Influence of relative humidity on HEPA filters during and after loading with soot particles

Figures & data

Table 1. Principal results already published.

Loading under humidity				Impact of humidity on loaded filters
Joubert et al. (2011)		Gupta et al. (1993)		Montgomery et al. (2015)		Joubert et al. (2011)
NaCl (below deliquescence point)	Alumina	NaCl (below deliquescence point)	Alumina	NaCl (below deliquescence point)	Alumina	NaCl (below deliquescence point)	Alumina
d50 = 0.6 µm	d50 = 4.2 µm	d50 = 0.5 µm d50 = 1 µm	d50 = 0.45 µm d50 = 1.19 µm	d50 = 0.1 µm	Bimodal dmod1 = 0.1 µm dmod2 = 0.4 µm	d50 = 0.6 µm	d50 = 4.2 µm
Decrease of flow resistance with increase of the relative humidity	Decrease of flow resistance start from HR > 94%	Decrease of flow resistance with increase of the relative humidity	Decrease of flow resistance start from HR > 80%	Sudden decrease of flow resistance with RH > RH loading	No change	Sudden decrease of flow resistance with RH > RH loading	Slight and rapid increase of flow resistance

Figure 1. Changes in experimental specific cake resistance of alumina oxide particles versus relative humidity and for various aerosol diameters (from Joubert et al. 2011).

Figure 2. Experimental test bench design.

Figure 3. Description of the experimental protocol.

Table 2. Experimental characterization of two soots from the results of (Bescond et al. 2014; Yon et al. 2015) D_f fractal dimension, k_f fractal prefactor, ρ_pp density, D_p primary diameter, OC/TC organic carbon on total carbon.

CAST (Propane (mL/min)/ Nitrogen (mL/min)/ Air oxygen (L/min)/ Air dilution (L/min))	60/0/1.5/20	50/200/1.2/20
Overall ratio	0.95	0.99
Df	1.73	1.74
kf	1.94	1.94
ρpp (kg/m^3)	1543	1227
Dp (nm)	18.1	26.5
OC/TC (%)	16.2	22

Figure 4. Particle size distribution of the two generated soot.

Figure 5. Evolution of the pressure drop of a clean filter subjected to increasing levels of relative humidity.

Figure 6. Evolution of the pressure drop of flat HEPA filters versus collected surface mass of soot particles at two different relative humidity.

Figure 7. Time variation in pressure drop across flat filters D-309 during clogging until 3500 Pa with soot particles for three different rates of relative humidity (soot 18).

Figure 8. Time variation in pressure drop across flat filters D-309 during clogging until 2500 Pa with soot particles for three different rates of relative humidity (soot 18).

Figure 9. Time variation in pressure drop across flat filters D-309 during clogging until 1500 Pa with soot particles for three different rates of relative humidity (soot 18).

Figure 10. Evolution of the flow resistance in function of the relative humidity (soot 18).

Figure 11. Evolution of the flow resistance in function of the relative humidity (soot 26).

Figure 12. Evolution of the pressure drop in function of the time (Deposit 3500, soot 26): comparison between the numerical expression (line) and experimental results (point).

Table 3. Characteristic parameters (soot 18).

	Loading 3500			Loading 2500			Loading 1500
RH (%)	85	68	62	85	66	55	90	66	50
$\mathit{\tau }$ (s)	9.9	29.9	23.6	17.8	15.4	82	11.6	33.5	8
α (Pa)	1029	734	608	538	332	278	189	69	19

Table 4. Characteristic parameters (soot 26).

	Loading 3500			Loading 2500			Loading 1500
RH (%)	90	66	53	90	68	54	90	67	53
$\mathit{\tau }$ (s)	6.7	20.6	16.7	14.2	21	22.8	14.8	33.6	16.7
α (Pa)	1251	900	705	850	500	440	245	159	87

Table 5. Values a1, b1, a2, b2 found for the two soot.

	soot 18	soot 26
a1	0.0069	0.0049
b1	−6.71	−2.22
a2	−0.15	0.025
b2	58	−212

Figure 13. Evolution of the coefficient of proportionality as a function of the relative humidity (soot 18).

Figure 14. Evolution of the coefficient of proportionality as a function of the relative humidity (soot 26).

Table 6. Experimental pressure drop of clogging $\Delta P_0,$ relative humidity (HR), final pressure drop after humid air $\Delta P_{HR}$ and model pressure drop $\Delta P_{\mathit{model}}$ for soot 18.

$\Delta {\mathit{P}}_0$ (Pa)	HR (%)	$\Delta {\mathit{P}}_{\mathit{HR}}$(Pa)	$\Delta {\mathit{P}}_{\mathit{model}}$(Pa)
3380	90	2347	2333
3397	68	2689	2710
3413	62	2806	2822
2396	85	1850	1862
2420	66	2085	2065
2567	55	2336	2288
1481	85	1292	1346
1520	50	1500	1501
1528	66	1472	1446

Table 7. Experimental pressure drop of clogging $\Delta P_0,$ relative humidity (HR), final pressure drop after humid air $\Delta P_{HR}$ and model pressure drop $\Delta P_{\mathit{model}}$ for soot 26.

$\Delta {\mathit{P}}_0$(Pa)	HR (%)	$\Delta {\mathit{P}}_{\mathit{HR}}$(Pa)	$\Delta {\mathit{P}}_{\mathit{model}}$(Pa)
3485	90	2234	2272
3487	66	2410	2630
3510	53	2797	2840
2489	90	1623	1740
2467	68	1954	1946
2469	53	2017	2095
1475	87	1223	1214
1520	67	1373	1343
1515	53	1425	1413

Figure 15. Model pressure drop as a function of the final experimental pressure drop.

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