MICROSTRUCTURES AND MACROSTRUCTURES OF EVAPOURATOR TUBES AND ACTIVATION OF NUCLEATION SITES IN POOL BOILING
The trend towards a better understanding of the fundamentals of nucleate boiling by the introduction of the characteristic features of the heating surface are supported by new developments in computer calculations and in measurement techniques. However, little progress has been made in the development of theoretically based predictive methods. The main reason is the lack of quantitative information especially about the topography of the heated surface and of the bubble formation and the knowledge of the important cavity size and form for different superheats.The influence of micro- and macrostructures on the heat transfer coefficient is investigated with propane boiling at low temperatures on surfaces of different roughness and on structured surfaces. First measurements of propane boiling on structured surfaces of mild steel tubes in a recently modified standard apparatus for pool boiling are presented and compared to the result of a literature survey on propane boiling on steel tubes. A detailed description of the examined micro surface structures is given by photorealistic and isometric representations and with surface profiles measured by a contactless stylus instruments. The cavity sizes are determined from the roughness profiles and topography identified by enveloped curves produced by different roller radii. The curves represent the amount of vapour that could be trapped in each surface cavity. Finally, statistical analyses of the roughness and of the cavity size parameters are established (e.g. size and density distributions).
O.Kruck A.Luke
Institut für Thermodynamik, Leibniz Universit?t Hannover,30167 Hannover, Germany
国际会议
The 22nd International Congress of Refrigeration(第22届国际制冷大会)
北京
英文
2007-08-21（万方平台首次上网日期，不代表论文的发表时间）