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  ## 傅立叶定律
  
  ### 微分形式
  
  ${\displaystyle {\overrightarrow {q}}=-k{\nabla }T}$
  
  ${\displaystyle {\overrightarrow {q}}}$ 是热通量密度，单位W·m−2
  ${\displaystyle {\big .}k{\big .}}$ 是这种材料的热导率，单位W·m−1·K−1
  ${\displaystyle {\big .}\nabla T{\big .}}$ 是温度梯度，单位K·m−1
  
  ${\displaystyle q_{x}=-k{\frac {dT}{dx}}}$
  
  ### 积分形式
  
  ${\displaystyle P={\frac {\partial Q}{\partial t}}=-k\oint _{S}{{\overrightarrow {\nabla }}T\cdot \,{\overrightarrow {dA}}}}$
  
  • ${\displaystyle {\big .}P={\frac {\partial Q}{\partial t}}{\big .}}$ 是热传导功率，即单位时间通过面积S的热量，单位W，而
  • ${\displaystyle {\overrightarrow {dA}}}$ 是面元矢量，单位m2
  
  ${\displaystyle {\big .}P={\frac {\Delta Q}{\Delta t}}=-kA{\frac {\Delta T}{\Delta x}}}$
  
  A 是介质的截面积，
  ${\displaystyle \Delta T}$ 是两端温差，
  ${\displaystyle \Delta x}$ 是两端距离。
  
  ## 热导
  
  ${\displaystyle {\big .}U={\frac {kA}{\Delta x}},\quad }$
  
  ${\displaystyle {\big .}P={\frac {\Delta Q}{\Delta t}}=U\,(-\Delta T).}$
  
  ${\displaystyle {\big .}R={\frac {1}{U}}={\frac {\Delta x}{kA}}={\frac {-\Delta T}{P}}.}$
  
  ${\displaystyle {\big .}{\frac {1}{U}}={\frac {1}{U_{1}}}+{\frac {1}{U_{2}}}+{\frac {1}{U_{3}}}+\cdots }$
  
  ${\displaystyle {\big .}P={\frac {\Delta Q}{\Delta t}}={\frac {A\,(-\Delta T)}{{\frac {\Delta x_{1}}{k_{1}}}+{\frac {\Delta x_{2}}{k_{2}}}+{\frac {\Delta x_{3}}{k_{3}}}+\cdots }}.}$
  
  ## 相關條目
  
  This article uses material from the Wikipedia article "热传导", which is released under the Creative Commons Attribution-Share-Alike License 3.0. There is a list of all authors in Wikipedia
  
  ### Electrical Engineering
  
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