Modeling and validation of heat and mass transfer in a direct contact packed bed crossflow humidifier

This study addresses the critical need for accurate modeling of crossflow humidifiers in humidificationdehumidification desalination systems, a technology that offers sustainable water production through its low operational pressure, cost-effectiveness, and ability to operate with low-grade thermal energy. While humidification-dehumidification technology shows significant promise for addressing water scarcity challenges, existing models still fail to capture the complex heat and mass transfer dynamics in crossflow configurations. A comprehensive two-dimensional mathematical model was developed and validated for direct contact packed bed crossflow humidifiers, incorporating key factors often overlooked in previous studies, such as spatial variability in packing material temperature and non-saturated conditions. The model employs conservation of mass and energy principles, using enthalpy as the dependent variable to enhance accuracy across diverse operating conditions. Experimental validation was conducted using a custom-built test facility equipped with 38 temperature sensors and 7 humidity probes, allowing for detailed spatial measurements. For most of the regions, the simulated results align with the thermocouple measurements with error margins less than 6%. The deviation of humidification capacities between experimental and simulation results is approximately 5 %, demonstrating the model's accuracy and reliability. Notably, the model maintained its accuracy when adapted for seawater feed through the incorporation of salinity-dependent correlations, with prediction errors remaining between -10 % and 20 % among all temperature measurements at 3.5 % salinity, addressing a significant gap in existing literature. The validated model can provide valuable insights for optimizing crossflow humidifier design and operation, and its ability to handle both freshwater and seawater feeds makes it particularly valuable for practical desalination applications.