Modeling and optimization of a greenhouse-type solar dryer system

Abstract

Solar drying in greenhouses is an economical and safe alternative for drying, it allows to increase the shelf life of products in an innocuous way. The objectives of the thesis were 1) to model the drying kinetics of tomato in a greenhouse-type solar dryer; 2) to model and control the internal conditions in a greenhouse-type solar dryer; 3) to evaluate design alternatives to improve the drying process. The greenhouse-type solar dryer is located at the Universidad Autonoma Chapingo (Mexico) and has a 6- mm-thick parabolic-shaped polycarbonate cover; 15 cm thick concrete floor; two exhaust fans for the air and four air inlets; with an approximate volume of 211 m3 . Thirty-five thin-layer models were tested for drying tomato slices. The innovation at this stage was to analyze the models in terms of their structure, and number of parameters and evaluate them with data from another experiment. The best model was the Page VI model with an RMSE of 0.06 and an R2 of 0.993. To improve drying, a controller based on "Model Predictive Control" for the greenhouse was modeled and designed. The main innovation was the use of system identification with the N4SID algorithm, obtaining a model with product temperature as state and control based on product temperature and not air temperature. Finally, a literature review on the modeling of greenhouse-type solar dryers using CFD was carried out and a computational model (CFD) for the dryer was developed. The model was validated, and two designs were tested to recirculate the air and improve the temperature distribution inside the greenhouse. Both systems showed higher temperatures and a more uniform velocity throughout the volume.