Evaporation Rate Analysis Of Raw Water In Salt Production Using a Prototype At Salt House

In Indonesia, the famous method of the salt production process is evaporation using solar energy. The important aspect of this method is the evaporation rate. The evaporation rate is nearly related to the physical conditions of the surrounding environment. The aim of this study is to determine the evaporation rate of raw water in the production process using a prototype and determine the effect of physical parameters on the rate of evaporation of raw water in the production process in the salt house. The causal method with a quantity approach was used in this research. The results obtained are the total evaporation rate on the prototype at the Salt House is 1.68 litters/day and the results of Spearman rank correlation show that luminous intensity, air temperature, and wind speed have a significant impact on the evaporation rate because the significant value is <0.005 while the humidity level is not s significant effect.


Introduction
Nowadays, the number of salt imports in Indonesia is considered quietly dominant.It's caused by many factors, one of which is the amount and quality of salt produced by Indonesian farmers have not significantly increased [1].As per the 2018 data regime, it is stated that the production of salt in Indonesia has not meet the national salt demand [2].The lack of fulfillment of salt both in terms of quantity and quality is caused by lack of knowledge and technology of salt management [3,4].
In Indonesia, salt products are divided into two: salt for consumption and industrial salt [5][6][7][8][9].Generally in this country, the most famous salt production process is traditional method, which namely as the evaporation technique [10].Of course, this traditional evaporation method is too challenging and highly dependent on weather and climatic conditions [11][12][13].In 2018 the national salt output produced lisby salt farmers and PT Garam was totally 2.35 million tons.This amount has not reached the national target of 4.1 million tons in the same year.Weather constraints are a significantly influential factor in the achievement of salt production in 2018, one of which is due to the long rainy season [14], [15].The frequency of rain is made the physically reduce density in the water which has an impact on the delay in the production plan until harvest fail [16].With the length of the rainy season, it directly reduces the evaporation rate of water.Meanwhile, in the salt process, the evaporation rate is playing a significant role [17,18].The rate of evaporation is also influenced by several physical factors including solar radiation, temperature, wind, and humidity [10,19,20].In regard to these problems, the farmers have created innovative technologies in salt production, including prisms, salt production troughs, valves, tunnels and salt houses [18,21,22].This is an innovation method applied to the crystallization table by adding roofs of different shapes to prevent rainwater, specifically for the salt house, which is an innovation developed by building houses mostly made of a glass wall with small plots of land inside the greenhouse for the production process.This method considered as new technique and hence the proper information which significantly affects such as the rate of evaporation and other physical parameters are limited.Based on this, the target of this research is to define the rate of evaporation in Salthouse, as well as the condition of physical parameters in influencing the value of the evaporation rate.This is important to know so that it can be a reference for consideration in the selection and application of salt ponds.

Materials and Methods
This research was carried out at the Salt House, owned by Trunojoyo University, Madura.The research location showed in figure 1.This study uses a quantitative approach since the data needed for calculations are in the form of numbers [23,24].The data collection process was carried out by taking primary data which included water level, seawater concentration, humidity, water temperature, air temperature, light intensity, and wind.Primary data is subject to data which obtained from primary sources.
Figure 1.Research location (red point) Primary data measurements are carried out at three points in single prototype, there are plotted at the upper right corner, middle, and lower left corner of the prototype.The parameters have observed and collected in a 6 hours frequents a day, at 06.00, 12.00, 18.00, and 00.00.The environmental parameters were directly observed including water temperature, air temperature, air humidity, seawater thickness, baume degree, and light intensity.It has sampled from the prototype in the form of a beam measuring 60cm x 40cm x 15cm within Salthouse.This Salthouse is the innovation developed by the marine science study program at Trunojoyo Madura University in the salt production process as shown in Figure 2. The building is constructed by glass wall with a triangular roof.The roof of the Salt House uses corrugated steel roofs as a connector for the glass sides of the building.The use of glass in the Salt House building is for insulating heat so that it accelerates the rate of evaporation and during the rainy season the production process is not affected [21,25].Statistical analysis method is used, the data visualization were simulated using R programming language with R Studio IDE.Spearman rank correlation analysis was applied to the visualization in order to determine the strength of the relationship between physical parameters and evaporation rate.In addition, to determine the significance value between the independent variables affecting the dependent variable.

