| Pulsating heat pipe (PHP) is a relatively new and special type of heat pipes, especially suited for the micro-electronics cooling of high heat flux. The internal fluid flow condition inside the capillary channels of the PHP is so complicated that the theoretical and experimental investigation are still at a primary stage.Electrical capacitance tomography (ECT) is a process tomography (PT) based on capacitance sensor. It has the advantage of being real-time, non-intrusive, non-hazardous and being capable of acquiring 2D/3D image information of process parameters. It provides an effective tool for the recognition of flow patterns and the measurement of multi-phase flow parameters. Currently, it is widely used and becoming a hot spot in PT research. However, it is rarely used in the micro-size condition.In the dissertation, the ECT system was used to visualize flow patterns, and to measure film thickness of the annular flow in the PHP. Then, the relationship between the heat transfer characteristics and the flow patterns was investigated. In order to actualize the micromation and increase the measurement accuracy of the ECT system, the capacitance sensor, the data-acquisition system and the image reconstruction algorithm were improved. In addition, some improved configurations for the PHP were developed to achieve high thermal performance. Two special configurations were found to be advantageous in establishing and maintaining reliable circulation of the working fluid. And nano-fluid was applied as working fluid in the PHP. The flow and heat transfer performances of the nano-fluid in the PHP were discussed.The main contents of the dissertation include three experiments and two mathematical models:In the experimental research, a series of experiments were performed on three types of test-beds, including the glass PHP for optical visualization, the two-phase closed thermosyphon (TPCT), and the copper PHP. The experimental results indicate: 1) the new-developed ECT micro-sensor is competent for the identification of the flow patterns and the measurement of the film thickness; 2) the PHP has the self-adjusting characteristic for the flow patterns (from slug flow to semi-annular and then to annular flow) to meet the demands of the increasing heat input; 3) as the flow path geometry of the PHP becomes less symmetric, the likelihood of circulatory flow increases; 4) the nano-fluid with adequate volume fraction of nano-particles is testified to be advantageous in enhancing heat transfer.In the theoretical research, the sepatated two-phase flow model for the PHP and the condensation heat transfer modified model for the TPCT were developed: 1) on the base of the foregoing experimental studies, the sepatated two-phase flow model based on simultaneous consevation of mass, momentum and energy, was developed for an equivalent single-loop PHP. The model allows prediction of two-phase flow parameters in each sub-section of the device, and therefore provides important insights into its flow condition from the flow pattern maps. The prediction results are in good accordance with the experimental data; 2) The modified mathematical model that accounts for the interfacial shear and surface wave was developed based on the first principles. The model prediction was compared with the Nusselt's solution and the ECT measuring results. The theoretical solutions of the film thickness predicted by the prsent work agree well with the ECT measuring data.
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