Experimental investigation of supercritical carbon dioxide in horizontal microchannels with non-uniform heat flux boundary conditions
Experimental investigation of supercritical carbon dioxide in horizontal microchannels with non-uniform heat flux boundary conditions
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DOI：
10.1016/j.ijheatmasstransfer.2018.10.027
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发表时间：
2019-03
影响因子：
5.2
通讯作者：
S. A. Jajja;Kyle R. Zada;B. Fronk
中科院分区：
文献类型：
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作者：
S. A. Jajja;Kyle R. Zada;B. Fronk
超临界二氧化碳（sCO 2）在热力学临界点附近的热物理性质发生了剧烈的变化.非线性热物性的变化会影响sCO 2的传热行为，这是传统的单相传热理论不能很好地预测的。这可能成为使用sCO 2作为传热流体并在临界点附近操作的热交换器的有效设计的主要障碍。以前的研究sCO 2加热主要集中在宏观尺度，圆形和均匀加热的通道在相对较低的热通量。目前还不清楚，如果模型和相关性开发的大型圆管数据可以按比例缩小到微尺度，非圆形通道受到不均匀加热。实验研究了水平布置的单壁非均匀热流边界条件下sCO 2在微通道换热器中的湍流传热性能。试验段有五个平行通道，水力直径为0.75 mm，纵横比为1。使用计算机数控加工制造的通道和使用扩散结合方法密封的测试部分。数据分析技术，采用2-D和3-D的实验测试部分的传热模型的开发，以计算一组给定的实验条件下的平均传热系数。数据是在广泛的实验参数范围内获得的，包括试验段施加的热通量（20 Ω ″ × 40 W cm− 2）、质量通量（500 Ω G × 1000 kg m− 2 s− 1）、减压（1.03 Ω P R × 1.1）和入口温度（16 Ω T，150 ° C）。的热传递数据进行了筛选存在的浮力和流动加速的影响，然后对湍流亚临界和超临界流体流动的相关性进行比较。
Supercritical carbon dioxide (sCO 2) experiences a drastic change in its thermophysical properties near the thermodynamic critical point. A non-linear thermophysical property variation can influence the heat transfer behavior of sCO 2 which is not predicted well by conventional single phase heat transfer theory. This can become a major hindrance in the effective design of heat exchangers using sCO 2 as a heat transfer fluid and operating in the vicinity of the critical point. Previous investigations of sCO 2 heating have been primarily focused on macroscale, circular and uniformly heated channels at relatively low heat fluxes. It is unclear if models and correlations developed from large circular tube data can be scaled down to the microscale, non-circular channels subject to non-uniform heating. The present study experimentally investigates the turbulent heat transfer performance of sCO 2 in a microchannel heat exchanger operating in a horizontal configuration with a single wall non-uniform heat flux boundary condition. The test section has five parallel channels with a 0.75 mm hydraulic diameter and an aspect ratio of 1. The channels are fabricated using computer numerical control machining and the test section sealed using a diffusion bonding approach. Data analysis techniques which employ 2-D and 3-D heat transfer models of the experimental test section are developed to calculate the average heat transfer coefficients for a given set of experimental conditions. Data are obtained over a wide range of experimental parameters including test section applied heat flux (20⩽ q ″⩽ 40 W cm− 2), mass flux (500⩽ G⩽ 1000 kg m− 2 s− 1), reduced pressure (1.03⩽ P R⩽ 1.1), and inlet temperatures (16⩽ T in⩽ 50° C). The heat transfer data were screened for the presence of buoyancy and flow acceleration effects and then compared against correlations developed for turbulent subcritical and supercritical fluid flows.