Thin layer drying model of local rice grain Siam mutiara variety from tidal swamp land in South Kalimantan

As staple food in many countries, rice is one of the most important cultivated plant. Indonesia is the third largest rice producer in the world with annual production of 54,65 million tons. South Kalimantan province has 191,740 ha of tidal swamp land, which equivalent to 30% of its total area. Paddy rice variety planted in this region is dominated by local varieties, such as Siam Mutiara. Local farmers prefer this variety due to its high demand and high selling price than other local rice varieties. This variety produces soft textured rice which is preferred by the people of South Kalimantan. In addition to the taste and texture, physical aspects such as wholeness of the grain is also important for consumers, and this aspect is affected by post-harvest processed such as drying. In this study, drying characteristics of Siam Mutiara variety was studied. Samples of Siam Mutiara from Jelapat 1 village, Barito Kuala district were dried using a Fixed Bed Dryer at three temperatures (40, 50, and 60°C) and an airflow rate of 1 m/s. The samples were dried in five trays made of PVC pipes (5” diameter and 1” length) which arranged vertically. The first four trays were used to dry paddy rice sample with a layer of 1 cm thick, and the lowest tray were used to dry the sample in a single layer grain (with average thickness of grain width 1,66 mm). The temperature and humidity at each tray monitored continuously, and the weight of the sample in each tray was measured every 30 minutes. The results of this study indicate that the temperature and humidity varied among the trays, where the lowest tray had the highest temperature and the lowest air humidity. However, moisture content of the samples in all of the trays are relatively similar for both the top four trays (with total of 4 cm) and the lowest tray (single layer). This result indicates that for Siam Mutiara variety, a total of 4 cm thick layer can still be considered as a thin layer drying. It also found that the effect of drying temperature on drying rate is significant. In addition, the drying characteristic of this rice variety can be best modelled using Page Model.


Introduction
Rice (Oryza sativa), a rice-producing plant commodity, is the primary source of carbohydrates for the majority of the world's population.In the economic field, rice is a source of income for some Indonesians, as an index for determining financial stability and the primary basis for government food policy.In commodity trading, un hulled rice is an important stage in the post-harvest processing of rice before consumption because the wholesale trade carries out in the form of unhusked rice [1].The Food and Agriculture Organization has made Indonesia the third largest rice-producing country in the world, with a total of 54.65 million tons of production in 2020.The South Kalimantan Province extensively uses tidal swamps as paddy fields, which has helped increase the country's rice production.[2].Siam Mutiara is the most widely planted local rice varietyin Jelapat I Village, Temban sub-district, Barito 1230 (2023) 012161 IOP Publishing doi:10.1088/1755-1315/1230/1/012161 2 Kuala, and the surrounding areas because its selling price is higher than other local varieties, the people of South Kalimantan prefer its taste, and it is saidto be suitable for people with diabetes due to its low carbohydrate content [3] With physical characteristics, the color of the grain is clean yellow, and the shape of the grain is slender (cylindrical).In the post-harvest process of local rice, farmers still use traditional systems and tools.However, drying can only sometimes use this method due to weather factors.The harvested grain has a moisture content of around 21-26%, while the maximum moisture content of the grain is 14% (SNI 01-6128-1999).Various drying equipment technologies have emerged using mechanical devices to speed up thedrying process and control the desired parameters.Post-harvest handling is essential to maintain grain quality [4].This research aims to discover the degree of grain thickness that may be classed as a thin layer and develop a drying model that best matches the characteristics of local rice grain.The benefit of this research is to provide basic information and reference for modeling thin layer drying of local rice grainas information for improving local rice dryers for industries or local rice milling plants, especially in South Kalimantan.

