Superabsorbent Ternary Composite Desiccants Towards Energy-Efficient Dehumidification in Cooling Systems

Desiccant-coated heat exchangers (DCHEs) enable energy-efficient dehumidification, alleviating the overall heat load on vapor compression refrigeration systems. However, conventional desiccants have limited water uptake capacities and high regeneration temperature requirements. This work presents ternary composite desiccants comprising the metal-organic framework, MIL-101(Cr) (where MIL denotes Materials Institute Lavoisier), the superabsorbent polymer polyvinyl alcohol (PVA), and hygroscopic salts for enhanced moisture sorption. Gravimetric water sorption analyses revealed that desiccants containing lithium chloride ($\mathbf{L i C l}$) attained water uptakes greater than their calcium chloride- and copper (II) sulfate-containing counterparts. Subsequent cyclic tests identified the optimal MIL-101(Cr)/PVA/LiCl composite that adsorbed and desorbed moisture readily. From its water sorption isotherm, the 3MIL-101(Cr)/1PVA/1 LiCl desiccant has a water uptake capacity of $2.49 \mathrm{~g}_{\text {water }} \mathbf{g}_{\text {desiccant }}{ }^{-1}$ - nearly double that of MIL-101(Cr) and more than nine times that of silica gel. When coated onto a prototype heat exchanger, the 3MIL-101(Cr)/1PVA/1 LiCl composite demonstrated a gravimetric water uptake more than double that of the silica gel-coated control across three adsorption-desorption cycles. Moreover, low-grade waste heat of $50^{\circ} \mathrm{C}$ could partially regenerate these DCHEs, leaving behind residual moisture of less than $0.5 \mathbf{g}_{\text {water }}$ $\mathbf{g}_{\text {desiccant }}{ }^{-1}$. Consequently, the 3MIL-101(Cr)/1PVA/1LiCl-coated heat exchangers are effective dehumidifiers for addressing the latent heat load towards energy savings in cooling systems.