Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2001
Publication Date: 8/31/2001
Citation: BARKER, GARY L., LAIRD, J. WELDON, PELLETIER, MATHEW G., HOLT, GREG A. RELATIVE VELOCITY, DENSITY, AND TEMPERATURE EFFECTS ON COTTON MOISTURE TRANSFER RATES. JOURNAL OF COTTON SCIENCE. 2001. V. 5. P. 243-251. Interpretive Summary: Moisture affects every aspect of cotton harvesting and processing. Excessive moisture results in grade losses, fiber deterioration, and decreased machine performance, while low moisture can cause fiber breakage and results in operating difficulties. Moisture transfer rates of lint, seed, and burs were determined as a function of air velocity. All of the components were exposed to a temperature of 40 deg C (104 deg F). In addition, the burs were also exposed to a temperature of 75 deg C (167 deg F) and the lint to a temperature of 80 deg C (176 deg F). The air flow rates were varied from 104 to 944 cc/s (0.22 to 2.00 CFM) through a 6.9 cm (2.75 in) diameter pipe. Lint density was varied from 0.005 to .03 g/cc. The goal was to look at relative air velocities in a range which is equivalent to cotton flowing in a pipe with no acceleration. Within the range tested, air velocity had no effect on cotton seed and affected only the moisture transfer rates of cotton burs under humidification at the 75 deg C temperature. As expected, lint density and temperature both had a very pronounced effect on lint moisture transfer rates. Increasing the lint density reduced transfer rates, while increasing the air velocity resulted in increased moisture transfer rates within the range tested. A generalized regression equation was developed for predicting the effects of air velocity, temperature and lint density on cotton lint moisture transfer rates. This information will be used in conjunction with equilibrium moisture data to estimate the moisture content of harvested seed cotton during cotton harvesting and ginning.
Technical Abstract: Moisture control during the harvesting, storage, and processing phases of cotton production is essential for producing a quality product. The objective of this study was to quantify the effects of relative velocity of the air, air temperature, and lint density on moisture transfer rates for cotton burs, cottonseed, and cotton lint during the drying or moisture restoration process. The volumetric flow rate of the air passing over, through, and around the sample was varied from 104 to 944 cc/s (0.22 to 2.0 ft3/min). This provided air relative velocities, depending on the sample holder utilized, varying from 4.45 to 50 cm/s (9 to 98 ft/min). The density of the cotton lint was varied from .005 to .03 g/cc (0.31 to 1.87 lb/ft3). A 40 degree C temperature was used for all samples. In addition, the burs were exposed to a 75 deg C temperature and the lint to a 80 deg C tempera- ture. As expected, temperature had a pronounced effect on moisture transfer rrates. Increasing the relative velocity for burs in humid air, and for cotton lint in both humid and dry air, resulted in increased moisture transfer rates. However, cottonseed and burs exposed to dry air showed no apparent change in moisture transfer rates with changes in air velocity. Increasing the density resulted in significantly reduced moisture transfer rates for cotton lint. A generalized equation consisting of temperature, relative velocity, and density was developed for predicting the coefficient D (containing diffusivity) for cotton lint exposed to the experimental conditions.