fiber glass board is fabricated by printed circuit... 

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... 

The use of nanofluids to improve the heat transfer has a special attention in the industry. researches focus on the efficiency of heat transfer nanofluids dates back to 1998. Ferrofluids are a particular type of nanofluids which their nanoparticles have magnetic effect and heat transfer can be increased by applying magnetic field to them. In this work, thermal and hydrodynamic performance of ferromagnetic fluid which flows through a copper tube in thermal entrance region has been studied. The flow in the tube is laminar and is affected by constant heat flux. Part of the tube contains a porous medium with paramagnetic properties and porosity of 0.46. Ferrofluid is composed of F e3O4 and water... 

Desalination of seawater is one of the best solutions for freshwater supply. Solar desalination is an appropriate way to desalinate seawater. The main disadvantage of solar desalination systems is low daily production. Considering the free radiative cooling potential, the purpose of this project is the increment of the daily yield of solar still by enhancement of condensation process. For transferring cooling potential of radiative cooling from nighttime to the daytime, phase change materials (PCMs) are used. Two types of condensers are fabricated in this project. One of them uses ambient air as a thermal sink and the other one uses radiative cooling which is saved in PCM. Describing... 

In this study, a mixture of nano-encapsulated phase change materials in water has been used as a working fluid in a pulsating heat pipe in order to investigate its thermal performance. The results of the experiments showed that using the nano-encapsulated paraffin dispersed in water as working fluid improves heat transfer and decreases the thermal resistance of the pulsating heat pipe. On the other hand, there is an optimal concentration among tested concentrations for nano-encapsulated paraffin, in which increasing its concentration due to the increased dynamic viscosity of the fluid causes an increase in the thermal resistance of the pulsating heat pipe. Enhancement in the thermal... 

Since oil prices continue to increase, energy conservation remains the prime industrial concern. Existing processes in power plants and oil refineries are not energy efficient as they should be therefore new projects can be defined to increase the energy efficiency without incurring any cost. The most appropriate utility for the processes should be explored to reduce emissions, increase the plant capacities and improve product qualities and energy efficiencies by one coherent strategic plan for the overall site which can be achieved by a full understanding of pinch technology and awareness of the available tools for applying it in practical way. Since the distillation unit of crude oil... 

One of the different methods of heat transfer, is pool boiling process. In this method, the operating fluid starts to boil on a hot surface whose temperature is more than boiling point of the fluid. Based on difference between between surface temperature and fluid boiling point, amount of heat flux from hot surface to fluid and fluid behavior will be different. In recent years, many researchers have tried to improve the amount of heat transfer in the boiling process by using various methods such as nanoparticle addition or using magnetic field.Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process, usually a first-order...