Sharif Digital Repository

Thermal management of micro-electronic devices is a contemporary issue which is increasingly gaining importance in line with the advances in packaging technology. Immediate and consistent multi-disciplinary research is needed to cater to the prevailing trends of net power and flux levels of upcoming micro-electronics products. Material science, packaging concepts, fabrication technology and novel cooling strategies are some of the key areas requiring synchronal research for successful thermal management. Focusing on the latter area, this thesis presents an experimental study on thermal performance of Micro-Closed Loop Pulsating Heat Pipes (MCLPHPs) which are new entrants in the family of... 

Today, the usage of hollow membrane contactors is considered by the researchers as a novel solution in the separation and purification industry, including the sweetening of gas. Improving the performance of these devices requires a more detailed study of the process factors and changes in its chemistry. Hence, providing a suitable mathematical model by examining the details of the flow pattern within the contactor is based on the computational fluid dynamics technique in the agenda. Also, improving the absorption of components such as carbon dioxide and hydrogen sulfide from the gas mixture using chemical absorbents such as monoethanolamine will be investigated. The change in the mass... 

Experiments were performed to explore the free convective hat transfer characteristics of water based nanofluids. Experiments of natural convection over a vertical flat plate with constant heat flux in water-based nanofluids with Ag and TiO2 nanoparticles were performed. Velocity boundary layer measured using PIV method. Also convective heat transfer coefficient obtained using three thermometers behind the wall. Various test cases with different heat fluxes on the wall are considered. Two volumetric concentrations of Ag nanofluid, 1% and 2%, and TiO2 nanofluid, 1% and 2%, were tested in the present study. It was shown that, with increasing nanofluid concentration, velocity boundary layer... 

Pulsating heat pipe (PHP) is a two-phase device for the means of transferring high heat fluxes and is used extensively for the electronic cooling. In this study the different flow regimes in PHP with different fluids have been investigated. In this research, 3 different fluids including: Pure fluids, Ferro-fluid and surfactant solution with %50 filling ratio have been used. For ferro-fluid, 5 different concentrations and 3 type of magnetic fields have been operated in 2 different heat pipes. Results show that ferrofluid is more stable in Pyrex made-heat pipe for long period of time and no magnet mode has the best thermal performance due to high conductivity of fluid. In copper made-heat pipe... 

Pulsating heat pipe (PHP) is a type of wickless heat pipe that has a simple structure and an outstanding thermal performance. Nanofluid is a type of fluifid in which nanoparticles are dispersed in a base fluid and has a better thermal conductivity in comparison with its base fluid. In this article, the performance of a nanofluid PHP is investigated. In order to simultaneously investigate the thermal performance and flow regimes in the PHP, a one-turn copper PHP with a Pyrex glass attached to its adiabatic section was used. A one-turn Pyrex PHP was also used to fully visualize flow patterns in the PHP. Our results showed that the material that a PHP made of and temperature of working fluid... 

Modern microelectronic systems generate a large amount of heat which must be transferred out of the system without excessive temperature rise. Conventional forced air convection and microchannel cooling plates have reached their performance limits Nanofiuids are proposed as an innovative way to solve the problem. A nanofiuid is nanoscale solid particles dispersed in a traditional heat transfer liquid. Some studies show an anomalous increase in the thermal conductivity for stationary nanofiuids. However, there are only few previous studies on the convection heat transfer rate and viscosity of nanofiuids. Both convection and stationary measurements of the thermal conductivity are widely... 

In this article, the problem of mixed convection in vertical rectangular microchannels for both regular fluids and nanofluids have been solved, using the CFD technique in the entrance regions of momentum and heat transfer taking in account the influences of viscous heating, inertial force and sleep conditions. In case of nanofluid flow, both the Brownian and thermophoresis molecular transfer mechanisms were considered.The predicted results were validated using fully developed distributions of velocity and temperature. Furthermore, the influences of mixed convection parameter (Gr/Re) and Kn number values on distributions of velocity and temperature through the entrance and fully-developed... 

The advances of technology of microelectrical devices and their computational capacity and so, their heat rates, make the thermal control of them more complex. Utilizing nanopfluids is one of proposing options. The current research investigates the effectiveness of using nanoparticles on the heat transfer rate of fluids in the natural convection. A two-component two-phase lattice Boltzmann method (LBM) has been implemented for this purpose. A wide range of Rayleigh number (Ra), namely 103 to 109, 0 to 0.05 volume fraction s of nanoparticles and nanoparticle diameters below 100 nm has been investigated in this research. The method is optimized for complex geometries. Two and three dimensional... 

In liquid-liquid extraction, as in gas absorption, two phases must be brought into good contact to permit transfer of material. The presence of nanoparticles in liquid phase can enhanced the rate of gas-liquid mass transfer. The benefits of nanofluids can be used to enhance the heat and mass transfer of liquid-liquid extraction. Standard test system with low interfacial tension that recommended by EFCE: n-butanol/water/succinic acid, was used in this project. The CNTs/n-butanol that was saturated of water used as dispersed phase. Water and succinic acid used as continuous phase and solute. Since there is no chemical reaction to take place between CNTs and n-butanol, In order to obtain well... 

Regarding to the effect of nanoparticles on mass transfer and hydrodynamics characteristics, limited number of studiesavailableinthe literature.In this work, mass transfer performanceand hydrodynamic characteristics nanofluidshavebeeninvestigated in the liquid−liquid extraction process. The chemical system of toluene-acetic acid-water was used, and two Extraction columnswith diameter of 10cm and height of 55cm and 6 cm were designed. The drops were organic nanofluids containing silica nano-particles and carbon nano-tubes.Synthesized silica nanoparticles by sol-gel methods, were modified with Triethoxyoctylsilane and Polydimethylsiloxane as well as Carbon nano-tubes were modified with dodecyl... 

