The efficiency increased with increasing drying air velocity. Drier must expel air to discard moisture, therefore allow new, lower humidity air to enter the system. The rate the air is exhausted from a drier affects the entrance of new air and therefore affects the relative humidity and rate of drying. This is the primary way, the moisture gets out of the drier after it has evaporated from the fish. The rate of surface evaporation from fish is proportional to the velocity of air passing over it. The influence of loading mass changes at a constant velocity and temperature are as shown in the Figs. 7 and 8. The graph of moisture content as a function of drying time (Fig. 7) and that of drying rate as a function of drying time (Fig. 8) show that moisture content decrease of 1 layer of fish is faster than 2 layers of fish. Surface area per kilogram of fish for 1 layer is twice larger than 2 layers. This shows the more surface area per kilogram of fish the higher the water evaporation
from fish. After 10 h of drying, the moisture content of 1 layer and 2 layers of fish experiment is 23.6% and 45.4%, respectively. To get the same final moisture content, 2 layers of fish experiment need twice period than 1 layer of fish. From the visual inspection after experiment, for 2 layers of fish experiment shows that the moisture content is not uniform. The study was not able to obtain optimum drying condition using variation of temperatures and velocities data. The higher temperature and velocity of drying air the shorter the time to reach the critical moisture content. At the same time, this higher temperature will reduce the efficiency of the system while higher velocity helps to increase the efficiency of the system. With this condition, it is difficult to conclude optimum drying condition. In order to be able to obtain optimum drying condition some modifications should be made. The drying rate and energy used should be taken into account. From the experimental data, the optimum drying conditions may be obtained through three steps of the drying process. First step is to run experiment at 70 °C for 150 min of drying time, the second is at 50 °C for next 100 min, and then the third one is at 40 °C till the equilibrium moisture content. The measurements of thermal properties were done in the initial and final experiment. Measurement of thermal properties of fish used KD2 PRO Thermal Properties Analyzer, Decagon Devices, Inc. Only thermal conductivity (k) and specific heat (cp) are measured. The average of thermal properties measured of anchovy fish as a function of moisture content is as shown in Table 2. The value of thermal conductivity and specific heat decreased with decreasing moisture content.
เพิ่มประสิทธิภาพ ด้วยการเพิ่มความเร็วอากาศแห้ง Drier ต้องขับไล่อากาศให้ละทิ้งความชื้น ดังนั้น ต่ำกว่าความชื้นอากาศใส่ระบบให้ใหม่ อัตราอากาศจะหมดจาก drier ที่มีผลกระทบต่อทางเข้าของอากาศใหม่ และจึง มีผลต่อความชื้นสัมพัทธ์และอัตราการอบแห้ง นี้เป็นวิธีหลัก ได้รับความชื้นจาก drier ที่หลังจากนั้นได้หายไปจากปลา อัตราการระเหยที่ผิวจากปลาเป็นสัดส่วนกับความเร็วของอากาศที่ผ่านไปนั้น อิทธิพลของโหลดเปลี่ยนแปลงโดยรวมที่ความเร็วคงและอุณหภูมิจะแสดงใน Figs. 7 และ 8 กราฟของชื้นเป็นฟังก์ชันของเวลาทำให้แห้ง (Fig. 7) และของแห้งอัตราเป็นฟังก์ชันของเวลา (Fig. 8) การทำแห้งแสดงว่าความชื้นเนื้อหาลดชั้น 1 ของปลาได้เร็วกว่าปลา 2 ชั้น พื้นที่ผิวต่อกิโลกรัมของปลาสำหรับชั้น 1 มีสองขนาดใหญ่กว่า 2 ชั้น นี้แสดงพื้นที่มากขึ้นต่อกิโลกรัมของปลายิ่งระเหยน้ำ from fish. After 10 h of drying, the moisture content of 1 layer and 2 layers of fish experiment is 23.6% and 45.4%, respectively. To get the same final moisture content, 2 layers of fish experiment need twice period than 1 layer of fish. From the visual inspection after experiment, for 2 layers of fish experiment shows that the moisture content is not uniform. The study was not able to obtain optimum drying condition using variation of temperatures and velocities data. The higher temperature and velocity of drying air the shorter the time to reach the critical moisture content. At the same time, this higher temperature will reduce the efficiency of the system while higher velocity helps to increase the efficiency of the system. With this condition, it is difficult to conclude optimum drying condition. In order to be able to obtain optimum drying condition some modifications should be made. The drying rate and energy used should be taken into account. From the experimental data, the optimum drying conditions may be obtained through three steps of the drying process. First step is to run experiment at 70 °C for 150 min of drying time, the second is at 50 °C for next 100 min, and then the third one is at 40 °C till the equilibrium moisture content. The measurements of thermal properties were done in the initial and final experiment. Measurement of thermal properties of fish used KD2 PRO Thermal Properties Analyzer, Decagon Devices, Inc. Only thermal conductivity (k) and specific heat (cp) are measured. The average of thermal properties measured of anchovy fish as a function of moisture content is as shown in Table 2. The value of thermal conductivity and specific heat decreased with decreasing moisture content.
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