• Journal of the Korean Wood Science and Technology
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• v.30 no.2
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• pp.108-114
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• 2002

Red pine(Pinus densiflora) square timbers with 14.0 cm and 16.5 cm of face size and 24 m long were dried in a vacuum-press kiln and in a radio-frequency/vacuum(RF/V) kiln to compare drying rate, moisture content(MC) distribution and specific energy. RF/V drying rate was higher than vacuum-press drying rate. The effect of size of cross section on the RF/V drying rates were more pronounced than those of vacuum-press drying. The longitudinal- and the transverse MC distribution of dried square timber showed convex profile for the vacuum-press drying and concave profile for the RF/V drying. Moisture gradient of width direction was similar to the thickness direction in vacuum-press dried square timber and was more slight than that of the thickness direction in the RF/V dried large square timber. The specific energy consumption curve increased as MC decreased. Specific energy(kWh/kg of water evaporated) of the vacuum-press process required more than that of the RF/V process.

• Journal of the Korean Society of Food Science and Nutrition
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• v.19 no.6
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• pp.555-564
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• 1990

The headspace gas chromatographic(analytical) technique was used to evaluate the retention of volatiles in fruit juices during freeze drying as a function of freezing rate, the content of initial solid and chamber pressure. The effects of freezing rate and drying time on the volatile retention under the experimental conditions were marked, particulary at long freezing time. The retention of volatiles in the freeze dried was largely affected by the freezing rate. The highest volatile loss under the freeze drying conditions was observed during the first stage of drying. The behavior during freeze drying of the volatile substances was affected by high content of initial solid. The volatile retention was higher in quick freeze drying than slow freeze drying and low pressure than high.

• Korean Journal of Plant Resources
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• v.17 no.3
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• pp.219-226
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• 2004

Transplantings of onion (Allium cepa L.) seedlings are required for higher germinability and uniformity. This study was done to determine effects of various seed treatments (seed cleaning, priming, GA$_3$, prechilling, drying, and light quality during seed drying) on germination and seedling emergence. Nongwoodaego and Changnyungdaego were used as cultivars for checking seed germination, and two cultivars and Cheonjuguhyeonghwang were investigated with seedling production rate. Seed cleaning using water prior to the other treatments greatly increased germination rate. Priming with 200mM Ca(NO$_3$)$_2$ solution somewhat alleviated the germination rate while GA$_3$ did not. Prechilling had the highest rate among the treatments. Seed drying after prechilling enhanced the rate compared to non drying, and during drying the prechilled seeds red light illumination showed the greatest rate in comparison with dark, blue, and far-red ones. Seedling production rate was enhanced in sequential treatments of seed cleaning, prechilling for 3 to 5 days, and red light treatment during 6 hour seed drying.

• Journal of the Korean Wood Science and Technology
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• v.17 no.3
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• pp.67-81
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• 1989

This experiment was carried out to know the mothod of changing the step of moisture content schedule with time in conventional kiln drying. For the purpose of this object. we made drying model by applying the moisture diffusion model by J.FSiau(1984) to average moisture content equation by J.Crank(1956) derived it from Fick's second law. And to verify this method of drying model. 2.5cm-thick boards and 5.0cm-thick dimension lumbers of Pinus densiflora were kiln-dried with the schedule of T11-C3 and T10-C4, respectively. And then the drying rates were investigated and compared with those calculated from drying model. The results obtained were as follows 1. Average drying rate and total drying time of board to dry to 6.5% moisture content were 0.64%/hr and 109hr., and those of dimension lumber to dry to 8.3% moisture content were 0.4%/hr. and 162hr., respectively. 2. The moisture content of shell and core decreased by equalizing treatment and increased by conditioning treatment both on board and dimension lumber. But the moisture gradient was lower after conditioning than after equalizing. 3. As the drying was proceeded, the transverse bound water diffusion coefficient all but linearly decreased, the water vapor diffusion coefficient abruptly curvilinearly increased, while the transverse diffusion coefficient curvilinearly decreased both on board and dimension lumber. But each of diffusion coefficients on board was larger than that on dimension lumber. 4. Compared to experimential drying rate of board. theoretical drying rate was larger at 30.0%-21.8% moisture content range and was similiar at 21.8%-5.4% moisture content. And in case of dimension lumber, the drying rate was similiar at 30.0%-16.1% moisture content range but theoretical drying rate was much lower at 16.1%-8.3% moisture content range. 5. The possibility of adapting this drying model to changing the moisture content schedule step with time was in the range of 21.8%-5.4% moisture content on board. And in the case of dimension lumber that was in the range of 30.0%-16.1% moisture content.

