Enhancement of freshwater production of the seawater greenhouse condenser

doi:10.1007/s40333-021-0063-8

Journal of Arid Land

2021, Vol. 13

Issue (4): 397-412 DOI: 10.1007/s40333-021-0063-8 CSTR: 32276.14.s40333-021-0063-8

Research article

Enhancement of freshwater production of the seawater greenhouse condenser

Tahani K BAIT SUWAILAM¹, Abdulrahim M AL-ISMAILI¹^,^*(

), Nasser A AL-AZRI², L H Janitha JEEWANTHA¹, Hemesiri KOTAGAMA³

¹Department of Soils, Water and Agricultural Engineering, Sultan Qaboos University, Al-Khoud 123, Oman
²Department of Mechanical and Industrial Engineering, Sultan Qaboos University, Al-Khoud 123, Oman
³Department of Natural Resource Economics, Sultan Qaboos University, Al-Khoud 123, Oman

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Abstract

Seawater greenhouse (SWGH) is a technology established to overcome issues related to open field cultivation in arid areas, such as the high ambient temperature and the shortage of freshwater. It adopts the humidification-dehumidification concept where evaporated moisture from a saline water source is condensed to produce freshwater within the greenhouse body. Various condenser designs are adopted to increase freshwater production in order to meet the irrigation demand. The aim of this study was to experimentally investigate the practicality of using the packed-type direct contact condenser in the SWGH to produce more freshwater at low costs, simple design and high efficiency, and to explore the impact of the manipulating six operational variables (inlet air temperature of the humidifier, air mass flowrate of the humidifier, inlet water temperature of the humidifier, water mass flowrate of the humidifier, inlet water temperature of the dehumidifier and water mass flowrate of the dehumidifier) on freshwater condensation rate. For this purpose, a direct contact condenser was designed and manufactured. Sixty-four full factorial experiments were conducted to study the effect of the six operational variables. Each variable was operated at two levels (high and low flowrate), and each experiment lasted for 10 min and followed by a 30-min waiting time. Results showed that freshwater production varied between 0.257 and 2.590 L for every 10 min. When using Minitab statistical software to investigate the significant variables that contributed to the maximum freshwater production, it was found that the inlet air temperature of the humidifier had the greatest influence, followed by the inlet water temperature of the humidifier; the former had a negative impact while the latter had a positive impact on freshwater production. The response optimizer tool revealed that the optimal combination of variables contributed to maximize freshwater production when all variables were in the high mode and the inlet air temperature of the humidifier was in the low mode. The comparison between the old plastic condenser and the new proposed direct contact condenser showed that the latter can produce 75.9 times more freshwater at the same condenser volume.

Key words： seawater greenhouse humidification-dehumidification direct contact condenser freshwater production water desalination

Received: 11 March 2020 Published: 10 April 2021

Corresponding Authors:

About author: * Abdulrahim M AL-ISMAILI (E-mail: abdrahim@squ.edu.om; abdrahim@hotmail.co.uk)

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	K BAIT SUWAILAM Tahani
	M AL-ISMAILI Abdulrahim
	A AL-AZRI Nasser
	H Janitha JEEWANTHA L
	KOTAGAMA Hemesiri

Cite this article:

Tahani K BAIT SUWAILAM, Abdulrahim M AL-ISMAILI, Nasser A AL-AZRI, L H Janitha JEEWANTHA, Hemesiri KOTAGAMA. Enhancement of freshwater production of the seawater greenhouse condenser. Journal of Arid Land, 2021, 13(4): 397-412.

URL:

http://jal.xjegi.com/10.1007/s40333-021-0063-8 OR http://jal.xjegi.com/Y2021/V13/I4/397

Fig. 1 Schematic diagram of the seawater greenhouse (SWGH). 1, first evaporative cooler; 2, second evaporative cooler; 3, condenser; 4, solar heater; 5, fan; 6, saline groundwater well; 7, freshwater tank. Red arrows, hot water cycle; blue arrows, cold water cycle.

