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Inhibition of premature transient boiling crisis induced by heat-load step pulses in a helium natural circulation loop by dynamic initial condition

机译:动态初始条件抑制氦自然循环回路中热负荷阶跃脉冲引起的过早瞬时沸腾危机

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Boiling helium natural circulation loops constitute a cooling option for large superconducting magnets. Their steady state thermalhydraulic behavior has already been studied quite thoroughly. However, the transient response of these systems has started being studied only recently. Although transient boiling experiments with other fluids or heating configurations exist, their findings are difficult to extrapolate to the case of natural circulation loops. In this work, we present the continuation of an experimental study on helium natural circulation loops. In this case, the system is excited by a stepwise power increase from a dynamic initial condition (a stable initial heat flux is applied). Boiling crisis onset during the transient was identified from the measurement of wall temperature on the heated section. The increase of the initial heat flux and the consequent initial flow increase have been found to have a partial or complete inhibiting effect on transient boiling crisis onset in the premature boiling crisis regime with respect to the static initial condition case. Behavior charts could be drawn on the initial-final heat flux plane. A general empirical criterion based on the evolution of vapor fraction along the section is provided for the prediction of boiling crisis onset by this mechanism. (C) 2018 Elsevier Ltd. All rights reserved.
机译:沸腾的氦气自然循环回路构成了大型超导磁体的冷却选择。他们的稳态热工水力行为已经进行了相当详尽的研究。但是,这些系统的瞬态响应直到最近才开始研究。尽管存在使用其他流体或加热方式进行的瞬时沸腾实验,但很难将其发现推论为自然循环回路的情况。在这项工作中,我们介绍了氦自然循环回路实验研究的继续。在这种情况下,系统会从动态初始状态开始逐步增加功率(施加稳定的初始热通量)。通过测量加热部分的壁温可以确定瞬态过程中的沸腾危机。已经发现,相对于静态初始状态,初始热通量的增加和随之而来的初始流量的增加对于过早沸腾危机状态中的瞬时沸腾危机的发作具有部分或完全的抑制作用。可以在初始-最终热通量平面上绘制行为图。为预测这种沸腾危机的起因,提供了基于截面中蒸气分数演变的一般经验标准。 (C)2018 Elsevier Ltd.保留所有权利。

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