• Journal of Biosystems Engineering
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• v.29 no.1
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• pp.37-44
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• 2004

This study was conducted to develop a new drying method far reducing the drying cost and time and to investigate the drying characteristics of oak mushroom. A far infrared dryer of down draft air flow type used for this experiment can control the drying parameters, such as far infrared heater temperature and aeration velocity. The far infrared drying tests were performed at aeration velocities of 0.3 and 0.6m/s under the temperature of 90 and 100$^{\circ}C$ in for infrared heater, respectively. The results were compared and analyzed with those of an heated air drying method used as a control in terms of properties representing the drying characteristics. such as shrinkage rate, color, energy consumption amino acid components, drying rate and moisture ratio. The results obtained from this research can be summarized as follows. 1. The drying rate of far infrared drying was faster than that of heated air drying. With high temperature of far infrared heater and slow aeration velocity, the far infrared drying of down draft air flow type was superior to the heated air drying. 2. Most of far infrared drying conditions required less energy consumption than heated air drying. 3. The shrinkage rates of heated air drying and far infrared drying were decreased by 17.0% and 18.2∼19.8%, respectively. 4. The difference of color on oak mushroom surface before and after drying can be represented as $\Delta$E. $\Delta$E values of far infrared drying and heated air drying were 2.39∼4.55 and 6.77, respectively. 5. The amounts of free amino acids were higher in the far infrared than in the heated air drying. In addition the amounts of Gln and Glu generally were increased and those of Ala, Leu, and Val were decreased in order.

• Journal of Biosystems Engineering
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• v.4 no.2
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• pp.65-83
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• 1979

Low-temperature drying systems have been extensively used for drying cereal grain such as shelled corn and wheat. Since the 1973 energy crisis, many researches have been conducted to apply solar energy as supplemental heat to natural air drying systems. However, little research on rough rice drying has been done in this area, especially very little in Korea. In designing a solar drying system, quality loss, airflow requirements, temperature rise of drying air, fan power and energy requirements should be throughly studied. The factors affecting solar drying systems are airflow rate, initial moisture content, the amount of heat added to drying air, fan operation method and the weather conditions. The major objectives of this study were to analyze the effects of the performance factors and determine design parameters such as airflow requirements, optimum bed depth, optimum temperature rise of drying air, fan operation method and collector size. Three hourly observations based on the 4-year weather data in Chuncheon area were used to simulate rough rice drying. The results can be summarized as follows: 1. The results of the statistical analysis indicated that the experimental and predicted values of the temperature rise of the air passing through the collector agreed well. 2. Equilibrium moisture content was affected a little by airflow rate, but affected mainly by the amount of heat added, to drying air. Equilibrium moisture content ranged from 12.2 to 13.2 percent wet basis for the continuous fan operation, from 10.4 to 11.7 percent wet basis for the intermittent fan operation respectively, in range of 1. 6 to 5. 9 degrees Centigrade average temperature rise of drying air. 3. Average moisture content when top layer was dried to 15 percent wet basis ranged from 13.1 to 13.9 percent wet basis for the continuous fan operation, from 11.9 to 13.4 percent wet basis for the intermittent fan operation respectively, in the range of 1.6 to 5.9 degrees Centigrade average temperature rise of drying air and 18 to 24 percent wet basis initial moisture content. The results indicated that grain was overdried with the intermittent fan operation in any range of temperature rise of drying air. Therefore, the continuous fan operation is usually more effective than the intermittent fan operation considering the overdrying. 4. For the continuous fan operation, the average temperature rise of drying air may be limited to 2.2 to 3. 3 degrees Centigrade considering safe storage moisture level of 13.5 to 14 perceut wet basis. 5. Required drying time decrease ranged from 40 to 50 percent each time the airflow rate was doubled and from 3.9 to 4.3 percent approximately for each one degrees Centigrade in average temperature rise of drying air regardless of the fan operation methods. Therefore, the average temperature rise of drying air had a little effect on required drying time. 6. Required drying time increase ranged from 18 to 30 percent approximately for each 2 percent increase in initial moisture content regardless of the fan operation methods, in the range of 18 to 24 percent moisture. 7. The intermittent fan operation showed about 36 to 42 percent decrease in required drying time as compared with the continuous fan operation. 8. Drymatter loss decrease ranged from 34 to 46 percent each time the airflow rate was doubled and from 2 to 3 percent approximately for each one degrees Centigrade in average temperature rise of drying air, regardless of the fan operation methods. Therefore, the average temperature rise of drying air had a little effect on drymatter loss. 9. Drymatter loss increase ranged from 50 to 78 percent approximately for each 2 percent increase in initial moisture content, in the range of 18 to 24 percent moisture. 10. The intermittent fan operation: showed about 40 to 50 percent increase in drymatter loss as compared with the continuous fan operation and the increasing rate was higher at high level of initial moisture and average temperature rise. 11. Year-to-year weather conditions had a little effect on required drying time and drymatter loss. 12. The equations for estimating time required to dry top layer to 16 and 1536 wet basis and drymatter loss were derived as functions of the performance factors. by the least square method. 13. Minimum airflow rates based on 0.5 percent drymatter loss were estimated. Minimum airflow rates for the intermittent fan operation were approximately 1.5 to 1.8 times as much as compared with the continuous fan operation, but a few differences among year-to-year. 14. Required fan horsepower and energy for the intermittent fan operation were 3. 7 and 1. 5 times respectively as much as compared with the continuous fan operation. 15. The continuous fan operation may be more effective than the intermittent fan operation considering overdrying, fan horsepower requirements, and energy use. 16. A method for estimating the required collection area of flat-plate solar collector using average temperature rise and airflow rate was presented.

