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Research Papers

A Controllable Membrane-Type Humidifier for Fuel Cell Applications—Part I: Operation, Modeling and Experimental Validation

[+] Author and Article Information
Denise A. McKay1

Picker Engineering Program, Smith College, Ford Hall, 100 Green Street, Northampton, MA 01063dmckay@smith.edu

Anna G. Stefanopoulou

Mechanical Engineering, University of Michigan, 1231 Beal Ave., Ann Arbor, MI 48109

Jeffrey Cook

Electrical Engineering, University of Michigan, 1301 Beal Ave., Ann Arbor, MI 48109

1

Corresponding author.

J. Fuel Cell Sci. Technol 7(5), 051006 (Jul 16, 2010) (12 pages) doi:10.1115/1.4000997 History: Received March 31, 2008; Revised October 29, 2009; Published July 16, 2010; Online July 16, 2010

For temperature and humidity control of proton exchange membrane fuel cell (PEMFC) reactants, a membrane based external humidification system was designed and constructed. Here we develop and validate a physics based, low-order, control-oriented model of the external humidification system dynamics based on first principles. This model structure enables the application of feedback control for thermal and humidity management of the fuel cell reactants. The humidification strategy posed here deviates from standard internal humidifiers that are relatively compact and cheap but prohibit active humidity regulation and couple reactant humidity requirements to the PEMFC cooling demands. Additionally, in developing our model, we reduced the number of sensors required for feedback control by employing a dynamic physics based estimation of the air-vapor mixture relative humidity leaving the humidification system (supplied to the PEMFC) using temperature and pressure measurements. A simple and reproducible methodology is then employed for parameterizing the humidification system model using experimental data.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic diagram of a two-cell membrane based humidifier

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Figure 2

Schematic of the gas humidification system, detailing sensor, and actuator hardware (with plumbing indicated in solid lines) along with the computer signal communication (with wiring indicated in dotted lines)

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Figure 3

Controllable humidifier system indicating states, disturbances, and measurements. Thin arrows represent mass flow directions and large thick arrows indicate locations where control action is applied.

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Figure 4

Experimental inputs to the relative humidity estimator

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Figure 5

Relative humidity estimator experimental validation

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Figure 6

Relative humidity estimation as compared with the measurement versus time after removing the estimation bias

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Figure 7

General description of the heat transfer mechanisms for control volumes containing bulk and gas states

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Figure 8

Simulation schematic of the general two volume system

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Figure 9

Membrane based gas humidifier volumes

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Figure 10

Model structure for open the loop simulation of the gas humidification system

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Figure 11

Bypass experimental validation results. Given the measured air mass flow rate and temperature of the air supplied to the bypass, the air outlet temperature is estimated and compared with measurements.

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Figure 12

Reservoir validation results. Given the measured liquid water mass flow rate and the estimated liquid water temperature supplied to the reservoir, the liquid water outlet temperature is estimated.

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Figure 13

Water heater validation results. Given the measured liquid water mass flow rate supplied and the estimated inlet temperature, the liquid water outlet temperature is estimated.

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Figure 14

Humidifier validation results. Given the measured air and liquid water mass flow rates supplied, the estimated liquid water inlet temperature, and the measured air inlet temperature, the air and liquid water outlet temperatures are estimated.

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Figure 15

Mixer validation results. Given the measured air mass flow rate and estimated bypass and humidifier air outlet temperatures supplied to the mixer, the mixer air outlet temperature is estimated.

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Figure 16

Required water heater input Qwh necessary as a function of total dry air mass flow rate Wa and desired cathode inlet temperature Tg,mx,o under steady conditions. The air mass flow rates selected correspond to changes in the current density from the nominal operating conditions (Wa=0.6 g/s) to 0.15 A/cm2(Wa=0.3 g/s) and 0.45 A/cm2(Wa=0.9 g/s).

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