Sharif Digital Repository

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,... 

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... 

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... 

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 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... 

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... 

Pulsating heat pipes have been more studied in recent two decades as effective tools in dissipating waste heat from electronic components. Due to oscillating fluid flow model, these tubes have the potential of converting waste energy to power. This research presents a system that makes this potential to act. In this system, the oscillating slug-plug fluid flow pattern in an open-looped pulsating heat pipe makes a permanent magnet which is levitated in Ferrofluid to vibrate in an electromagnetic vibration-based generator in order to induce electro motive force. The fluid flow regime in pulsating heat pipe has been simulated numerically with finite element scheme. The model results for fluid... 

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... 

Considering the advantages and disadvantages of reported micropumps, we aimed to introduce a novel idea to diminish the disadvantages and promote the advantages of PiezoElectric micropumps. This novel idea operates based on a mercury slug actuation in a microchannel. This cyclic motion of the mercury slug which is similar to a piston, push the fluid in the microchannel and pump the flow. However, to bring this idea into the practice, a control system must be designed. This system contains: LABVIEW code, DAQ board & a switching Board. The pattern of actuating mercury is drawn in LABVIEW. DAQ Board produces electrical signals according to LABVIEW code. Switching board will transform the... 

First by reviewing some built micropumps, the importance of rotary magnetohydrodynamic micropump has been highlighted. Then some information about the performance and rules applied to these specific micropumps has been provided. Based on the research, the necessity of using transient flow relations for analyzing the procedure of these micropumps would become crucial. The next step would be extracting the information out of dimensionlessrelations of magnetohydrodynamic theory and dimension less equations of momentum in transientsingle-phase fluid flow which is moved by theoverall Lorentzforce in between 2 parallel surfaces. It would be done in two state of using constantcurrent source and... 

In this investigation Magneto Mercury Reciprocating Micrpump (MMRM) the combination of Magneto-Hydrodynamic and Reciprocating micropumps has been analyzed. To achieve the analytical and numerical solution of one-tank and three-tank MMRM, the momentum, continuity, volume fraction and magnetohydrodynamic equations have been presented. The dimensionless analytical solution of one-phase and two-phase three dimensional MHD flow in the condition of using constant current and potential electrical source, has been offered.
The boundary between mercury and air has been tracked via VOF method in OpenFOAM software. VOF equation has been solved by explicit method with variable time step and maximum... 

Design, fabrication and performance of the reciprocating micropumps with actuated fluid slug have been investigated. In these micropumps, pumping principle is based on reciprocating movement of a fluid slug. The fluid slug must be conductive in magnetohydrodaynamic micropump to be actuated by Lorentz force and have good magnetic properties in ferrofluidic micropumps to be actuated by an external magnetic field.
On the other hand, a theory is developed in ahead of design and fabrication process to diagnose the critical and the most influential parameters. Magnetohydrodynamic micropumps in 4 distinict design using nozzle-diffuser element, passive ball valve and active mercury valve have...