NUMERICAL SIMULATION OF NATURAL CONVECTION HEAT TRANSFER IN NANOFLUIDS

The goal of this thesis is to model the behavior of the nanofluids so that their performances can be evaluated analytically and computationally. In this thesis, we consider analytical models that describe molecular viscosity f.!, thermal conductivity k. density p, specific heat c" and the coefficient of thermal expansion f3 for a nanofluid in terms of volume fraction ljJ of nanoparticles, size of the nanoparticles (e.g radius of the nanoparticle, rp), size of the base fluid molecule (e.g. radius of the liquid molecule, r1) and the temperature T. In order to validate these analytical models, we study numerically the natural convection heat transfer in a closed pipe using the commercially available CFD software FLUENT 6.0, since the experimental data is available for this configuration. In particular, we study the natural convection flow field in two configurations of L/0=0.5 and LID=l.O, where L is the length of the pipe and D is the diameter. For nanofluids, we consider the suspensions of Ab03 and CuO particles in water. Three cases with volume fraction ljJ = 0, l% and 4% for both AhOJ and CuO are considered. It is assumed that the nanoparticles of AbOJ or CuO are uniformly suspended in water; there is no aggregation of nanoparticles in the fluid medium. It is shown that the use of experimentally measured values of k. or the kinetic model of k, gives better correlation with experimental data for heat transfer compared to the Maxwell model

SIMULATION STUDY ON VORTEX-INDUCED VIBRATION AIR WAKE ENERGY FOR AIRPORT RUNAWAY APPLICATION: A PRELIMINARY ANALYSIS

The objective of this research paper is to conduct a preliminary analysis of the effects of various cylindrical cross-sectional shapes on vortex-induced vibration for airport runaway air wake energy generation. In the case of the airport runway, vortices are generated from the aeroplane bodies that exit and enter the runway during take-off and landing operations. These oscillations can be utilized to generate power due to the large fluctuations produced by the vortices. Vortexinduced vibration works on the principle of Kármán vortices where a cylindrical or bluff-body shaped object oscillates due to the alternate vortex formation on the boundary layers by adverse fluid pressure. The oscillation depends on the unsteady lift force generated. This mechanical oscillation is later converted to electrical energy. Five cylindrical crosssection cases are investigated by computational fluid dynamics (CFD) k-ω turbulence model to identify the best case that will provide the largest lift force; hence the maximum power output generation. These cases are simulated using typical take-off air speeds for jetliners in order to finalize the overall performance. The observed results show that the elliptical cross-section with 3” height and 2” length provides the best cross-section in producing the greatest amount of energy. The total power generated from a single-cylinder was 707.1 Watts. The system can be optimized for larger aeroplanes and operation frequencies as well as could be expanded for larger energy output

In-cylinder radiation heat transfer in a small direct injection diesel engine

Diesel engine downsizing is of current interest because of the infinite nature of crude oil reserves and the high efficiency of the diesel cycle. Scaling and downsizing studies can make substantial contributions to the optimization of small diesel engine designs but the scaling of heat transfer losses has not been the focus of recent studies. Radiation heat transfer can represent a significant fraction of the total in-cylinder heat transfer of the diesel engine and hence, developments in radiation heat transfer scaling can have an impact on the success of the overall diesel engine scaling efforts. The present work contributes new radiation heat transfer data from a small direct injection diesel engine and investigates the relationship between radiation heat transfer and engine size. A radiation heat flux probe was developed based on the optical two-colour method. It was used to measure instantaneous radiation heat flux and the associated parameters KL and apparent flame temperature for a 0.21 L direct-injection diesel engine at 4 operating conditions giving indicated power values between 1.0 and 2.1 kW. A convective heat flux probe was also developed and used in the same engine for the measurement of instantaneous convective heat flux at these same operating conditions. In the radiation heat flux measurements, an approach based on post-run calibration of the probe in its sooted state was adopted to compensate for the problem of signal attenuation by probe sooting. In the convection heat flux measurements, the sooting problem on the thermocouple probe was compensated by deduction of the soot layer thickness through the tuning of results during compression to match the motoring results obtained with a soot-free probe. The radiation heat flux results from the present work are compared with results from other works which have used engines of a larger scale and the present radiation heat flux data are at the lower end of the overall range. The peak radiation values obtained in the present work are in the range of 0.14 to 0.38MW/m2 which is about half the magnitude obtained with the nearest engine size reported in the available literature. These results point to the significant influence of the soot cloud volume in the radiation heat flux losses. The convective heat flux values obtained in this work are in the same range of values identified from other published works. However, relative to the existing literature, the present work has produced the smallest values for the ratio of radiation heat flux to convective heat flux in terms of both peak and time-averaged values. This result also reflects the significant influence of engine size on radiation heat flux. A radiation heat flux scaling analysis was performed based on the time-averaged and peak radiation heat flux experimental data from the present work and other published literature. The indicated power per unit piston area, IP=Ap has been adopted as a scaling parameter. The time-averaged data appears to be linearly related to IP=Ap while the peak radiation heat flux appears to scale via a power law relationship with an index of 0.83. The linearity of the time-averaged radiation heat flux scaling implies that the time-averaged radiation heat flux is strongly influenced by same size effects while the peak radiation heat flux results are also influenced by emissions originating from soot particles near the surface of the flame. A new empirical radiation model based on available KL data from various sources including the present work has been developed and implemented in a thermodynamic engine simulation tool. Results from these simulations support the notion that both time-averaged and peak radiation heat flux are influenced by flame scale but that the peak radiation results are more strongly affected by emissions from soot particles near the flame surface

