Variation of Critical Heat Flux by Flow Oscillation in a Small Vertical Channel
Variation of Critical Heat Flux by Flow Oscillation in a Small Vertical Channel
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DOI：
10.1115/icone17-75147
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
Toshihiro Murakami;Rei Takei;T. Okawa
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文献类型：
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作者：
Toshihiro Murakami;Rei Takei;T. Okawa
通过实验和数值计算研究了入口质量流量正弦振荡对强迫对流沸腾临界热流密度的影响。实验中，试验段为内径为5mm的不锈钢小圆管，试验流体为过滤后的去离子自来水，流动方向为垂直向上。加热长度为1，600 mm。周期性地改变供给到循环泵的电功率以使入口质量通量正弦振荡。直流电通过试验段管，以欧姆加热。临界热通量条件的发生是使用来自点焊在测试段管外壁上的热电偶的信号来检测的。在目前的实验条件下，预计临界热流条件是由环形两相流区的液膜干涸触发的。主要实验参数为时均进口质量流量、流量振荡幅度和周期。由于沸水堆在高压条件下运行，系统压力也被用作重要的实验参数。如果振荡周期足够长，则可以预期，当流量等于振荡条件下的最小流量时，流量振荡条件下的临界热通量接近于稳态的临界热通量。另一方面，由于沸腾通道内薄膜区和厚膜区之间会发生相互作用，缩短振荡周期可以减缓临界热流密度的降低。根据这一预期，在流动振荡条件下测得的临界热流密度随着振荡周期的增加而减小。结果表明，采用无量纲加热长度的概念，可以较好地关联流动振荡条件下的临界热流密度降低。采用一维三流体模型进行了数值计算。计算出的流动振荡条件下的临界热通量随着无量纲加热长度值的增加而增加，如本实验所示。
The effect of sinusoidal oscillation of inlet mass flux on the critical heat flux (CHF) in forced convective boiling was investigated in experiment and numerical calculation. In the experiment, the test section was a small stainless steel round tube of 5 mm in inside diameter, filtrated and deionized tap water was used as a test fluid, and the flow direction was set to vertical upward. The heated length was 1,600 mm. Electric power supplied to a circulation pump was varied periodically to oscillate the inlet mass flux sinusoidally. Direct current was passed through the test section tube to heat it ohmically. The occurrence of critical heat flux condition was detected using the signal from the thermocouples that were spot-welded on the outer wall of the test section tube. In the present experimental conditions, it was expected that the critical heat flux condition was triggered by the dryout of liquid film in annular two-phase flow regime. The main experimental parameters were the time-averaged inlet mass flux and the amplitude and period of flow oscillation. The system pressure was also used as an important experimental parameter since a boiling water reactor is operated under high pressure condition. If the oscillation period is long enough, it is expected that the critical heat flux under the flow oscillation condition is close to that for the steady state when the flow rate is equal to the minimum flow rate in the oscillatory condition. On the other hand, the decrease of the critical heat flux would be mitigated if the oscillation period is shortened, since interaction would take place between the thin and thick film regions within a boiling channel. In accordance with this expectation, the critical heat flux measured under the flow oscillation condition was reduced with an increase in the oscillation period. It was demonstrated that the reduction of critical heat flux under flow oscillation condition can be correlated fairly well using the concept of dimensionless heated length. Numerical calculations using a one-dimensional three-fluid model were also carried. The calculated critical heat fluxes for flow oscillation conditions increased with increased value of dimensionless heated length, as in the present experiment.Copyright © 2009 by ASME