Fundamental Study Of A New Cooling Technique Based On Thermally Driven Theory

The proper design of cooling system is one of the most important aspect of the functions in modern industry. A new and efficient cooling technique will contribute to the development of the national economy greatly. In this thesis, a new cooling technique, which is based on the theory of thermally driven, was studied at the background of turbine blade's cooling design in aero-engine.The key point of this new cooling technique is using the liquid's thermally driven in a micro-circular enclosure which is placed in a high body-force field. Firstly a theoretical analysis of the basic governing equations describing these physical phenomena was carried out. Using similitude, dimensionless variables, groups and governing equations are generated. The results of theoretical analysis show that thermally driven is affected by many factors, such as the magnitude of the body-force, geometry of the circuit, and the fluid's properties.Secondly, the circuit 's width d and height h , and the relation between d and h were studied by numerical simulations in gravitational field, which is one of the most representative body-force field. The results give that only a specific range of the width d and a proper ratio of h/d can get a maximum average heat transfer coefficient of the water. Based on the numerical simulations, flow visualization and heat transfer measurements are carried out to investigate the flow pattern and the heat transfer efficiency of the water respect to different heat flux. In flow visualization experiment, there was no movement of water in the circuit unless the heating flux achieved a specific value. Experiments' results show that the velocity and heat transfer capacity KH of water increase with the increasing of heating flux.Then, a numerical study in centrifugal field, a kind of high body-force field, was carried out to investigate the influence of the geometry of the circuit and the direction, magnitude of the body-force. The numerical results show that the flow direction changes with the direction of body-force and the average heat transfer coefficient increases with the increasing of the rotating speed at the same circuit geometry. Also a higher centrifugal force can be used to generate larger thermally driven force, which can balance the resistance increment due to micro-circular enclosure. These result in a higher heat transfer rate when the characteristic size of the circuit decreases in a high centrifugal field.Besides the numerical simulations, the temperature distribution of thermally driven was observed using a liquid crystal method, and the heat transfer measurements were also carried out to investigate the relations between the rotating speed and the heat flux. Theexperiments show that the temperature difference of the fluid decreases, heat transfer capacity KH of thermally driven increase when the heating flux and rotating speed increase.All the numerical simulations and experiment studies in this thesis show that heat transfer can be enhanced using the liquid's thermally driven in a micro-circular enclosure in high body-force field. The effect of this new cooling technique is validated fundamentally by the investigations in this thesis.