Wärmestromdifferenz

Wärmestromdifferenz is a term used in thermodynamics and heat transfer to describe the difference between heat flow rates at two positions or boundaries within a thermal system. It can arise from spatial variation in temperature, material properties, or boundary conditions. In one-dimensional conduction across a finite segment, the local heat flux q(x) is given by Fourier's law q = -k ∂T/∂x; the Wärmestromdifferenz across a segment from x1 to x2 is Δq = q(x2) − q(x1). If the material is homogeneous and in steady state with no internal heat sources, Δq is zero, reflecting a constant heat flux through the segment. Nonzero Wärmestromdifferenz indicates either nonuniform conductivity, internal heat generation, phase changes, or contact resistances at interfaces.

In multilayer or composite structures, different layers can impose thermal resistance at interfaces, leading to a step in heat flux and thus a finite Wärmestromdifferenz across interfaces where contact resistance is relevant. In transient heat transfer, the Wärmestromdifferenz can vary with time as the temperature field evolves, and is closely connected to boundary conditions in the heat equation.

Measuring and managing Wärmestromdifferenz is important in thermal design of buildings, electronics cooling, and industrial processes, where mismatches in heat flow can cause hotspots or thermal stresses. The term is used mainly in German-language texts; in English literature one would often discuss heat flux differences, heat flux discontinuities, or boundary heat flux.