View All Items
(1 - 6 of 6)
- Title
- LATTICE VIBRATION STUDY OF SILICA NANOPARTICLE IN SUSPENSION.
- Creator
-
Sachdeva, Parveen, Kumar, Ranganathan, University of Central Florida
- Abstract / Description
-
In recent years considerable research has been done in the area of "nanofluids". Nanofluids are colloidal suspensions of nanometer size metallic or oxide particles in a base fluid such as water, ethylene glycol. Nanofluids show enhanced heat transfer characteristics compared to the base fluid. The thermal transport properties of nanofluids depend on various parameters e.g. interfacial resistance, Brownian motion of particles, liquid layering at the solid-liquid interface and clustering of...
Show moreIn recent years considerable research has been done in the area of "nanofluids". Nanofluids are colloidal suspensions of nanometer size metallic or oxide particles in a base fluid such as water, ethylene glycol. Nanofluids show enhanced heat transfer characteristics compared to the base fluid. The thermal transport properties of nanofluids depend on various parameters e.g. interfacial resistance, Brownian motion of particles, liquid layering at the solid-liquid interface and clustering of nanoparticles. In this work atomic scale simulation has been used to study possible mechanisms affecting the heat transfer characteristics of nanofluids. Molecular dynamics simulation for a single silica nanoparticle surrounded by water molecules has been performed. Periodic boundary condition has been used in all three directions. The effect of nanoparticle size and temperature of system on the thermal conductivity of nanofluids has been studied. It was found that as the size of nanoparticle decreases thermal conductivity of nanofluid increases. This is partially due to the fact that as the diameter of nanoparticle decreases from micrometer to nanometer its surface area to volume ratio increases by a factor of 103. Since heat transfer between the fluid and the nanoparticle takes place at the surface this enhanced surface area gives higher thermal conductivity for smaller particles. Thermal conductivity enhancement is also due to the accumulation of water molecules near the particle surface and the lattice vibration of the nanoparticle. The phonon transfer through the second layer allows the nanofluid thermal conductivity to increase by 23%-27% compared to the base fluid water for 2% concentration of nanosilica.
Show less - Date Issued
- 2006
- Identifier
- CFE0001278, ucf:46897
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001278
- Title
- Convective Heat Transfer in Nanofluids.
- Creator
-
Schraudner, Steven, Vajravelu, Kuppalapalle, Mohapatra, Ram, Rollins, David, University of Central Florida
- Abstract / Description
-
In recent years, the study of fluid flow with nanoparticles in base fluids has attracted the attention of several researchers due to its various applications to science and engineering problems. Recent investigations on convective heat transfer in nanofluids indicate that the suspended nanoparticles markedly change the transport properties and thereby the heat transfer characteristics. Convection in saturated porous media with nanofluids is also an area of growing interest. In this thesis, we...
Show moreIn recent years, the study of fluid flow with nanoparticles in base fluids has attracted the attention of several researchers due to its various applications to science and engineering problems. Recent investigations on convective heat transfer in nanofluids indicate that the suspended nanoparticles markedly change the transport properties and thereby the heat transfer characteristics. Convection in saturated porous media with nanofluids is also an area of growing interest. In this thesis, we study the effects of radiation on the heat and mass transfer characteristics of nanofluid flows over solid surfaces. In Chapter 2, an investigation is made into the effects of radiation on mixed convection over a wedge embedded in a saturated porous medium with nanofluids, while in Chapter 3 results are presented for the effects of radiation on convection heat transfer about a cone embedded in a saturated porous medium with nanofluids. The resulting governing equations are non-dimensionalized and transformed into a non-similar form and then solved by Keller box method. A comparison is made with the available results in the literature, and the results are found to be in very good agreement. The numerical results for the velocity, temperature, volume fraction, the local Nusselt number and the Sherwood number are presented graphically. The salient features of the results are analyzed and discussed for several sets of values of the pertinent parameters. Also, the effects of the Rosseland diffusion and the Brownian motion are discussed.
Show less - Date Issued
- 2012
- Identifier
- CFE0004214, ucf:49024
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004214
- Title
- MOLECULAR DYNAMICS STUDY OF THERMAL CONDUCTIVITY ENHANCEMENT OF WATER BASED NANOFLUIDS.
- Creator
-
Sachdeva, Parveen, Kumar, Ranganathan, University of Central Florida
- Abstract / Description
-
A systematic investigation using molecular dynamics (MD) simulation involving particle volume fraction, size, wettability and system temperature is performed and the effect of these parameters on the thermal conductivity of water based nanofluids is discussed. Nanofluids are a colloidal suspension of 10 -100 nm particles in base fluid. In the last decade, significant research has been done in nanofluids, and thermal conductivity increases in double digits were reported in the literature. This...
