Condensation flow in PDMS microchannels with detectable wall deformation caused by flow condensation

doi:10.11949/0438-1157.20250374

Abstract

Abstract:

The development of flexible electronic devices has put forward the demand for microchannel heat exchangers made of elastically deformable materials. The condensation flow of FC-72 in rectangular microchannels made of PDMS with deformable soft wall was studied. The microchannels have a width of 300 μm and a height of 150 μm. Flow mass fluxes of 290 and 482 kg/(m²‧s) and vapor mass quality varying from 0.1 to 0.9 were experimentally studied. The images of the condensation flow patterns were collected using a fast camera. The data on soft wall deformation was measured using a white light confocal displacement sensor. The wall thickness increasing appears for intermittent flow. This wall thickening gets more significant with increasing inlet vapor mass quality and mass flux. By analyzing the curvature of the liquid-vapor interface, it is found that surface tension is not sufficient to cause the wall deformation observed in the experiments. This soft wall thickening phenomenon is caused by the local pressure drop in the liquid slug. This pressure drop occurs as a result of shrinking elongated bubbles due to the vapor vanishing during the condensation process. Therefore, if condensation is strong enough, it may induce a sudden local pressure drop in the liquid slug, causing the soft wall to move towards the channel inside. A theoretical model is proposed to predict the deformation of this soft wall. The results of the model are in good agreement with the measured deformation data for higher mass flux.

Key words: condensation, microchannel, elastic, deformation, soft material, FC-72

摘要：

针对FC-72在具有可弹性变形壁面的PDMS矩形微通道中的冷凝流动特性进行了实验研究，采用截面为300 μm×150 μm的微通道，质量流率为290和482 kg/(m²·s)、入口干度为0.1~0.9。通过高速摄像系统捕捉两相流型的演变过程，并采用白光共焦同轴位移计实时测量壁面变形量。实验结果表明，流型为间歇流时，液塞流经位置的壁面呈现显著的厚度增加现象，且壁厚变化率与质量流率及干度呈正相关。分析发现，表面张力作用不足以解释实验中观测到的壁面变形程度。进一步研究表明，弹性壁面厚度的变化主要来源于液塞内部的局部压降，这种压降是由冷凝过程中气体液化导致细长气泡收缩所引发的。当冷凝速率达到一定程度时，液塞内部将产生显著的局部压降，从而驱动弹性壁向通道内部移动。基于上述机理，建立了预测由于内部流动凝结导致微通道弹性壁面变形的理论模型，该模型在高干度条件下与实验测量结果表现出良好的一致性。

关键词: 凝结, 微通道, 弹性, 变形, 柔性材料, FC-72

CLC Number:

TK 172.4

Ziqi LIU, Ji WANG, Hai YU, Yuning ZHANG. Condensation flow in PDMS microchannels with detectable wall deformation caused by flow condensation[J]. CIESC Journal, 2025, 76(10): 5076-5092.

刘子琦, 王吉, 俞海, 张宇宁. PDMS微通道冷凝流动导致弹性壁面变形的研究[J]. 化工学报, 2025, 76(10): 5076-5092.

Figures/Tables 22

Fig.1 Schematic of the experimental setup

Table 1 Experimental apparatuses

设备	型号	基本参数和精确度
磁力驱动齿轮泵	3030-045-B-MK11	最大耐压1.2 MPa，2900 r/min
恒温水浴	THX-0510	-5~100℃，±0.1℃
直流电源	SS-K6010SPD	60 V±0.1 V，10 A±0.1 A
科里奥利质量流量计	DMF-1-B	30 kg/h，±0.2%
压力变送器	EJA110A	0~100 kPa，±0.1%
数据采集器	Agilent 34970A	±0.004%
高速摄像机	Photron Mini UX50	最大像素1280×1024，最大拍摄速率2000 帧/s

Fig.2 Test section

Fig.3 Soft wall deformation measurement system

Fig.4 Optical visualization system

Fig.5 Schematic diagram of the measurement section

Table 2 Uncertainties for all measurements

参数	不确定性
温度（RTD）	±0.1℃
质量流速	±0.2%[0~1000 kg/(m²‧s)]
压力	±0.3%（0~6 MPa）
时间	±18.5 ns
长度	±0.1 mm
变形量	±0.001 mm

Fig.6 Flow chart of image processing

Fig.7 Liquid-vapor interface morphology(visible image)

Fig.8 Geometry shape of gas-liquid interface (hypothetical surface)

Fig.9 Condensation flow regimes

Fig.10 Flow pattern map

Fig.11 Deformation data processing

Fig.12 PDMS wall thickness distribution of test points for mass flux 482 kg/(m2‧s)

Fig.13 PDMS wall deformation distribution for mass flux 482 kg/(m2‧s)

Fig.14 PDMS wall thickness distribution of test points for mass flux 290 kg/(m2‧s)

Fig.15 Effects of mass flux and inlet vapor mass quality on the maximum wall deformation

Fig.16 Effect of mass flux and inlet vapor mass quality on flow pattern percentage

Fig.17 The curvature and perimeter ratio of gas-liquid interface varing with the direction of liquid towards vapor

Fig.18 The pressure drop of the liquid-vapor interface due to surface tension

Fig.19 Liquid slug theoretical model in microchannel

Fig.20 Comparison of predicted and measured wall thickness variation

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