Saturation models of oleophilic coalescing filters

doi:10.11949/0438-1157.20200426

Abstract

Abstract:

Fibrous coalescing filters are widely used in a series of processes such as compressed air purification, engine crankcase ventilation, processing and cutting, and are used to remove liquid aerosol particles in the airflow. Pressure drop and ef?ciency of coalescence filters are greatly affected by saturation. It is of importance to establish the relationship among saturation, filter media parameters and operating conditions, which is helpful to optimize the filter design. Coalescence ?lters composed of thin glass fibrous media with micron fiber diameters are widely used in industry, while the saturation of which cannot be accurately predicted by the existing saturation models. This work investigated the relationship between pressure drop and saturation of multi-layered filters with different oleophilic filter media. In this study, there was no sharp boundary between wetting and non-wetting regions within filter media, thus a filter was regarded as a whole capillary system. According to the Jump-and-Channel model and capillary theory, a saturation model was developed. Compared with a large number of published literature data, it is found that when the saturation value is greater than 0.2, the predicted value is in good agreement with the experimental results, and the relative deviation is ≤20%. With the decrease in saturation, the boundaries become more and more obvious between the wetting and non-wetting regions. In this case, there is no need to modify to the capillary radius in the developed model. However, the developed model was also limited by the need for the channel pressure drop measurement, which should be solved in further work.

Key words: coalescence, filtration, aerosol, saturation, model

摘要：

纤维聚结滤芯广泛用于压缩空气净化、发动机曲轴箱通风、加工和切割等一系列工艺过程中，用于除去气流中的液体气溶胶颗粒。由于聚结滤芯饱和度对于过滤效率及阻力具有重要影响，因此建立饱和度与滤材参数及操作条件之间的关系将有助于优化滤芯结构并提高过滤性能。目前实际工业用聚结滤芯通常由多层微米级玻璃纤维材料组成，然而现有计算模型无法用于此类滤芯的饱和度预测。因此，本文基于多种常用亲油型聚结滤芯压降及饱和度实验测试结果，根据“跳跃-通道”模型及毛细管理论建立了新的饱和度预测模型。通过与大量已发表文献数据对比发现，当饱和值大于0.2时，预测值与实验结果吻合度较好，相对偏差≤20%。随着饱和度的降低，滤芯润湿区域和非润湿区域之间界限逐渐明显，此时无需对毛细管半径进行修正。然而，新模型仍然要依靠压降测量值进行计算，这一问题需在后续工作中加以解决。

关键词: 聚结, 过滤, 气溶胶, 饱和度, 模型

CLC Number:

TE 832

CHANG Cheng,JI Zhongli,LIU Jialin. Saturation models of oleophilic coalescing filters[J]. CIESC Journal, 2020, 71(12): 5610-5619.

常程,姬忠礼,刘佳霖. 亲油型聚结滤芯饱和度预测模型研究[J]. 化工学报, 2020, 71(12): 5610-5619.

Figures/Tables 13

Table 1 Saturation models and the applicable filter material parameters

Ref.	Model	Filter material	Fiber diameter/μm	Thickness/mm
[11]	$S e = 0.0829 α Z d f - 0.321 C a n - 0.431$ (1) $C a n = Q μ g A f σ c o s θ Δ P e Δ P d r y$ (2)	stainless steel fiber	4—22	7.1—7.8
[12]	$S e = α 0.39 ± 0.09 B o 0.47 ± 0.06 + 0.24 ± 0.07 l n B o C a 0.11 ± 0.04 × e x p - 0.04 ± 0.36 + 6.6 ± 1.5 × 105 D r$ (3) $B o = ρ l g d f 2 σ × 105$ (4) $C a = μ g u σ × 105$ (5) $D r = μ l D σ Z W$ (6)	glass fiber	2.9, 8.5	8.8
[13]	$x ∞ = - Δ P c r c + 2 σ c o s θ r c ρ l g$ (7) $Δ P c = (π + 1) π r f r c Δ P e$ (8) $r c = - A l o g e α r f - B c f$ (9)	glass fiber	0.62—1.24	0.53—0.65
[13]		stainless steel fiber	4.0—6.4	5.16—6.90
[14]	$S c h a n n e l = 1 1 + u u *$ (10)	glass fiber	2.99	0.5

