Authors: Olivier Montmayeur
Source: RIT Scholar Works (Rochester Institute of Technology) (article, 2019-01-01)
Field: Materials Science — Polymers and Plastics

Testing and Modeling of the Indirect Solar Drying of Thin Film Mangos In Haiti, 80% of rural people live in dire poverty living on less than a dollar a day. Cultivated and wild grown foods such as mangos and breadfruit could be used to reduce the economic and nutritional disparity for rural communities. Unfortunately in these areas there is a high amount of spoilage due to short harvesting seasons with high yields and lack of preservation options. 80% of breadfruit and 60% of mangoes are lost annually according to a local farmer’s co-op in Borgne, Haiti [1]. Based on a 2018 three-week collaborative design session with Rochester Institute of Technology (RIT) and the local women’s group SEE FANM (women for health, education, and economy), we identified mangos as a potential option for “transfòmayson fwi” - food transformation. Our team proposed drying mangos and then selling them as a juice powder in the off-season.\nFood preservation by solar drying has become a widespread practice in developing countries. Dryers use solar energy and other supplementary energy sources to heat air entering a drying chamber. Drying is a complex heat and mass transfer process that can take hours or days depending on the properties of the food such as ripeness and temperature and humidity of the drying air. Many studies have attempted to model the transport of moisture within fruits to predict drying performance while others have experimented with different styles of solar dryer designs. These systems are mostly tested outside in variable ambient conditions where the local temperature, relative humidity, and solar flux constantly fluctuate introducing a significant amount of noise . This “noise” is a product of these varying external conditions which affects the quality of the drying air and the performance of solar-thermal systems. Testing thermal systems in cold climates such as Rochester makes it impossible to predict performance in tropical regions like Haiti. This work focuses on eliminating many of these external factors in order to remove noise to provide faster and more repeatable testing.\nA testing system was designed and built to simulate the output of a solar collector in a tropical environment to explore the impact of the collector size and dryer volumetric flowrate on drying performance in a highly consistent and controlled manner. Testing demonstrated the importance of external conditions during the falling drying rate regime, where internal diffusion typically dominates drying performance. The results of these tests are used to empirically fit a bulk drying model for a shrinking fruit film that exemplifies the impact of external conditions. This model allows for the prediction of drying performance for the first 85% of moisture removed from a fruit film. A system model is also proposed that seeks to capture the deep layer effect associated with drying multiple stacks of fruit. By fitting the thin layer and system model to experimental data, a predictive model is proposed and used to explore design choices for the unglazed transpired solar collector and horizontal drying chamber used in this study. Personal experience with prototyping in Haiti led to the coupling of a simple preliminary economic model with the thin layer model to provide the predicted output per capital spent for this solar dryer design. Environmental science ; Materials science Textile materials and evaluations ; Building Energy and Comfort Optimization