A study on vapor transport characteristics in hollow-fiber membrane humidifier with empirical mass transfer coefficient

•An empirical mass exchanger model is presented for a tubular membrane humidifier.•Effectiveness–NTU approach is employed to investigate the vapor mass transport.•Relative humidity of the wet air is the most critical operating parameter.•Dry flow rate has greater influences on the humidification process than wet flow.•Membrane area and arrangement are design parameters that pose considerable effects. Proton exchange membrane fuel cells are used in vehicles as a power source that generates electrical energy from hydrogen fuel and oxygen. Proton diffusion through the membrane module requires a certain level of water content in the supply air to maintain its performance. Therefore, water management plays an essential role in fuel cell operation. For large cells, external humidifiers are commonly installed to deliver the desired amount of water to the reactant gasses. This study investigated the performance of a hollow-fiber membrane humidifier through water transport in the membrane module using a mass exchanger model and various operating variables. In the humidifier, water particles from the high-concentration side, or wet air flow, transfer through the membrane to the dry air flow, which has a lower concentration rate. The vapor transport depends on the membrane's physical characteristics and the flow properties on both sides. These influences are represented by a parameter called the overall mass transfer coefficient, which is estimated by experiments. Then, the effectiveness–NTU (number of transfer units) approach is employed to analyze the mass transfer in the humidifier as a mass exchanger model. The analogy between heat transfer and mass transfer helps in applying the traditional effectiveness–NTU method from heat transfer analysis to a mass transfer analysis with additional information from experiments. In this study, a best fit equation is generated from experimental data and employed mass transfer calculations at varying temperatures, humidities, and flow rates. The results suggest that the wet air's relative humidity is the most crucial operating parameter that influences the dry air humidity. The dry air flow rate has more significant effects on the humidification process than the wet flow. In the case of geometric parameters, the length, number of membranes, and type of arrangement are discussed.