Fig. 2 Schematic diagram of the experimental setup of the packed-type direct contact dehumidification (DCD) system. Red arrows, hot water cycle; blue arrows, cold water cycle.

Fig. 3 Two-dimension design (a) and layout (b) of the direct contact dehumidification (DCD) system. T1-T7, thermocouple sensors; RHT1-RHT3, relative humidity and temperature sensors.

Table S1 Technical specification of the instruments used in the study

Table 1 Experimental values (high and low) of the six operational variables used in this experiment

Fig. 4 Typical 3-d water temperature data of the SWGH as recorded in May 2005 (Bait-Suwailam and Al-Ismaili, 2019)

Fig. 5 Typical 3-d air temperature data of the SWGH as recorded in May 2005 (Bait-Suwailam and Al-Ismaili, 2019)

Fig. 6 Typical 3-d relative humidity data of the SWGH as recorded in May 2005 (Bait-Suwailam and Al Ismaili, 2019)

Experiment	m_wh (kg/s)	m_wd (kg/s)	m_a,h (kg/s)	T_wh (°C)	T_wd (°C)	T_a,in (°C)	Measured production (L/10 min)	Measured production (L/h)
1	0.19	0.15	0.04±0.01	50.0±5.0	24.0±5.0	23.0±3.0	0.970	5.820
2	0.27	0.15	0.04±0.01	50.0±5.0	24.0±5.0	23.0±3.0	1.800	10.800
3	0.27	0.15	0.02±0.01	35.0±5.0	31.0±5.0	23.0±3.0	1.090	6.540
4	0.27	0.15	0.02±0.01	50.0±5.0	24.0±5.0	23.0±3.0	2.300	13.800
5	0.19	0.13	0.04±0.01	50.0±5.0	31.0±5.0	23.0±3.0	1.520	9.120
6	0.27	0.13	0.04±0.01	35.0±5.0	31.0±5.0	23.0±3.0	2.362	14.172
7	0.27	0.13	0.04±0.01	50.0±5.0	31.0±5.0	23.0±3.0	1.200	7.200
8	0.27	0.13	0.02±0.01	35.0±5.0	24.0±5.0	28.0±3.0	0.590	3.540
9	0.19	0.15	0.04±0.01	35.0±5.0	31.0±5.0	23.0±3.0	1.380	8.280
10	0.19	0.13	0.02±0.01	35.0±5.0	31.0±5.0	23.0±3.0	1.152	6.912
11	0.19	0.13	0.04±0.01	35.0±5.0	31.0±5.0	28.0±3.0	0.674	4.044
12	0.27	0.15	0.04±0.01	50.0±5.0	31.0±5.0	23.0±3.0	2.209	13.254
13	0.19	0.13	0.02±0.01	50.0±5.0	31.0±5.0	23.0±3.0	2.249	13.494
14	0.27	0.13	0.02±0.01	35.0±5.0	31.0±5.0	28.0±3.0	0.617	3.702
15	0.27	0.15	0.02±0.01	35.0±5.0	24.0±5.0	23.0±3.0	2.373	14.238
16	0.27	0.15	0.04±0.01	50.0±5.0	31.0±5.0	28.0±3.0	1.415	8.490
17	0.19	0.15	0.04±0.01	50.0±5.0	24.0±5.0	28.0±3.0	0.485	2.910
18	0.27	0.13	0.02±0.01	50.0±5.0	31.0±5.0	23.0±3.0	1.570	9.420
19	0.27	0.13	0.02±0.01	35.0±5.0	24.0±5.0	23.0±3.0	1.513	9.078
20	0.27	0.13	0.02±0.01	35.0±5.0	31.0±5.0	23.0±3.0	0.874	5.244
21	0.19	0.15	0.02±0.01	35.0±5.0	31.0±5.0	23.0±3.0	1.041	6.246
22	0.19	0.15	0.04±0.01	35.0±5.0	31.0±5.0	28.0±3.0	0.630	3.780
23	0.19	0.13	0.04±0.01	50.0±5.0	24.0±5.0	23.0±3.0	1.920	11.520
24	0.27	0.13	0.04±0.01	50.0±5.0	24.0±5.0	23.0±3.0	2.590	15.540
25	0.19	0.15	0.02±0.01	50.0±5.0	31.0±5.0	23.0±3.0	1.836	11.016
