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RESEARCH PAPERS

In Situ Optical Diagnostics for Measurements of Water Vapor Partial Pressure in a PEM Fuel Cell

[+] Author and Article Information
Saptarshi Basu, Hang Xu, Michael W. Renfro

Department of Mechanical Engineering, 191 Auditorium Rd.,  University of Connecticut, Storrs, CT 06269-3139

Baki M. Cetegen1

Department of Mechanical Engineering, 191 Auditorium Rd.,  University of Connecticut, Storrs, CT 06269-3139cetegen@engr.uconn.edu

1

Corresponding author

J. Fuel Cell Sci. Technol 3(1), 1-7 (Jul 21, 2005) (7 pages) doi:10.1115/1.2133799 History: Received October 29, 2004; Revised July 21, 2005

A fiber optic coupled diode laser sensor has been constructed for in situ measurements of water vapor partial pressure in active proton-exchange membrane (PEM) fuel cell systems. The bipolar plate of a prototypical PEM fuel cell was modified to allow for transmission of a near infrared laser beam through the flow channels on either the fuel or oxidizer side of its membrane-electrode assembly. The laser wavelength was scanned over several water rotational and vibrational transitions and the light absorption was detected by measuring the transmitted laser power through the device. The intensity and line shape of the measured transition was used to extract path-averaged values for the water vapor partial pressure. Measurements were initially taken in a non-operating cell with known temperature and humidity input gas streams to calibrate and test the optical device. A technique for rapid determination of the water partial pressure was developed. The optical technique is applicable over a significant temperature and humidity operating range of a PEM fuel cell. The measurement technique was applied to an operating PEM fuel cell system to examine the effects of incoming gas humidity and load on the water vapor partial pressure variation in one of the flow channels.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of a PEM fuel cell

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Figure 2

Experimental setup for calibration tests. Numerous thermocouples (T) were used to control the humidity of the cell.

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Figure 3

Simulated water absorption spectra using Voigt profile convolution with the HITRAN database

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Figure 4

Photographs of (a) assembled optically accessible fuel cell and (b) bipolar plate modified for laser beam delivery

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Figure 5

Measured reference and signal photodiode signals versus laser wavelength. The arrows indicate locations of absorption peaks.

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Figure 6

Measured absorption coefficient and components of the curve fitting algorithm using four Voigt profile and a quadratic background

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Figure 7

Comparison of measured absorption coefficients (symbols) at two water partial pressure conditions to predictions (lines) from HITRAN database simulations

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Figure 8

Calibration for system partial pressure versus measured halfwidths from Lorentzian curve fits

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Figure 9

Measured water partial pressure in operating fuel cell versus cell current at inlet water partial pressure Ps=0.07atm for a cell temperature of 60°C

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Figure 10

Measured water partial pressure in operating fuel cell versus cell current at inlet water partial pressures of (a) Ps=0.19atm and (b) Ps=0.26atm for a cell temperature of 80°C

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Figure 11

Measured distorted and undistorted absorption profiles for an inlet relative humidity of 93% and cell temperature=60°C

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