Comparison of nanofluid heat transfer properties with theory using generalized property relations for EG-water mixture

A numerical analysis for the determination for turbulent characteristics of fluid flow and heat transfer have been developed by employing the eddy diffusivity equation of Van Driest. The properties of Silicon dioxide (SiO2) nanofluid with spherical particles in base liquid ethylene glycol (EG) -water (W) mixture of 60:40 ratio is employed for a wide range of concentrations and bulk temperature. A good agreement of the numerical results with the experimental data for properties and heat transfer is observed. A comparison of Copper oxide (CuO), Aluminum dioxide (Al2O3) and Silicon dioxide (SiO2) nanofluids revealed that SiO2 attain higher temperature gradients in comparison to CuO nanofluid at the same concentration and temperature

Experimental and computational studies of nanofluids

Thesis (Ph.D.) University of Alaska Fairbanks, 2014The goals of this dissertation were (i) to experimentally investigate the fluid dynamic and heat transfer performance of nanofluids in a circular tube, (ii) to study the influence of temperature and particle volumetric concentration of nanofluids on thermophysical properties, heat transfer and pumping power, (iii) to measure the rheological properties of various nanofluids and (iv) to investigate using a computational fluid dynamic (CFD) technique the performance of nanofluids in the flat tube of a radiator. Nanofluids are a new class of fluids prepared by dispersing nanoparticles with average sizes of less than 100 nm in traditional heat transfer fluids such as water, oil, ethylene glycol and propylene glycol. In cold regions of the world, the choice of base fluid for heat transfer applications is an ethylene glycol or propylene glycol mixed with water in different proportions. In the present research, a 60% ethylene glycol (EG) or propylene glycol (PG) and 40% water (W) by mass fluid mixture (60:40 EG/W or 60:40 PG/W) was used as a base fluid, which provides freeze protection to a very low level of temperature. Experiments were conducted to measure the convective heat transfer coefficient and pressure loss of nanofluids flowing in a circular tube in the fully developed turbulent regime. The experimental measurements were carried out for aluminum oxide (Al₂O₃), copper oxide (CuO) and silicon dioxide (SiO₂) nanoparticles dispersed in 60:40 EG/W base fluid. Experiments revealed that the heat transfer coefficient of nanofluids showed an increase with the particle volumetric concentration. Pressure loss was also observed to increase with the nanoparticle volumetric concentration. New correlations for the Nusselt number and the friction factor were developed. The effects of temperature and particle volumetric concentration on different thermophysical properties (e.g. viscosity, thermal conductivity, specific heat and density) and subsequently on the Prandtl number, Reynolds number and Nusselt number of three nanofluids were investigated. The three nanofluids studied were Al₂O₃, CuO and SiO₂ nanoparticles dispersed in a base fluid of 60:40 EG/W. Results showed that the Prandtl number of nanofluids increased with increasing particle volumetric concentration and decreased with an increase in the temperature. The Reynolds number of nanofluids for a specified geometry and velocity increased with an increase in temperature and decreased with an increase in particle volumetric concentration. The Mouromtseff numbers of nanofluids were higher than those of the conventional fluids under both laminar and turbulent flow conditions, proving the superiority of nanofluids in electronic cooling applications. Experiments were performed to investigate the rheological properties of various nanoparticles dispersed in a 60:40 PG/W base fluid. The nanoparticles studied were; Al₂O₃, CuO, SiO₂, zinc oxide (ZnO), titanium oxide (TiO₂) with particle diameters ranging from 15 to 75 nm and particle volumetric concentrations of up to 6%. All the nanofluids exhibited a non-Newtonian Bingham plastic behavior at the lower temperature range of 243 K to 273 K and a Newtonian behavior in the temperature range of 273 K to 363 K. A new correlation was developed for the viscosity of nanofluids as a function of temperature, particle volumetric concentration, particle diameter, the properties of nanoparticles and those of the base fluid. Measurements were also conducted for single wall, bamboo-like structured and hollow structured multi-wall carbon nanotubes dispersed in a base fluid of 20:80 PG/W. A low-volume concentration (0.229%) of these carbon nanotubes (CNT) nanofluids revealed a non-Newtonian behavior over a measured temperature range of 273 K to 363 K. From the experimental data, a new correlation was developed which related viscosity to temperature and the Péclet number for CNT nanofluids. A three-dimensional CFD study was performed to analyze the heat transfer and fluid dynamic performance of nanofluids flowing in the turbulent regime in a flat tube of an automotive radiator. Computations were carried out for the Al₂O₃ and CuO nanoparticles of 0 to 6% particle volumetric concentrations dispersed in a base fluid of 60:40 EG/W. The numerical study revealed that under equal pumping power basis, the Al₂O₃ and CuO nanofluids up to 3% and 2% particle volumetric concentrations respectively, provided higher heat transfer coefficients than those provided by the base fluid. From this study, several new correlations to determine the Nusselt number and friction factor for the nanofluids flowing in the flat tubes of a radiator were developed for the entrance as well as the fully developed regions