Experimental design and procedure
This research uses a Fixed Bed Dryer and five trays (constructed of pipes and ram wire).A series of temperature and humidity meters comprised the following components: Microcontroller Mega 2500, Real Time Clock (RTC), 5 DHT-22, Micro SD card, Adapter, Bread Board, I2C LCD, Memory Card, and Cable.The material used in this study was local rice of the Siam Mutiara variety obtained from tidal swamp land in Jelapat I Village, Temban District, Barito Kuala Regency, South Kalimantan.The first procedure is for soaking the local rice grain of the Siam Mutiara variety.The local rice grain is the Siam Mutiara variety, where the rice is harvested from tidal swamp land, separated from the stalk.Then put in plastic packaging and sent to Makassar, South Sulawesi.Before carrying out the drying process, they soaked the grain for 60 minutes to rehydrate it to uniform the moisture content of the grain.Next, the grain is drained and stored in a standing pouch for 2 hours to allow the water in the seeds to spread evenly, and Grain moisture content is measured using the oven method at 105 ºC for 24 hours.Grains weighing 5 grams, then fill in three containers made of aluminum foil to determine the initial moisture content before drying.The sample's water content is determined using an equation.(1).The second procedure After measuring the moisture content of the soaked grain, drying is carried out after adjusting the treatment parameters on the Fixed Bed Dryer, using three drying temperature levels set at 40 ºC, 50 ºC, and 60 ºC respectively, at one level of the airflow velocity of 1 m/s.Each sample of grain weighs on an analytical balance.The grain fill in a container of five trays, with tray 1 (the bottom tray) containing one layer of grain and trays 2-5 containing 1 cm of grain each.Each tray features a sensor at the top of the grain to measure the tray's temperature and relative humidity during drying.Every 30 minutes, weights take, and data was collected.This technique repeats until the target grain weight's moisture content reaches 12%.Research Procedure 2.1.1.Stage I.This research was the preparation of grain samples of the Siam Mutiara varietyfrom paddy fields in Jelapat 1 Village, Tamban District, Barito Kuala District, South Kalimantan, withan area consisting of swamps with a height of between 0-1.1 meters above sea level.It has a 0-8% height and is subject to tidal influences.Rice harvested at a moisture content of around 24-26% wet weight.After threshing, Send the grain to Makassar for trial drying.However, the grain cannot be directly processed for drying since other necessary instruments must prepare.Because it causes natural drying of the grain samples, resulting in less than 15% moisture content.Therefore, the grain wassoaked before the drying experiment, increasing moisture content to 24-26% wet.

Stage III.
This study was drying soaked local rice grain samples using a fixed bed dryer.Then it was weighed every 30 minutes until a moisture content of 12% was obtained, which was the target in this study.The samples from the drying results determine their water content.Collecting Temperature and humidity data from sensors placed in each tray using a Micro SD as a place for RTC (Real Time Clock) to collect data.

Measurement and data analysis
During the drying process, the parameter references in data processing include measurement data at intervals of 30 minutes at 40°C, 50°C and 60°C, which are then processed as follows: 2.2.1.Temperature and RH of the drying air.The temperature is determined and regulated on the Fixed bed dryer device, and the temperatureand RH readings of the drying air on each tray use the DHT-22 sensor circuit.

Moisture content.
After the sample weight reaches the target moisture content of 12%, the sample is in the oven, thenthe percentage of wet and dry basis moisture content is calculated (MCwb and MCdb).

Moisture ratio (MR).
Calculation of the Moisture Ratio (MR) using the equation.
Where MR is the Moisture Ratio, Mt is the water content at time t (time during drying, minutes), M0 is the initial moisture content of the material, and Me is the moisture content obtained after theweight of the material is constant.The unit values of Mt, M0, and Me are the percentage of moisture content on a dry basis of the material.

Drying rate.
The determined weight of the material every hour to compute the rate of water evaporationthroughout the drying process.Calculate the drying rate using the equation.
Where wt is the weight of the material at the time (t, hour) and wt-1 is the initial weight of the material before time t, and t1 and t2 are changes in time every hour.The rate of water evaporation is the amount of water that evaporates per unit of time or the decrease in the moisture content of thematerial per unit of time.
2.2.5.Thin layer drying model.Each prior Moisture Ratio estimate evaluates for compatibility with a preset thin-layer dryingmodel, specifically the Newton, Page and Henderson, and Pabis models [6].
Where Mr exp, i is the moisture ratio of the experimental data, MRpred, i is the predicted moistureratio of the mathematical model data used for thin film drying, N is the amount of observational data, and Z is the number of constants in the drying mathematical model.

Effective water diffusivity. Calculation of Effective
Water Diffusivity is carried out by using the cylindrical approach and finding the slope value of the MR value.
Where 4/π^2 is the form factor and depends on the geometry of the drying material (4/π^2 for cylinders and 6/π^2 for spheres).Only the first term can use with increasing time to estimate the drying rate (n = 0).For long drying times, it can simplify to From the above equation, the effective diffusivity can calculate by plotting ln(MR) against drying time (t); this gives a straight line whose slope can express as follows: Where MR = moisture ratio.(moisture content ratio), M = moisture content at time t (%), Mo = initial moisture content (%), Me = equilibrium moisture content (%), t = drying time (hours), K = Drying Constant, N = Drying power parameters, A,B = Drying parameters, Deff = Effective moisture diffusivity (m2/sec), L = half product thickness (m), n = 1,2,3….5,R2 = coefficient of determination

