農耕地における熱的現象の模型実験

(3) 温室外表面からの顕熱伝達に及ぼす防風垣の効果

抄録

In order to make clear the influnce of a shelter-hedg on the sensible heat transfer from the surface of a greenhouse, experiments were carried out in field and in a wind tunnel, respectively.
The geometries of the greenhouse and the shelter-hedge are shown in Fig. 1. Similarity problem between field measurement and model test was examined by using the data of heat transfer at the outersurface of greenhouses which were protected from wind by the shelter-hedge. The results of the model test in the wind tunnel were in well accordance with those from field measurements (Fig. 3).
The effects of shelter-hedge on sensible heat transfer from the greenhouse were studied more minutely by using a model house in the wind tunnel. The results obtained are summerized as follows:
1) The average heat transfer coefficients of greenhouses with and without the shelter-hedge were calculated from eq. 5, respectively. Fig. 4 indicates the wind dependence of h_F/h_o (where h_F and h_o denote respectively the average heat transfer coefficients for greenhouses with and without the shelter-hedge).
The ratio h_F/h_o decreased firstly with wind velocity, reached the minimum at wind velocity of 2m/sec, increased secondary with wind velocity and became nearly constant in the wind range over 8m/sec.
2) The experiments were carried out under conditions that x=1·C, V_N=3.7 and 12.8m/sec and CL=60 and 50% (where z denotes the distance between the greenhouse and the shelter-hedge, C the height of greenhouse, V_N the wind velocity and CL the closeness of shlter-hedge) to find out the influence of height of shelter-hedge upon the heat transfer from the greenhouse. Experimental results indicate that the shelter-hedge higher than that of greenhouse is more effective from the standpoint of greenhouse heating (Fig. 5).
3) The infuluence of shelter-hedge on the heat transfer from the greenhouse was found to change with the distance between the greenhouse and the shelter-hedge, as can be seen in Fig. 6. These relations were approximated by concave curves. The minimum value of ratio h_F/h_o was found in the range from x=2·H to x=3·H.