• Journal of Biosystems Engineering
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• v.4 no.2
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• pp.64-64
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• 1979

Low-temperature drying systems have been extensively used for drying cereal grain such as shelled corn and wheat. Since the 1973 energy crisis, many researches have been conducted to apply solar energy as supplemental heat to natural air drying systems. However, little research on rough rice drying has been done in this area, especially very little in Korea. In designing a solar drying system, quality loss, airflow requirements, temperature rise of drying air, fan power and energy requirements should be throughly studied. The factors affecting solar drying systems are airflow rate, initial moisture content, the amount of heat added to drying air, fan operation method and the weather conditions. The major objectives of this study were to analyze the effects of the performance factors and determine design parameters such as airflow requirements, optimum bed depth, optimum temperature rise of drying air, fan operation method and collector size. Three hourly observations based on the 4-year weather data in Chuncheon area were used to simulate rough rice drying. The results can be summarized as follows: 1. The results of the statistical analysis indicated that the experimental and predicted values of the temperature rise of the air passing through the collector agreed well.2. Equilibrium moisture content was affected a little by airflow rate, but affected mainly by the amount of heat added, to drying air. Equilibrium moisture content ranged from 12.2 to 13.2 percent wet basis for the continuous fan operation, from 10.4 to 11.7 percent wet basis for the intermittent fan operation respectively, in range of 1. 6 to 5. 9 degrees Centigrade average temperature rise of drying air.3. Average moisture content when top layer was dried to 15 percent wet basis ranged from 13.1 to 13.9 percent wet basis for the continuous fan operation, from 11.9 to 13.4 percent wet basis for the intermittent fan operation respectively, in the range of 1.6 to 5.9 degrees Centigrade average temperature rise of drying air and 18 to 24 percent wet basis initial moisture content. The results indicated that grain was overdried with the intermittent fan operation in any range of temperature rise of drying air. Therefore, the continuous fan operation is usually more effective than the intermittent fan operation considering the overdrying.4. For the continuous fan operation, the average temperature rise of drying air may be limited to 2.2 to 3. 3 degrees Centigrade considering safe storage moisture level of 13.5 to 14 perceut wet basis.5. Required drying time decrease ranged from 40 to 50 percent each time the airflow rate was doubled and from 3.9 to 4.3 percent approximately for each one degrees Centigrade in average temperature rise of drying air regardless of the fan operation methods. Therefore, the average temperature rise of drying air had a little effect on required drying time.6. Required drying time increase ranged from 18 to 30 percent approximately for each 2 percent increase in initial moisture content regardless of the fan operation methods, in the range of 18 to 24 percent moisture.7. The intermittent fan operation showed about 36 to 42 percent decrease in required drying time as compared with the continuous fan operation.8. Drymatter loss decrease ranged from 34 to 46 percent each time the airflow rate was doubled and from 2 to 3 percent approximately for each one degrees Centigrade in average temperature rise of drying air, regardless of the fan operation methods. Therefore, the average temperature rise of drying air had a little effect on drymatter loss. 9. Drymatter loss increase ranged from 50 to 78 percent approximately for each 2 percent increase in initial moisture content, in the range of 18 to 24 percent moisture. 10. The intermittent fan operation: showed about 40 to 50 percent increase in drymatter loss as compared with the continuous fan operation and the increasing rate was higher at high level of initial moisture and average temperature rise.11. Year-to-year weather conditions had a little effect on required drying time and drymatter loss.12. The equations for estimating time required to dry top layer to 16 and 1536 wet basis and drymatter loss were derived as functions of the performance factors. by the least square method.13. Minimum airflow rates based on 0.5 percent drymatter loss were estimated.Minimum airflow rates for the intermittent fan operation were approximately 1.5 to 1.8 times as much as compared with the continuous fan operation, but a few differences among year-to-year.14. Required fan horsepower and energy for the intermittent fan operation were3. 7 and 1. 5 times respectively as much as compared with the continuous fan operation.15. The continuous fan operation may be more effective than the intermittent fan operation considering overdrying, fan horsepower requirements, and energy use.16. A method for estimating the required collection area of flat-plate solar collector using average temperature rise and airflow rate was presented.

