The structural and surface characteristics of the proposed collector must reflect the above-mentioned performances. The proposed water collector model consists of the main elements represented by the collector net responsible for condensing the droplets carried with wind or fog that lends through the network, and a water tank centered at the bottom of the model. The major element of design in the proposed system is to change materials used in the classic nets. Since now we must specify that atmospheric conditions play important role in the design process, it is possible to classify environmental conditions in three types: high mountains characterized by diffused and continuous wind and fog, hot humid zones characterized by high level of saturation (high humidity and temperature) and arid and semi-arid zones characterized by summer-night dew formation. The indicated zones have as commune element the low level of precipitations due different reasons. Traditional elements used in hot-humid zones have not the capacity to transform humidity from gas status into liquid one. As shown in Figure 2 classic materials absorb humidity from atmosphere this means that works in just high level of saturation. The time for this process is long and reduce sensibly the capacity of the net to collect water. While traditional elements used in very high mountains are designed for the specific geographical conditions and cannot function in semi or arid zones.
The novel system must combine other performances of the used materials, as shown in Figure 3 a solid surface has major capacity to attract humidity from the atmosphere. This capacity is referred to physical principles related to the conditions of the dew point verification. The solid surface as the anodized aluminum or other metal elements, (see Table 2) lose heat rapidly respect the environment satisfying the first condition, the smooth surfaces generally satisfy the second dew point condition.
The above-mentioned conditions are necessary to be employed in the realization of our novel system. Figure 4 presents the concept of realization. The introduction of metallic elements increases the quantity of water collected because together the absorption of water as in classic meshes because adds the water quantity collected be the dew point verification. Adding to these metallic elements a hydrophobic capacity we will reduce the evaporation loss of collected water on the net.
The innovative part is the design of the grid’ surface and the introduction of a hydrophobic performance obtained by the use of substances as nano ceramic, liquid ceramic or other suitable paints. The Nano Ceramic which has the advantage of not interacting with water and it does not alter the properties of the materials with which it is painted, its function is only to accelerate the fall of the droplets after condensation.
On the other hand, the materials used in the novel design of water collecting systems must reflects the desired performances. It can be classified in three steps, the first the high capacity of absorption and wettability, the second the high capacity to lose heat in manner that favor the condensation rapidly. The third is the capacity to release the accumulated water rapidly. Last element but not the least is the design’ configuration of the proposed systems, a mesh disposed in horizontal mode do not benefit from gravity to release condensation rapidly, the very smooth surface does not attack the surface tensity of the water droplets for example.
4.1 WETTING PHENOMENA AND THERMAL RADIATION CAPACITY
Wettability and super-wettability happen once a water drop is placed on a surface, it forms a sphere or wets the surface completely and called “super-wetting”. Antiwetting and super-anti wetting are the capacity of a surface to release water drops formed by condensation process [6] (Durand et al., 2011). Wettability and anti-wetting have particular importance when studying phenomena related to heat transfer and humidity applications generally. In our case these concepts guarantee the functionality of our novel system. The high wettability in our case is guaranteed from the selected materials having high capacity to lose heat by radiation (heat emissivity).
The process of wetting phenomena is related to thermal radiation capacity which standing to the Stefan-Boltzmann Law [9] (Nelly Durand et Al 2011), compared with the radiation of heat from an ideal “black body” with the emissivity coefficient (ε) = 1. the emissivity coefficient (ε) for some common materials can be found in the Table 2. It is note that the emissivity coefficient (ε) for some materials varies as environmental temperature are changed [10].
Table 2. Thermal Radiation Capacity-Emissivity Coefficient (ε) [10]
Material
|
Emissivity coefficient
|
Material
|
Emissivity based on 26.85 C Emissivity coefficient
|
Alumina, Flame sprayed
|
0.80
|
PVC
|
0.91 – 0.93
|
Aluminum Commercial sheet
|
0.09
|
Plastics
|
0.90-0.97
|
Aluminum Anodized
|
0.77
|
Wood, Pine
|
0.95
|
Asphalt
|
0.93
|
Wrought Iron
|
0.96
|
Black Body Matt
|
1.00
|
Black Epoxy Paint
|
0.89
|
Black lacquer on iron
|
0.83
|
Glass smooth
|
0.92 – 0.94
|
Paper
|
0.93
|
Black Silicone Paint
|
0.93
|
Clay
|
0.91
|
Oil paints, all colors
|
0.92 – 0.96
|
Table 2 shows the emissivity of some materials at 26.85 C. The emissivity expresses the capacity of certain material to lose heat resulting colder than the environment. This propriety determines the possibility of the condensation on the surface in question. At lower temperatures from zero to 26 grads C the behavior of surfaces may be different. To understand better this aspect, we conduced some Laboratory tests which consists in exposing different materials with same geometric measures without altering the bulk density to zero C temperature and with environmental temperature 26 C in the same method and time of exposing. Measuring their surface temperature in progressive time intervals in this way materials that reach faster the equilibrium with surrounding environment will result the better than the others because have the highest level of exchanging heat at low temperatures, (see Table 3).
Table 3. Thermal Radiation Capacity at low temperatures based on Laboratory tests (Source the Author 2021).
Material 5X5 centimeters with thickness 0.2 mm
|
Temp. After 1 minute
|
Temp. After 10 minutes
|
Temp. After 20 minutes
|
Temp. After 60 minutes
|
Material
|
Temp. After 1 minute
|
Temp. After 10 minutes
|
Temp. After 20 minutes
|
Temp. After 60 minutes
|
Smooth glass
|
0
|
7
|
15
|
26
|
PVC
|
0
|
7
|
14
|
25
|
Not treated Aluminum
|
0
|
3
|
10
|
20
|
Plastic
|
0
|
7
|
14
|
25
|
Aluminum Anodized
|
0
|
6
|
13
|
24
|
Wood
|
0
|
6
|
14
|
25
|
Iron
|
0
|
7
|
15
|
25
|
Oil painted surface
|
0
|
7
|
14
|
25
|
Asphalt
|
0
|
7
|
15
|
26
|
porcelain
|
0
|
7
|
15
|
25
|
Black lacquer
|
0
|
6
|
14
|
25
|
Black Epoxy Paint
|
0
|
7
|
15
|
25
|
The capacity of the selected material for construction of the proposed system depends on its wettability, availability, and durability.
4.2 HYDROPHOBIC PHENOMENA
The industrial applications of superhydrophobic performances are a consolidated reality especially in field of paints production. These applications noted as: anti-fog coating, anti-freeze surfaces, oil and water separation, anti-bacterial surfaces are applied in medical and industrial camps to prevent bacterial accumulation and to improve performances against corrosion of metals and implants. [11] (Gh. Barati Darband et AL. 2020). Hydrophobic phenomena consist in anti-wetting surface capacity to prevent water accumulation. In nature, the lotus effect means that water drop on a lotus surface showing contact angles of approximately 147° (cutting angle) caused from the surface configuration [12] (Latthe S. S. et AL. 2014).
Lotus effect describes the behavior of the superhydrophobic surfaces where water contact angle is greater than 150° with low sliding angle, under 10°. Attract important research interest related to the potential anti-icing properties. Applicability in daily life issues, in agriculture, and in many industrial processes as: antiadhesive coatings, self-leaning materials, antifouling, anticorrosion, [13] (L. YU et Al.). The use of superhydrophobic paints and other industrial applications as the use of nano ceramic on surface simulates the lotus effect and can be easily used in the proposed system.