Two-stage MOF-coated heat exchanger for efficient humidity control under wide humidity range

Desiccant coated heat exchanger (DCHE) is a promising and energy-efficient dehumidification unit, which uses cooling source to overcome sorption heat effect. Recently, metal–organic framework (MOF) is emerging in this filed due to its S-shaped isotherms, leading to reduced requirements for regeneration temperature differences. However, this unique characteristic of MOF also means that each adsorbent can only function under conditions where the relative humidity (RH) is limited, and adsorbents with high stepwise relative humidity are difficult to function under low humidity conditions. This work proposes a two-stage MOF-coated heat exchanger (MCHE), where the first stage utilizes MOFs that operate under high RH, while the second stage employs adsorbents capable of functioning at low RH, aiming to achieve efficient cascade dehumidification over a wide humidity range. MIL-101(Cr) and Al-fumarate were respectively selected for the first and second stages for experimental verification. The influence mechanisms of key parameters such as switching period, cooling/hot water temperatures, and air conditions were investigated. Compared with the single stage configuration, the two-stage MCHE in this work exhibits better heat and mass transfer performance, achieving a lower supply air temperature (2–3 °C lower) and a higher dehumidification efficiency (10 % higher). This study verifies the feasibility and applicability of the proposed system, providing a new approach for efficient dehumidification under wide humidity range.