Physical Parameters
The salt production process in Indonesia still uses the evaporation method [12].The evaporation process is depending by certain variables such as air temperature, humidity, light intensity and wind speed [26].In this study, the observation of physical parameters is done to determine the rate of evaporation in Salt house.Observation of physical parameters was carried out when the first raw material water entered until the crystallization process with four measurements daily base.The results of daily observations on physical parameters are presented in Figure 3.The intensity of sunlight at 06.00 AM has the lowest value of 21 lumen/m 2 and the highest value is 58 lumen/m 2 .At 12.00 PM the lowest value of sunlight intensity is 288 lumen/ m 2 and the highest is 646 lumen/ m 2 at 06.00 PM and 00.00 AM the value remains 0 lumen/ m 2 from the start of the measurement to completion.High light intensity values were detected during the day at 12.00 PM with a vulnerable value of 288-646 lumen/ m 2 , the value of sunlight intensity at 06.00 AM is low because at that time the sun has just risen so the radiation emitted is also still small.At 06.00 PM the sun has set and is not visible, causing the intensity value to be 0 lumen/ m 2 , the intensity at 00.00 is also 0 lumen/ m 2 because there is no solar radiation from the sun that has sunk.Light intensity plays a role in the increase in air temperature when the evaporation process takes place [27,28].The greater intensity of the light equal with the temperature.This is considered caused basically caused by the intensity of sunlight is the main factor that affects the value of air temperature and large evaporation [29,30].The intensity of light can evaporate water thereby accelerating the process of salt production [31].Effendy et al. (2012) define the salt production ratio as a function of the evaporation rate of seawater which is completely dependent on the availability of solar heat as an energy source [32].
Figure 2 shows that at 06.00 AM the lowest temperature is 29.4˚C while the highest temperature is 31.2˚C.At 12.00 PM the lowest temperature was 40.2˚C and the highest temperature was 47.4˚C.Next, at 06.00 PM the lowest temperature was noted at 30.7˚C and the highest is 32.1˚C and at 00.00 AM the lowest temperature is 29.8˚C whilst the highest one is 30.5˚C.The air temperature at 06.00 AM tends to be low in direct proportion to the light intensity at that time which is also still low since the sun has just risen.The temperature at 12.00 PM is increased equal to the light intensity is high too, but at 06.00 PM and 00.00 AM the air temperature drops affected by the light intensity also drops due to the sun setting.The temperature changes at any time will cause the evaporation rate to be unstable.The changing of temperature is a reflection by the light intensity at salthouse.The intensity of light plays a role in increasing the air temperature, the higher of light intensity is directly proportional with the increasing of air temperature.The best evaporation occurs during the day because high intensity is obtained during the day [33].The air temperature that needs for salt production is more than 32˚C, the higher temperature will followed the evaporation is faster.High air temperature can affect the humidity, where the higher the air temperature make the humidity is lower value and conversely to the lower air temperature is the higher humidity [34].
The results of the observation on humidity is indicate that the high humidity mostly are in the morning, afternoon, and evening.This is caused by at that time, the temperature in the environment dropped due to lack of or not receiving the sun's rays that had drown.Humidity in the afternoon is around 78%, at night it is around 71%.The low humidity mostly is during the day is around 34% due to the high temperature factor.The difference in temperature outside and inside the Salthouse pushes the wind to move from outside to the inside of the Salthouse because the temperature within salthouse is higher than the environment outside, hence the air saturated with water vapor can be replaced with unsaturated air and ultimately lowers the humidity value in the salthouse.The air humidity parameter is expressed inversely with air temperature and intensity (Figure 4).If the air temperature and luminous intensity are high, the humidity level will be low and vice versa, if the air temperature and luminous intensity are low, the humidity level will be high [26].Hadi and Ahied (2017), told that humidity has an influence on the salt production process [6].The proper humidity for salt production is < 60%.High humidity levels will inhibit the evaporation rate but when the humidity is low it will accelerate the evaporation rate [35].If the humidity is high it is still possible for salt production to be supported by the availability of wind for mass transfer of water vapor [10].
The results against wind speed observations show that at 06.00 AM the lowest wind is 0.53 m/s and the highest wind is 0.8 m/s.At 12.00 PM the lowest wind was 0.73 m/s and the highest wind was 1.19 m/s.At 06.00 AM the lowest wind is 0.57 m/s and the highest is 0.77 m/s and at 00.00 AM the lowest wind is 0.36 m/s and the highest is 0.69 m/s.The wind speed that noted at 06.00 AM, 06.00 PM and 00.00 AM is smaller than the wind speed at 12.00 PM.According to Cahyadi et al (2019) wind is air that moves from a place of high pressure (cold) to a place of low pressure (hot) to move into the salthouse and generate higher wind speeds [31].The presence of wind greatly affects the rate of evaporation [36,37].The evaporation process will occur more quickly when the water vapor above the water surface is carried by the wind, causing the air humidity above the water surface to decrease [38,39].

