锯齿波纹板对挥发性有机物低温脱除过程强化模拟分析

doi:10.16085/j.issn.1000-6613.2023-0591

摘要/Abstract

摘要：

针对可挥发性有机物（VOCs）的低温脱除，采用波纹通道可破坏不凝气（NCG）层积聚、减小低温相变脱除传质阻力。本文建立了针对锯齿波纹板通道内少量R134a与氮气混合气的低温相变脱除的二维模型，揭示了锯齿齿板底角角度对R134a相变脱除效果的影响特性。结果表明，与平板通道相比，本文采用的对照组等腰三角锯齿波纹板可显著提升单位面积冷壁面上R134a的脱除效率，在本研究条件下R134a时空平均相变速率（α）为0.1268g/(m²·s)，提高了144.6%；锯齿波纹板底角（θ）增加时，NCG层在近冷壁面处会依次发生贴壁流动、脱壁掺混，最终形成稳定漩涡的流动阻滞区。当θ为13.30°~35.45°时，NCG层发生显著的脱壁掺混，α在0.082~0.1268g/(m²·s)之间；当θ=17.46°时，α达到最大值0.1268g/(m²·s)。当θ过大或过小时，脱壁掺混效果都将衰减，α在较低的水平。本文对用于低浓度VOCs的冷凝-冻结脱除的锯齿波纹板结构设计具有参考意义。

关键词: 废物处理, 传质, 低温脱除, 数值模拟, 波纹板

Abstract:

The corrugated channel can be used to break the accumulation of non-condensable gas (NCG) layers and reduce the resistance to mass transfer in the cryogenic removal of volatile organic compounds (VOCs). In this study, a two-dimensional model for the cryogenic removal of low concentration R134a from nitrogen on a sawtooth corrugated plate channel was established, and the impact of the sawtooth bottom angle on the removal performance of R134a were revealed. The results showed that the isosceles triangular sawtooth corrugated plate can significantly improve the removal efficiency of R134a on the cold wall surface per unit area compared with the flat plate channel. The spatio-temporal average phase change rate (α) of R134a on the sawtooth plate under the conditions of present study was 0.1268g/(m²·s), which increased by 144.6% compared with flat surface. The NCG flow near the cold wall surface will convert from the flowing adjacent to the wall, to off-wall mixing with the bulk flow, and finally to forming the flow blocking zone with stable vortex with the increase in the bottom angle (θ) of the sawtooth corrugated plate. Significant off-wall mixing with the bulk flow of the NCG layer occurred when θ was 13.30°—35.45°, with α ranged from 0.082—0.1268g/(m²·s). The α reached the maximum value of 0.1268g/(m²·s) when θ was 17.46°. The effect of the off-wall mixing with the bulk flow of the NCG layer will decay and the α will keep at a lower level when θ deviated the aforementioned range. The present study can provide a reference for the design of sawtooth corrugated plate structure for cryogenic condensation-freeze removal of low concentration VOCs.

Key words: waste treatment, mass transfer, cryogenic removal, numerical simulation, corrugated plate

中图分类号:

TE85

邵博识, 谭宏博. 锯齿波纹板对挥发性有机物低温脱除过程强化模拟分析[J]. 化工进展, 2023, 42(S1): 84-93.

SHAO Boshi, TAN Hongbo. Simulation on the enhancement of cryogenic removal of volatile organic compounds by sawtooth plate[J]. Chemical Industry and Engineering Progress, 2023, 42(S1): 84-93.

图/表 18

图1 对照组锯齿板结构与计算域尺寸

图2 对照组锯齿形冷壁面板计算区域网格划分及网格质量

表1 计算初始条件

参数	工质混合气体
组分	R134a/氮气
入口流速/m·s^-1	0.2
压力/MPa	4.0
R134a入口摩尔分数	0.02
入口温度/K	246（饱和）
锯齿壁面过冷度/K	100

图3 忽略多相流时近冷壁面R134a质量浓度分布示意图

表2 不同源项中的ϕ取值

源项类型	ϕ
质量源项S_m	1
能量源项S_e	h_l
x方向动量源项S_u	u
y方向动量源项S_v	v
组分方程源项S_s	ω_v

图4 壁面冷凝法程序编写流程图

表3 物性拟合公式参数取值

分压力范围/Pa	m₁	n₁	c₁	温度范围/K	m₂	n₂	c₂
p_v＜137	127.280	0.04615	-0.2078	T＜160	3.04×10^-7	0.1248	-4.7482
137≤p_v＜6531	119.463	0.05813	0.4989	160≤T＜180	7.15×10^-5	0.0928	-62.706
6531≤p_v＜43287	104.720	0.07341	0	180≤T＜200	5.30×10^-3	0.0705	-505.197
p_v≥43287	93.997	0.08378	-0.6147	200≤T＜220	0.165	0.0547	-2648.809
—	—	—	—	220≤T＜240	2.593	0.0432	-10094.798
—	—	—	—	T≥240	40.630	0.0330	-38445.289

图5 网格数与时间无关性验证

图6 不同时间段长度下的时空平均相变速率

图7 沿长度方向热通量变化实验与仿真结果对比

图8 混合气体中R134a在平板及锯齿形冷壁上相变时的R134a浓度云图

图9 平板及锯齿形冷壁上R134a时间平均相变速率的空间分布图

图10 某一时刻某处背风面与迎风面处的流线图与速度云图

图11 不同底角θ的锯齿冷壁面R134a相变摩尔浓度云图

图12 θ=35.45°时的速度云图与局部流线图

图13 不同锯齿底角情况下R134a时间平均相变速率的空间分布图

图14 不同锯齿底角情况下R134a时空平均相变速率

图15 不同锯齿底角情况下平均流动静压损失变化情况

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