熱傳導係數之溫度相關性對土壤溫度的效應

Effects on Soil Temperature Due to Temperature-Dependent Thermal Conductivity

方文村(Wen-Tsun Fang) ； 簡傳彬(Chuan-Pin Chien)

《農業工程學報》 55卷3期 (2009/09) Pp. 30-41

https://doi.org/10.29974/JTAE.200909.0003

摘要

土壤熱傳導係數通常隨溫度之變化而改變，而正確的土壤熱傳導係數可以幫助數值模式對土壤熱量傳遞問題獲得正確之預測。由Sepaskhah & Boersma (1979)的實驗結果發現土壤溫度由25℃增加至45℃時，低合水量之土壤的熱傳導係數有顯著的增加，這樣的現象可以顯示在土壤熱量傳遞之間題中使用一個固定的土壤熱傳導係數可能會因該問題所存在之溫度範圍較大而導致可觀的計算誤差。
本研究利用孔隙物質中的一維熱量傳遞模式之控制方程式，忽略熱對流效應，模擬表層土壤在受不同週期氣溫變化下，表層土壤溫度及熱通量之變化情形。參考一般固體熱傳現象問題所使用之熱傳導係數與溫度間的線性關係（參考如Goodman, 1961）來設定土壤熱傳導係數及溫度之數學關係，此關係可以一線性變化參數β來表示。藉由套裝軟體Mathematica 5.1解得不同邊界變化條件下之數值解，吾人可以發現當β值越大，在相同時間下，土壤原來的起始溫度越容易被抬昇，值得在土壤環境之長期熱平衡數值模擬之研究上注意。

關鍵字

土壤熱傳導係數 ； 熱量傳遞 ； 線性變化參數

並列摘要

Soil thermal conductivity usually changes according to temperature. An accurate soil thermal conductivity can help numerical models to obtain accurate predictions in soil heat transfer problems. From the experiment results by Sepaskhah & Boersma (1979), it is found that thermal conductivity for soils with low water contents can increase significantly when the soil temperature is from 25℃ up to 45℃. This shows that a constant soil thermal conductivity used in the problems for numerical soil heat transfer with wide temperature range might cause significant calculation errors.
This study uses the one-dimensional governing equation of heat transfer for porous media with neglect of heat convection. The simulation is performed for soil temperature and heat flux changes in surface layer due to various periodical air temperature. Linear relationship between thermal conductivity and temperature which is commonly used in the heat transfer problems for solids (of. Goodman, 1961) is assumed to be the one for the soils of concerns. The relationship is expressed in terms of, β which is the linear relationship parameter. This study uses Mathematica 5.1 to obtain the numerical solutions for various boundary conditions. It is found that the initial temperature of the soil with larger β will be raised higher at same time duration. This is worthy of notices in the numerical simulation for long-range heat balance in soil environments.

並列關鍵字

Soil thermal conductivity ； Heat transfer ； Linear relationship parameter