| Abstract: | In a natural circulation loop, flow instabilities, such as density wave oscillations, occur under certain operating conditions, but the influence of flow oscillations on the heat transfer is not well understood. An experiment was conducted using a natural circulation loop of liquid nitrogen with test tubes of dimensions of 3.0 mm/5.0 mm I.D., and 900 mm heated length. Experimental results indicated that the heat transfer correlations of Schrock-Grossman and Roko-Shiraha were in good agreement with the experimental results in the saturated boiling and postdryouts regions, respectively, even under oscillatory flow conditions. On the other hand, the critical heat flux (CHF) correlation obtained under stable flow conditions, such as Katto, predicted significantly larger values compared with the experimental data under oscillatory flow condition. The CHF value of the natural circulation loop was well predicted by using the numerical simulation based on a lumped-parameter model, taking account of the circulation rate, oscillation period, and amplitude. © 1998 Scripta Technica, Heat Trans Jpn Res, 26(7): 449–458, 1997 |
