Thermal characterization and moisture adsorption performance of calcium alginate hydrogel/silica gel/polyvinylpyrrolidone/expanded graphite composite desiccant

• A solid adsorbent is synthesized by adding expanded graphite to calcium alginate hydrogel. • Synthesis methods of calcium alginate hydrogel and its composites are optimized. • Performance of composites such as permeability and adsorption isotherm are characterized. • Dehumidification performances under various conditions are revealed with a fixed bed system. Solid desiccant dehumidification system can use low-grade energy for regeneration process and reduce the electrical energy consumption, thus saving energy and reducing carbon emissions. The choice of desiccant can significantly affect the dehumidification performance of the system. In the present study, the composite desiccant was synthesized by adding silica gel (SG), polyvinylpyrrolidone (PVP) and expanded graphite (EG) with calcium alginate hydrogel (CAH) as the matrix, named CAH/SG/EG. Subsequently, the characteristics of the samples were analyzed, and a dehumidification system was built to reveal the effects of different working conditions on the dehumidification performances. The results show that CAH/SG/20 wt.% EG has the optimal adsorption kinetics among all samples. Its moisture adsorption capacity reaches up to 1.009 g/g at 25 °C and 70 % relative humidity (RH), and its adsorption rate is 0.0179 g/(g·min). Especially, its moisture adsorption capacity can still reach 0.44 g/g at 30 % RH, showing a good adsorption capacity at lower RH. Simultaneously, the thermal conductivity of composites gradually increases from 0.449 W/(m·K) to 0.716 W/(m·K) with the addition of EG, increasing by about 60 %. In addition, the dehumidification performance of CAH/SG/20 wt.% EG is higher than that of CAH/SG, and the dehumidification performance of the system shows an ascending, descending and descending trends with the increase of inlet air moisture content, inlet air temperature and inlet air flow, respectively.