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Research on the Influencing Factors of Dehumidification Efficiency during the Dehumidification Process of Hollow Fiber Membrane Dehumidifiers
DOI: 10.12677/MOS.2024.131083, PDF, HTML, XML, 下载: 77  浏览: 128

Abstract: In industrial production, low-temperature biomedical and other fields, it is often necessary to achieve lower relative humidity in the air, so dehumidification treatment is required. This article takes the construction of a single membrane tube hollow fiber dehumidifier using PVDF membrane as the research object and studies the influence of some parameters in the dehumidification pro-cess of the hollow fiber membrane dehumidifier on the dehumidification efficiency through CFD (Computational Fluid Dynamics) numerical simulation method. Through analysis, it is found that increasing the inlet flow rate of moist air within a certain range can improve dehumidification effi-ciency while increasing the flow rate of blowing air can lead to a decrease in dehumidification effi-ciency. Increasing the temperature difference between moist air on both sides of the membrane and blowing air can enhance heat transfer and improve dehumidification efficiency. The relative humidity of moist air at the inlet should be within a reasonable range, and the optimal porosity range is 60% to 80%. Excessive relative humidity can easily cause a decrease in dehumidification efficiency under wet conditions.

1. 引言

2. 几何模型

Figure 1. Model of single membrane dehumidifier

Table 1. Related parameters of hollow fiber membrane dehumidifier

3. 数值模拟

3.1. 控制方程

(1)

$\begin{array}{c}\frac{\partial }{\partial t}\left(\rho v\right)+\nabla \cdot \left(\rho vv\right)=-\nabla p+\left[\mu \left(\nabla v+\nabla {v}^{\tau }\right)\right]+\rho g+{\stackrel{˙}{S}}_{E}^{}\end{array}$ (2)

$\frac{\partial \rho }{\partial t}+\nabla \cdot \left(\rho v\right)={\stackrel{˙}{S}}_{m}^{}$ (3)

$\frac{\partial }{\partial t}\left(\rho {Y}_{i}\right)+\nabla \cdot \left(\rho v{Y}_{i}\right)=-\nabla \cdot {J}_{i}+{\stackrel{˙}{S}}_{i}$ (4)

3.2. 模型选择

3.2.1. 多相流模型

VOF模型可通过求解一组动量方程并且跟踪整个流域中的所有流体的体积分数对多种不混溶流体进行建模。高湿气体在流动中凝结有明显的相界面，在分层流动和拥有自由界面的流动情况中VOF模型有高适用性。

Lee模型是相变源项模型，其采用气体动力学以温差描述相变过程。

$\frac{\partial }{\partial t}\left({\alpha }_{v}{\rho }_{v}\right)+\nabla \cdot \left({\alpha }_{v}{\rho }_{v}{V}_{v}\right)={\stackrel{˙}{m}}_{v}-{\stackrel{˙}{m}}_{l}$ (5)

If ${T}_{ı}>{T}_{\text{sat}}$

${\stackrel{˙}{m}}_{lv}=\text{coeff}\ast {\alpha }_{l}{\rho }_{l}\frac{\left({T}_{l}-{T}_{\text{sat}}\right)}{{T}_{\text{sat}}}$ (6)

If ${T}_{v}<{T}_{\text{sat}}$

${\stackrel{˙}{m}}_{vl}=\text{coeff}\ast {\alpha }_{v}{\rho }_{v}\frac{\left({T}_{sat}-{T}_{v}\right)}{{T}_{\text{sat}}}$ (7)

3.2.2. 多孔介质模型

J. Bear提出用多孔介质具有多项、固体骨架大且孔隙狭窄和孔隙互相连通三个特点定义多孔介质。多孔介质中各向同性的多孔介质动量方程源项：

${S}_{i}=-\left(\frac{\mu }{\alpha }{v}_{i}+{C}_{2}\frac{1}{2}\rho |v|{v}_{i}\right)$ (8)

${C}_{1}=\frac{1}{\alpha }=\frac{150}{{D}_{p}^{2}}\frac{{\left(1-\epsilon \right)}^{2}}{{\epsilon }^{3}}$ (9)

${C}_{2}=\frac{3.5}{{D}_{p}}\frac{\left(1-\epsilon \right)}{{\epsilon }^{3}}$ (10)

4. 结果与分析

4.1. 湿空气侧入口流速的影响

Figure 2. The influence of dehumidification efficiency on the flow rate of humid air on the side

4.2. 吹扫气侧入口流速的影响

Figure 3. The effect of dehumidification efficiency on the flow rate of the blowing gas side

4.3. 孔隙率的影响

$\varphi =孔隙体积/总体积={V}_{p}/{V}_{l}$ (11)

Figure 4. The influence of porosity on dehumidification efficiency

4.4. 入口处湿空气含湿量的影响

Figure 5. The influence of moisture content at the inlet on dehumidification performance

4.5. 膜两侧流体温差的影响

Figure 6. The effect of dehumidification efficiency on the temperature difference between the two sides of the fluid

5. 结论

1) 在一定范围内增大湿空气进气流速有利于提升除湿效率，最大可以将除湿效率提升58.6%。继续增加湿空气进气流速，流体在膜组件中停留时间过短，导致传热传质过程不充分。除湿效率降低33.5%。

2) 在一定范围内增大吹扫气流速会使除湿效率明显下降，增大到一定范围后吹扫气流速对除湿效率的影响减小，由最大下降21.6%到最小4.1%。

3) 膜材料参数对除湿过程至关重要，提高孔隙率有利于强化除湿过程。最佳孔隙率范围在60%~80%。

4) 增加入口处湿空气相对湿度可以提高除湿效率，最高可以将除湿效率提高61.1%。继续增加入口处湿空气相对湿度会出现湿工况的情况不利于除湿过程，使除湿效率降低。

5) 在正向传热的情况下，增加湿空气和吹扫气之间的温差能够提高除湿效率。温差增大到20 K后除湿效率增长逐渐放缓。

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