Author
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Hardin Iv, Robert |
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Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only Publication Acceptance Date: 2/15/2013 Publication Date: 6/1/2013 Citation: Hardin IV, R.G. 2013. Determining seed cotton mass flow rate by pressure drop across a blowbox. National Cotton Council Beltwide Cotton Conference. p 990. Interpretive Summary: An accurate measurement of seed cotton mass flow rate would be useful for gin operators, providing feedback on gin performance. The development of improved process control systems for cotton gins also requires accurate measurement of seed cotton mass flow rate. Previous research has tested optical systems for determining mass flow rate; however, use in a commercial gin may require multiple sensors at a single location, resulting in higher costs. Researchers have used differential static pressure measurements in horizontal and vertical pipes to estimate mass flow rate, but achieving high accuracy was difficult because of the small range in pressure measurements. When a material, such as seed cotton, is introduced into a moving air stream, energy is required to accelerate this mass. The energy loss of the air stream can be determined by measuring the static pressure difference from a point in the conveying system immediately before the material is introduced to a point where the material has reached maximum velocity. This pressure difference should be proportional to the mass flow rate of material and the air velocity. The feeding system for seed cotton in gins is well-suited to making the necessary measurements. A conveying system was constructed to develop a system for predicting seed cotton mass flow rate based on the pressure drop caused by accelerating the seed cotton. Duct diameter, seed cotton feed rate, fan speed, cotton cultivar, and moisture content were varied during testing. The mean absolute error in predicting the mass of 11 to 29 kg lots of seed cotton was 7.35%. Cultivar and moisture content did not affect the regression coefficients in the model used to predict mass. Significant differences existed between the regression coefficients of different feed rates, but these only occurred at mass flow ratios much larger than achieved in commercial gins. The effect of fan speed was small and likely not practically significant. Measuring the pressure drop due to acceleration of seed cotton is a suitable basis for further development of a seed cotton mass flow rate sensor for commercial gins. Technical Abstract: 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 duct 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 duct 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 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. |
