Empirical correlation of water diffusivity in hollow fiber membrane humidifier by measuring latent effectiveness

Abstract

A hollow fiber membrane serves as a crucial component for the membrane humidifier in proton-exchange membrane fuel cell applications. This study established an empirical correlation of a fundamental characteristic, water diffusivity in the annulus membrane, employing a latent effectiveness-number of transfer units approach under isothermal conditions. Initially, experiments are conducted on a specifically designed membrane humidifier, considering temperature, flow rates, relative humidity, and pressure to determine the latent effectiveness. Subsequently, the overall mass transfer coefficient of a hollow fiber tube bundle, possessing latent effectiveness, is utilized to determine the water diffusivity in the hollow fiber membrane.The empirical correlation of water diffusivity is established through dimensionless parameters, including Reynold and Schmidt numbers. Using measured water diffusivity data, the regression coefficients of the empirical correlation were calibrated. The deviation of the correlation was assessed in terms of the coefficient of determination (R2), which exceeded 0.87, demonstrating a high degree of accuracy upon comparing the correlated diffusivity and experimental data. As substantiated by the results, this correlation provides reliable predictions for an actual membrane humidifier, with a mean deviation of only 7.72% during the validation process. Thus, the present findings will aid the design and operation of membrane humidifiers in fuel cells, improving their performance and efficiency by facilitating precise control of water diffusivity.