Seasonal Migration and Moving Out of Poverty in Rural India: Insights from Statistical Analysis

Rural households in many countries have used temporary or seasonal migration as a strategy to cope with natural shocks such as drought, means of employment and income generation during lean season, and to move out of poverty. This paper studies the linkages between migration, employment in economic activities, asset accumulation, and poverty reduction among rural households in a droughtprone village of India over the last four decades. The Dokur Village of Mahbubnagar District in Telangana State of India experienced persistent drought over a decade. To cope with this situation, many households of the village temporarily migrated to the nearby and faraway cities. ICRISAT had conducted household surveys in Dokur under the Village Level Studies (VLS) and Village Dynamics Studies (VDS) program since 1975. The present study has used the VLS-VDS dataset (1975–2012) and reorganized sample households into 46 dynasty households. Based on their participation in migration, sample households were grouped into two categories: migrant and non-migrant households. Household income was computed by sources for all households for all the study years. Contribution of migratory income and remittances to the total household income was quantified. To identify the factors responsible for migration decision, probit analysis was carried out. For each year, sample households were grouped into poor and non-poor category using both lower (USD 1.25 ppp per day per person) and upper (USD 2.00 ppp per day per person) poverty line. The study revealed that seasonal out-migration helped many households to come out of poverty even though they had experienced a decade of drought. In-depth analysis of asset accumulation behaviour of the households over time revealed important insights regarding their coping mechanism and the process of moving out of poverty

A review on the heat and mass transfer phenomena in nanofluid coolants with special focus on automotive applications

Engineered suspensions of nanosized particles (nanofluids) are characterized by superior thermal properties. Due to the increasing need for ultrahigh performance cooling in many industries, nanofluids have been widely investigated as next-generation coolants. However, the multiscale nature of nanofluids implies nontrivial relations between their design characteristics and the resulting thermo-physical properties, which are far from being fully understood. This pronounced sensitivity is the main reason for some contradictory results among both experimental evidence and theoretical considerations presented in the literature. In this Review, the role of fundamental heat and mass transfer mechanisms governing thermo-physical properties of nanofluids is assessed, from both experimental and theoretical point of view. Starting from the characteristic nanoscale transport phenomena occurring at the particle-fluid interface, a comprehensive review of the influence of geometrical (particle shape, size and volume concentration), physical (temperature) and chemical (particle material, pH and surfactant concentration in the base fluid) parameters on the nanofluid properties was carried out. Particular focus was devoted to highlight the advantages of using nanofluids as coolants for automotive heat exchangers, and a number of design guidelines was suggested for balancing thermal conductivity and viscosity enhancement in nanofluids. This Review may contribute to a more rational design of the thermo-physical properties of particle suspensions, therefore easing the translation of nanofluid technology from small-scale research laboratories to large-scale industrial applications

A numerical study of magnetohydrodynamic transport of nanofluids from a vertical stretching sheet with exponential temperature-dependent viscosity and buoyancy effects

In this paper, a mathematical study is conducted of steady incompressible flow of a temperature-dependent viscous nanofluid from a vertical stretching sheet under applied external magnetic field and gravitational body force effects. The Reynolds exponential viscosity model is deployed. Electrically-conducting nanofluids are considered which comprise a suspension of uniform dimension nanoparticles suspended in viscous base fluid. The nanofluid sheet is extended with a linear velocity in the axial direction. The Buonjiornio model is utilized which features Brownian motion and thermophoresis effects. The partial differential equations for mass, momentum, energy and species (nano-particle concentration) are formulated with magnetic body force term. Viscous and Joule dissipation effects are neglected. The emerging nonlinear, coupled, boundary value problem is solved numerically using the Runge–Kutta fourth order method along with a shooting technique. Graphical solutions for velocity, temperature, concentration field, skin friction and Nusselt number are presented. Furthermore stream function plots are also included. Validation with Nakamura’s finite difference algorithm is included. Increasing nanofluid viscosity is observed to enhance temperatures and concentrations but to reduce velocity magnitudes. Nusselt number is enhanced with both thermal and species Grashof numbers whereas it is reduced with increasing thermophoresis parameter and Schmidt number. The model is applicable in nano-material manufacturing processes involving extruding sheets

Heterogeneous nanofluids: natural convection heat transfer enhancement

Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case