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Highlights: • Regeneration experiments were performed in a multilayer fixed bed desiccant dehumidifier. • Silica based high purity Micro Sphere Gel (M. S. Gel) of 2.7 nm pore dia was used as desiccants. • Dynamic heat and mass transfer behavior of the desiccant beds were evaluated during regeneration. • Effects of altering regeneration air temperature, humidity and flow velocity were investigated. • Impact of heat loss during regeneration was determined by using a constant temperature oven. Abstract In this study, regeneration experiments were performed in a previously developed multilayer fixed-bed, binder-free desiccant dehumidifier (MFBDD) in order to investigate the transient heat and mass transfer characteristics during the desorption of condensed water from desiccant material inside the device. A microsphere silica gel (M.S.GEL manufactured by AGC Si-Tech. Co., Ltd., Japan) having a pore diameter of 2.7 nm was used as the desiccant, which was feasible for regeneration at a temperature slightly above 50 °C. To prevent heat loss during regeneration, the test section was placed inside a constant-temperature oven. Experiments were performed under several regeneration conditions to investigate the influence of temperature, humidity, and flow velocity of the regeneration air on the heat and mass transfer characteristics of the device. The influence of heat loss from the test section to the surroundings during regeneration was also determined by precisely controlling the oven temperature. The results revealed that the regeneration capacity of the device improved with an increase in the regeneration air temperature. However, the maximum temperature of regeneration air should be optimized for energy-efficient operation of the device according to the regeneration conditions. [ABSTRACT FROM AUTHOR]

A novel multilayer fixed-bed binder-free desiccant dehumidifier (MFBDD) was designed as part of this study, to be operated in combination with a conventional vapor-compression system to attain higher moisture removal capacity with lower electricity consumption. Silica-based high-purity spherical gel, Micro Sphere Gel (M. S. Gel), of 2.7 nm pore diameter and exhibiting an S-shape isotherm was used as adsorbents during the experiment. Transient adsorption, heat transfer, and pressure drop characteristics of the proposed device were evaluated experimentally for varying process air velocity, process air humidity, and desiccant bed thickness. The results revealed that while the pressure drop of the proposed device was approx. 98% lower, the average dehumidification capacity (during first 10 min of adsorption) was approx. 36% higher compared to a conventional desiccant wheel. Multilayer desiccant beds with adequate process airflow channel height and the usage of adsorbents without polymer binders in innovative sheet-type beds has led to such lower pressure drop and improved dehumidification capacity of the device. [ABSTRACT FROM AUTHOR]

Highlights • A CFD model is constructed for regeneration in a multilayer desiccant dehumidifier. • Model predicted results are compared with the experimental ones for validation. • The model is validated for a range of temperature and velocity of regeneration air. • Upon validation, the proposed model is employed to conduct a parametric study. • Impacts of material properties and mechanical design on regeneration are analyzed. Abstract A numerical model is presented for the prediction of transient heat and mass transfer characteristics during the regeneration process in a multilayer fixed-bed, binder-free desiccant dehumidifier. Experiments were carried out in a previous study that provided the benchmark data for validation of the current model under different temperatures and velocities of the regeneration air. A spherical microsphere silica gel having a pore diameter of 2.7 nm was used as the adsorbent during the experiments. In the first part of this study, model validation was performed for different temperatures (314.4–325.0 K) and velocities (0.6–0.9 m s−1) of regeneration air. The results showed that at a fixed regeneration temperature (325.0 K), the model predicted mass of the desorbed water as well as the desiccant bed and air temperatures were in a good agreement with the previously reported experimental results. With a decrease in the temperature and velocity of the regeneration air, the model slightly underpredicted the experimentally obtained mass of the desorbed water; however, the deviation remained within a reasonable limit. Upon validation, a parametric study was carried out to show how the heat and mass transfer characteristics of the microsphere silica gel during desorption depended on the intrinsic material properties (e.g., desorption rate constant, diffusivity, and desorption isotherm) and mechanical design parameters of the device (e.g., convective heat transfer coefficient, porosity, and thickness of the desiccant bed). [ABSTRACT FROM AUTHOR]

The interdependent physics involved in the transport, adsorption, and thermal phenomena within desiccant-based dehumidifiers makes the construction of theoretical models essential to investigate intrinsic mechanisms. In Part II of this series, a computational model is established that increases an understanding of transient mass and heat transfer phenomena in a multilayer fixed-bed binder-free desiccant dehumidifier (MFBDD). A two-dimensional (2D) model incorporating the principles of momentum, mass and heat conservation is constructed. A modification of Darcy’s law is employed to evaluate the frictional resistance due to the presence of Micro Sphere Gel (M. S. Gel) beads in the desiccant bed. In the study, the moisture adsorption characteristics of M. S. Gel are theoretically described by employing a Linear Driving Force (LDF) model and a modified Langmuir-Sips model (based on the local relative humidity RH) owing to the unique sigmoid-shape of its adsorption isotherm at various temperature levels. The energy conservation is considered to estimate phase transition latent heat because of the moisture adsorption and heat loss to surroundings through the metal frames at different process air conditions. The validity of the model is tested by comparing the theoretical predictions with experimental observations. The results indicate that the predicted adsorbed water within the MFBDD, dehumidification capacity, temperature increase, and pressure decrease based on the simulation are in quantitative agreement with the experimental results obtained in Part I. The experimentally observed transient translocation of maximum temperature inside the M. S. Gel bed is theoretically reproduced and analyzed. [ABSTRACT FROM AUTHOR]