Evaporation Rate Analysis
Evaporation rate is affected by several independent variables including light intensity, air temperature, humidity and wind speed [10,40].The dependent variable that affects is the density (˚Be) and the difference in raw water level on the prototype in the salthouse.The results of the observations of these two parameters are presented in Figure 4.The density is slowly increased within the early 15 days, then increased exponentially on the day 16th to the day 20th.This condition is identified by within the first 15 days, the volume of fresh water contained in the raw water is still large so make the salt content in the raw water is also small and causes the density (˚Be) to rise slowly, while on the 16th day the volume of fresh water has decreased a lot and there are remaining only salt compounds so that the density (˚Be) increases exponentially.Therefore, the increase in density depends on the volume of fresh water that is still contained in sea water [41,42].The production time is 20 days from raw water entering the prototype until the water shrinks to a density of 27 Be.The optimum point of increasing density (˚Be) noted on day 16 where the increase in salt content is exponential.The salt content is closely related to the shrinkage of the water level, where the higher the salt content, the lower the water level [20].

Figure 4. Density and water level of raw water
The difference of raw water level is inversely proportional to the density(˚Be).The difference in the raw water level in the prototype is considered as one of indicator of the evaporation process.The difference in the raw water level shows the amount of water volume that slightly reduced due to the evaporation process.The water level decreases faster when the evaporation rate is high, and vice versa [10,43,44].The observation results for twenty days showed that the largest difference in water level occurred on day 3 where the water level decreased by 0.7 cm.The reduction in water level results in an evaporation rate of 1.68 liters/day.The high rate of evaporation is influenced by the high physical parameters in the salt production process.On the 3rd day the light intensity is 544 lumen/m2 with sunny weather without being covered by clouds, high intensity causes an increase in air temperature of 46˚C.The air temperature within salthouse which is higher than the air temperature outside causes the wind to move into the salthouse at a speed of 1.07 m/s on day 3rd.The moving wind circulates the air in the salthouse by bringing saturated air to be replaced with unsaturated air, resulting in a humidity value of 48%.This criterion is confirmed to support the evaporation process of salt production [45].The greatest decrease in water level occurs during the day, due to the process of converting water into water vapor with the help of sunlight.
The rate of evaporation rate could be estimated by identifying the difference of the water level during the evaporation process [46].In this research, the evaporation process are occurred in the morning and afternoon (Figure 5).The highest evaporation rate occurred on the third day of 0.96 liters/6 hours.In the afternoon and evening there is no evaporation process since no solar radiation.Therefore, the solar intensity received at Salthouse is 0 lumen/m2.The highest evaporation rate is 1.68 liters/day while the lowest evaporation rate is 0.48 liters/day.The results of evaporation rate in the salthouse was measured based on the size of the land area per day resulting in an evaporation rate of 2-7 L/m2/day.The daily evaporation rate on Greenhouse Salt Tunnel (GST) in Cempokorejo Village produces an evaporation rate of 1-2 L/m2/day [18].The rate of evaporation is depending on the availability of solar heat as a source of energy to change the liquid state to gas.The water evaporates into the atmosphere through the boundary layer between the surface of the water and the air will accumulate water vapor.

