• Journal of Bio-Environment Control
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• v.15 no.3
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• pp.231-238
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• 2006

The physical properties of seven perlites different in particle size distribution were investigated to develop perlite bag culture in Korea. Particle sizes of 1.0-2.8mm and larger than 2.8 mm were rather evenly distributed in S-1 (1.2-5 mm), S-2 (0.15-5 mm) and S-5 (parat No.1). Larger particles were less in S-3 (1-3 mm), S-4 (Parat No.2), S-6 (OTAVI) and S-7 (Agroperl B-3). S-4, S-6 and S-7 contained lots of particles less than 1 mm in size. Total porosity was similar among substrates with the value of $59{\sim}62%$. Container capacity was between 35-40% regardless of substrates except in S-2 with 27.7%. Water content, which was about 60% at 0 kPa, was decreased sharply at 4.90 kPa regardless of substrates, which meant the easily available water was plenty in any kind of perlite tested. Substrates, S-1, S-2 and S-3 with different particle size distribution, were investigated to evaluate for perlite bag culture. Six tomatoes (Licopersicon esculentum Mill. cv. Rokkusanmaru) were planted in a perlite bag of 40 liters with the dimension of 120cm in length and 34cm in width. The amount of nutrient solution supplied and its drainage dependent on daily integrated radiation didn't show any regular trend during the growth. Roots in the bag were distributed evenly in S-1 and S-2 than in S-3. Plant grown in S-1 showed the highest total and marketable yield of 8,628 and 7,759 kg/10a, respectively. The number of small size fruits and malformed fruits were more in S-3. Consequently, S-1 with the particle size distribution of 1.2-5 mm is suggested as desirable substrate for perlite bag culture.

• Journal of Bio-Environment Control
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• v.22 no.2
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• pp.138-145
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• 2013

In order to develop the efficient control algorithm of the two-fluid fogging system, cooling experiments for the many different types of fogging cycles were conducted in tomato greenhouses. It showed that the cooling effect was 1.2 to $4.0^{\circ}C$ and the cooling efficiency was 8.2 to 32.9% on average. The cooling efficiency with fogging interval was highest in the case of the fogging cycle of 90 seconds. The cooling efficiency showed a tendency to increase as the fogging time increased and the stopping time decreased. As the spray rate of fog in the two-fluid fogging system increased, there was a tendency for the cooling efficiency to improve. However, as the inside air approaches its saturation level, even though the spray rate of fog increases, it does not lead to further evaporation. Thus, it can be inferred that increasing the spray rate of fog before the inside air reaches the saturation level could make higher the cooling efficiency. As cooling efficiency increases, the saturation deficit of inside air decreased and the difference between absolute humidity of inside and outside air increased. The more fog evaporated, the difference between absolute humidity of inside and outside air tended to increase and as the result, the discharge of vapor due to ventilation occurs more easily, which again lead to an increase in the evaporation rate and ultimately increase in the cooling efficiency. Regression analysis result on the saturation deficit of inside air showed that the fogging time needed to change of saturation deficit of $10g{\cdot}kg^{-1}$ was 120 seconds and stopping time was 60 seconds. But in order to decrease the amplitude of temperature and to increase the cooling efficiency, the fluctuation range of saturation deficit was set to $5g{\cdot}kg^{-1}$ and we decided that the fogging-stopping time of 60-30 seconds was more appropriate. Control types of two-fluid fogging systems were classified as computer control or simple control, and their control algorithms were derived. We recommend that if the two-fluid fogging system is controlled by manipulating only the set point of temperature, humidity, and on-off time, it would be best to set up the on-off time at 60-30 seconds in time control, the lower limit of air temperature at 30 to $32^{\circ}C$ and the upper limit of relative humidity at 85 to 90%.