Stability and Entropy Generation of Boiling Systems

• Main Authors: Lin, Wen-Wei, 林文煒
• Other Authors: Lee Duu-Jong
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/12030320930180306864

博士 === 國立臺灣大學 === 化學工程學系 === 86 === The aim of this research is to study the characteristics of heat transfer and stability of different system. The second law of thermodynamics is utilized to obtain the minimum entropy generation, that is, the maximum effective work of the system. For heat transfer system of fin, it exists very complex states if the boiling happens on the surface of fins. If the base temperature is at the film boiling, at least three states happens: only film boiling occurs on the all fin, film boiling occurs accompanying with transition boiling, and film＋ transition＋nuclear boiling coexist. If the boiling happens on the fins, the heat fluxes could be higher than the one without fins for one order, and the range of operational base temperature also increases Plate boiling system has similar characteristics to the wire boiling. An "equilibrium heat flux" exists to divide the boiling curve into stable and meta-stable region. Below the equilibrium heat flux the nucleate boiling will be more stable, and above the flux film boiling will be the stable state. The porous layer on the plate will not only increase the heat transfer efficiency but also the stability. The change in locations of heating surface will influence the equilibrium heat flux. If the heati In the second law analysis, both the irreversibility of heat transfer and hydrodynamics are considered to obtain the best Reynolds number to minimum entropy generation. One or two branch numbers of fractal-like fin has excellent heat transfer efficiency. The second law suggests that one or two branch numbers of fractal-like fin, and its subfins should be close to their mother fin base, and the size should as small as possible. For pin fin arrays, when on some array regions, the in-line arrangement w