農業気象
Online ISSN : 1881-0136
Print ISSN : 0021-8588
ISSN-L : 0021-8588
28 巻, 4 号
選択された号の論文の5件中1~5を表示しています
  • 武智 修, 長谷場 徹也
    1973 年 28 巻 4 号 p. 213-221
    発行日: 1973/03/15
    公開日: 2010/02/26
    ジャーナル フリー
    Fundamental analyses and some experiments regarding to water-vapor transfer by foced convection over a wetted leaf-shaped plane surface were made.
    In general, for a leaf-shaped plate, local water-vapor transfer coefficient (Dx) which is a function of wind velocity (u) and distance (x) over the surface from the leading edge in the direction of air-flow is written as follows:
    Dx=Bum2x-n2,
    where, B is a numerical coefficient affected by the shape of the plate, its relative position to wind, natures of air-flow and the boundary-layer, the vapor-concentration distribution over the surface, properties of air and so on; m1 and n1 are exponents related to the structure of the boundary-layer, respectively.
    Water-vapor concentration departure (ΔCx) of the surface from the air outside the boundary-layer is generally expressed as follows;
    ΔCx=Co+bu-m2xn2,
    where, b is a numerical coefficient and Co is a constant. When the temperature of the leading edge of the plate is identical to the air temperature, Co is the saturation deficit of air in vapor-concentration.
    A local evaporation-rate is obtained as the product of the local values of vapor transfer coefficient and vapor-concentration departure.
    Then, the relationships between a local and the average values of transfer coefficient, concentration departure and evaporation-rate were theoretically analysed and the effect of the surface-temperature distribution in the air-flow direction upon the convection vapor transfer coefficients was experimentally examined.
    I. For the plane-surface with the above described transfer coefficient and the distribution of vapor-concentration departure, each correction factor for obtaining the average value of transfer coefficient, concentration departure or evaporation-rate from each local value was calculated. These results are shown in figures (Figs. 1, 2-A and 3). For example, the correction factor of vapor transfer coefficient at the point where the distance from the leading edge in the air-flow direction is 40% of the surface dimension are 1.26 and 1.04 for laminar and turbulent boundary-layer, respectively.
    Further, the positions where a local value coincided with the average value for each quantity were derived. The distance of the position where a local vapor-concentration departure agrees with its average is about 40% of the surface dimension from the leading edge in the flow direction.
    The position for evaporation-rate is complicated as it is related to air-temperature, humidity, wind velocity, surface dimension and temperature departure of the surface from air. However, under moderate air conditions local evaporation-rates at positions whose distance from the leading edge being between about 26 and 30% of the surface-dimension in the flow direction agrees with the average rate for a flat leaf.
    II. Three representations of average evaporation-rate were shown in the cases of using (i) both local values of transfer coefficient and vapor-concentration departure, (ii) the average transfer coefficient and a local concentration departure, (iii) both average values of transfer coefficient and concentration departure.
  • 1973 年 28 巻 4 号 p. 222
    発行日: 1973/03/15
    公開日: 2010/02/25
    ジャーナル フリー
  • 3. 自然換気による暖房負荷
    岡田 益己, 高倉 直
    1973 年 28 巻 4 号 p. 223-230
    発行日: 1973/03/15
    公開日: 2010/02/25
    ジャーナル フリー
    温室のすきま風による自然換気量を推定するために, 理論的考察から, 2つの実験定数をもつ経験式を導き出した。この式は外部風速と温室内外の温度差の関数である。2つの定数は実験的に求められ, さらにこの式が他の温室にも適用できることを証明した。
    自然換気による伝熱係数は, 顕熱伝達に潜熱伝達を加味して決定された。この過程で潜熱による伝熱が大きいことが認められた。
  • 三原 義秋, 古牧 弘
    1973 年 28 巻 4 号 p. 231-236
    発行日: 1973/03/15
    公開日: 2010/02/25
    ジャーナル フリー
    Fog and fan method, a new evaporative cooling method of greenhouse has been developed.
