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首页> 外文期刊>International Journal of Heat and Mass Transfer >Time-resolved characterization of microchannel flow boiling during transient heating: Part 2 - Dynamic response to time-periodic heat flux pulses
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Time-resolved characterization of microchannel flow boiling during transient heating: Part 2 - Dynamic response to time-periodic heat flux pulses

机译：瞬态加热期间微通道流沸腾的时间分辨表征：第2部分 - 对时间周期热通量脉冲的动态响应

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Flow boiling in microchannels is an effective method for dissipating high heat fluxes. However, two-phase heat sink operation during transient heating conditions remains relatively unexplored. In Part 1 of this two-part study, the dynamic response of flow boiling to a single heat flux pulse was experimentally studied. In this Part 2, the effect of heating pulse frequency on microchannel flow boiling is explored when a time-periodic series of pulses is applied to the channel. HFE-7100 is driven through a single 500 μm-diameter glass microchannel using a constant pressure reservoir. A thin indium tin oxide layer on the outside surface of the microchannel enables simultaneous transient heating and flow visualization. High-frequency measurements of heat flux, wall temperature, pressure drop, and mass flux are synchronized to the flow visualizations to characterize the boiling process. A square-wave heating profile is used with pulse frequencies ranging from 0.1 to 100 Hz and three different heat fluxes levels (15, 75, and 150 kW/m~2). Three different time-periodic flow boiling fluctuations were observed for the heat flux levels and pulse frequencies investigated in this study: flow regime transitions, pressure drop oscillations, and heating pulse propagation. For heat flux pulses between 15 and 75 kW/m~2 and heating pulse frequencies above 1 Hz, time-periodic flow regime transitions between single-phase and two-phase flow are reported. For heating profiles involving 150 kW/m~2 heat flux pulses, fluid in the microchannel is always boiling and thus the flow regime transitions are eliminated. For heating pulse frequencies between approximately 1 and 10 Hz, the thermal and flow fluctuations are heavily coupled to the heating characteristics, forcing the pressure drop instability frequency to match the heating frequency. Outside this heating pulse frequency range, the pressure drop instability occurs at the intrinsic frequency of the system. For heating pulse frequencies above 25 Hz, the microchannel wall attenuates the transient heating profile and the fluid essentially experiences a constant heat flux.
机译：微通道的流动沸腾是一种散发高热量通量的有效方法。然而，瞬态加热条件期间的两相散热器操作仍然仍然是未开发的。在这两个部分研究的第1部分中，实验研究了流沸腾流到单一热通量脉冲的动态响应。在该部分2中，当将时间周期性系列脉冲施加到通道时，探讨了加热脉冲频率对微通道流沸腾的影响。 HFE-7100使用恒压储存器通过单个500μm直径的玻璃微通道驱动。微通道外表面上的薄铟锡氧化物层可以同时瞬时加热和流量可视化。热通量，壁温，压降和质量通量的高频测量与流量可视化同步以表征沸腾过程。方波加热曲线与脉冲频率一起使用，范围为0.1至100Hz和三种不同的热通量水平（15,75和150 kW / m〜2）。观察到三种不同的时间周期流沸腾波动，用于本研究中研究的热通量水平和脉冲频率：流动调节，压降振荡和加热脉冲传播。对于15至75kW / m〜2之间的热通量脉冲和高于1 Hz以上的加热脉冲频率，报告单相和两相流之间的时间周期性流动调节。对于涉及150kW / m〜2热量脉冲的加热型材，微通道中的流体总是沸腾，因此消除了流动调节。对于大约1和10Hz之间的加热脉冲频率，热量和流量波动很大耦合到加热特性，强制压降不稳定性频率以匹配加热频率。在该加热脉冲频率范围之外，压降不稳定性发生在系统的内在频率下。对于高于25Hz的加热脉冲频率，微通道壁衰减瞬态加热曲线，并且流体基本上经历恒定的热通量。

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