Table 1 Saturation models and the applicable filter material parameters

Ref.	Model	Filter material	Fiber diameter/μm	Thickness/mm
[11]	$S e = 0.0829 α Z d f - 0.321 C a n - 0.431$ (1) $C a n = Q μ g A f σ c o s θ Δ P e Δ P d r y$ (2)	stainless steel fiber	4—22	7.1—7.8
[12]	$S e = α 0.39 ± 0.09 B o 0.47 ± 0.06 + 0.24 ± 0.07 l n B o C a 0.11 ± 0.04 × e x p - 0.04 ± 0.36 + 6.6 ± 1.5 × 105 D r$ (3) $B o = ρ l g d f 2 σ × 105$ (4) $C a = μ g u σ × 105$ (5) $D r = μ l D σ Z W$ (6)	glass fiber	2.9, 8.5	8.8
[13]	$x ∞ = - Δ P c r c + 2 σ c o s θ r c ρ l g$ (7) $Δ P c = (π + 1) π r f r c Δ P e$ (8) $r c = - A l o g e α r f - B c f$ (9)	glass fiber	0.62—1.24	0.53—0.65
[13]		stainless steel fiber	4.0—6.4	5.16—6.90
[14]	$S c h a n n e l = 1 1 + u u *$ (10)	glass fiber	2.99	0.5

Table 2 Properties of experimental filter materials

Filter	Material	Thickness /mm	Packing density	Fiber diameter /μm	Contact angle/ (°)
A	glass fiber	0.51±0.01	0.063±0.001	2.92±0.10	35.3±1.9
B	glass fiber	0.62±0.02	0.062±0.001	2.00±0.08	39.1±1.7
C	glass fiber	0.41±0.01	0.072±0.001	1.79±0.06	46.2±2.1

Fig.1 SEM images of filter material B

Fig.2 Schematic of experimental apparatus

Fig.3 Pressure drop profile of filter A4

Fig.4 Pressure drop of filters with different layers

Fig.5 Total saturation and saturation profiles of filters with different layers

Fig.6 Comparison of predicted saturation with experimental results of filters A4, B4 and C4

Fig.7 Liquid distribution in layer 3 of filters A4, B4 and C4 at steady state

Table 3 All parameters used to predict the saturation of filters A4, B4 and C4

Parameter	Filter A4	Filter B4	Filter C4
d_f/μm	2.92	2.00	1.79
α	0.063	0.062	0.072
Z /mm	2.03	2.48	1.64
W /m	0.15	0.15	0.15
N	4	4	4
Q /(m³/s)	0.002124	0.002124	0.002124
A_f /m²	0.0177	0.0177	0.0177
u /(m/s)	0.12	0.12	0.12
u^*/(m/s)	0.0176	0.0176	0.0176
D /(m³/s)	9.69×10^-10	9.69×10^-10	9.69×10^-10
ΔP_dry/kPa	0.53	1.36	1.40
ΔP_e /kPa	4.55	7.38	10.11
ρ_l/(kg/m³)	912	912	912
σ /(N/m)	0.03	0.03	0.03
μ_g /(Pa·s)	17.9×10^-6	17.9×10^-6	17.9×10^-6
μ_l /(Pa·s)	0.023	0.023	0.023
θ[式(2)]/(°)	35.3	39.1	46.2
θ[式(7)]/(°)	65.8	67.4	71.6
c_f	1	1	1
A	50.7	50.7	50.7
B	42.1	42.1	42.1

Fig.8 Comparison of predicted saturation with different characteristic capillary radii and fractions

Table 4 All parameters used for predicting saturation

Authors	d_f/μm	α	l/mm	n	A_f/m²	L/m	u/(m/s)	ΔP_channel/kPa	ρ_l/(kg/m³)	σ/(N/m)
this work-A	2.92	0.063	0.51	1~4	0.0177	0.15	0.12	0.82~1.64	912	0.03
this work-B	2.00	0.062	0.62	1~4	0.0177	0.15	0.12	1.81~4.06	912	0.03
this work-C	1.79	0.072	0.41	1~4	0.0177	0.15	0.12	2.21~5.46	912	0.03
Mead-Hunter等^[13]-GF1	1.1	0.064	0.53	1	0.0017	0.047	0.153	3.15	841	0.028
Mead-Hunter等^[13]-GF4	1.24	0.054	0.65	1	0.0017	0.047	0.153	2.28	841	0.028
Kolb等^[14]	2.99	0.05	0.5	10	0.0064	0.08	0.05~0.7	1.37~6.60	900	0.031
Chang等^[23]	1.93	0.076	0.52	4	0.0198	0.188	0.1	3.09	912	0.03
Kampa等^[3]	1	0.05	0.5	10	0.0064	0.08	0.3	21.35	900	0.03
Kolb等^[8]	4.0	0.061	0.64	3	0.0064	0.08	0.25	1.79	900	0.031
Chen等^[24]-A	4.08	0.072	0.41	4	0.0177	0.15	0.12	0.67	912	0.03
Chen等^[24]-B	3.07	0.067	0.46	4	0.0177	0.15	0.12	1.36	912	0.03
Chen等^[24]-C	2.33	0.070	0.46	4	0.0177	0.15	0.12	2.17	912	0.03
Chen等^[24]-D	1.92	0.071	0.45	4	0.0177	0.15	0.12	4.25	912	0.03
Frising等^[25]	1.21	0.078	0.409	1	0.0095	0.11	0.058~0.25	2.81~5.41	913.4	0.03

Fig.9 Predicted and measured total saturation

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