農耕地における熱的現象の模型実験

(4) 温床外表面からの顕熱伝達に及ぼす防風垣の効果

抄録

The effects of a shelter-hedge on sensible heat transfer from the surface of a hotbed were measured about a prototype of hotbeds in field and a model in a wind tunnel. The similarity problem between field measurement and model test was examined by using the data of heat transfer from the outer surface of hotbeds. And some model experiments were carried out to make clear the proper usage of shelter-hedge for the hotbed.
The results obtained are summarized as follows:
(1) Eq. (3) and Eq. (4) were used as a similarity law to compare the results obtained in model tests with those from field measurements. And the results of model test were in well accordance with those from field measurements (Fig. 4).
(2) When the wind direction was perpendicular to a shelter-hedge, the effect of the shelter-hedge on reduction of heat transfer from a hotbed was distinguished. But in the case of the angle of the wind direction to a shelter-hedge was 45deg., the effect decreased extremely (Fig. 4).
(3) The difference between the surface temperature of the hotbed and the air temperature slightly influenced the coefficient of sensible heat transfer under the calm condition. But the influence became negligible under the windy condition (Fig. 5).
(4) The effects of closeness of the shelter-hedges on sensible heat transfer from the outer surface of the hotbed were examined by using the shelter-hedges with closeness of 30, 65 and 80%. The results indicated that the shelter-hedge with closeness of 30% was not useful to diminish the heat transfer. But the shelter-hedges with closeness of 65 and 80% were useful to diminish the heat transfer from the upper surfaces of hotbeds.
(5) When the purpose of the shelter-hedge was to reduce heat transfer from hotbeds, the optimum distance between the shelter-hedge and the hotbed was about four times of the height of the shelter-hedge.