Determining seed cotton mass flow rate by pressure drop across a blowbox
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© 2015 American Society of Agricultural and Biological Engineers. A seed cotton mass flow rate sensor would offer useful feedback for gin managers and provide a critical input for advanced process control systems. Several designs of seed cotton mass flow rate sensors have been evaluated in the laboratory, but none have found acceptance in commercial gins. The objectives of this research were to develop a system for predicting seed cotton mass flow rate based on the pressure drop measured across a blowbox; investigate the effect of pipe diameter, cultivar, moisture content, feed rate, and fan speed on this relationship; and provide recommendations for developing a prototype system for testing in commercial gins. A negative pressure pneumatic conveying system was constructed with a variable-speed feed control and fan. The inlet air velocity, blowbox pressure drop, temperature, and relative humidity were recorded during testing. A model was developed to predict the seed cotton mass flow rate based on the blowbox pressure drop, air velocity, air density, and pipe cross-sectional area. The model was calibrated by conveying a known mass of seed cotton through the system and integrating the model over this time. Mean absolute error in predicting seed cotton mass was 7.35%. Cultivar and moisture content had no effect on the model regression coefficients. Significant differences existed between the regression coefficients of different feed rates; however, these only occurred at mass flow ratios much larger than those achieved in commercial gins. The effect of fan speed was small and likely not practically significant. Measuring the pressure drop across a blowbox is a suitable basis for further development of a seed cotton mass flow rate sensor for commercial gins.
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