Mechanism of Macrolayr Formation and Measurement of Macrolayr Thickness

Research Project

Project/Area Number	05650188
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	Thermal engineering
Research Institution	Hokkaido University
Principal Investigator	KUMADA Toshiaki Hokkaido University, Fac.of Engineering, Associate Professor, 工学部, 助教授 (70001782)
Project Period (FY)	1993 – 1994
Project Status	Completed (Fiscal Year 1994)
Budget Amount *help	¥2,400,000 (Direct Cost: ¥2,400,000) Fiscal Year 1994: ¥1,400,000 (Direct Cost: ¥1,400,000) Fiscal Year 1993: ¥1,000,000 (Direct Cost: ¥1,000,000)
Keywords	Pool Boiling / Liquid macrolayr / Critical heat flux / Transition boiling / Measurement / Analysis / 伝熱 / 熱工学 / 自然対流
Research Abstract	The macrolayr thickness is determined at critical heat flux (CHF) and in transition boiling, by measuring heat flux and bubble frequency in the energy balance relation q_<CHF> or q_<TR>=rho _1H_<fg>delta_1・f.And the mechanism of macrolayr formation is discussed and the correlation of macrolayr thichness is proposed.The conclusions of this research are as follows : (1) Macrolayr at higher pressures is formed by the simultaneous coalescence of coalesced bubbles. (2) Correlations of macrolayr thickness are deduced by two ways.One is obtained by assuming that bubbles forming macrolayr grow as similar to primary bubble growth.The other is obtained by assuming that bubbles forming macrolayr grow according to the uniform vapor supply from a heated surface.Both correlations can well correlate the data of macrolayr thickness obtained for the wide range of vapor blowing velocity. (3) The existing data of macrolayr thickness measured by a probe method are thicker than those measured by the present method and show the dependence on heat fluxes different from those measured by the present method. (4) The data of macrolayr thickness for transition boiling are well correlated with the proposed correlations, if q_<TR> is given by the heat flux on a boiling curve exrapolated to the time average temperature of heated surfaces. The final conclusion is that the mechanisms of heat transfer for nucleate, CHF and transition boiling are not essentially different each other.