Statistical Analysis
Table 1 shows the results of the Spearman rank correlation coefficient analysis.Based on Table .1,the parameters of light intensity, air temperature and wind show a positive relationship to the evaporation rate.However, the humidity parameter showed a significant and negative correlation with the evaporation rate (rho = -0.79915,p < 0.05).This shows that if the humidity rating is increased, the evaporation rate will decrease.Hadi W, et al (2018), stated that humidity has an influence on the salt production process [47].Humidity is stated to be inversely proportional to the rate of evaporation [17,48].The humidity affects the rate of evaporation, if the humidity is high, the rate of evaporation will be low because in the environment becomes saturated faster so that it cannot hold water vapor anymore.In this research, light intensity had a high positive correlation and a significant relationship between the evaporation rate (rho = 0.9228, p < 0.05).Pang Y. et al (2020) explains that basically the intensity of sunlight is the main factor used to get the temperature and the amount of evaporation, therefore the amount of evaporation that occurs is influenced by the value of light intensity as the main factor [30]. Efendy et al (2012) define the speed of salt production as a function of the evaporation rate of seawater which is completely dependent on the availability of solar heat as an energy source [32].Wind speed has a positive correlation and strongly relation between evaporation rate (rho = 0.66376, p < 0.05).This shows that if the wind speed assessment is increased, the rate of evaporation will increase.The presence of wind in the evaporation process is very important since it brings saturated air to replace it with unsaturated air, when the air is saturated with water vapor, the evaporation process will be hampered due to the water vapor cannot be accommodated by the air so wind is needed to replace the saturated air with air unsaturated so that the evaporation process can take place again [36].The air temperature parameter has a positive correlation with the evaporation rate.However, air temperature showed a low correlation with a significant relationship between evaporation rates (rho = 0.34653, p < 0.05).This shows that if the temperature rating is increased, the evaporation rate will increase.The air temperature required for salt production, which is more than 32 0 C, the higher the temperature, the faster the evaporation process so that the temperature also affects the acceleration of the evaporation rate [34].Evaporation in the salt production process.

Conclusion
The daily average evaporation rate in the salt production process at Salthouse is 1.02 liters/day.The highest evaporation rate in the prototype at Salthouse is 1.68 liters/day and the lowest is 0.48 liters/day.The highest peak of the evaporation process occurred at 12.00 PM at 0.96 liters/hour.Based on the results of Spearman rank correlation, light intensity, air temperature and wind speed show a positive relationship with evaporation rate.And light intensity showed the strongest correlation with evaporation rate (rho= 0.923) compared to other physical parameters.While humidity shows a negative relationship with the rate of evaporation.

Figure 2 .
Figure 2. Salthouse The deformation of liquid molecule into the gas is called by evaporation, this process is the opposite of the condensation process.Evaporation rate for brine using the Toledo formula:  =    ....................................................... (1) W = evaporation rate (liters of hour -1 ) mw= evaporator land area x difference in seawater height (cm 3 ) t = time (hours) (6 hours)Statistical analysis method is used, the data visualization were simulated using R programming language with R Studio IDE.Spearman rank correlation analysis was applied to the visualization in order to determine the strength of the relationship between physical parameters and evaporation rate.In addition, to determine the significance value between the independent variables affecting the dependent variable.

Table 1 .
Spearman rank correlation coefficient (rho) for physical parameters and evaporation rate