Comprehensive evaluation of residual water based on vacuum drying methods
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In this study, lab-scale vacuum drying experiments were conducted using canisters with a volume of 196 L and a height of 1 m, along with vacuum pumps with various intake capacities of 100, 200, 400, and 600 L/min. Through these experiments, when performing direct pressure-reduction vacuum drying tests, we calculated the evaporation rate of residual water over time. We identified a significant increase in the evaporation rate near approximately 40–50 torr, marking a critical transition point where residual water undergoes a phase change from liquid to vapor. This zone was experimentally determined and subsequently termed the "Evaporation-Acceleration Zone." Before entering this zone, the likelihood of ice formation is theoretically negligible even when employing high-capacity pumps. Based on these observations, our research team concluded that direct pressure reduction is feasible and opted for a strategy to maximize evaporation efficiency by prolonging the duration within the phase change boundary, rather than employing the traditional stepwise pressure reduction method. The conventional stepwise pressure reduction technique, widely used in the industry, exhibited an average evaporation efficiency of 9.66 mg/s. In contrast, when hold times at the phase change boundary were extended to 25 and 50 min, evaporation efficiencies were recorded at 18.526 mg/s and 12.698 mg/s, respectively, showing an increase of 1.92-fold and 1.31-fold. Additionally, initiating stepwise pressure reduction at 5 min into the phase change boundary led to a 1.62-fold improvement in efficiency. Beaker and simulated drainage hole tests yielded similar results, with evaporation rates measuring 9.668 mg/s and 9.256 mg/s, respectively
Abstract
In this study, lab-scale vacuum drying experiments were conducted using canisters with a volume of 196 L and a height of 1 m, along with vacuum pumps with various intake capacities of 100, 200, 400, and 600 L/min. Through these experiments, when performing direct pressure-reduction vacuum drying tests, we calculated the evaporation rate of residual water over time. We identified a significant increase in the evaporation rate near approximately 40–50 torr, marking a critical transition point where residual water undergoes a phase change from liquid to vapor. This zone was experimentally determined and subsequently termed the "Evaporation-Acceleration Zone." Before entering this zone, the likelihood of ice formation is theoretically negligible even when employing high-capacity pumps. Based on these observations, our research team concluded that direct pressure reduction is feasible and opted for a strategy to maximize evaporation efficiency by prolonging the duration within the phase change boundary, rather than employing the traditional stepwise pressure reduction method. The conventional stepwise pressure reduction technique, widely used in the industry, exhibited an average evaporation efficiency of 9.66 mg/s. In contrast, when hold times at the phase change boundary were extended to 25 and 50 min, evaporation efficiencies were recorded at 18.526 mg/s and 12.698 mg/s, respectively, showing an increase of 1.92-fold and 1.31-fold. Additionally, initiating stepwise pressure reduction at 5 min into the phase change boundary led to a 1.62-fold improvement in efficiency. Beaker and simulated drainage hole tests yielded similar results, with evaporation rates measuring 9.668 mg/s and 9.256 mg/s, respectively