Effects of relative humidity and particle type on the performance and service life of automobile cabin air filters

Figures & data

Table 1. Properties of the NF and CF.

	Dimensions (cm)	Number of pleats	Thickness of each pleat (cm)	Effective filtration surface area (cm^2)	Average porosity
NF	33 × 6 × 3	100	0.04	4800	NF(1):0.765
CF	33 × 16 × 3	82	0.16	3936	N/A

* For CF, the method was unavailable due to the existence of the activated carbon layer. Because the size, mass as well as the arrangement state of the activated carbon particulates in the layer were various among different CFs, significant uncertainties in the measurements were observed.

Figure 1. Schematic of the wind tunnel, filter holder, and experimental setup.

Table 2. Summary of the six sets of experimental conditions.

	I	II	III	IV	V	VI
RH	30%	30%	30%	80%	80%	80%
Loaded dust	ARD	Soot+ARD	ARD	ARD	Soot+ARD	ARD
Filter type	NF	NF	CF	NF	NF	CF

Figure 2. Size distributions of ARD and soot particles: (a) ARD measured by SMPS; (b) ARD measured by APS; and (c) soot particles measured by SMPS.

Figure 3. Influence of the RH on the loading curves of cabin air filters: (a) NF loaded by ARD; (b) CF loaded by ARD; (c) NF loaded by ARD and soot particles. Inserted images were the SEM images of clean NF and CF, and the loaded ones by ARD or ARD with soot particles. More SEM images with higher magnification were shown in the SI.

Table 3. Summary of the sources of experimental errors.

Sources of errors	Explanation	Method for estimation	Estimated proportion to the total loaded mass
Transportation of filters	Detachment of collected particles due to the transportation of filters	Estimated by experimental experience	Up to 5%
Evaporation of adsorbed water	Evaporation of adsorbed water on the filter when they were transported from wind tunnel to ambient for the weight measurements	Estimated experimentally	Around 1%
Instability of air flow and particle generation	Fluctuations of air flow generated by wind tunnel and the size distributions of the loaded particles	Estimated from the monitoring data of the wind tunnel and experimental experience	1% to 2%

Figure 4. Comparison of water adsorbing capacities of the filters: (a) the change of loaded mass with the time exposed to airflows with different RH values; (b) the change of pressure drop with the time exposed to airflows with different RH values.

Figure 5. Loading curves under different conditions: (a) NF loaded by ARD and ARD with soot particles, respectively, and (b) NF and CF, taking into account the initial pressure drop and the face velocity.

Figure 6. Evolution of the average filtration efficiencies in different particle size ranges during the loading process under different experimental conditions: (a) NF loaded by ARD (as a function of pressure drop); (b) NF loaded by ARD and soot particles (as a function of pressure drop); (c) NF loaded by ARD (as a function of loaded mass); and (d) CF loaded by ARD (as a function of loaded mass).

Figure 7. Evolution of the MPPS as a function of the increasing pressure drop for the filters loaded by ARD and ARD with soot particles.