density btu ft material lb cu ft hr ft sup 2 u00b0 f ______________________________________soil dry 64 0 0 1 0 3soil average 0 3 0 5soil soaked 0 5 1 5clay soil dry 0 5clay soil moist 0 6 0 9clay soil wet to soaked 1 0 1 5sandy soil dry 95 0 0 2 0 65sandy soil moist 102 0 0 65 1 2sandy soil wet to soaked 1 2 2 4______________________________________ obviously from the above table the drying out of the soil as occurs during drouths especially with high water using crops like corn generally reduces the rate of heat transfer between the soil and the buried tube and on the average the heat transfer is increased by a factor of 3 and only a third as much area of tubes is required roughly when soil is wet than when it is dry this is an enormous advantage for heat transfer between the soil and heat buried tubes also it is evident that the low heat transfer coefficients k of soil will be counterbalanced by a reduction of the distance the heat has to be transferred before the area it is transferred through is greatly increased in other words heat transferred per hour is not only proportional to the heat transfer constant k but also the distance from the tube where the cross sectional area the heat has to be transferred through greatly increases this is the advantage of the small tube where the heat from the.