Research on a device for drying raw cotton using solar energy
Keywords:
raw cotton, solar collector, heat and mass transfer, Nusselt number, drying kinetics, Page model, exergy analysis, response surface methodology, automatic controlAbstract
The article addresses the analytical substantiation of the key design and technological parameters of a solar-powered drying unit intended to reduce the moisture content of raw cotton (from field harvest levels to the standard 7–9%) prior to its delivery to processing facilities. This substantiation is based on an integrated approach incorporating interdisciplinary heat and mass transfer, convective heat transfer theory, drying kinetics, and exergetic analysis. The convective heat transfer coefficient within the collector's airflow channel was determined using Reynolds, Nusselt, and Prandtl criteria, while the collector's thermal efficiency was calculated via the second-order Hottel–Whillier–Bliss characteristic equation. The drying process was modeled using the Page semi-empirical model and an Arrhenius-type temperature-diffusion relationship, with the process's thermodynamic efficiency evaluated through exergetic efficiency. Multi-factor optimization regarding collector surface area and airflow rate was performed using a second-order regression model based on the Response Surface Methodology (RSM). For a unit with a capacity of 1000 kg/h, numerical values for collector surface area, airflow rate, temperature, and drying duration were determined to meet the requirement of reducing moisture content from 10% to 7%, and their sensitivity to fluctuations in solar radiation was analyzed through a combined graphical and analytical approach. Given Uzbekistan's high solar potential and the fact that the cotton harvesting season coincides with sunny months, it is recommended to implement an adaptive automatic control system to stabilize the exhaust air temperature
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