Show moreA systematic investigation using molecular dynamics (MD) simulation involving particle volume fraction, size, wettability and system temperature is performed and the effect of these parameters on the thermal conductivity of water based nanofluids is discussed. Nanofluids are a colloidal suspension of 10 -100 nm particles in base fluid. In the last decade, significant research has been done in nanofluids, and thermal conductivity increases in double digits were reported in the literature. This anomalous increase in thermal conductivity cannot be explained by classical theories like Maxwell's model and Hamilton-Crosser model for nanoparticle suspensions. Various mechanisms responsible for thermal conductivity enhancement in nanofluids have been proposed and later refuted. MD simulation allows one to predict the static and dynamic properties of solids and liquids, and observe the interactions between solid and liquid atoms. In this work MD simulation is used to calculate the thermal conductivity of water based nanofluid and explore possible mechanisms causing the enhancement. While most recent MD simulations have considered Lennard Jones (LJ) potential to model water molecule interactions, this work uses a flexible bipolar water molecule using the Flexible 3 Center (F3C) model. This model maintains the tetrahedral structure of the water molecule and allows the bond bending and bond stretching modes, thereby tracking the motion and interactions between real water molecules. The choice of the potential for solid nanoparticle reflects the need for economic but insightful analyses and reasonable accuracy. A simple two body LJ potential is used to model the solid nanoparticle. The cross interaction between the solid and liquid atoms is also modeled by LJ potential and the Lorentz-Berthelot mixing rule is used to calculate the potential parameters. The various atomic interactions show that there exist two regimes of thermal conductivity enhancement. It is also found that increasing particle size and decreasing particle wettability cause lower thermal conductivity enhancement. In contrast to the previous studies, it is observed that increasing system temperature does not enhance thermal conductivity significantly. Such enhancement with temperature is proportional to the conductivity enhancement of base fluid with temperature. This study demonstrates that the major cause of thermal conductivity enhancement is the formation of ordered liquid layer at the solid-liquid interface. The enhanced motion of the liquid molecules in the presence of solid particles is captured by comparing the mean square displacement (MSD) of liquid molecules in the nanofluid to that of the base fluid molecules. The thermal conductivity is decomposed into three modes that make up the microscopic heat flux vector, namely kinetic, potential and collision modes. It was observed by this decomposition analyses that most of the thermal conductivity enhancement is obtained from the collision mode and not from either the kinetic or potential mode. This finding also supports the observation made by comparing the MSD of liquid molecules with the base fluid that the interaction between solid and liquid molecules is important for the enhancement in thermal transport properties in nanofluids. These findings are important for the future research in nanofluids, because they suggest that if smaller, functional nanoparticles which have higher wettability compared to the base fluid can be produced, they will provide higher thermal conductivity compared to the regular nanoparticles.
Show less - Date Issued
- 2009
- Identifier
- CFE0002944, ucf:47969
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002944
- Title
- EXPERIMENTAL STUDIES OF THE HEAT TRANSFER CHARACTERISTICS OF SILICA NANOPARTICLE WATER-BASED DISPERSION IN POOL BOILING USING NICHROME FLAT RIBBONS AND WIRES.
- Creator
-
Vazquez, Diane, Kumar, Ranganathan, University of Central Florida
- Abstract / Description
-
This work deals with a study of enhanced critical heat flux (CHF) and burnout heat flux (BHF) in pool boiling of water with suspended silica nanoparticles using ribbon-type and wire heaters. Previously our group and other researchers have reported three-digit percentage increase in critical heat flux in silica nanofluids. This study investigates the effect of various heater surface dimensions and cross-sectional shapes on pool boiling heat transfer characteristics of water and water-based...
Show moreThis work deals with a study of enhanced critical heat flux (CHF) and burnout heat flux (BHF) in pool boiling of water with suspended silica nanoparticles using ribbon-type and wire heaters. Previously our group and other researchers have reported three-digit percentage increase in critical heat flux in silica nanofluids. This study investigates the effect of various heater surface dimensions and cross-sectional shapes on pool boiling heat transfer characteristics of water and water-based nanofluids. CHF and BHF were analyzed for circular and rectangular cross-section nichrome wires and ribbons of increasing sizes in the range of 0.32mm to 2.38mm width, approaching a flat-plate scenario. Experimental trends showed that the CHF and BHF in water pool boiling decrease as heater surface area increases, and for similar surface area, the wire had a 25% higher CHF than that of the ribbon. For concentrations from 0.1vol% to 2vol%, various properties such as viscosity, pH, and surface tension as well as silica deposition on surface and glowing length of ribbon were measured in order to study the possible factors in the heat transfer behavior of nanofluids. The deposition of the particles on the wire allows high heat transfer through inter-agglomerate pores, resulting in a nearly 3-fold increase in burnout heat flux at very low concentrations. Results have shown a maximum of up to 340% CHF enhancement for ribbon-type heaters, and the relationship of CHF with respect to nanoparticle concentration has been found to be non-monotonic with a peak around 0.2vol% to 0.4vol%. Visualization of boiling experiments aided with determination of relative bubble sizes, nucleation, and flow regimes. The surface morphology of the heater was investigated using SEM and EDS analyses, and it was inferred that the 2vol% concentration deposition coating had higher porosity and rate of deposition compared with 0.2vol% case.
Show less - Date Issued
- 2010
- Identifier
- CFE0003141, ucf:48635
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003141
- Title
- Agglomeration, Evaporation and Morphological Changes in Droplets with Nanosilica and Nanoalumina Suspensions in an Acoustic Field.
