(378ak) Humidity Tracking By Mixing Dry and Humidified Gases with Internal Model Control for PEM Fuel Cells

Sathish Swaminathan ^a, Srinivasan Raman ^b, Raghunathan Rengaswamy ^a,b *

^a Department of Chemical Engineering, Indian Institute of Technology – Madras, Chennai, India

^b Department of Chemical Engineering, Texas Tech University, Lubbock, Texas

* raghur@iitm.ac.in, raghu.rengasamy@ttu.edu

Abstract

Humidification of gases is widely employed in various manufacturing industries, medical and energy equipment including proton exchange membrane (PEM) fuel cells. Humidification of fuel cell reactants is essential for maintaining the proton conductivity. PEM fuel cells produce excessive water under high current operation which sometimes result in detrimental operating conditions. Hence, controlling the humidity in reactants gases is essential to maintain optimal functioning of the fuel cell system. Changes to humidity of gases can be achieved by mixing of dry and humidified gases as shown in literature. The reactants passing through the humidifier for absorbing water vapors, induces a time delay in the humidified gases before reaching the fuel cells. It was experimentally observed that this time delay due to humidification results in a mismatch between the humidity set points and output, while using a conventional PI/PID controller for tracking humidity changes.

In this work, the humidity of a stream of gases was controlled using internal model control to eliminate the time delays in set point tracking, before supplying the gases to a fuel cell system. Experiments were conducted to obtain a desired humidification level in the gases by mixing dry and humidified gases, as decided by the controller. Accurate tracking of step and sinusoidal changes in humidity set points were achieved. The advantages, challenges, and limitations of using internal model control strategy for humidity set point tracking will be highlighted.