A review of the utilisation of natural gas with high carbon dioxide content as automotive fuel in an indirect injection diesel engine

The persistent consumption of fossil fuels by modern transportation tends toward feared depletion in crude oil and infliction of health risks on human beings and the environment due to the noxious emissions from the combustion of fossil fuels. This work examines the prospects of fuel modification in improving engine performance by utilising compressed natural gas (CNG) mixed with varying proportions of carbon dioxide (CO2) as fuel in Diesel engines. The extent to which the addition of CO2 to CNG could help simulate the effects of exhaust gas recirculation (EGR) as employed in modern engine technology will be established

Numerical investigation on effect of leaflet thickness on structural stresses developed in a bileaflet mechanical heart valve for its sustainable manufacturing

Flow induced structural stresses can cause mechanical prosthetic aortic valve to fail due to yielding. In this study, we have performed the structural analysis, especially the effect of leaflet thickness on equivalent stresses developed in a Bileaflet mechanical heart valve (BMHV) due to blood flow through it has been investigated. The leaflet thickness varies from 0.5mm to 0.7mm, by 0.1mm. A fluid-structure interaction approach based on Arbitrary Lagrangian Eulerian (ALE) technique has been employed with the aid of an user defined function (UDF). Results of the analysis show that high von Mises stresses are developed in BMHV with leaflet thickness of 0.5mm and 0.6mm, being 75% and 13% higher than allowable equivalent stress respectively. Such thinner leaflets are therefore, not sustainable to be replaced with diseased aortic valve

Numerical investigation on effect of leaflet thickness on structural stresses developed in a bileaflet mechanical heart valve for its sustainable manufacturing

Flow induced structural stresses can cause mechanical prosthetic aortic valve to fail due to yielding. In this study, we have performed the structural analysis, especially the effect of leaflet thickness on equivalent stresses developed in a Bileaflet mechanical heart valve (BMHV) due to blood flow through it has been investigated. The leaflet thickness varies from 0.5mm to 0.7mm, by 0.1mm. A fluid-structure interaction approach based on Arbitrary Lagrangian Eulerian (ALE) technique has been employed with the aid of an user defined function (UDF). Results of the analysis show that high von Mises stresses are developed in BMHV with leaflet thickness of 0.5mm and 0.6mm, being 75% and 13% higher than allowable equivalent stress respectively. Such thinner leaflets are therefore, not sustainable to be replaced with diseased aortic valve

Determination of Remaining Useful Life of Gas Turbine Blade

The aim of this research is to determine the remaining useful life of gas turbine blade, using service-exposed turbine blades. This task is performed using Stress Rupture Test (SRT) under accelerated test conditions where the applied stresses to the specimen is between 400 MPa to 600 MPa and the test temperature is 850°C. The study will focus on the creep behaviour of the 52000 hours service-exposed blades, complemented with creep-rupture modelling using JMatPro software and microstructure examination using optical microscope. The test specimens, made up of Ni-based superalloy of the first stage turbine blades, are machined based on International Standard (ISO) 24. The results from the SRT will be analyzed using these two main equations – Larson-Miller Parameter and Life Fraction Rule. Based on the results of the remaining useful life analysis, the 52000h service-exposed blade has the condition to operate in the range of another 4751 hr to 18362 hr. The microstructure examinations shows traces of carbide precipitation that deteriorate the grain boundaries that occurs during creep process. Creep-rupture life modelling using JMatPro software has shown good agreement with the accelerated creep rupture test with minimal error

Determination of Remaining Useful Life of Gas Turbine Blade

The aim of this research is to determine the remaining useful life of gas turbine blade, using service-exposed turbine blades. This task is performed using Stress Rupture Test (SRT) under accelerated test conditions where the applied stresses to the specimen is between 400 MPa to 600 MPa and the test temperature is 850°C. The study will focus on the creep behaviour of the 52000 hours service-exposed blades, complemented with creep-rupture modelling using JMatPro software and microstructure examination using optical microscope. The test specimens, made up of Ni-based superalloy of the first stage turbine blades, are machined based on International Standard (ISO) 24. The results from the SRT will be analyzed using these two main equations – Larson-Miller Parameter and Life Fraction Rule. Based on the results of the remaining useful life analysis, the 52000h service-exposed blade has the condition to operate in the range of another 4751 hr to 18362 hr. The microstructure examinations shows traces of carbide precipitation that deteriorate the grain boundaries that occurs during creep process. Creep-rupture life modelling using JMatPro software has shown good agreement with the accelerated creep rupture test with minimal error