Varmeflow

Varmeflow, often referred to as heat flow or thermal flux, is the rate at which thermal energy is transferred between bodies or regions due to a temperature difference. In engineering contexts it is expressed as a total rate Q, measured in watts (W), or as heat flux q'' per unit area, measured in watts per square meter (W/m^2). The sign convention usually assigns positive values to heat moving from hotter to cooler regions.

The primary mechanisms are conduction, convection, and radiation. In conduction through solids, Fourier's law relates the heat flux to the temperature gradient: q'' = -k dT/dx, where k is the material's thermal conductivity (W/m·K). For a slab of thickness Δx and area A, the total heat flow is Q = -k A ΔT/Δx. In fluids, convection involves fluid motion; radiation follows the Stefan-Boltzmann law.

In transient problems, the material's thermal diffusivity α = k/(ρ c) governs how temperature evolves in time, via the heat equation ∂T/∂t = α ∇^2 T. Practical analysis often uses the concept of thermal resistance to simplify series conduction.

Applications include building insulation, electronic device cooling, automotive thermal management, and industrial process design. Understanding varmeflow is essential for energy efficiency, safety, and performance in systems where temperature differences drive energy transfer.