Design, development and CFD modeling of indirect solar food dryer

Abstract

In this study, a solar powered indirect food dryer is designed and developed. The dryer design consists of a solar collector unit, drying chamber with two columns of four rack shelves, chimney for the exhaust air, and a solar powered fan. The outlet of the dryer is designed in a truncated pyramid geometry so that precipitation of condensed water would be minimized and additional heating of the drying air is possible at the exit. The dryer is developed and manufactured in Mekelle, Ethiopia. Computational Fluid Dynamics, CFD is employed for predicting a transient three dimensional flow field and temperature distribution within the drying chamber using a symmetric flow domain. The predicted air flow distribution in the vicinity of the rack shelves showed that the mean flow velocity is 0.14 m sec for the lowest shelf and 0.12 m sec for the other shelves due to cooling of the air. A significantly uniform airflow distribution is observed on the top three shelves compared to the bottom shelf. The inside of the drying chamber evolves towards a steady operating temperature of 315K. The temporal temperature distribution reveals that the food to be dried will evolve to this temperature in about 35 minutes. For validating the model, the temperature distribution on each rack shelf is measured along with the global solar irradiation. The maximum average temperature difference between the measurement and the CFD simulation is found to be 4.3 °C. Hence, the CFD model is able to produce a good qualitative and quantitative insight into the temperature distribution within the drying chamber, rack shelves, and symmetry plane.