Performance investigations of hybrid adsorption and thermo electric dehumidification desalination system

Abstract

In recent years, thermally driven Adsorption Desalination Systems (ADS) have been gaining attention as an eco-friendly and energy saving solution for water scarcity. However, ADS faces challenges related to low water productivity and scalability issues associated with the adsorbent. To overcome these challenges, it is advantageous to integrate ADS with other desalination technologies, thereby creating a decentralised, small-scale hybrid desalination system. The current study introduces an innovative approach to enhance the performance of ADS by integrating it with a Thermo Electric Dehumidification (TED) unit that utilises the cold side of Thermo Electric Coolers (TECs). The proposed hybrid system is designed to operate at the elevated evaporator temperature ranges from 35 °C to 60 °C. This is achieved by connecting the hot side of the TECs to the evaporator of the ADS. This approach facilitates a fundamental shift from the conventional adsorption desalination cycle, enabling the system to work at higher evaporator temperature and pressures. A small-scale hybrid ADS integrated with a Thermo Electric Dehumidification unit (hybrid AD-TED desalination system) has been designed and developed to investigate performance parameters such as Coefficient of Performance (COP) and water productivity. Experimental study of the hybrid AD-TED system has been carried out in two operating modes: open flow and closed flow modes of water between the hot side of TEC and the evaporator. These operating modes are tested with and without implementing humidification process in the humidifier. The results have shown that the hybrid AD-TED desalination system working in open flow mode with humidification process has produced the highest water productivity of 1.25 l during one cycle of operation, lasting one hour. Furthermore, when operating in open flow mode without humidification, the hybrid AD-TED system can generate dehumidified air within a temperature range of 16–28 °C, making it suitable for cooling applications. Closed flow mode is the preferred choice for desalination applications. In the closed flow mode with and without humidification condition, the water productivity is found to be 1.15 l/hr and 1.05 l/hr, respectively. The significant feature of this hybrid AD-TED system is that it can be operated in two working modes with an elevated adsorption desalination cycle, making it a unique option compared to the single operating mode of standalone ADS in desalination and cooling applications. The study also compares the elevated adsorption desalination cycle with the conventional adsorption desalination cycle and reveals that the elevated cycle increases water uptake by 45 %.