Heat transfer analysis in the chimney of the indirect solar dryer under natural convection mode

An attempt is established to investigate the heat transfer from a heated chimney of an indirect solar dryer and predicted the chimney outlet temperature using energy balance equation. Tests were carried out with no-load condition under natural convection mode. Data of air velocity, temperatures, ambient relative humidity and solar radiation of the drying process are presented in order to solve the heat transfer coefficients. The result shows that temperature difference between mean air inside a chimney and ambient was 23.8 °C at maximum solar radiation of 812 W/m², where maximum airflow is observed. The predicted chimney outlet temperature was found in good agreement with that of the experimental value. Temperature variation, correlation coefficient, and average absolute error are less than 10%, 0.977, and 5%, respectively. Replacing the normal chimney by heated chimney can significantly reduce the heat loss and increase the chimney efficiency.