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Volume 28, Issue 1
Displaying 1-7 of 7 articles from this issue
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Yuko OGURA1972 Volume 28 Issue 1 Pages 3-10
Published: July 31, 1972
Released on J-STAGE: February 25, 2010
JOURNAL FREE ACCESS -
On the Radiation BalanceAkiyoshi MATSUDA, Tomohisa YANO, Toso CHO1972 Volume 28 Issue 1 Pages 11-17
Published: July 31, 1972
Released on J-STAGE: February 25, 2010
JOURNAL FREE ACCESSMeasurements on the radiation balance in the Tottori Sand Dune were made, especially on the total short-wave radiation, the net radiation and the albedo as a function of the soil moisture ratio. The results were as follows:
1. Continuous observations of the radiation flux components showed that the ratio of the net radiation to the total short-wave radiation, S/(Q+q), varied from 0.38 to 0.65 and 0.48 in average, where Q is the direct short-wave radiation and q is the diffused short-wave radiation. The ratio was generally larger in the cloudy day than in the clear day. In the non-dimensional equation of the radiation balance, S/(Q+q)=(1-a)-F/(Q+q), here a denotes the albedo and F is the effective long-wave radiation, the variations in the term of the left-hand side were affected by those of right-hand side with the weights of the ratio 2:3.
2. According to the results observed in the clear day of August, 1970, both the total short-wave radiation and the net radiation showed the maximum value, 1.22 and 0.68ly/min. respectively, at noon and the ratio of the latter to the former was 55.7%. Also, it was showed that the upward total radiation containing the short-wave radiation at noon was about 0.55ly/min and it was equivalent to 45% of the downward total short-wave radiation
3. The obvious diurnal variations in the albedo were found in the clear day of July through October, as seen from Fig. 5. The value in average was in the range of 26.5-28% and the value of the albedo was higher in the fall than in the Summer. Concerning the relation between the albedo and the moisture ratio, the albedo increased with decreasing of moisture, especially below 3% of soil moisture (Fig. 6 and 7).View full abstractDownload PDF (710K) -
(2) Sensible Heat Transfer from the Outer Surface of the GreenhouseH. TAKAHASHI1972 Volume 28 Issue 1 Pages 19-22
Published: July 31, 1972
Released on J-STAGE: February 25, 2010
JOURNAL FREE ACCESSIn order to make clear heat transfer between in and out vinyl houses, sensible heat transfer coefficient at the outer surface of vinyl houses as shown in Figs. 1 and 2 were determined from Eqs. 1 and 2. Heat transfer experiments were made in a wind tunnel and in a open field, respectively. The similarity of heat transfer between a model and an actual vinyl houses was also discussed theoretically.
The results obtained can be summarized as follows:
(1) The similarity law for heat transfer was found to be somewhat different from those obtained for model experiments of wind regime behind wind-shelter (Eqs. 3 and 4). The discrepancy in heat transfer coefficients obtained respectively from the model and the actual vinyl houses increased as the ratio LM/LN (where LM and LN are respectively the representative scales of model and actual houses) increased (see Fig. 3).
(2) Under conditions that the similarity law for wind regime was applied into model experiments and that the scale of vinyl houses is in the range used here, the sensible heat transfer coefficients obtained from both the experiments are in good agreement with each other (Fig. 4). The results indicate that the value of heat transfer coefficient obtained from model experiments in a wind tunnel may be applicable to analysis the heat transfer of vinyl houses.
(3) Fig. 5 indicates that the heat transfer coefficient at the outer surface of vinyl houses is remarkably influenced by the surface portion in relation to wind. The heat transfer coefficient is larger for the foreward surface portion than for the leeward surface portion. Especially, the heat transfer coefficient was the highest at the front surface portion of R1.View full abstractDownload PDF (533K) -
Mamoru HAGIWARA, Ikuo HORIGUCHI1972 Volume 28 Issue 1 Pages 23-28
Published: July 31, 1972
Released on J-STAGE: February 25, 2010
JOURNAL FREE ACCESSWith recent commercial development of materials, some plastic films and cheese clothes are broadly used in agriculture. These materials are used for the protection of plants against unfavourable climatic conditions, so that it is important to consider the characteristics of heat loss by long-wave radiation. This paper deals with the total transmission of long-wave radiation for some commercial materials; plastic films and cheese clothes.
The radiative exchange of the ambient field between two radiative heating plates, A and B, can be written by eq. (1) (see Fig. 1-a). If the materials (named AM and BM) are inserted into this radiation field, the radiative exchange of the field between AM and BM can be expressed by eq. (2) (see Fig. 1-b). In eq. (2), the terms higher than second order of α and γ are neglected since their effects are small, and if the radiation flux from AM (RAM) is equal to from BM (RBM), the equation can be simplified to eq. (4). From eq. (1) and eq. (4), the transmissivity can be calculated by eq. (5).
The experimental arrangement is shown in Fig. 2. As preliminary experiment, the instrument was tested that the output of the net radiometer was zero when the surface temperature of the plates A and B were the same, and was the radiation flux calculated from the surface temperature of these two plates (see Fig. 3). Moreover, it is necessary to satisfy that the radiation flux from AM is equal to from BM, so that the material was rotated continuously around a fixed net radiometer by an electric motor. To determine the rotation speed of this material, tests were performed by using clear p.v.c., and silver p.v.c., and 20 r.p.m. was chosen as the standard rotation speed (see Fig. 4).
The measured transmission of some materials are shown in table 1. The transmittances for p.v.c., e.v.a. and p.e. 0.1mm thick are 21-25%, 49% and 71-74% respectively. But these values are increased by reducing their thicknesses. The transmittance values of cheese clothes for crop protection are 38-71%. These values are affected with the amount of thread per unit area and the thickness of thread in the cheese clothes.
(p.v.c.=polyvinyl chloride)
(e.v.a.=ethylenevinyl acetate copolymer)
(p.e.=polyethylene)View full abstractDownload PDF (619K) -
Tadashi TAKAKURA1972 Volume 28 Issue 1 Pages 29-38
Published: July 31, 1972
Released on J-STAGE: February 25, 2010
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I. ABE1972 Volume 28 Issue 1 Pages 39-44
Published: July 31, 1972
Released on J-STAGE: February 25, 2010
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T. OIKAWA1972 Volume 28 Issue 1 Pages 45-51
Published: July 31, 1972
Released on J-STAGE: February 25, 2010
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