Thin layer drying characteristics of freshwater algae and determination of model equality

In this study, thin layer drying characteristics of freshwater algae growing in natural and artificial pools were investigated by using a laboratory type tray dyer set up. Alga samples harvested were kept in a refrigerator at the temperature of +4 °C. The drying experiments were conducted in the air flow rates between 0.5 and 1.5 m/s, at the temperature ranges of 40-60 °C, and at the atmospheric conditions. A typical drying experiment was carried out by placing a certain weight of algae sample in the dryer chamber at a known air flow rate and temperature and by making weight measurements at certain times. The experiments were ended when the last two weight values of freshwater alga samples were approximately the same. The drying and drying rate curves of alga samples were obtained. As the time progressed, the moisture content values of freshwater algae samples decreased at all temperature values studied. It was observed that the drying time of Alga-1 sample was lower than that of Algae-2 sample. When the drying rate curves of the Algae-1 sample are examined, a generally falling rate period is observed for all air flow rates and at 40-50 °C, while a constant rate period is also occured. However, the drying period of Algae-1 sample was falling rate period at the temperature of 60 °C (for all air flow rate). In the drying rate curves of the Algae-2 sample, a constant velocity period was encountered in all drying conditions except for the 60 °C 1 and 1.5 m/s air flow rate experiments. It was thought that the reason for obtaining different drying rate periods was due to the difference in the solid structure of the two algae species studied. In this study, the moisture ratio values obtained from drying experiments were also fitted to the drying model equations as two stages. The first stage statistical analysis results showed that the best model equation of algae spescies studied was Difusion equation. In the scond satge, the derived model equations obtained by rearranging the constansts of Diffusion equation by using some definitions. So, statistical analyses were done by these equations. As a result, the best equations were the equation numbered as 6 for Algae-1 and the equation numbered as 5 for Algae-2, respectively. Finally, the characterization analyses of algae species dried in this study were carried out. The properties such as species analysis, oil content, SEM, FTIR were similar to that of previous studies in the literature.