 Heat current

A heat current is the rate of heat transfer across a specified oriented boundary, $\dot{Q}$, measured in watts. For a heat flux field $\mathbf{q}$ and outward unit normal vector $\mathbf{n}$, the outward heat current through a surface isThe sign convention matters: outward and inward currents for the same physical transfer have opposite signs.

A uniform normal heat flux $100\mathrm{W}{\mathrm{m}}^{-2}$ through $0.02{\mathrm{m}}^2$ gives a heat current of $2\mathrm{W}$. Maintaining it for $30\mathrm{s}$ transfers $60\mathrm{J}$. In steady one-dimensional thermal conduction without internal sources, the current is constant along a bar even if changing cross-sectional area makes the local heat flux vary. This separates a whole-path transport rate from its concentration over a surface.

Heat current, also known as thermal current, refers to the rate at which heat energy is transferred from one location to another, typically measured in watts (W). It describes the flow of thermal energy due to a temperature difference between two bodies or regions. Heat current can occur through various mechanisms, including conduction, convection, and radiation: 1. **Conduction**: Heat is transferred through direct contact between materials, where differing temperatures cause heat to flow from the hotter object to the cooler one.