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Experimental investigation of regular fluids and nanofluids during flow boiling in a single microchannel at different heat fluxes and mass fluxes.

机译：在单个微通道中以不同热通量和质量通量进行流动沸腾过程中常规流体和纳米流体的实验研究。

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摘要

The dissipation of high heat flux from integrated circuit chips and the maintenance of acceptable junction temperatures in high powered electronics require advanced cooling technologies. One such technology is two-phase cooling in microchannels under confined flow boiling conditions. In macroscale flow boiling bubbles will nucleate on the channel walls, grow, and depart from the surface. In microscale flow boiling bubbles can fill the channel diameter before the liquid drag force has a chance to sweep them off the channel wall. As a confined bubble elongates in a microchannel, it traps thin liquid films between the heated wall and the vapor core that are subject to large temperature gradients. The thin films evaporate rapidly, sometimes faster than the incoming mass flux can replenish bulk fluid in the microchannel. When the local vapor pressure spike exceeds the inlet pressure, it forces the upstream interface to travel back into the inlet plenum and create flow boiling instabilities. Flow boiling instabilities reduce the temperature at which critical heat flux occurs and create channel dryout. Dryout causes high surface temperatures that can destroy the electronic circuits that use two-phase micro heat exchangers for cooling.;Flow boiling instability is characterized by periodic oscillation of flow regimes which induce oscillations in fluid temperature, wall temperatures, pressure drop, and mass flux. When nanofluids are used in flow boiling, the nanoparticles become deposited on the heated surface and change its thermal conductivity, roughness, capillarity, wettability, and nucleation site density. It also affects heat transfer by changing bubble departure diameter, bubble departure frequency, and the evaporation of the micro and macrolayer beneath the growing bubbles.;Flow boiling was investigated in this study using degassed, deionized water, and 0.001 vol% aluminum oxide nanofluids in a single rectangular brass microchannel with a hydraulic diameter of 229 microm for one inlet fluid temperature of 63°C and two constant flow rates of 0.41 ml/min and 0.82 ml/min. The power input was adjusted for two average surface temperatures of 103°C and 119°C at each flow rate. High speed images were taken periodically for water and nanofluid flow boiling after durations of 25, 75, and 125 minutes from the start of flow. The change in regime timing revealed the effect of nanoparticle suspension and deposition on the Onset of Nucelate Boiling (ONB) and the Onset of Bubble Elongation (OBE). Cycle duration and bubble frequencies are reported for different nanofluid flow boiling durations. The addition of nanoparticles was found to stabilize bubble nucleation and growth and limit the recession rate of the upstream and downstream interfaces, mitigating the spreading of dry spots and elongating the thin film regions to increase thin film evaporation.
机译：集成电路芯片的高热通量的散发以及大功率电子设备中维持可接受的结温需要先进的冷却技术。一种这样的技术是在受限流沸腾条件下在微通道中进行两相冷却。在宏观流中，沸腾的气泡将在通道壁上成核，生长并从表面离开。在微尺度流动中，沸腾的气泡可以在液体阻力有机会将其扫出通道壁之前填满通道直径。当密闭气泡在微通道中伸长时，它会在受热壁和蒸气核之间捕获易受较大温度梯度影响的薄液膜。薄膜迅速蒸发，有时比进入的质量通量能补充微通道中的大量流体更快。当局部蒸汽压力峰值超过入口压力时，它将迫使上游界面返回入口气室并产生流动沸腾不稳定性。流动沸腾的不稳定性降低了发生临界热通量的温度，并导致通道变干。干out会导致较高的表面温度，从而可能破坏使用两相微热交换器进行冷却的电子电路。沸腾不稳定性的特征是流态的周期性振荡，从而引起流体温度，壁温，压降和质量流量的振荡。当使用纳米流体进行沸腾煮沸时，纳米颗粒会沉积在加热的表面上，并改变其导热系数，粗糙度，毛细作用，润湿性和成核位置密度。它还会通过改变气泡离开的直径，气泡离开的频率以及正在生长的气泡下面的微层和大分子层的蒸发来影响传热。本研究使用脱气，去离子水和0.001vol％的氧化铝纳米流体对流沸腾进行了研究。一个矩形黄铜微通道，其液压直径为229 microm，用于一种进口流体温度为63°C，并且两个恒定流速分别为0.41 ml / min和0.82 ml / min。在每种流速下，针对两个平均表面温度103°C和119°C调整功率输入。在开始流动25、75和125分钟后，定期为水和纳米流体的流动沸腾拍摄高速图像。方案时间的变化揭示了纳米粒子悬浮和沉积对Nucelate沸腾（ONB）发生和气泡伸长（OBE）发生的影响。报告了不同纳米流体流沸腾持续时间的循环持续时间和气泡频率。发现添加纳米颗粒可稳定气泡成核和生长，并限制上游和下游界面的后退速率，从而减轻了干斑的扩散并延长了薄膜区域，从而增加了薄膜的蒸发。

著录项

  • 作者

    Edel, Zachary J.;

  • 作者单位

    Michigan Technological University.;

  • 授予单位 Michigan Technological University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 97 p.
  • 总页数 97
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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