相分离结构微细通道流动沸腾压降分析与可视化

doi:10.16085/j.issn.1000-6613.2023-0045

摘要/Abstract

摘要：

为探究相分离结构对微细通道流动沸腾压降的影响，利用数控技术加工了相分离结构微细通道实验段。以质量分数为30%的甘油水溶液作为实验工质，在工质入口温度为70℃、质量流率为121.25kg/(m²·s)、热流密度为76.61~150.70kW/m²的工况下分析了两种（多孔/少孔）相分离结构和无排气孔的普通微细通道的压降变化，同时对通道内气泡行为进行了可视化研究，引入气相分离系数对受限气泡在通道内的生长行为进行定量分析。实验结果表明，相分离结构可以改善通道内两相总压降，在多孔、少孔和普通微细通道中，微细通道的气相转移面积越大，气相分离系数越大，通道内受限气泡长径比越小，两相总压降损失越小。此外，通过对相邻通道增加压差，调整合适的压力切换周期，可以进一步改善相分离膜的气相转移速率，减缓通道内两相总压降。

关键词: 相分离, 微细通道, 压降, 流动沸腾, 可视化

Abstract:

To investigate the effect of the above phase separation structure on the boiling pressure drop of the flow within the microchannels, an experimental section of the microchannels with the phase separation structure was machined using CNC technology. The pressure drop of two (porous/low-porous) phase separation structures and a normal microchannels without venting holes were analyzed at an inlet temperature of 70℃, a mass flow rate of 121.25kg/(m²·s) and a heat flow density of 76.61—150.70kW/m² using an aqueous glycerol solution with a mass fraction of 30% as the experimental working medium. To examine how different phase separation structures of microchannels affect the length-to-diameter ratio (l/w) of confined bubbles, the bubble dynamics in the channels were visualized and a gas phase separation coefficient was employed to quantify the growth behavior of confined bubbles in the channels. The experimental results showed that the phase separation structure could improve the total pressure drop of the two phases in the channels. In the porous, less porous, and ordinary microchannels, the larger the gas phase transfer area of the microchannels, the larger the gas phase separation coefficient, the smaller the length-diameter ratio of the confined bubbles in the channels, the smaller the total pressure drop loss of the two phases, and could improve the system reliability. In addition, by increasing the pressure difference between adjacent channels and adjusting the appropriate pressure switching period, the gas phase transfer rate of the phase separation membrane could be further improved and the total pressure drop of the two phases in the channels could be slowed down. This study could provide a new design idea for the improvement of flow boiling pressure drop in microchannels.

Key words: phase separation, microchannels, pressure drop, flow boiling, visualization

中图分类号:

TK124

罗小平, 周家玉, 李桂中. 相分离结构微细通道流动沸腾压降分析与可视化[J]. 化工进展, 2023, 42(12): 6157-6170.

LUO Xiaoping, ZHOU Jiayu, LI Guizhong. Analysis and visualization of flow boiling pressure drop in microchannels with phase separation structure[J]. Chemical Industry and Engineering Progress, 2023, 42(12): 6157-6170.

图/表 19

表1 实验工质（质量分数为30%的甘油水溶液）物理特性

物性	数值
气相密度/kg·m^-3	0.60
液相密度/kg·m^-3	1027
饱和温度/℃	102.4
表面张力/mN·m^-1	59.92
液相比热容/J·kg^-1·K^-1	3640
气化潜热/J·kg^-1	2304
液相黏度/Pa·s	0.00053

图1 实验工质与PTFE相分离膜的接触角

表2 微细通道热沉设计参数

长度L/mm	宽度W/mm	高H/mm	单条通道宽度W_ch/mm	单条通道高度H_ch/mm	肋厚W_w/mm	平行通道数量N/条
220	66	10	2	2	2	12

图2 微通道相分离膜固定腔结构和工质流向水平示意图La—导气道中线与最近一端膜固定腔的距离；Lb—相邻导气道中轴线距离；Ld—导气道宽度；Lw—膜固定腔长度；Hsp—膜固定腔深度；Ww—相邻微细通道间的肋厚

图3 相分离示意图

表3 膜固定腔参数

型号	L_a/mm	L_b/mm	L_d/mm	L_w/mm	L_l/mm	H_sp/mm	N_ps（导气道条数）/条
LPC-1	5.7	3.6	0.6	22.2	216.4	3	4
LPC-2	5.7	4.1	0.6	23.7	165.2	3	4
LPC-3	5.7	4.6	0.6	20.6	111.4	3	3
LPC-4	5.7	5.1	0.6	21.6	64.6	3	3

表4 不同结构热沉排气孔设计参数

型号	N₁/个	N₂/个	N₃/个	N₄/个	N_tot/个	固定孔尺寸 /mm	排气孔尺寸 /mm
SPP-1	8	8	6	6	336	1.2	0.6
SPP-2	4	4	2	2	144	1.2	0.6
SPP-3	0	0	0	0	0	1.2	0.6

图4 实验系统简图1—注液装置；2—储液罐；3-1、3-2—变频器；4-1、4-2—磁力泵；5-1、5-2—过滤器；6—预热水箱；7-1~7-12—手动调节阀；8-1、8-2—转子流量计；9-1、9-2—压力换向装置；10-1、10-2—止回阀；11—实验段；12—高速摄像机；13—高压直流电场发生器；14—工控机；15—减压装置；16—冷凝器；17—冷却水箱；18—工业冷水机组；19—真空表；20-1、20-2—单向针阀

图5 微细通道实验段

图6 热损失测试拟合曲线

表5 主要仪表型号及精度

测量参数	测量仪器	型号	量程	精度
压力	压力传感器	HY-131	0~100kPa	0.2%
压差	压差传感器	HY-3351	0~10kPa	0.2%
温度	热电偶	PT-100	0~1200℃	0.1℃
流量	转子流量计	LZB-WS-10	6~60L/h	2.5%

表6 主要参数的最大相对不确定度

测量参数	最大不确定度/%	测量参数	最大不确定度/%
G	2.50	∆P_sp,f	3.72
q_eff	3.31	∆P_tp,grav	3.21
L_sp	2.76	∆P_tp,a	3.41
x_e,out	7.31	∆P_tp,f	6.59
∆P_sp,grav	2.76

图7 不同换向周期下三种结构微细通道ΔPtot、ΔPtp和ΔPtpf变化趋势

图8 120s换向周期下SPP-1型微细通道总压降瞬态变化

图9 不同热流密度下不同相分离结构微细通道ΔPtot、ΔPtp和ΔPtpf变化趋势

图10 不同结构微细通道局部区域受限气泡大小

图11 有效热流密度为130.60kW/m2时不同结构微细通道局部区域受限气泡大小

图12 有效热流密度为150.70kW/m2时不同结构微细通道局部区域受限气泡大小

图13 受限气泡生长过程受力分析

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