Sharif Digital Repository

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... 

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... 

This project reports an experimental work on the convection heat transfer of nanofluids, made of -AL2O3 nanoparticles and de-ionized water, flowing through a copper tube in the laminar flow regime. The results showed considerable enhancement of convective heat transfer using the nanofluids. The enhancement was particularly significant in the entrance region, and was much higher than that solely due to the enhancement on thermal conduction. It was also shown that the classical Seider and Tate equation failed to predict the heat transfer behavior of nanofluids. Possible reasons for the enhancement were discussed. Migration of nanoparticles and the resulting disturbance of the boundary layer... 

Pulsating heat pipes (PHP) are complex heat transfer devices which unlike conventional heat pipes do not contain any wick in their structure. The effective parameters consist of; working fluid, volumetric filling ratio, operational orientation and input heat power have been investigated here. The experimental set-up we have contemplated, fabricated and tested included five turns, made of copper tube coupled with two glass tube of internal diameter 1.8 mm. The height of evaporator, condenser and adiabatic section was 60, 60 and 150 mm, respectively. The evaporator was heated with electrical element connected to an AC variant power supply and the condenser was connected to a constant... 

The main objective of this project is to study the effect of the presence of nanoparticles on mass transfer in liquid-liquid systems. To do this research, TiO2/water, Al2O3/water, CNTs/water and CNTs/toluene have been used as nanofluids. The experiments of TiO2/water nanofluid were been carried out in water-acetone-toluene system at two weigh percents of TiO2 nanoparticles. The result showed that mass transfer decreased in 0.5wt% of TiO2, compared to base fluid, and it increase in 1 %wt. Also in 0.5%wt the decrease in interfacial tension decreased diameter of drops and as a result mass transfer decreased too. In 1%wt the increase in viscosity increased the diameter of drops and then the... 

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... 

In the present study, Nano-fluid natural convection on a constant temperature vertical plate is numerically investigated, following the similarity analysis of transport equations. After changing the governing differential equations to the ordinary differential equations, they were numerically solved by the fourth order Runge-Kutta method.. The analysis shows that all three main profiles, velocity, temperature and concentration in their specific boundary layers, and the Prandtle number, depend on three important additional dimensionless parameters, namely a Brownian motion parameter, a thermophoresis parameter, and a buoyancy ratio parameter. Finally, it was found that the Nusselt number in... 

In this study, thermal and rheological properties of nanofluids of water/carbon nanotubes, water/spherical silica nanoparticles and water/hybrid nanoparticles (hybrid of carbon nanotubes and spherical silica nanoparticles) have been investigated. To do so, carbon nanotubes have been synthesized by CCVD process and spherical silica nanoparticles and hybrid nanoparticles by wet chemical method. After synthesis of nanomaterials, nanofluids have been prepared by using SDBS as a dispersant with the concentration of 1.5 times of concentration of nanomaterials and then thermal conductivity, kinematic viscosity, dynamic viscosity and density of nanofluids have been investigated. As the results show,... 

Nanofluids are new engineering materials with great potential for application in process industries. Their enhanced heat-transfer properties are reported in recent literatures. However, with respect to the influence of nanoparticles on mass transfer characteristics, limited number of studies available in the literature, deal primarily with gas-liquid systems. In this work, mass transfer performance and droplet behavior along a pulsed liquid-liquid extraction column, is studied where SiO2 nanoparticles with concentrations of 0.01, 0.05 and 0.1 vol% and different hydrophobicities are applied to the dispersed phase. Using ultrasonication, nanoparticles were dispersed in kerosene as the base... 

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... 

We studied dynamics of droplets inside channels under surface forces created by chemicalsteps on the channel walls. A multi-component Shan-Chen lattice Boltzmann method isused for this purpose.The effects of parameters such as the channel height, viscosity anddensity ratios on the results were investigated for homogeneous and grooved substrates. Alsoan analytical solution was developed for droplets under chemical heterogeneities in channels with smooth surfaces. The solution considers a general condition, namely, asymmetry of the contact angles on the top and bottom walls, the viscosity of the gas as the second fluid and the effect of the channel height. Then using Shan-Chen lattice... 

In the present study, mixed-convective heat transfer of nanofluids in a vertical rectangular channel partially filled with open-cell metal foam has been investigated experimentally and numerically. Al2O3–H2O nanofluids with different concentrations were synthesized and their stability was inspected with UV-Vis spectroscopy. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature profiles were obtained using finite difference method. The Brinkman–Forchheimer extended Darcy model and the... 

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... 

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... 

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... 

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 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... 

In the present work, the experiments were carried out for two types of PAM (3330 and 3630) with three distinct concentrations (25, 40 and 55 ppm) and TiO_2-water nanofluid for four concentrations (1.5, 2, 2.5 and 3 vol. %), and the Nusselt number and friction factor for each of them expressed separately. The Reynolds number was in the range from 11000 to 21000. The steady state turbulent convective heat transfer and friction factor of the combination of TiO_2-water nanofluid and polymer 3330 in the coiled tube were investigated. The effects of the Reynolds number for 2 vol. % nanoparticles which consists of 25 ppm PAM (3330) determined at the constant temperature of 24°C. It was observed... 

Despite of passing many years from invention of Computational Fluid Dynamics (CFD), simulation of the fluid-solid interfaces and free surfaces are still completely challenging and progressive problems. In addition knowing and understanding nanotechnology huge applications,modeling of nano-fluids have been became a priority for researchers. Adding importance of Non-Newtonian fluids (especially polymeric solutions) to this two subjects, triangle topics of this research becomes vivid. In this research tried to consider and examine behavior of Newtonian,Generalized-Newtonian, Viscoelastic and nano-filled viscoelastic fluids in one and two phase mediums. we followed mesh free methods which are... 

The theory of mass transfer accompanied by chemical reaction for gas-liquid systems was used to measure the specific interfacial area and mass transfer coefficient in a two impinging jets reactor (TIJR) in the presence of γ-Al_2 O_3 nanoparticles.The absorption of oxygen in sulfite solutions used for the determination of mass transfer characteristics. First 3 liters of nanofluids were prepared at concentration of 1 w% then diluted To produce 10 Liters of nanofluids containing 0.3 w%. The stability of this nanofluid was determined using uv-vis to be less more than 95% in the first 3 hours. The influence of weight percent of nanoparticles (0, 0.05, 0.1, 0.15, 0.2, 0.3) on the specific...