Abstract
The method to regulate the heat environment in the root zones of crops by the establishment of heating equipment in soil is used widely.
This paper is concerned with the dimensionless term (HTF) corresponding to heat transfer coefficients on soil surface which affect the temperature distribution in a ridge. The results of discussion are as follows.
1) It shows that the values of HTF on soil surface have a tendency, that is, 3 (HTF at the middle of ridge surface) : 3/2 (end of ridge surface) : 1 (top of ridge surface) .
2) HTFs are calculated from natural convection and radiation classifying the heat transfer phenomena. From the results, it is proved that HTF by radiation is greater than by natural convection.
3) Noctural radiation calculated using HTF by radiation is roughly in accord with measurement in field.
4) It brings the HTF of the ridge top closer to the sum of HTF by natural convection and by radiation.
5) As the evaporation of soil surface water has an effect on the heat transfer, a term of evaporation should be added to the heat transfer coefficient.
