Qiu, Can = / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 82-87). / Abstracts in English and Chinese. / Qiu, Can = / Abstract --- p.i / 摘要 --- p.ii / Acknowledge --- p.iii / Table of Contents --- p.iv / List of Figures --- p.v i i / List of Tables --- p.xi / Chapter Chapters I --- Introduction --- p.1 / Chapter 1.1 --- Turbulence --- p.1 / Chapter 1.2 --- Rayleigh-Benard convection --- p.3 / Chapter 1.2.1 --- Physics picture-Motion in the convection cell --- p.4 / Chapter 1.2.2 --- The governing equations and parameters --- p.6 / Chapter 1.2.3 --- Multilayer convection --- p.9 / Chapter 1.2.4 --- The Nu scaling --- p.9 / Chapter 1.2.5 --- Boundary layers --- p.11 / Chapter 1.3 --- Present work and the organization of the thesis --- p.14 / Chapter II --- Experimental Setup --- p.16 / Chapter 2.1 --- The convection cell --- p.16 / Chapter 2.2 --- The thermistors --- p.20 / Chapter 2.2.1 --- Calibration --- p.20 / Chapter 2.3 --- The multimeter --- p.21 / Chapter 2.4 --- Thermostat box --- p.22 / Chapter 2.5 --- Visualization --- p.23 / Chapter 2.6 --- Motorized translation stage --- p.24 / Chapter 2.7 --- AC Wheatstone Bridge and Lock in amplifier --- p.24 / Chapter 2.8 --- Test different heaters --- p.26 / Chapter III --- "Heat flux, boundary layer and Reynolds number measurement of one-layer FC77 thermal convection" --- p.30 / Chapter 3.1 --- Heat flux measurement with correction --- p.30 / Chapter 3.1.1 --- Sidewall correction --- p.31 / Chapter 3.1.2 --- Bottom plate correction --- p.31 / Chapter 3.1.3 --- Post correction --- p.31 / Chapter 3.2 --- The Nu result --- p.32 / Chapter 3.3 --- Boundary layer measurement --- p.34 / Chapter 3.4 --- The Pr dependence of the Reynolds number Re --- p.37 / Chapter 3.5 --- Summary --- p.40 / Chapter IV --- "Heat transfer, thermal boundary layer and flow property measurement of multilayer immiscible fluid turbulent thermal convection" --- p.41 / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Experiment --- p.44 / Chapter 4.3 --- The temperature and temperature fluctuation across the interface --- p.46 / Chapter 4.3.1 --- The temperature near the interface --- p.46 / Chapter 4.3.2 --- Position and temperature of the interface --- p.47 / Chapter (a) --- Using the profile to get the temperature of the interface --- p.47 / Chapter (b) --- Using the traveling microscope to get the absolute position of the interface --- p.50 / Chapter 4.4 --- The Nu result --- p.50 / Chapter 4.5 --- Boundary layer thickness and scaling --- p.54 / Chapter 4.6 --- Statistical properties of the temperature field across the interface --- p.58 / Chapter 4.6.1 --- Temperature time series and the corresponding histogram of the interface --- p.58 / Chapter 4.6.2 --- "The mean, root mean square, skewness, time derivative skewness and flatness of the temperature profiles across the interface" --- p.64 / Chapter 4.6.3 --- Scaling of the temperature fluctuation in two-layer system --- p.71 / Chapter 4.7 --- The temperature oscillation --- p.74 / Chapter 4.8 --- Passive scalar and active scalar --- p.77 / Chapter 4.9 --- Summary --- p.79 / Chapter V --- Conclusion --- p.80 / Chapter 5.1 --- One-layer thermal convection --- p.80 / Chapter 5.2 --- Two-layer thermal convection --- p.80 / Chapter 5.3 --- Future works --- p.81 / References --- p.82

Thesis (M.Eng.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 88-92.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2011. / Nanofluid, which was first discovered by the Argonne laboratory, is a nanotechnology- based heat transfer fluid. This fluid consists of particles which are suspended inside conventional heat transfer liquid or base fluid. The purpose of this suspension is for enhancing thermal conductivity and convective heat transfer performance of this base fluid. The name nanofluid came about as a result of the nanometer- sized particles of typical length scales 1-100nm which are stably suspended inside of the base fluids. These nanoparticles are of both physical and chemical classes and are also produced by either the physical process or the chemical process. Nanofluid has been discovered to be the best option towards accomplishing the enhancement of heat transfer through fluids in different unlimited conditions as well as reduction in the thermal resistance by heat transfer liquids. Various manufacturing industries and engineering processes such as transportation, electronics, food, medical, textile, oil and gas, chemical, drinks e.t.c, now aim at the use of this heat transfer enhancement fluid. Advantages such organisations can obtain from this fluid includes, reduced capital cost, reduction in size of heat transfer system and improvement of energy efficiencies. This research has been able to solve numerically, using Maple 12 which uses a fourth- fifth order Runge -kutta- Fehlberg algorithm alongside shooting method, a set of nonlinear coupled differential equations together with their boundary conditions, thereby modelling the heat and mass transfer characteristics of the boundary layer flow of the nanofluids. Important properties of these nanofluids which were considered are viscosity, thermal conductivity, density, specific heat and heat transfer coefficients and microstructures (particle shape, volume concentration, particle size, distribution of particle, component properties and matrixparticle interface). Basic fluid dynamics equations such as the continuity equation, linear momentum equation, energy equation and chemical species concentration equations have also been employed.

