Analysis of heat transfer and entropy generation of TiO2-water nanofluid flow in a pipe under transition

Single and multi-phase numerical simulations are carried out to investigate the heat transfer and entropy generation behaviour of transitional flow of TiO2H2O nanofluid in a circular pipe. Results reveal that the small diameter of nanoparticles has the highest heat transfer rate for χ = 6% and the TiO2-water nanofluid shows higher heat transfer rate using multi-phase model compared to that of the single phase model. Also no optimal Reynolds has been observed which could minimise the total entropy generation. New correlations are proposed to calculate the average Nusselt number using a nonlinear regression analysis with a standard deviation of error of less than 0.5%

Entry Flow and Heat Transfer of Laminar and Turbulent Forced Convection of Nanofluids in a Pipe and a Channel

This thesis presents a numerical investigation of laminar and turbulent fluid flow and convective heat transfer of nanofluids in the entrance and fully developed regions of flow in a channel and a pipe. In recent years, nanofluids have attracted attention as promising heat transfer fluids in many industrial processes due to their high thermal conductivity. Nanofluids consist of a suspension of nanometer-sized particles of higher thermal conductivity in a liquid such as water. The thermal conductivity of nanoparticles is typically an order-of-magnitude higher than the base liquid, which results in a significant increase in the thermal performance of the nanofluid even with a small percentage of nanoparticles (~4% by volume) in the base liquid. In this study, Al2O3, CuO and carbon nanotube (CNT) nanoparticles with the particle concentration ranging from 0 to 4 % by volume suspended in water are considered as nanofluids. Entrance flow field and heat transfer of nanofluids in a channel and pipe are computed using the commercially available software ANSYS FLUENT 14.5. Both constant wall temperature and constant heat flux boundary conditions are considered. An unstructured two-dimensional mesh is generated by the software ICEM. For turbulent flow simulations, two-equation k-epsilon, standard k-omega and SST k-omega models as well as the one-equation Spalart-Allmaras models are employed. The results are validated and compared using the experimental data and other empirical correlations available in the literature. The entrance length of laminar and turbulent flows in a circular pipe and channel are calculated and compared with the established correlations in the literature. The effect of particle concentrations, Reynolds number and type of the nanoparticles on the forced convective heat transfer performance are estimated and discussed in detail. The results show significant improvement in heat transfer performance of nanofluids, especially the CNT nanofluids, compared to the conventional base fluids

Investigation Of Laminar Convective Heat Transfer And Pressure Drop Of SiO2 Nanofluid In Ducts Of Different Geometries

Engineers are seeking alternatives to conventional heat transfer fluids and in an attempt to improve their thermal transport properties, they added thermally conductive solids into the conventional fluids resulting in a fluid called nanofluid. Nanofluid was suggested as an alternative solution to the problem and many publications reported its potential for heat transfer enhancement. This thesis describes the experimental study of 9.58% by vol. silica/water nanofluid flow through different flow geometries which are circular, hexagonal and rectangular ducts of close hydraulic diameter. The experiments are performed at uniform heat flux condition. The aim of this thesis is to determine experimentally the best duct geometry for optimal thermal performance in nanofluids. The effect of the cross-section of the flow geometry on the enhancement capability of nanofluid is the focus of this research and four different geometries of relatively equal hydraulic diameters were studied. This study compares the result from the different duct geometries in order to identify the best flow channel for optimal heat transfer using nanofluids. Based on the test data, the thermal performance comparisons are made under three constraints (similar mass flow rate and Reynolds number). It was observed from the comparisons that the rectangular duct showed the highest heat transfer capability through a higher Nusselt number and heat transfer coefficients at for the silica/water nanofluid flow. The circular duct was next to the rectangular duct in thermal performance. There was no significant change in friction factor between the ducts for both water and nanofluid flow

Numerical investigation of Al2O3/water nanofluid laminar convective heat transfer through triangular ducts

In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article. Sometimes, because of pressure drop limitations, the need for non-circular ducts arises in many heat transfer applications. The low heat transfer rate of non-circular ducts is one the limitations of these systems, and utilization of nanofluid instead of pure fluid because of its potential to increase heat transfer of system can compensate this problem. In this article, for considering the presence of nanoparticl: es, the dispersion model is used. Numerical results represent an enhancement of heat transfer of fluid associated with changing to the suspension of nanometer-sized particles in the triangular duct. The results of the present model indicate that the nanofluid Nusselt number increases with increasing concentration of nanoparticles and decreasing diameter. Also, the enhancement of the fluid heat transfer becomes better at high Re in laminar flow with the addition of nanoparticles

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

Conjugate heat transfer of laminar mixed convection of a nanofluid through an inclined tube with circumferentially non-uniform heating

Laminar mixed convection of a nanofluid consisting of water and Al2O3 in an inclined tube with heating at the top half surface of a copper tube has been studied numerically. The bottom half of the tube wall is assumed to be adiabatic (presenting a tube of a solar collector). Heat conduction mechanism through the tube wall is considered. Three-dimensional governing equations with using two-phase mixture model have been solved to investigate hydrodynamic and thermal behaviours of the nanofluid over wide range of nanoparticle volume fractions. For a given nanoparticle mean diameter the effects of nanoparticle volume fractions on the hydrodynamics and thermal parameters are presented and discussed at different Richardson numbers and different tube inclinations. Significant augmentation on the heat transfer coefficient as well as on the wall shear stress is seen

Mathematical Modeling for Nanofluids Simulation: A Review of the Latest Works

Exploiting nanofluids in thermal systems is growing day by day. Nanofluids having ultrafine solid particles promise new working fluids for application in energy devices. Many studies have been conducted on thermophysical properties as well as heat and fluid flow characteristics of nanofluids in various systems to discover their advantages compared to conventional working fluids. The main aim of this study is to present the latest developments and progress in the mathematical modeling of nanofluids flow. For this purpose, a comprehensive review of different nanofluid computational fluid dynamics (CFD) approaches is carried out. This study provides detailed information about the commonly used formulations as well as techniques for mathematical modeling of nanofluids. In addition, advantages and disadvantages of each method are rendered to find the most appropriate approach, which can give valid results

A Critical Review of Experimental Investigations about Convective Heat Transfer Characteristics of Nanofluids under Turbulent and Laminar Regimes with a Focus on the Experimental Setup

In this study, several experimental investigations on the effects of nanofluids on the con- vective heat transfer coefficient in laminar and turbulent conditions were analyzed. The aim of this work is to provide an overview of the thermal performance achieved with the use of nanofluids in various experimental systems. This review covers both forced and natural convection phenomena, with a focus on the different experimental setups used to carry out the experimental campaigns. When possible, a comparison was performed between different experimental campaigns to provide an analysis of the possible common points and differences. A significant increase in the convective heat transfer coefficient was found by using nanofluids instead of traditional heat transfer fluids, in general, even with big data dispersion from one case to another that depended on boundary condi- tions and the particular experimental setup. In particular, a general trend shows that once a critic value of the Reynolds number or nanoparticle concentrations is reached, the heat transfer perfor- mance of the nanofluid decreases or has no appreciable improvement. As a research field still under development, nanofluids are expected to achieve even higher performance and their use will be crucial in many industrial and civil sectors to increase energy efficiency and, thus, mitigate the en- vironmental impact