抄録
The characteristics af the water temperature under the canopy of framepaper used for temperature arising were studied. The frame papers with various heat transmissivity were stretched on the shallow ponds of 5 and 10cm depths, and temperatures of water and sub-soil were measured.
On the amplitude of diurnal temperature change of water, the following relation was obtained,
RΔT=1+0.021s⋅T
where, RΔT is the ratio of the amplitude under frame paper with various heat transmissivity T to the calculated amplitude of temperature change caused by air temperature by means of heat transfer, s amplitude of the incident radiation.
The constant (0.021) may generally vary with intensity of heat transport to the above air layer and the thermal properties of water and soil layer, but the variance of the constant will be slightly, because the transport of heat through the frame paper will not change so largely with air conditions and the thermal properties are constant. So above relation will be applicable to the temperature condition in the ordinary hot beds.
The heat transfer at interface of bottom in both the water covered by the frame paper and “free” water was compared. As the frame paper extremely obstructs the heat loss from water to the lower air layer and the disturbance of water layer by air motion, Gr's number becomes very small compared with that of “free”. Consequently, from the following relation, it is expected that heat transfer coefficient interface of the bottom in the covered is very small.
α=a(Pr⋅Gr)1/3, 1/4
where α: heat transfer coefficient, a: constant, Pr: prandtl's number, Gr: Grashof' s number.
When we compute the value of Micrometeorological Charaterristic Index (R=ΣL/ΣB; H. Lettau) at the interface of the bottom of 10cm deep, R becomes -1.5 in the covered pond and 0.53 in the “free”.
