Visualization And Analysis On Flow Boiling In Microgroove

With the rapid development of microsystem, the study on microscale heat and mass transfer has been paid great attention. Boiling heat transfer maintains yet a complex subject, thus making the research work in microenvironment even more difficult. Boiling flow shows a variety of flow patterns in confined space, and we scarcely have any plain idea about its mechanism on flow and heat transfer. Many conclusions have been put forward in the past years, some of which are out of accord with each other, some even contradictory. To clarify the heat transfer mechanism in microsystem should be a tough scientific and engineering challenge. This paper contributes to the experimental data accumulation in this field through micro-groove flow boiling and visualization experiments, and makes efforts to suggest the mechanism of micro-groove flow boiling.Chapter One reviews previous works on micro-groove flow boiling, by summarizing their results about: heat transfer, pressure drop, and flow pattern visualization. The experiment is outlined accordingly.Chapter Two deals with (1) the experimental method and principle, (2) setup of experimental system, and (3) processing of data. The experimental scheme and method are described in detail in the first part of this chapter. The second part is about experimental equipment, the processing of experiment elements, and the difficulties encountered. The last part includes mathematical description on basis of experiment principle, listing the viewpoint and formula used in heat transfer and pressure drop calculation.Chapter Three gives the experiment of heat transfer and visualization. Two micro-grooves are prepared as the samples, that is, micro-groove I with 0.4mm in width and 0.4mm in depth, and micro-groove II with 0.4mm in width and 0.2mm in depth. At different inlet temperature and mass flux rate, through increasing electricalcurrent at various intervals, the heat flux of micro-groove keeps increasing, and the vapor quality is going up too. In this way, the correlation between the heat transfer coefficient and the vapor quality under different situation is obtained, and by comprehensive analysis, comparison with the literature results, we come to a conclusion. In synchronous visualization experiment, the flow pattern change with time is observed, which is used to explain the trend of h-x curve under varied conditions.Chapter Four deals with the experiments of pressure drop. With the same micro-groove I and micro-groove II, the correlation between pressure drop (Ap) and heat flux (ge), and that between two-phase frictional factor (G^fl) and Lockhart-Martinelli parameter (X) is obtained under different circumstances. Then the curve of ^p-qe and &FL-X is analyzed, and the trend is explained. Finally a comparison is made with previous studies.Chapter Five gives the summary of this work and some suggestions on future work in the field of micro flow boiling.