Mathematical Modeling and Simulation of Mixed Mode Natural Convection Solar Dryer for Green Banana Flour Production
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Date
2021
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Addis Ababa University
Abstract
Fruit drying is one of fruit preservation technique so as to increase shelf life of the produces and reduce food losses. Open air is an old and usual way of drying systems, it consumes a lot of time and also other problems related with contamination. It also consumes bigger space. Solar dryer uses direct solar energy in a better way to produce great amount of heat by using different means, such as, solar air heater and drying chamber with many compartments to handle more products in a good air circulation, only consuming small space. The main objective of this thesis work is to design, model and simulate a natural convection mixed mode solar greenhouse dryer integrated with solar air collector (SAC) for drying of green banana. The dryer consists of an arc roof structure covered with polyethylene plastic on a concrete floor. Solar air collector tilted at an angle of 21⁰ is connected with the greenhouse. To investigate the drying performances of the mixed mode natural convection solar greenhouse dryer, dynamic model of heat and mass transfer was developed and thin layer drying model was selected and this system of non-linear partial differential equations was solved numerically using MATLAB/Simulink software. Comparative study on the performance of the green house dryer with and without SAC was conducted with software simulation. The result showed that the maximum air temperature, maximum product temperature, and maximum cover temperature, without and with solar air collector are found to be 33℃, 46℃, and 78℃ and, 34℃, 54℃, and 79℃ respectively. The moisture ratio of green banana reduced from 1.58 % (db) to 0.2 % (db) within 3 days. Effect of wind speed on the drying performance was also simulated and as a result wind speed has inverse effect on the drying temperature. Therefore, the designed greenhouse solar dryer with solar air heater has a good performance for drying of fruits within a reduced time span and better quality.
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Keywords
Mixed mode, Natural convection, MATLAB/Simulink, Dynamic model, Solar air collector