小波分解方法分辨出跨越2到3个时间尺度的针肋型微通道沸腾传热机理
发布时间：2018-11-08 15:30
【摘要】：微小型化是当代科技发展的重要方向之一。随着时代发展,空间、信息及生物等高新技术领域亟待解决超小面积、超高热流密度条件下的换热问题。在这一背景下,本文针对微流体在硅基微通道内的流动沸腾波动特性进行了创新性的实验研究。本研究采用微电子机械系统(MEMS)加工工艺,设计并加工了一种具有微针肋结构的硅基微通道芯片,设计并搭建了微流体闭式循环回路系统和微流体光学平台,建成了高速的、高空间分辨率的、高精度的、时钟同步的流体传热和可视化数据采集系统。采用去离子水为工质,进行了单相水校核实验和气液两相流动沸腾实验。微通道中的流动沸腾特性受流量、热流密度、通道结构,入口温度等各参数的影响,由44个工况归纳出三类流动沸腾不稳定区间：当q/G 0.62 kJ/kg时,微通道内沸腾初始,呈现准稳定沸腾模式；当0.62 kJ/kg q/G 1.13 kJ/kg时,微通道内出现自维持的周期性沸腾模式,进出口压差和壁温呈现周期10-15s的波动；当q/G1.13 kJ/kg时,微通道内沸腾剧烈,呈现准稳定沸腾模式。观察到新的沸腾现象,如液岛、锥形两相沸腾发展区、两种沸腾核化模式等。创新性地使用小波分析方法处理以上流动沸腾的波动信号,明确分辨出这三类不稳定流动沸腾类型和机理：第一类沸腾不稳定性为密度波不稳定性与气液流型转换引起的不稳定性耦合,包含两个时间尺度；第二类沸腾不稳定性为压力降型不稳定性、密度波不稳定性以及气液流型转换引起的不稳定性耦合,包含三个时间尺度；第三类沸腾不稳定性为密度波不稳定性与变速液膜蒸发引起的不稳定性耦合,包含两个时间尺度。温度信号分析结果与可视化照片对应良好,确切地解释了毫秒级的沸腾现象和传热趋势。在通道内流动传热实验研究领域,结合小波分析方法的对于毫秒级温度信号波动的分析和机理解释,在国内外文献中尚无报道。
[Abstract]:Miniaturization is one of the most important directions in the development of modern science and technology. With the development of the times, the problem of heat transfer under the condition of ultra-small area and ultra-high heat flux is urgently needed to be solved in the field of space, information and biology. In this context, the flow boiling wave characteristics of microfluids in silicon-based microchannels have been investigated experimentally. In this study, a silicon microchannel chip with micro-needle rib structure was designed and fabricated by using microelectromechanical system (MEMS) process, and a micro-fluid closed loop system and a micro-fluid optical platform were designed and built, and a high-speed microfluidic microchannel chip was built. High spatial resolution, high precision, clock-synchronous fluid heat transfer and visual data acquisition system. Using deionized water as working medium, single phase water verification experiment and gas liquid two phase flow boiling experiment were carried out. The characteristics of flow boiling in microchannels are affected by flow rate, heat flux density, channel structure and inlet temperature. From 44 operating conditions, three types of flow boiling instability zones are concluded: when Q / G is 0.62 kJ/kg, The initial boiling in the microchannel shows a quasi-stable boiling mode. At 0.62 kJ/kg Q / G 1.13 kJ/kg, the self-sustaining periodic boiling mode appeared in the microchannel, and the pressure difference between inlet and outlet and the wall temperature fluctuated for 10-15 s. When q/G1.13 kJ/kg, the microchannel boiling is intense, showing a quasi-stable boiling mode. New boiling phenomena such as liquid island, conical two-phase boiling developing region and two boiling nucleation modes were observed. Innovative wavelet analysis is used to process the wave signals of the above flow boiling. The types and mechanisms of these three types of unstable flow boiling are clearly distinguished. The first type of boiling instability is the coupling of density wave instability and gas-liquid flow pattern transition, which includes two time scales; The second type of boiling instability is pressure drop instability, density wave instability and instability coupling caused by gas-liquid flow pattern conversion, which includes three time scales. The third type of boiling instability is the coupling of density wave instability and variable velocity liquid film evaporation, which includes two time scales. The results of temperature signal analysis correspond well with the visual photos, which explain exactly the boiling phenomenon and heat transfer trend in millisecond order. In the field of experimental study of flow heat transfer in channels, the analysis and mechanism explanation of millisecond temperature signal fluctuation based on wavelet analysis method have not been reported in the literature at home and abroad.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK124
本文编号：2318897
[Abstract]:Miniaturization is one of the most important directions in the development of modern science and technology. With the development of the times, the problem of heat transfer under the condition of ultra-small area and ultra-high heat flux is urgently needed to be solved in the field of space, information and biology. In this context, the flow boiling wave characteristics of microfluids in silicon-based microchannels have been investigated experimentally. In this study, a silicon microchannel chip with micro-needle rib structure was designed and fabricated by using microelectromechanical system (MEMS) process, and a micro-fluid closed loop system and a micro-fluid optical platform were designed and built, and a high-speed microfluidic microchannel chip was built. High spatial resolution, high precision, clock-synchronous fluid heat transfer and visual data acquisition system. Using deionized water as working medium, single phase water verification experiment and gas liquid two phase flow boiling experiment were carried out. The characteristics of flow boiling in microchannels are affected by flow rate, heat flux density, channel structure and inlet temperature. From 44 operating conditions, three types of flow boiling instability zones are concluded: when Q / G is 0.62 kJ/kg, The initial boiling in the microchannel shows a quasi-stable boiling mode. At 0.62 kJ/kg Q / G 1.13 kJ/kg, the self-sustaining periodic boiling mode appeared in the microchannel, and the pressure difference between inlet and outlet and the wall temperature fluctuated for 10-15 s. When q/G1.13 kJ/kg, the microchannel boiling is intense, showing a quasi-stable boiling mode. New boiling phenomena such as liquid island, conical two-phase boiling developing region and two boiling nucleation modes were observed. Innovative wavelet analysis is used to process the wave signals of the above flow boiling. The types and mechanisms of these three types of unstable flow boiling are clearly distinguished. The first type of boiling instability is the coupling of density wave instability and gas-liquid flow pattern transition, which includes two time scales; The second type of boiling instability is pressure drop instability, density wave instability and instability coupling caused by gas-liquid flow pattern conversion, which includes three time scales. The third type of boiling instability is the coupling of density wave instability and variable velocity liquid film evaporation, which includes two time scales. The results of temperature signal analysis correspond well with the visual photos, which explain exactly the boiling phenomenon and heat transfer trend in millisecond order. In the field of experimental study of flow heat transfer in channels, the analysis and mechanism explanation of millisecond temperature signal fluctuation based on wavelet analysis method have not been reported in the literature at home and abroad.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK124
【参考文献】
相关期刊论文 前1条
1 马友光;季喜燕;王东继;付涛涛;朱春英;;矩形截面微通道内气-液两相流压力降的实验测定及关联(英文)[J];Chinese Journal of Chemical Engineering;2010年06期
，本文编号：2318897
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