Instabilities in parallel channel of forced-convection boiling upflow system, (IV). Instabilities in multi-channel system and with boiling in downcomer.:Instabilities in Multi-Channel System and with Boiling in Downcomer

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The steam generator for LMFBR is composed of multiple tubes with the different flow conditions from each other. Most of the computer codes developed to evaluate the stability analyze a representative tube on the basis of the assumption of the constant pressure drop between the feedwater header and the steam one as single channel. Although the method selecting the representative channel has never been investigated, it is one of the purposes of this paper to examine the approximate method to evaluate the stable boundary exactly.<BR>It is another purpose of this paper to research the mechanism of the limit cycle oscilla-tion observed in 1 MW SG without the thermal insulated downcomer of Power Reactor and Nuclear Fuel Development Corp., so that the effect of boiling in downcomer on the flow in-stability is studied experimentally. The slug excursion instability, which does not belong to Boure's classification of two-phase flow instability, is observed in our experimental ap-paratus. Then, this mechanism is studied under the various conditions of heat fluxes of downcomer and riser, liquid temperature and inlet velocity.
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