Greenhouse Desalination by Humidification–Dehumidification Using a Novel Green Packing Material

Abstract

Humidification–dehumidification (HD) is a non-traditional desalination process in which water evaporates from a saline liquid stream and the vapour condenses into purified water. In nature, seawater is heated by solar radiation and evaporates from the air that moistens it. This is known as the rainy cycle. The artificial version of this cycle is called the HD desalination cycle. The latter has received a lot of attention in recent years, and many researchers have studied the complexities of the technology. In the present work, experimental work with a simple configuration was developed and built, consisting of a humidification column followed by a condenser, in which the humidified air is dehumidified to produce fresh water. A novel and unique packaging material was used in the humidifier, consisting of a cellulose plant grown on the banks of the River Nile. In all previous work, the main problem was the type of packaging material that could ensure intimate contact and uniformity between aqueous flow and airflow. Consequently, this new filler material proved extremely suitable in terms of hydrophilicity and interconnectivity. Several variables, including the packing mass of each stage, the number of stages, the flow of air and saltwater, the concentration of saltwater, and the inlet temperature of saltwater and condensation temperature, were examined to determine their influence on the production of fresh water and its salinity. The best results arrived at in this study were wet packing conditions, 0.5 m/s air flowrate, 26 g packing for each of the 6-stage columns, and 500 mL/min water flow rate at 70 °C. It was found that this present setup, which can be coupled with solar heating to make the greenhouse desalination process cost-effective, could produce a high production of fresh water and be competitive compared with other commercial applications.

Study on the Heat and Mass Transfer Characteristics of Humidifiers in Humidification–Dehumidification Desalination Systems

“…In this study, the mass transfer coefficient correlation equation described in [24] was used. Eight packing materials that can be used in HDH systems were selected from the related studies [7,22,25]. The correlation equation coefficients for the eight packing materials listed in Table 1 ensure the accuracy and reliability of the calculations.…”

“…In Equation (22), ε hum represents the humidification efficiency of the humidifier, h a,in and h a,out represent the enthalpy of the inlet and outlet of air in the humidifier (kJ/kg), h w,in and h w,out represent the enthalpy of the inlet and outlet of spray water in the humidifier (kJ/kg), h a,out,max represents the ideal enthalpy of air when its temperature at the humidifier outlet equals the temperature of the inlet spray water and its relative humidity is 100% (kJ/kg), and h w,out,min represents ideal enthalpy of water when its temperature at the humidifier outlet equals the temperature of inlet air (kJ/kg).…”

“…However, the increase in m w is linear. Consequently, the outlet temperature of the spray water rises, leading to a reduction in ε hum , as indicated by Equation (22). and polypropylene decreases from 30.25%, 49.10%, 28.98%, 61.79%, 25.91%, 89.59%, 93.86%, and 80.31% to 8.43%, 28.06%, 12.58%, 38.08%, 9.39%, 70.21%, 71.45%, and 57.09%, with a reduction of 72.15%, 42.85%, 56.58%, 38.37%, 63.75%, 21.63%, 23.88%, and 28.91%, respectively.…”

“…However, the increase in mw is linear. Consequently, the outlet temperature of the spray water rises, leading to a reduction in εhum, as indicated by Equation (22). Figure 9 shows the effect of the mass flow rate of spray water on the specific humidification energy ratio with different packing materials.…”

“…The results indicated that at a spray water mass flow rate of 150 L/h and an air mass flow rate of 0.55 m 3 /h, the humidifier achieved the highest humidification efficiency, reaching 75%. Ghazouani et al [22] conducted experiments using the unique Egyptian sponge gourd as the packing material. The results showed that the humidifier achieved maximum humidification efficiency when the air velocity was 0.5 m/s, and the spray water temperature and mass flow rate were 70 • C and 30 kg/min, respectively.…”