冻融作用对系统与环境间能量交换的影响

Impact of Freezing and Thawing on Energy Exchange Between the System and Environment

通过求解古典Neumann问题 ,研究土壤在冻结和融化过程的热交换特征 ,从理论上分析了冻融作用对系统与环境间能量交换的影响 .以草炭亚粘土和亚粘土为例 ,计算了广泛环境条件下的冻融作用对系统温度变化和与环境间热交换的影响 .结果表明 ,冻融作用使相应过程表层温度梯度加大 。

On the basis of the solution of the Neumann problem, the surface thermal exchange between environment and the systeminvolved and the temperature gradient inthe range of 0<\%x\%<\%ξ\% are given, where \%x\% is variable of a depth and \%ξ\% is depth of active layer. Comparedwith the problem without phase change, the freezing or thawing process increasesthe thermal exchange between environment and the system and the temperature gradient in the range of 0<\%x<ξ\%. \ \ The classic Neumann problem in freezing and unfreezing regions are expressed in Equations (5) ～ (7). \ \ The energy equilibriumexpressions at thefreezing and thawing front and their combining expression are Equations (8) and (9). The solutions of the problem in the freezing and unfreezing regioncan be expressed as Equations (18) and (19). where \%β\% is determined by Equation (26). The thermal flow at\%x\%=0is given by Equation (23). \ \ When the system phase does not occur, however, the solution of the problem is given by Equation (11). Meanwhile, the thermal flow at\%x\%=0 is representedby Equation (14). Hence, the ratio of thermal exchange between the system and environment (γ) can be expressed as Equation (25). \ \ For demonstrating theimpact of freezing and thawing process on thermal exchange between the system and environment, parameters β and γ(the ratio of thermal exchange between the system and environment during freezing and thawing with phase change andduring temperature rising and lowering without phase change) are computed. The computation is performed with several ground soil dataduring freezing and thawing. The computationresults show thatγdecreases with system temperature rising and environmental temperature loweringwhen temperatures of the system and environment keep constant in the process of soil freezing; And that γ decreases with system temperature lowering and environmental temperature rising when temperatures of the systemand environment keep constantin the process of soil thawing,; And γincreases with moisture content rising in ground soilor with freezing and thawing speed lowering. The characteristicsof energy exchange between the system and environment during ground soil freezing and thawing process maybe influence climate′sformation and change under naturalconditions at a regional orglobalscale