Continuous monitoring of moisture content during hay bale drying

Abstract

Continuous and accurate measurement of moisture content (MC) would represent a significant improvement for on-site monitoring of commercial baled hay drying. A meter based on electrical resistance was used to determine MC of hay continuously in a laboratory dryer. Two moisture probes and one thermocouple were inserted in eight superimposed layers of hay of 135 mm thickness each. The probe MC measurements were compared with the exact MC obtained by oven drying and mass balance. Three initial levels of MC (20, 30 and 40%) and two levels of drying air temperature (40 and 50C) were repeated during three weeks. Linear regression was used to predict the exact MC from the readings of the probes. The best prediction model had an R=0.919 at an initial MC of 30% and a drying temperature of 40C. The probes were less accurate at a high initial MC of 40% with R as low as 0.601. Results indicated that air temperature within the hay influenced the MC readings of the probes. When temperature was included in the prediction model, all R improved and values ranged from 0.685 at high initial MC to 0.949 at a low initial MC of 20%. The smallest standard errors were observed at low MC ( 0.81%) and increased with the initial MC up to 4.62%.