**4. Conclusion**

336 Mass Transfer - Advanced Aspects

moisture recovery for the channel height is fixed. As same, the fact that the increase in the pressure drop with respect to the increasing air flow and decreasing channel height, as shown in Figure 14, shows that a proper channel height (the mass flux increase hardly if even the channel height is decreased further. For example, approximately 1.0 mm for the conditions of the channel length 100 mm and the pressure drop 200 Pa) is favorable to

In order to evaluate the utilization degree of the moisture absorption capacity of the air, the

where *d*out and *d*in are the absolute humidities of the air at the exit and entrance, respectively, of the channel in which the air is flowing, and *d*w is the absolute humidity of saturated air at

Figure 15 shows the variations in moisture absorption rate with respect to the air volumetric flow for porous plates having different thermal conductivities. This figure shows that the moisture absorption rate decreases as the air volumetric flow increases, and the values for both the high- and low-thermal-conductivity plates were approximately the same and exceeded 80% at an air volumetric flow of 3.3×10-5 m3/s. However, as the air volumetric flow increases, the moisture absorption rates of the high- and low-thermal-conductivity plates gradually diverge, and at a volumetric flow rate of 24.7×10-5 m3/s, the moisture absorption rate for the low-thermal-conductivity plate is 26%, while that for the highthermal-conductivity plate is 40%, approximately 1.5 times that for the low-thermalconductivity plate. That is, from the standpoint of the moisture recovery, it is effective to use

the high-thermal-conductivity plate for the case of the large air volumetric flow.

 plate thickness 1mm channel height 1mm porosity 20% pore diameter 2 μm

Fig. 15. Effect of thermal conductivity of the porous plate on moisture absorption rate

, which is the ratio of the increase in the absolute humidity to the

10 20 30


thermal conductivity W/(mK)

1.7 20.2

Air velometric flow *V* 10 m /s

= (*d*out - *d*in)/(*d*w – *d*in) (7)

moisture recovery for the pressure drop is limited.

η

the temperature of the constant-temperature water.

0.2

0

0.4

Moisture absorption rate

η

0.6

0.8

1

maximum moisture absorption of the air, is introduced and is given by

η

**3.6 Moisture absorption rate** 

moisture absorption rate

The present study attempted to clarify the characteristics of the heat and moisture transport in the process of moisture recovery from the exhaust gas of fuel cell vehicles using a porous plate having extremely small pores. As a first step, the moisture transport from constanttemperature water to dry air through the porous plate was measured. The general characteristics of moisture and the effects of the thermal conductivity, porosity and pore diameter in the porous plate, and the height of the channel of flowing air on the performance of moisture transport were examined experimentally. The results are summarized as follows:


ρ

σ

**Subscripts** 

**7. References** 

air density (kg/m3)

c plate surface, water side in inlet of the channel out outlet of the channel s plate surface, air side w constant-temperature water

surface tension of water (N/m)

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