    For evaporative cooling, not only the volume of water to evaporate but also the voiume of fresh air wihch is taken into the greenhouse is one of the most important factors to be consdered. In pad and fan method, water spray and resulting evaporation are occured at the pad installed at the greenhouse wall which forms a large resistance for the air flow through the pad. In the present method, fine water droplets are sprayed in the greenhouse directly and evaporation takes place simultaneously in the greenhouse. Therefore, there is no resistance for intake air flow and a fan with considerably smaller capacity will be able to produce the same flow rate. Furthermore, horizontal variation of air temperature will be smaller.
    In the present method, droplets must de small enough to evaporate completely before they reach the floor, when nozzles are arranged at 3m height dry bulb temperature is 30.0°C and relative humidity is 80% in the greenhouse, droplets whose diameters are smaller than 88 microns can evaporate completely before they reach the floor. In order to generate fine droplets, the authors developed a new impaction nozzle. This nozzle is made of plastics and designed to be used at rather high pressures, 5-20kg/cm2.
    The generated droplet diameter becomes smaller as the pressure increases and a mode of diameter distribution exists in the range between 30 and 40 microns at the pressure of 10kg/cm2. Relative frequency of droplet diameters at three different pressures is shown in Fig. 2.
    A field experiment has been conducted using a seven-spanned greenhouse (49×42). Air space under the single span of the east end is separated by the polyethylene film from the other and is installed by 30 nozzles and 2 fans. The other is installed by six pairs of pad and fan system, although their capacities are too small to cool the rest greenhouse space. Results of cooling are shown in Figs. 4, 5 and 6. Air temperature in the fog and fan compartment is always lower than the outside air temperature, and is lower about 5°C than that of pad and fan compartment at noon. The horizontal variation of air temperature in the fog and fan compartment is within 1.1°C. It is remarkably small comparing with that of pad and fan compartment. Total volume of sprayed water is 3.0kg/min, and the floor area of the compartment is 280m2. Then, the volume of sprayed water per unit floor area is 10.7g/m2min.
    This fog and fan system can be installed easily and inexpensively at conventional greenhouses.
  • 固形燃料による燃焼法の昇温効果
    小中 原実, 渡辺 康夫, 中川 行夫
    1973 年 28 巻 4 号 p. 237-243
    発行日: 1973/03/15
    公開日: 2010/02/25
    ジャーナル フリー
    カンキツ園を対象として開発された固形燃料を用い, その燃焼特性や燃焼量と昇温効果との関係などを明らかにするために実験を行なった。
    (1) 固形燃料は20cm×8cm×6cmのレンガ状で, 1個の重量は750gであるが, これを2個重ねて1組として燃焼させる。燃料素材は石油コークスで, 発熱量は7,000Kcal/Kg, 燃焼盛期に達してからの燃焼時間は4~6時間程度である。
    (2) 燃焼量を増すにしたがって昇温効果は増大するが, 燃焼量と樹冠内の昇温効果との間には次の回帰式が求められた。
    Q=88.8T1.2+104.8
    Q=100.7T0.5+29.7
    ただしT1.2およびT0.5は, それぞれ樹冠中央部の高さ1.2mおよび0.5mにおける昇温効果であり, Qは10a当たりの燃焼量 (Kg) である。
    また昇温効果は粗植園よりも密植ぎみで, 葉による密閉度の高い成木園のほうが昇温効果が大きい。さらに昇温効果は気温よりも葉温のほうが大きく, 燃焼量が3~4.5Kg/Treeのとき, 樹冠内1m付近で気温の2~6倍に達した。
    (3) 燃焼量3Kg/Treeのときに放射量の分布をみると, 0.1Cal/cm2・minの強さの放射は0.5mにしか達しない。
    (4) ha当たりの発熱量を一定にして固形燃料とリターンスタック型ヒーターの昇温効果を比較すると, 前者は後者の1.6~4倍の昇温効果がある。
    (5) 固形燃料の燃焼ガス中に含まれる亜硫酸ガスの濃度は0.01~0.05ppmであり, 一酸化炭素は煉炭なみである。
    (6) 10a当たりの防除労力をリターンスタック型ヒーターと比較すると固形燃料のほうが配置労力で3倍, 点労力では9倍の労力を必要とする。
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