Development of weight monitoring system for hot-air dryers

Drying is to stop the biochemical reactions and microorganism activities in the products by removing the freewater in the products. The drying process must be completed when the moisture content of the product falls to the desired final moisture content. Weight data are often used to determine the moisture content of the dried products. Purpose of the study is to develop a weight monitoring system to determine the instant moisture content of the dried products in hot air rack cabinet dryers. The drying rack and trays were hung in an s-type load cell and the weight of the dried spinach in the trays was converted to electrical signal. The electrical signals from the load cell are sent to the signal converter and the data acquisition card, respectively. The temperature and relative humidity values of the drying air at the inlet and outlet of the dryer cabinet were also measured with the help of sensors and sent to the data collection card. The data acquisition card transferred the incoming data to the computer once per second. "View Drying Process Monitoring Application" was developed by using Labview program. This application has performed different tasks simultaneously. In the drying experiments, it was seen that the air flow inside the cabinet oscillates on the drying rack and trays suspended in the load cell. This oscillation caused fluctuations in the weight change curves of dried spinach. The use of the load cell vibration damping mounting kit has greatly reduced the amplitude of these fluctuations but has not been able to reset them. The fact that fluctuations occur even at small amplitudes caused much greater fluctuations in the instant moisture content values towards the end of drying. This has shown that it is more accurate to use weight values instead of instant moisture content values as the finishing criterion to successfully complete the drying process.