Analysis of Heat Transfer and Efficiency of Rack Type Flash Dryer Machine in Purple Sweet Potato Drying Process Analisis Pindah Panas dan Efisiensi Mesin Pengering Flash Dryer Tipe Rak Pada Proses Pengeringan Ubi Ungu

Purple sweet potato ( Ipomoea batatas var Ayumurasaki ) has deep purple flesh and tuber skin. The variety of processed purple sweet potato products is increasingly diverse as purple sweet potato production increases, such as cookies and chips. Therefore, a process is needed to turn purple sweet potato into flour before being made into a variety of processed products, namely the drying process. Drying is a process of reducing the water content of a material to a certain level. To determine how much fuel is used by dryer machine, it is necessary to evaluate the effectiveness of the machine. So that in this study the aims were to determine the amount of energy needed to dry purple sweet potatoes, calculate the efficiency of the flash dryer machine and find out the temperature distribution on each tray of the drying machine. Based on the research results of the rack-type flash dryer drying machine, it can be concluded that the mechanism of the heat transfer rate in the purple sweet potato drying process occurs by forced convection heat transfer from the drying air to the purple sweet potatoes and a mass flow rate value of 0.1272 kg/s is obtained, the convection transfer rate in the drying chamber is 836.84 W and the sensible heat value is 1033.84 W. Hence, the amount of heat to dry 3 kg of purple sweet potato for 4 hours is 1870.68 W and an efficiency value of 55.26% is obtained. The total energy required to dry 3 kg of purple sweet potato in 4 hours is 5712.86 kJ.


Introduction
Purple sweet potato (Ipomoea batatas var Ayumurasaki) has deep purple flesh and tuber skin [1].Variations in processed purple sweet potato products are increasingly diverse as purple sweet potato production increases, such as cookies and chips, since purple sweet potatoes contain carbohydrates and calories, which are pretty high [2]- [4].Therefore, a drying process is needed to turn purple sweet potato into flour before being made into various processed products.Drying is a process of reducing the water content of a material to a certain level, which slows down the material's degradation rate due to biological and chemical processes.Several drying methods include natural drying with hot sun, drying with fuel, and combined drying [5], [6].Of course, a food company's production costs will increase if it uses machines to dry its products because it requires fuel.To determine how much fuel the dryer needs, it is necessary to evaluate the effectiveness of the machine.So, in this study, the aims were to determine the amount of energy needed to dry purple sweet potatoes, the efficiency of the flash dryer machine, and to find out the temperature distribution on each tray of the drying machine [7].The value of thermal efficiency is determined by calculating the effectiveness of the machine.It is necessary to calculate the dryer's thermal efficiency to assess the machine's performance [8].If the engine's thermal efficiency is low, indicating that more fuel is lost than is used to dry the material, the engine design must be improved.If the dryer has a high thermal efficiency value, less fuel is lost, and more heat is absorbed by dried material [6].

Research Methods
This research was conducted at the Laboratorium Logam, Politeknik Negeri Jember in August-September 2022.The research began with initial observations of the physical properties of purple sweet potatoes as the basis for conducting the research.This is related to the duration and temperature of the drying process.If drying is carried out at an inaccurate temperature and duration of time, it will give the substance a bitter and burnt taste.Initial activities are also related to ensuring the dryer functions properly.The dryer used is a rack-type flash dryer with a fan inside to spread hot air and is fueled with liquefied petroleum gas (LPG) as shown in The heat energy of the flash dryer is generated from an LPG stove which heats the combustion chamber and then hot air is pushed by a fan into the drying chamber.The air inside the drying chamber exits through the air outlet and is discharged into the environment.The specifications for the flash dryer are 120 cm in length, 60 cm in width and 125 cm in height with a maximum capacity of 15 kg for one drying.The purple sweet potato drying test procedure was carried out using a rack-type flash dryer, namely: a. Purple sweet potato preparation b.Purple sweet potato peeling c.Purple sweet potato wash d.Cutting or making purple sweet potato chips e. Weighing of purple sweet potato chips f.Setting the temperature sensor in the dryer g.Start the testing process by preheating the dryer for about 15 minutes h.Observation and weighing Return to weight after drying for 4 hours The formula for calculating the mass flow rate uses Equation 1 as follows [9], [10]: The convection heat transfer rate can be calculated by Equation 2 as follows [9]: Calculation of engine efficiency is obtained by Equation 9 as follows [9]:

Results and Discussion
The data acquired through direct measurements is presented in Table 1.Meanwhile, secondary data obtained from literature, both books and journals [9], [11] can be seen in Table 2.The graph of temperature changes in the drying chamber on each tray can be seen in Figure 2. Figure 3 shows that the air humidity for 4 hours of the drying process ranges from 47% to 56%.Where the highest value is the densest in the first minute, and the humidity of the ambient air begins to decrease during the drying process.The fan in the dryer circulates hot air in the drying chamber and releases it into the environment.If the ambient temperature is high, the air entering the drying chamber will have low humidity.Conversely, if the ambient temperature is low, the air entering the drying machine will have high humidity.A low humidity level accompanied by a high combustion chamber temperature can speed up the drying time so that the drying rate of the material increases [10].

Conclusion
Based on the results of research on the flash dryer machine rack type that the mechanism of the heat transfer rate in the process of drying purple sweet potato occurred forced convection heat transfer from the dryer air to the purple sweet potato and obtained a mass flow rate of 0.1272 kg/s, convection transfer rate in the drying room of 836.84 W and a heat sensible value of 1033.84W. Thus, the amount of heat needed to dry 3 kg of purple sweet potato for 4 hours was 1870.68 W and the efficiency of the drying process was 55.26%.The total energy needed to dry 3 kg of purple sweet potato in 4 hours was 5712.86 kJ.

Table 1 .
Initial parameter data

Table 2 .
Secondary data with the temperature is 55 °C = 328 K, and a value of 1033.84W is obtained.So that the amount of heat used in the dryer (Qin) = Q convection + Q sensible = 836.84 W + 1033.84W = 1870.68W, and an efficiency value of 55.26 is obtained.
Based on the primary data (Table1) and secondary (Table2) above and by using the calculations in Equation 1, the result is a mass flow rate of 0.1272 kg/s.Meanwhile, to calculate the convection transfer rate in the drying chamber using the calculations in Equation2, the result is 836.84W. When turned on, the sensible heat value doi https://doi.org/10.21776/ub.jkptb.2023.011.02.01