Abstract Having the advantage of durability (simple in structure without mechanical pump), two-phase natural circulation (TPNC) loops were widely used, but still limited by its inherent instability that may lead to evaporator dry out (boiling crisis). Till now, the mechanism of the TPNC instability are not fully understood. In our previous experiment in a TPNC close loop with a singly connected accumulator (Wen et al., 2018) [1], two types of the density wave oscillations (DWO) were identified by characteristic frequencies; and the stable region between the two types of DWO can be expanded by reducing the subcooling. In the present research, we found an effective way to suppress the two types of the oscillation by increasing the resistance coefficient of connection pipe between the accumulator and the loop, or even eliminate the oscillation simply by shutting off the pipe connection. We inferred that the exchange of fluid between two compressible volumes (the accumulator and the two-phase section of the loop in the present case) is a necessary condition for the two types of the DWO. It was found that, the type 2 density wave oscillation would lead to the evaporator dry out, causing about 25% deterioration of the loop’s heat dissipation capacity as compared with the stable loop when the oscillation was suppressed. Also, scaling analysis has been performed.

中文翻译：

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R134a两相自然循环闭环单接蓄电池振荡抑制实验研究

摘要 两相自然循环（TPNC）回路具有经久耐用（结构简单，无需机械泵）的优点，被广泛应用，但仍受限于其固有的不稳定性，可能导致蒸发器干涸（沸腾危机）。到目前为止，TPNC 不稳定性的机制尚未完全清楚。在我们之前在带有单连接累加器的 TPNC 闭环中的实验中（Wen 等人，2018 年）[1]，通过特征频率识别了两种类型的密度波振荡 (DWO)；并且通过降低过冷度可以扩大两种DWO之间的稳定区域。在目前的研究中，我们找到了一种通过增加蓄能器与回路之间连接管的阻力系数来抑制这两种振荡的有效方法，甚至只需关闭管道连接即可消除振荡。我们推断，两个可压缩体积（在本案例中为蓄能器和回路的两相部分）之间的流体交换是两种类型的 DWO 的必要条件。研究发现，2型密度波振荡会导致蒸发器干涸，与抑制振荡时的稳定回路相比，回路的散热能力下降约25%。此外，还进行了缩放分析。2型密度波振荡会导致蒸发器干涸，与抑制振荡时的稳定回路相比，回路的散热能力下降约25%。此外，还进行了缩放分析。2型密度波振荡会导致蒸发器干涸，与抑制振荡时的稳定回路相比，回路的散热能力下降约25%。此外，还进行了缩放分析。