الملخص الإنجليزي
Seawater greenhouse (SWGH) is a technology established to overcome issues related to open field cultivation in arid areas like the high ambient temperatures and freshwater shortage. It adopts the humidification-dehumidification (HDH) concept where evaporated moisture from a saline water source is condensed to produce freshwater within the greenhouse body. Many improvements have been studied and proposed throughout the past 25 years to optimize the SWGH among them is the use of Direct Contact Dehumidification (DCD). The DCD method seems to be very promising as it has low capital, operational, and maintenance costs and high freshwater production. The aim of this study was to investigate the performance of using a packed-type direct contact dehumidifier in producing freshwater. Full factorial design of 64 experiments were conducted to study the effect of six operational variables viz., inlet air temperature (Ta,in), air mass flowrate (ma,h), inlet water temperature (Twh) and mass flowrate of the humidifier (mwh), and inlet water temperature (Twd) and mass flowrate of the dehumidifier (mwd) on freshwater production. Each variable was operated in two values; high and low. In all the experiments, the dew point temperature was higher than the average inlet and outlet cold water temperature thus, freshwater was produced in all experiments with an amount varied between 0.257 and 2.590 liters. Minitab statistical software was used to investigate the significant variables that contributed to maximum water production and were; the inlet air temperature (Ta,in), and inlet water temperature of the humidifier (Twh). The R2 value for the significant variables and interactions was 65.1% while the adjusted R2 was 62.0%. Response optimizer tool showed that the best variables combination that can contribute to maximum water production was when all the variables were in high mode while the temperature of inlet air (Ta,in) was in low mode. The comparison between the new proposed DCD and the old plastic condenser unveiled that the former can produce about 75.8 times more freshwater compared to the latter at same condenser volume. At the end, it is highly advisable to replace the existing plastic condenser of the SWGH with a DCD system after being fully optimized. Therefore, further studies are highly recommended to find the optimal design and operational parameters of the proposed DCD system.