26	0.19	0.15	0.04±0.01	50.0±5.0	31.0±5.0	23.0±3.0	1.760	10.560
27	0.19	0.13	0.02±0.01	50.0±5.0	24.0±5.0	23.0±3.0	1.631	9.786
28	0.19	0.13	0.02±0.01	50.0±5.0	31.0±5.0	28.0±3.0	1.067	6.402
29	0.27	0.15	0.02±0.01	50.0±5.0	31.0±5.0	23.0±3.0	1.070	6.420
30	0.19	0.13	0.02±0.01	35.0±5.0	31.0±5.0	28.0±3.0	0.489	2.934
31	0.19	0.13	0.02±0.01	50.0±5.0	24.0±5.0	28.0±3.0	1.279	7.674
32	0.27	0.13	0.04±0.01	35.0±5.0	24.0±5.0	23.0±3.0	0.940	5.640
33	0.27	0.13	0.04±0.01	50.0±5.0	31.0±5.0	28.0±3.0	0.851	5.106
34	0.27	0.15	0.02±0.01	50.0±5.0	24.0±5.0	28.0±3.0	1.366	8.196
35	0.27	0.13	0.02±0.01	50.0±5.0	24.0±5.0	23.0±3.0	2.000	12.000
36	0.19	0.13	0.02±0.01	35.0±5.0	24.0±5.0	23.0±3.0	1.725	10.350
Experiment	m_wh (kg/s)	m_wd (kg/s)	m_a,h (kg/s)	T_wh (°C)		T_wd (°C)	T_a,in (°C)	Measured production (L/10 min)	Measured production (L/h)
37	0.19	0.15	0.02±0.01	35.0±5.0		24.0±5.0	23.0±3.0	1.423	8.538
38	0.19	0.15	0.02±0.01	50.0±5.0		31.0±5.0	28.0±3.0	1.007	6.042
39	0.27	0.15	0.02±0.01	35.0±5.0		31.0±5.0	28.0±3.0	0.694	4.164
40	0.19	0.15	0.02±0.01	35.0±5.0		31.0±5.0	28.0±3.0	0.620	3.720
41	0.27	0.13	0.02±0.01	50.0±5.0		31.0±5.0	28.0±3.0	1.015	6.090
42	0.27	0.15	0.04±0.01	35.0±5.0		31.0±5.0	28.0±3.0	0.700	4.200
43	0.19	0.15	0.04±0.01	35.0±5.0		24.0±5.0	28.0±3.0	0.720	4.320
44	0.19	0.13	0.04±0.01	35.0±5.0		24.0±5.0	23.0±3.0	1.519	9.114
45	0.19	0.15	0.04±0.01	35.0±5.0		24.0±5.0	23.0±3.0	1.433	8.598
46	0.27	0.15	0.04±0.01	50.0±5.0		24.0±5.0	28.0±3.0	1.065	6.390
47	0.27	0.15	0.04±0.01	35.0±5.0		24.0±5.0	28.0±3.0	0.932	5.592
48	0.19	0.15	0.02±0.01	35.0±5.0		24.0±5.0	28.0±3.0	0.984	5.904
49	0.19	0.13	0.04±0.01	50.0±5.0		31.0±5.0	28.0±3.0	0.648	3.888
50	0.27	0.15	0.02±0.01	35.0±5.0		24.0±5.0	28.0±3.0	0.828	4.968
51	0.27	0.13	0.02±0.01	50.0±5.0		24.0±5.0	28.0±3.0	1.106	6.636
52	0.19	0.13	0.04±0.01	50.0±5.0		24.0±5.0	28.0±3.0	1.007	6.042
53	0.27	0.15	0.04±0.01	35.0±5.0		31.0±5.0	23.0±3.0	0.885	5.310
54	0.19	0.13	0.04±0.01	35.0±5.0		31.0±5.0	23.0±3.0	0.997	5.982
55	0.27	0.15	0.02±0.01	50.0±5.0		31.0±5.0	28.0±3.0	0.830	4.980
56	0.19	0.15	0.02±0.01	50.0±5.0		24.0±5.0	23.0±3.0	1.327	7.962
57	0.27	0.13	0.04±0.01	35.0±5.0		24.0±5.0	28.0±3.0	0.795	4.770
58	0.19	0.13	0.04±0.01	35.0±5.0		24.0±5.0	28.0±3.0	0.432	2.592
59	0.19	0.15	0.04±0.01	50.0±5.0		31.0±5.0	28.0±3.0	0.662	3.972
60	0.27	0.15	0.04±0.01	35.0±5.0		24.0±5.0	23.0±3.0	2.030	12.180
61	0.19	0.13	0.02±0.01	35.0±5.0		24.0±5.0	28.0±3.0	0.515	3.090
62	0.27	0.13	0.04±0.01	35.0±5.0		31.0±5.0	28.0±3.0	0.257	1.542
63	0.19	0.15	0.02±0.01	50.0±5.0		24.0±5.0	28.0±3.0	0.350	2.100
64	0.27	0.13	0.04±0.01	50.0±5.0		24.0±5.0	28.0±3.0	0.290	1.740