Drying air temperature and rh based on data retrieval (real time clock) from the sensor
The temperature of the Fixed Bed Dryer used is regulated at three temperature levels of 40ºC, 50ºC, and 60ºC which then obtain data in the form of temperature and humidity from the DHT-22 sensor placed on each tray.Air temperature during the drying process is critical to see the effect of drying parameters on its characteristics.It is necessary to discuss the temperature changes on each traythrough which the drying air passes until it exits the tool [7].Figures 2a, 2b, and 2c show the differences in each tray.In tray 1 (bottom tray), in the first 30 minutes of drying, the temperature has reached the temperature set on the heater with a temperature degree that is always in the set temperature range.In 1a, with a temperature of 40˚C on tray 1, the drying air temperature displays a value of 41.2 C. In the subsequent tray arrangement, it tends to decline, with tray 2 obtaining a value of 40.9˚C, tray 3 with a value of 40.1˚C, tray 4 with a value of 39.8˚C, and tray 5 with a value of 37.7˚C.The same thing happened to the drying at 50˚C, sequentially from the bottom tray.The value was 51.5˚C; 50.7˚C; 49.2˚C; 47.4˚C; and 44.5˚C.As for the drying airtemperature of 60˚C, the drying air temperature for each tray is 61.5˚C; 60.4˚C; 58.3˚C; 56.5˚C; and 52.3˚C.This data shows that the degree of temperature on each tray, from the bottom to the top tray, decreases for the set temperature and the temperature of the drying air exiting the Fixed Bed Dryer.And on tray 5 (the top tray), it tends to be below the set temperature.At the beginning of the drying process, there is a decrease in temperature in the tray because it follows room temperature.While the drying process used the heat released from the drying air of the Fixed Bed Dryer to evaporate water from the material, a mechanism occurred that caused the drying air temperature to be lower than the temperature of the incoming drying air.Relative Humidity (RH) is affected by air temperature during the drying process.Air humiditydecreases when heated, so air drying uses it to move material moisture during drying.Based on the results shown by the graph, the average humidity in the first 30 minutes is 52.38%.Figures 3a, 3b, and 3c show that the humidity curve is inversely proportional to the temperature curve, where the higher the temperature, the lower the humidity.Conversely, a decreasein temperature causes humidity to increase.This results from the energy in the water vapor in the air approaching the latent heat of evaporation.As a result, the water vapor in the air moves upwards, making the air humidity in the device very high.That is due to the moisture in the drying air passing through the material.The drying air passes through the material from the bottom tray carrying the evaporated water vapor to the tray above.After the air passes through the material on the upper tray, the atmosphere brings a lot of water vapor.So it is clear that the bottom tray has the lowest humidity level compared to the other trays, where the RH of the drying air is higher because it absorbs upwards.

Water content
The research results on drying the local rice variety Siam Mutiara at a flow rate of 1 m/s using three drying temperature levels (40°C, 50°C, and 60°C) showed the pattern of changes in water content during the drying process decreased.The relationship between the length of the drying processand the decrease in moisture content on a dry basis.It can show in the following graph: The initial water content in the grain before drying was 24.8%, the moisture content on a wetbasis, which the grain previously soaked for 60 minutes.The grain moisture content calculations analysis shows that different temperature treatments decreased the water content.The trays arranged inthe dryer are tiers; the lower the tray tiers, the faster the drying process.The drying process in the first 30 minutes shows a relatively rapid decrease in water content and large quantities.Because the water that evaporates is free water found on the grain's surface and because the layout of the bottom tray is close to the drying air, resulting in a quicker decrease in water content on the bottom tray.The mass ofwater available in large quantities on the material's surface causes a rapid decline in water content.When the water group gets closer to equilibrium, the water content decreases because the water on the cover uses up so that the evaporated water comes from the material and conforms to the drying principle.As the water on the surface evaporates, water from within the material diffuses to the surface, where it disappears with the aid of drying air circulating the substance [9].
Various variations in temperature and pile thickness show that tray five at 40˚C, 50˚C and 60˚C tends to get high water content values.Figures 4a, 4b, and 4c at temperatures of 40˚C, 50˚C, and 60˚C with sample thicknesses of 1 cm depict the dry basis moisture content when ignored tray (1).Since the sample thickness consists of a single layer, a 4cm layer on the tray is still thin because the water content decrease is not statistically significant.Since the sample thickness consists of a single layer, the thickness can conclude that a 4cm layer on the tray is still thin because the water content decrease is not statistically significant.However, the conditions of tray 1 for each temperature variation are other due to the reflection of the drying air hitting the grain grains, causing stagnant grainpositions and congregating in dead spots.It suspects that the water content in tray number 1 at different temperatures varies.Based on Figure 5, the drying process in the first 30 minutes shows that the drying rate changes significantly, after which the drying rate slows down as it approaches equilibrium.The drying rate curve also indicates that the shift in drying rate is relatively small at lower drying temperatures and becomes significant at the highest temperature at 60˚C [11].