• Korean Journal of Food Science and Technology
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• v.27 no.3
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• pp.358-364
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• 1995

In order to determine the moisture content level for safe storage of wild vegetables, drying characteristics and water vapor sorption characteristics of four vegetables, i.e., zucchini slice, sweet potato stem, taro stem, and platycodon, were investigated. The drying curves of these vegetables were consisted of three characteristic stages which were the initial settling down period, the constant drying rate period, and the falling drying rate period. And the falling rate period of the vegetables showed 2 or 3 parts of falling rate. All of the falling rate curves of the vegetables showed upwardly convex shape which is known as a characteristic pattern for the drying of fibrous food materials. The critical moisture contents of the vegetables were $8.29{\sim}9.75,\;10.40{\sim}15.08,\;9.51{\sim}14.52\;and\;3.29{\sim}3.56g\;H_2O/g$ dry solids for zucchini slice, sweet potato stem, taro stem, and platycodon, respectively. Activation energy values of drying rate during falling rate period were 2.30, 2.11, 4.97, and 2.80 kcal/mol for zucchini slice, sweet potato stem, taro stem, and platycodon respectively. The BET monolayer moisture contents of the vegetables were $10.05{\sim}13.59,\;9.49{\sim}12.69,\;9.50{\sim}16.48\;and\;5.01{\sim}5.44g\;H_2O/g$ dry solids for zucchini slice, sweet potato stem, taro stem, and platycodon, respectively. And these values were found to be very compatible with the values of the critical moisture content. Consequently, it was found that the moisture of these vegetables should be removed below the BET monolayer moisture content or below the critical moisture content for the long term storage.

• Journal of Forest and Environmental Science
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• v.11 no.1
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• pp.50-60
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• 1995

This study was carried out to estimate drying schedules of Larix Leptolepis and Pinus koraiensis by oven-drying at $100^{\circ}C$ which aimed to elucidate the characteristics such as current moisture content, drying process. initial check, collapse, internal check and drying rate during drying following each board thickness (2, 3. 4, 5, 6cm). the results were summerized as follows; Current moisture content of each board showed a rapid drying curve with the decrease of board thickness. At 20% moisture content, the drying rate of Larix leptolepis was higher than that of Pinus koraiensis and the drying rate of boards was lower with the increase of board thickness. From the estimated drying schedules. the initial conditions of drying of Larix leptolepis had to be milder than those of Pinus koraiensis and the boards thickness of 5cm, 6cm had to be most mild conditions.

• Journal of Biosystems Engineering
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• v.7 no.1
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• pp.42-52
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• 1982

This study was intended to develop a cost function for the natural air in-bin drying: system which could lead to an optimization of the drying system cost. Based on the cost function developed, a series of simulated drying tests were conducted with 10-year weather data (1970~1979) for 7 different regions by applying an appropriate levels of system factors. System performance factors treated in this study were initial moisture content, airflow rate, bin diameter and grain depth. An optimization procedure to find the least cost system was developed as follows: First, the worst year of the past decade was determined in consideration of the dryiang time and maximum dry matter loss. Second, the minimum airflow rate for a fixed bin diameter and grain depth was determined. Third, the optimum grain depth was found for the minimum airflow rate with different initial moisture contents and bin diameters. The results obtained in this study are summarized as follows: 1. The optimization procedure developed in this study was able to reduce the time and efforts significantly. 2. Optimum values of drying parameters including airflow rate, grain depth, and fan size were determined for different initial moisture contents and bin diameters in each region. The results are shown in Tables 3 to 9. 3. Optimum grain depths decreased as the initial moisture content and airflow rate increased. 4. Drying time for the least cost system should be reduced with higher initial moisture content and lower drying potential to prevent grain spoilage. 5. The fixed cost was 65 to 75 percent of the total system cost and the variable cost was 25 to 35 percent. To reduce the fixed cost it is desirable to use a drying bin 2 or 3 times a year.