Journal of Applied Electrochemistry

, Volume 39, Issue 6, pp 815–825

Water transfer simulation of an electrolytic dehumidifier

Authors

    • Ryosai Technica Company Ltd.
  • Shiro Yamauchi
    • Mitsubishi Electric Corporation
  • Osamu Takai
    • Nagoya University
Original Paper

DOI: 10.1007/s10800-008-9727-8

Cite this article as:
Sakuma, S., Yamauchi, S. & Takai, O. J Appl Electrochem (2009) 39: 815. doi:10.1007/s10800-008-9727-8

Abstract

A model for a dehumidifying device using a solid polymer electrolyte membrane (Nafion 117, Dupont) is proposed. The dehumidifier in the model is represented by a physical model composed of a two-layer membrane and electrodes on the membrane surfaces. Measurement of the membrane weight shows that the ratio of the water content of the membrane to humidity in the surrounding air is a function of temperature under equilibrium conditions. The results for the water ratio are used for determining the parameters required for the modeling. The electrical resistance of the dehumidifier was measured and is given as a function of temperature and the membrane water content. Simulation of the characteristics of the dehumidifying device is presented and the results are found to agree with the measured characteristics of the device. We also report an attempt to determine the parameters describing the dehumidifying processes.

Keywords

DehumidifierPhysical modelSolid polymer electrolytic membraneWater transfer

List of symbols

Variables

D

Diffusion coefficient of water in the dehumidifying element

e

Electron charge = 1.602 × 10−19 (C)

I

Current of the dehumidifying element (A)

Ist

Current at steady state condition (A)

J

Current density of the dehumidifying element

kg

Coefficients relevant to the diffusion velocity of water from the air to the membrane

ks

Coefficient relevant to the diffusion velocity of water from the membrane to the air. This is defined by ks = kso exp(−Ws/RT)

L

Thickness of the dehumidifying element (= 0.017 cm)

Mo

Molecular weight of water

mg,p

Water mass in the space facing the anode (g)

NA

Avogadro number = 6.02 × 1023 (mol−1)

R

Gas constant = 8.31 (Pa m3 k−1 mol−1)

\( RH_{{t_{\text{x}} }} \)

Relative humidity at time tx

Rm

Electrical resistance of the membrane of the device (Ω)

pg,p, pg,n

Water vapor pressure in the air facing the anode and the cathode, respectively

Rs

Electrical resistance of the dehumidifying element (Ω)

S

Area of the dehumidifying element of the device

t

Time (s)

Tg

Temperature of the gas space surrounding the dehumidifying element (K)

Us

Applied voltage to the dehumidifying element (V)

Vg,p, Vg,n

Volumes of the spaces facing the anode and the cathode, respectively

Ws

Difference in potential energy between water in the air and in the element (J mol−1)

\( \langle X\rangle_{{[t_{1} ,t_{2} ]}} \)

Average value of variable X during the period from t1 to t2

α

The average number of water molecules carried by a proton moving to the cathode (electro-osmotic drag coefficient)

δ

Water content in the dehumidifying element represented by molH2O/molSO3H

Δmg,p

The change in water mass in the dehumidifying space (g)

Δt

Time required for the change in water mass in the dehumidifying space

λ

Water content in the dehumidifying element represented by gH2O/gSPEdry

ρs, ρg

Water content of the dehumidifying element of the device and water density in the air surrounding the element, respectively

ρg,p, ρg,n

Water content in the air facing the anode (positive electrode) and the cathode (negative electrode), respectively

ρs,p, ρs,n

Water contents in the anode half and cathode half of the dehumidifying element including its inner surfaces defined by a two-layer model of the element

ρg,sat

Saturated water density in the air

ρs,o

Initial water content in the dehumidifying element at switching-on of the device

Subscripts

g

Gas space

n

Negative electrode or cathode

on

At the switching-on

p

Positive electrode or anode

s

Polymer electrolytic dehumidifying element

sat

Saturated condition

st

Steady state condition

ti

Time ti

Copyright information

© Springer Science+Business Media B.V. 2008