Thin layer drying models
The thin-layer drying model tested in this study to detect the Moisture Ratio (MR) behavior uses three thin-layer drying models, namely the Newton, Page, and Henderson-Pabis models.Thegrain drying process tested the three drying models in this research because they are very suitable, can produce good calculations, and can predict the drying process of rice grain in the thin layer drying model.The exponential drying mathematical model used Microsoft Office Excel Solver precisely to determine the values of the constants k, n, and a.The utilized analysis is the slightest total squared difference between experimental MR and predictive MR.The solver automatically searches for and retrieves the constant values in each model such that the real squared difference between experimental MR and predicted MR has a minimal weight and is constant for each model.The Page Model at three temperature levels of 40˚C, 50˚C, and 60˚C with an airflow velocity of 1 m/s has a value of R 2 (Coefficient of Determinant), which is greater than the other models.The Page model is the best model to represent the thin layer drying of local rice varieties of Siam Mutiara because it has a high suitability value for the characteristics of the thin layer.Several other research results also show that the Page Model is sufficient to represent the grain drying mechanism.This result follows the research conducted [12], [13].
The values of R 2 (Coefficient of Determinant), χ2 (chi-square), and RMSE (Root Mean Square Error) use to see the suitability of the drying model with the observation results.For R 2 values close to 1, the level of conformity with the drying model tested with experimental results is substantial.For χ2 and RMSE deals close to zero, the drying model tested is close to the experimental results.Based on the three values tested, the Page drying model was the best under the drying characteristics of the thin layer of local rice grain of the Siam Mutiara variety.The result is in line with [14], assertion that the values of R 2 (Coefficient of Determinant), χ 2 (Chi-Square), and RMSE (Root Mean Square Error) are used to evaluate the fit between experimental data and the thin layer model.The value that best fits the data will have the highest R 2 value and the lowest 2 RMSE values [15], The following graph shows the relationship between the Moisture Ratio (MR) during the experiment and the Page model as a thin layer drying model, which can predict the experimental results using graphics as in the following Figure 6.

Effective water diffusivity
Effective water diffusivity shows water movement from inside the material to the surfacedue to differences in water vapor pressure.The ability to diffuse water from within the material increases with increasing temperature.It is also affected by parameters such as surface area, thickness, air velocity, relative humidity of the drying air, and drying time.
The effective water diffusivity (Deff) value is obtained from equation (7).The effective water diffusivity in the local rice variety Siam Mutiara with three temperature variables can be seen by regression from ln MR to time the slope value for equation ( 8) obtained.The results show that the effective diffusivity of water increases with increasing temperature and is also affected by the position of the tray in the Fixed Bed Dryer.Higher evaporation occurs at greater temperatures.Therefore, the effective diffusivity will also be higher, and the water evaporated will be more significant.By ignoring the position of tray 1, where there is only one layer of grain in trays 2 to 5 at 60 ˚C and which has the highest practical water diffusivity value, namely between 1.2577x10 -08 and 1.8678x10 -08 , the effect can begin that the amount of water evaporation is the largest because the highest temperature in the experiment.The tray closest to the dryer's heat While the lowest value is found at the tray location farthest from the dryer, the lowest temperature is found on trays 2 to 5 at 40 ˚C, with a practical water diffusivity value ranging from 2.0945x10 -09 to 2.1696x10 -09 .
Each tray 1 with only one layer of grain at three temperature levels showed the same thing, which also increased the value of the effective water diffusivity coefficient.Due to the same tendency, water's practical diffusivity value will be more excellent at a smaller capacity.The weight corresponds to the general range for foodstuffs of 10 -12 m 2 /s to 10 -8 m 2 /s [16], [17].

Conclusion
From the results of the research that founded, some conclusions are as follows: 1.The drying temperature dramatically influences the drying rate of the thin layer of local rice grain of the Siam Mutiara variety in Fixed Bed Dryer drying.2. The air temperature and humidity that pass through the pile of grain on each tray vary relatively due to the water vapor absorption from the samples given on each tray.3. The moisture content of the material from trays 1 to 5 is not significantly different, so the drying process was categorized as thin layer drying with a total thickness of 4 cm.4. The drying model that gives the lowest chi-square (χ2) value and the highest R 2 value is the Page model, which indicates that this model is the most suitable for estimating the drying characteristics of the local rice variety Siam Mutiara.

Figure 1 .
Figure 1.The layout of the Fixed Bed Dryer

Figure 2 .
Figure 2. Temperature graph of the Arduino RTC (Real Time Clock) data at temperatures of 40˚C (a), 50˚C (b), and 60˚C (c).

Figure 3 .
Graph of humidity from the RTC (Real Time Clock) data of the Arduino circuit at temperatures of 40˚C (a), 50˚C (b), and 60˚C (c).

Figure 4 .
Figure 4. Graph of decreasing water content on drying at 40˚C (a), 50˚C (b), and 60˚C (c).

Figure 6 .
Figure 6.Graph of experimental MR and Predicted MR Page model for drying time at drying temperatures of 40˚C (a), 50˚C (b), and 60˚C (c).