Hydrodynamic slip is known to suppress vorticity production at the solid-fluid boundary in bluff body flows. This suppression combined with the enhanced vorticity convection results in a substantial reduction in the unsteady vortex shedding and the hydrodynamic loads experienced by the bluff body. Here, using combined theoretical and computational techniques, we investigate the effect of slip on three-dimensional wake dynamics and convective scalar transport from a circular cylinder placed in the uniform cross-flow of a Newtonian incompressible fluid over Reynolds numbers ranging from 0.1 to 1000. We find the wake patterns to be strongly influenced by the degree of the slip, quantified through the non-dimensional slip length in the Naiver slip model, with the asymptotic slip lengths of zero and infinity characterizing no-slip and no-shear boundaries, respectively. With increasing slip length, the wake three-dimensionality, that is observed in the case of a no-slip surface for Re > 190, is gradually suppressed and eventually eliminated completely. For each Reynolds number, we identify the critical slip length beyond which the three-dimensionality is completely suppressed and the wake becomes two-dimensional, on the basis of the total transverse entropy present in the flow field. Over the Reynolds number range considered in this work, we find the critical slip length to be an increasing function of Reynolds number. For sufficiently large slip lengths, we observe suppression of two-dimensional vortex shedding leading to formation of a steady separated wake. Further increments in slip length lead to reduction in the intensity and size of the recirculating eddy pair eventually resulting in its complete disappearance for a no-shear surface for which the flow remains attached all along the cylinder boundary. Next, we quantify the effect of hydrodynamic slip on convective transport from an isothermal circular cylinder placed in the uniform cross flow of an incompressible fluid at a lower temperature. For low Reynolds and high P´eclet numbers, theoretical analysis based on Oseen and thermal boundary layer equations allows us to obtain explicit relationships for the dependence of transport rate on the prescribed slip length. We observe that the non-dimensional transport coefficients follow a power law scaling with respect to the P´eclet number, with the scaling exponent increasing gradually from the lower asymptotic limit of 1/3 for the no-slip surface to 1/2 for a no-shear boundary. Results from our simulations at finite Reynolds number indicate that the local time-averaged transport rates for a no-shear surface exceed the one for the no-slip surface all along the cylinder except in the neighbourhood of the rear stagnation region, where flow separation and reversal augment the transport rates substantially.

In this research, an elastic cylinder that utilized vortex-induced vibration (VIV) was applied to improve convective heat transfer rates by disrupting the thermal boundary layer. Rigid and elastic cylinders were placed across a fluid channel. Vortex shedding around the cylinder led to the periodic vibration of the cylinder. As a result, the flow-structure interaction (FSI) increased the disruption of the thermal boundary layer, and therefore, improved the mixing process at the boundary. This study aims to improve convective heat transfer rate by increasing the perturbation in the fluid flow. A three-dimensional numerical model was constructed to simulate the effects of different flow channel geometries, including a channel with a stationary rigid cylinder, a channel with a elastic cylinder, a channel with two elastic cylinders of the same diameter, and a channel with two elastic cylinders of different diameters. Through the numerical simulations, the channel maximum wall temperature was found to be reduced by approximately 10% with a stationary cylinder and by around 17% when introducing an elastic cylinder in the channel compared with the channel without the cylinder. Channels with two-cylinder conditions were also studied in the current research. The additional cylinder with the same diameter in the fluid channel only reduced the surface wall temperature by 3% compared to the channel without any cylinders because the volume of the second cylinder could occupy some space, and therefore, reduce the effect of the convective heat transfer. By reducing the diameter of the second cylinder by 25% increased the effect of the convection heat transfer and reduced the maximum wall temperature by around 15%. Compared to the channel with no cylinder, the introduction of cylinders into the channel flow was found to increase the average Nusselt number by 55% with the insertion of a stationary rigid cylinder, by 85% with the insertion of an elastic cylinder, by 58% with the insertion of two cylinders of the same diameter, and by approximately 70% with the insertion of two cylinders of different diameters (the second cylinder having the smaller diameter). Furthermore, it was also found that the maximum local Nusselt number could be enhanced by around 200%-400% at the entrance of the fluid channel by using the elastic cylinders compared to the channel without cylinders.

Shock-tube experiments are typically performed at high temperatures (≥1200K) due to test-time constraints. These test times are usually ~1 ms in duration and the source of this short, test-time constraint is loss of temperature due to heat transfer. At short test times, there is very little appreciable heat transfer between the hot gas and the cold walls of the shock tube and a high test temperature can be maintained. However, some experiments are using lower temperatures (approx. 800K) to achieve ignition and require much longer test times (up to 15 ms) to fully study the chemical kinetics and combustion chemistry of a reaction in a shock-tube experiment. Using mathematical models, analysis was performed studying the effects of temperature, pressure, shock-tube inner diameter, and test-port location at various test times (from 1 - 20 ms) on temperature maintenance. Three models, each more complex than the previous, were used to simulate test conditions in the endwall region behind the reflected shock wave with Ar and N2 as bath gases. Temperature profile, thermal BL thickness, and other parametric results are presented herein. It was observed that higher temperatures and lower pressures contributed to a thicker thermal boundary layer, as did shrinking inner diameter. Thus it was found that a test case such as 800K and 50 atm in a 16.2-cm-diameter shock tube in Argon maintained thermal integrity much better than other cases - pronounced by a thermal boundary layer ≤ 1 mm thick and an average temperature ≥ 799.9 K from 1-20 ms.

No description available.