Table S2 Production of freshwater from all 64 experiments with the high and low values of each variable

Fig. 7 Pareto chart of the standardized effects when only the significant variables and interactions were included (P=0.05). m_wh, water mass flowrate of the humidifier; m_wd, water mass flowrate of the dehumidifier; m_a,h, air mass flowrate of the humidifier; T_wh, inlet water temperature of the humidifier; T_wd, inlet water temperature of the dehumidifier; T_a,in, inlet air temperature of the humidifier.

Table 2 Analysis of variance (ANOVA) of the significant effects of the six selected variables and their interactions

Table 3 Regression coefficients for the significant variables and interactions

Table 4 Response optimizer tool with the goal of maximizing freshwater production

Table 5 Optimal variable combination that contributes to the maximum freshwater production and the fitted production value

Fig. 8 Optimal combination that contributes to the maximum freshwater production. The value of 1 denotes the high level of each variable while the value of -1 denotes the low level of each variable. Horizontal dashed blue line is the x-axis; red vertical line is the y-axis; black line is the slope that shows the impact of the variable on freshwater production. m_wh, water mass flowrate of the humidifier; m_wd, water mass flowrate of the dehumidifier; m_a,h, air mass flowrate of the humidifier; T_wh, inlet water temperature of the humidifier; T_wd, inlet water temperature of the dehumidifier; T_a,in, inlet air temperature of the humidifier.

Fig. 9 Overall effect of the six variables on the mean freshwater production. The value of 1 denotes the high level of each variable while the value of -1 denotes the low level of each variable. The effects shaded in grey are considered not significant therefore their impacts on the mean freshwater production are not explained. The slope of line indicates the strength of the effect on the mean freshwater production. The grey dotted line is the mean freshwater production of the 64 experiments, which equals to 1.180 L/10 min.

Fig. 10 Psychrometric chart for the experiments with maximum (P1, P2 and P3 in yellow) and minimum (P4, P5 and P6 in red) freshwater production. P1-P6, state points with the combination of temperature, relative humidity and humidity ratio.

Table 6 Values of different variables for each state point in the psychrometric chart of the experiments with the maximum and minimum freshwater production

Table 7 Specification of the three comparable condensers


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