Summary
In order to dry radish in cold season, a circulatory dehumidifying drying system in a greenhouse was developed and the water and heat balances in greenhouse were investigated. The results are summarized as follows:HomePage
(1) The amount of dehumidified water, M1, reached at maxmimum of 2.0kg/h in the initial stage of the drying period, but it decreased step by step, as the vaporized water from the radish was decreased in the latter stage of the drying period. The calculated average value was found to be about 0.8kg/h. The relationship between M1 in the region of 0.7-2.0kg/h and the consumptive electric power of the dehumidifier, W1, was estimated by the following equation.
W1 = 0.11 exp(6.379M1)
(2) The amount of dew condensation, M2, inside the greenhouse changed with absolute humidity. The calculated maximum and average values were 3.2kg/h, 0.86kg/h respectively. The relationship between M2 and absolute humidity was estimated by the following equation, and the moisture transfer coefficient, Kw, was assumed to be 13.8kg/(m2.h(kg/kg')).
M2 = 933.3 ( Xin - Xcov )
Xin : Absolute humidity inside the greenhouse
Xcov : Absolute humidity at the surface temperature of covering material
(3) The relationship between M2 and dew point temperature,TD, inside greenhouse, surface temperature of covering material, TCOV, was investigated and derived equation is given as follows:
M2 = Kw.2.14 x l0-4(TD - TCOV)(1 + 0.077(TD - TCOV)).As
Consequently, M2 was able to be estimated by measuring of TD and TCOV.
(4) The vaporized water from the radish was nearly equal to M1 + M2, while M1 was nearly equal to M2. The water balance in greenhouse was consisting of these two factors and hardly affected by others. Therefore, it would be suggested that the circulatory dehumidifying drying system in the greenhouse can be used for drying of agricultural products in cold season.
(5) The amount of heat in the greenhouse was mainly charged by solar radiation, Af.Q, and generating heat of the dehumidifier and fan, W1 + W2, but in the night-time, only W1 + W2 remained. Their average values were about 5,000kcal/h, 2,300kcal/h respectively. Although it would be expected that the amount of heat in the greenhouse is more charged by other heat, the amount of other heat was very small.
(6) The amount of heat in the greenhouse was mainly discharged as convective heat transfer, As . q, radiative heat transfer, Af.S, and latent heat transfer, i.M2.As.q maximized at 7,400kcal/h in the day-time and averaged at 1,500kcal/h in the night-time. Af.S was stable at all-time and its average value was 680kcal/h.i.M2 maximized at 1,900kcal/h but was nearly approaching to zero, due to humidity dropping inside the greenhouse in the latter stage of the drying period.
(7) In the heat balance in greenhouse, the amount of heat charged in greenhouse was dependent on Af.Q at 70 percent in the day-tiire and W1 + W2 at 95 percent in the night-time. The amount of heat discharged from the greenhouse was dependent on As.q at more than 60 percent in all-time.
(8) As a great amount of heat was transfered through the covering material of the greenhouse, it would be essential to discuss about more effective covering irethod and iraterial of the greenhouse in order to improve the dehumidifying drying efficiency.