Sharif Digital Repository

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... 

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... 

A biocompatible ferrofluid have been prepared by co-precipitation of FeCl2.4H2O and FeCl3.6H2O under ultrasonic irradiation and with NaOH as alkaline agent. Also cystein was used as capping agent in the solution. Magnetic properties of the produced ferrofluid then determined by VSM test and magnetite nanoparticles were characterized by XRD and TEM techniques. Results indicate the presence of a biocompatible superparamagnetic ferrofluid including magnetite nanoparticles with particle size ranging under 15 nm. The effect of ultrasonic irradiation on presence of a sharp particle size distribution then denoted by comparing the condition with production without ultrasonic irradiation  

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... 

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... 

This thesis presents the prototype design and fabrication of magnetically actuated miniature pumps which utilize self-sealing capability of ferrofluid-covered permanent magnets in both pumping and valving mechanisms. The contactless external actuation feature of the design enables integration of the pump with other PMMA-based microfluidic systems with low cost and disposability. The body of the 1st fabricated prototype pump consists of three nozzle/diffuser elements and two pumping chambers connected to the ends of a flat-wall pumping cylinder. A cylindrical permanent magnet placed inside the pumping cylinder acts as a piston which reciprocates by using an external magnetic actuator driven... 

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... 

Nowadays cancer is the second major cause of death in the world after cardiovascular diseases and scientists and researchers are making considerable efforts to fight it. Detection and isolation of circulating tumor cells in the blood is of paramount importance as it can be further used to measure the disease severity as well as efficacy of chemical drugs. Magnetophoresis has attracted researchers because of its simplicity, high effectiveness and non-invasiveness. Microfluidic systems have a high potential for implementing conventional biological methods in a microscale for detection, separation and incubation of CTCs, and they also lead to reduction in costs and required samples. Prior to... 

Present study is designed to determine the effect of manganese content in primitive inverse spinel structure of iron oxide nanoparticles. PEG coated water base ferrofluids of Mnx¬Fe3-xO4 (0<0>1)nanoparticles were prepared by co-precipitation method in presence of nitrogen gas and ultrasonic waves using NaOH as a base for biomedical purposes. The crystallite size and structure of synthesized nanoparticles were studied using atomic absorption spectroscopy (AAS), X-ray diffraction spectrometry (XRD), field emission scanning electron microscopy (FE-SEM) and dynamic light scattering (DLS) methods. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) were used to... 

A biocompatible ferrofluid containing ?Fe?_3 O_4 nanoparticles was produced using co precipitation of ?FeCl?_2.?4H?_(2 )O and ?FeCl?_3 ?6H?_2 O under ultrasonic irradiation power with NaOH being the alkaline. Two variables studied in this research were concentration and molecular weight of PEG, as the coating agent. The impact of these variables were carefully monitored on shape, size distribution and magnetic behavior of nanoparticles through SEM, DLS, XRD and VSM characterization techniques. Moreover, MRI relaxation times,T_1and T_2, were calculated using synthesized nanoparticles as contrast agents. Accordingly these nanoparticles were biologically evaluated by MTT assay. Results... 

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... 

In this project, two Ferrofluidic micropumps that do not need any mechanical moving parts are presented. These micropumps are including simple microchannels containing magnetic fluid plugs that are used as flow actuator and the on/off valve. Using external magnetic field actuation in this type of micropumps, the magnetic fluid would have continuous motion in a channel with micrometer dimensions that would provide the main fluid to be pumped. Although the plug of magnetic fluid has surface contact with operative fluid, but considering its specific features, it would not compine with the pumping fluid. These micropumps may be used to pump the fluids or gases. The outcomes of the investigation... 

It has been shown that absorption of carbon dioxide can be enhanced using nanoparticles and in the presence of magnetic field. In the present work, the influences of ferrofluids and magnetic fields on the absorption of CO2 in packed-bed contactors have been investigated carefully. In this regard, multi-tube approach has been applied to model the contactor. The simulation results were validated against experimental data reported in the literature in the absence of nanoparticles and magnetic fields and good agreement was obtained. The influences of variable operating conditions on the contactor performance were carefully investigated. It was found that for 3.4% volume percent of magnetic... 

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... 

Ferrofluids are used in various fields such as drug delivery systems, heat transfer, biotechnology and separation processes. In this study, the splitting of ferrofluid microdroplets in symmetric and asymmetric T-junctions in the presence of a magnetic field has been investigated numerically and experimentally. These studies have shown that the creation of an asymmetric magnetic field can either affect the phenomenon of ferrofluid microdroplet breakup or the volume of microdroplets that are created after breaking and leaving each branch. Furthermore, more control can be applied to the phenomenon of microdroplet breakup. In the numerical study, the ferrofluid microdroplet breakup at different... 

Droplet-based microfluidics offers a promising tool in engineering and biomedicine such as drug delivery, biochemistry, sample handling in lab-on-a-chip devices, and tissue engineering. These systems provide the droplets manipulation that can be used as reactors without any contamination for medical purposes. Utilizing magnetic force and ferrofluid droplets can help to better control over the droplet formation and manipulation. Considering the importance of this issue and its rich underlying physics, in this dissertation, ferrofluid droplets formation under a time-dependent, non-uniform magnetic field is studied. A Pulse-Width-Modulation signal (PWM) is utilized to apply the time-dependent... 

The main objective of the present work was to improve the turbulence in single drops using ferrofluids (magnetic nanoparticles) in the presence of uniform and oscillating magnetic fields. In this regard, magnetite nanoparticles ($\mathrm{Fe_3O_4}$) were synthesized by co-precipitation method, characterized using DLS, FT-IR, XRD, VSM, and TEM, and their stability was checked by UV-Vis. The obtained results indicate the proper synthesis of nanoparticles with a mean diameter of about 20 nm and by coating their surfaces by silane that were well stabilized in the base fluid. In the numerical section, the governing equations of transport phenomena for a single drop containing magnetic fluids were... 

Considerable increase in speed and decrease in size of electronic devices results in increase of heat flux, so there is a need to enhance efficiency of cooling electronic devices. In the present research two sets of OLPHPs with five turns for two different magnetic nano-fluids were fabricated and the effects of working fluid (water, and two types of magnetic nano-fluids), working pressure, concentration, magnetic field, magnets location, and inclination angle on the thermal performance of OLPHPs have been considered in both startup and steady thermal conditions.
Experimental results show that magnetic nano-fluids can improve thermal performance of the OLPHPs. Application of magnetic... 

Liquid marbles are droplets enwrapped by a layer of micro/nanoparticles. Due to the insulation of inner fluid from the environment, the lower evaporation rate of the fluid, and the capability of motion even on hydrophilic surfaces, these liquid marbles, as an alternative to conventional droplets, have attracted the attention of researchers in digital microfluidics. Utilizing ferrofluid as the liquid core of the liquid marbles enables remote control over the liquid marbles by an external magnetic field. In this research, the dynamic behavior of ferrofluid liquid marbles under the magnetic field generated by an electromagnet is investigated. In this research, governing physics on the motion of... 

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...