- Creator
-
Tijerino Campollo, Erick, Kumar, Ranganathan, Deng, Weiwei, Chow, Louis, Basu, Saptarshi, University of Central Florida
- Abstract / Description
-
Acoustic levitation permits the study of droplet dynamics without the effects of surface interactions present in other techniques such as pendant droplet methods. Despite the complexities of the interactions of the acoustic field with the suspended droplet, acoustic levitation provides distinct advantages of controlling morphology of droplets with nanosuspensions post precipitation. Droplet morphology is controlled by vaporization, deformation and agglomeration of nanoparticles, and therefore...
Show moreAcoustic levitation permits the study of droplet dynamics without the effects of surface interactions present in other techniques such as pendant droplet methods. Despite the complexities of the interactions of the acoustic field with the suspended droplet, acoustic levitation provides distinct advantages of controlling morphology of droplets with nanosuspensions post precipitation. Droplet morphology is controlled by vaporization, deformation and agglomeration of nanoparticles, and therefore their respective timescales are important to control the final shape. The balance of forces acting on the droplet, such as the acoustic pressure and surface tension, determine the geometry of the levitated droplet. Thus, the morphology of the resultant structure can be controlled by manipulating the amplitude of the levitator and the fluid properties of the precursor nanosuspensions. The interface area in colloidal nanosuspensions is very large even at low particle concentrations. The effects of the presence of this interface have large influence in the properties of the solution even at low concentrations.This thesis focuses on the dynamics of particle agglomeration in acoustically levitated evaporating nanofluid droplets leading to shell structure formation. These experiments were performed by suspending 500(&)#181;m droplets in a pressure node of a standing acoustic wave in a levitator and heating them using a carbon dioxide laser. These radiatively heated functional droplets exhibit three distinct stages, namely, pure evaporation, agglomeration and structure formation. The temporal history of the droplet surface temperature shows two inflection points. Morphology and final precipitation structures of levitated droplets are due to competing mechanisms of particle agglomeration, evaporation and shape deformation. This thesis provides a detailed analysis for each process and proposes two important timescales for evaporation and agglomeration that determine the final diameter of the structure formed. It is seen that both agglomeration and evaporation timescales are similar functions of acoustic amplitude (sound pressure level), droplet size, viscosity and density. However it is shown that while the agglomeration timescale decreases with initial particle concentration, the evaporation timescale shows the opposite trend. The final normalized diameter hence can be shown to be dependent solely on the ratio of agglomeration to evaporation timescales for all concentrations and acoustic amplitudes. The experiments were conducted with 10nm silica, 20nm silica, 20nm alumina and 50nm alumina solutions. The structures exhibit various aspect ratios (bowls, rings, spheroids) which depend on the ratio of the deformation timescale (tdef) and the agglomeration timescale (tg).
Show less - Date Issued
- 2012
- Identifier
- CFE0004610, ucf:49914
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004610
- Title
- Semi-Analytical Solutions of Non-linear Differential Equations Arising in Science and Engineering.
- Creator
-
Dewasurendra, Mangalagama, Vajravelu, Kuppalapalle, Mohapatra, Ram, Rollins, David, Kumar, Ranganathan, University of Central Florida
- Abstract / Description
-
Systems of coupled non-linear differential equations arise in science and engineering are inherently nonlinear and difficult to find exact solutions. However, in the late nineties, Liao introduced Optimal Homotopy Analysis Method (OHAM), and it allows us to construct accurate approximations to the systems of coupled nonlinear differential equations.The drawback of OHAM is, we must first choose the proper auxiliary linear operator and then solve the linear higher-order deformation equation by...
Show moreSystems of coupled non-linear differential equations arise in science and engineering are inherently nonlinear and difficult to find exact solutions. However, in the late nineties, Liao introduced Optimal Homotopy Analysis Method (OHAM), and it allows us to construct accurate approximations to the systems of coupled nonlinear differential equations.The drawback of OHAM is, we must first choose the proper auxiliary linear operator and then solve the linear higher-order deformation equation by spending lots of CPU time. However, in the latest innovation of Liao's " Method of Directly Defining inverse Mapping (MDDiM)" which he introduced to solve a single nonlinear ordinary differential equation has great freedom to define the inverse linear map directly. In this way, one can solve higher order deformation equations quickly, and it is unnecessary to calculate an inverse linear operator.Our primary goal is to extend MDDiM to solve systems of coupled nonlinear ordinary differential equations. In the first chapter, we will introduce MDDiM and briefly discuss the advantages of MDDiM Over OHAM. In the second chapter, we will study a nonlinear coupled system using OHAM. Next three chapters, we will apply MDDiM to coupled non-linear systems arise in mechanical engineering to study fluid flow and heat transfer. In chapter six we will apply this novel method to study coupled non-linear systems in epidemiology to investigate how diseases spread throughout time. In the last chapter, we will discuss our conclusions and will propose some future work. Another main focus is to compare MDDiM with OHAM.
Show less - Date Issued
- 2019
- Identifier
- CFE0007624, ucf:52551
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007624
