Prediction of Water Diffusivity in Hollow Fiber Membranes in a Humidifier Used for a Vehicular Fuel Cell System

Abstract

<div class="section abstract"><div class="htmlview paragraph">A membrane humidifier application is an effective water and thermal management technique in a vehicular fuel cell system. This fuel cell system could obtain high power density in high-temperature conditions, but this temperature also results in severe dehydration in fuel cell stacks. On the other hand, the water formation and transport complication in the system would flood the proton exchange membrane and flow channels if the system does not have an appropriate control strategy.</div><div class="htmlview paragraph">The membrane allows water vapor to permeate and migrate the moisture and heat from one side to another so that the heat and mass transfer benefits are considered. In this study, therefore, a shell-tube humidifier was designed with a 21-tube module of hollow fiber membrane, which can take advantage of the high packing density, to investigate water transfer and air humidification. To improve the efficiency of the humidifier in the fuel cell system, a proper geometry was designed to enhance the convection effect on both sides of the membrane. Water transport characteristics in the membrane were analyzed, and an empirical correlation was proposed to predict the vapor diffusion, the overall mass transfer, and the humidifier performance under the typical operating conditions of fuel cell systems. The fuel cell performance and durability are sensitive to temperature, pressure, flow rate, and relative humidity. Hence, the humidifier experiments were carried out with the range of temperature 60 to 80^oC, pressure 100 to 250 kPa, flow rate 10 to 30 slpm, and relative humidity 0.6 to 0.9. The 1-D model prediction of diffusivity was expressed via non-dimensional parameters, including Reynold number, Schmidt number, and Sherwood number.</div></div>