In this paper, carbon structures such as multi wall carbon nano tubes, graphene and hybrid graphene-iron oxide, for utilisation in wet cooling towers in order to improve heat transfer are being discussed. All synthesized nanoparticles are prepared by chemical vapour deposition and wet chemical methods. Nature and structure of the created particles is also being examined by using X-Ray diffraction, transmission electron microscope and scanning electron microscope. The water used in this research is a kind of brine water, currently being used in industrial cooling towers at oil-rich regions of southern Iran. Performing the ICP test on the available water and by exact determination of its... 

In recent years, Rheological behavior and heat transfer of nanofluid studies have been increasing considerably and results show significant progress in this area. In this study we analyze the laboratory examination of the influence of parameters of volume fraction and temperature on thermal conductivity coefficient, dynamic viscosity of new and useful nanofluid carbon nanotube in engine oil. Most of fluid comparing to solid has lower thermal conductivity coefficient therefore solid particles increase thermal conductivity coefficient. On the other hand by adding particles, the dynamic viscosity of nanofluid also increases. Since nanoparticles have high volume ratio to surface (SSA) they have... 

One of the critical challenges in droplet based micro- and nanofluidic devices is handling the droplet breakup such that a controllable droplet size is produced. The experimental and numerical investigations at the microscale indicate that the droplet size can be well controlled by T junction geometries. In the present study we use non-equilibrium molecular dynamics (NEMD) simulations to investigate this phenomenon at the nanoscale. In order to generalize the study the Lennard-Jones type potential between the fluids and the walls have been considered and the strength and the effective range of the potential are changed to consider a wide variety of materials. Our results reveal that the... 

Inhencemant of automobile radiator heat performance is the purpose of this study. Radiator fin shape, coolant fluid properties and influence of nanofluid studied in this research. Plain fin, louvered fin and vortex generator fin is choosen and design. With flow simulation influence of fin shape on heat performance is studied. After that, with considering radiator coolant fluid, the effect of antifreezing on fin heat transfer is evaluated. Then by addin nanoparticles to water and antifreezing solution, effect of nanofluid on heat transfer is evaluated. Results show that with increasing the air velocity for all geometries in the study , heat transfer and pressure drop is increased. But heat... 

Today, oscillating heat pipes play an undeniable role in energy recovery due to their high thermal capacity. Studies show that the working fluid plays a more effective role in improving the performance of the oscillating heat pipes. In this study, a model is proposed to determine the optimal concentrations of Fe3O4-MWCNT/DI Water hybrid nanofluid based on NSGA-II multi-objective optimization algorithm. The Thermophysical properties of the fluid have been optimized to obtain the concentrations that provide the highest thermal conductivity and specific heat capacity and the lowest dynamic viscosity and density for hybrid nanofluids. Then a number of these concentrations¬ have ¬been selected... 

Recently, the researchers try to identify the application of nanofluids for wettability alteration. Changing the wettability of reservoirs, which gas injects to them, to gas wet can lead to enhanced oil recovery. Although several studies have been conducted to introduce proper nanofluids for altering the wettability of reservoirs to gas wet, there is not enough study to investigate the application of nanocomposites for wettability alteration of carbonate reservoirs. In this study, 20 nanoparticles with different compositional structures were synthesized, and then various nanofluids were prepared for the experimental survey. Also, the potential of these nanofluids for wettability alteration... 

The use of nano-fluid, which is a stable solid liquid mixture, has been proposed as a new strategy for heat transfer operations. Much research has been done on heat transfer of nano-fluids until now, whereas the study of phenomena associated with phase change, such as boiling where there is heat transfer in larger scales is very necessary. The boiling process based on its potential for transferring high amounts of heat at low temperatures is a very effective and common mechanism, and it occurs in many engineering systems, including boilers at plants, evaporators in refrigeration systems and nuclear reactors. Also, a considerable amount of research was done recently in the field of... 

Resistive pulse sensing (RPS) has proved to be a viable method for detection and characterization of micro and nano particles. This method works based on ionic current variation inside nanopores. Modern fabrication methods have introduced different nanopore geometries for resistive pulse sensors therefore studing the effects of geometry on sensing performance of nanaopores is important. Numerical simulation has been used to study a wide variation of nanopore’s geometry configurations and study the physics behind this phenomena. Based on the results, numerical simulation could be used as a fast and easy tool for size determination for nanopore. To compare the sensing performance of different... 

The novel concept of using magnetic nanofluidic electrolyte for redox flow batteries (RFBs) is demonstrated for the first time. In this regard, the stable magnetic nanofluidic electrolytes are prepared by dispersing magnetic modified multiwalled carbon nanotubes (MMWCNTs) in the positive electrolyte of a polysulfide-iodide redox flow battery at mass concentrations of less than 0.3 g L−1. The electrochemical behavior of magnetic nanofluidic electrolyte was examined using cyclic voltammetry at different mass concentrations of MMWCNTs with a carbon felt electrode. Higher and stable peak current densities were observed at larger mass concentrations of MMWCNTs. A polysulfide-iodide redox flow... 

Enhanced oil recovery (EOR) techniques are gaining more attention worldwide as the proved oil is declining and the oil price is hiking. Although many giant oil reservoirs around the world were already screened for EOR processes, the main challenges such as low sweep efficiency, costly techniques, possible formation damages, transportation of huge amounts of EOR agents to the fields especially for offshore cases and the lack of analyzing tools in traditional experimental works, hinder the proposed EOR process.It has been shown that recently, nanoparticles are attractive agents to enhance the oil recovery at the laboratory scale.
In this study TiO2 nanoparticles were used to improve...