Composite Wall Heat Transfer

Method & assumptions

1. Model up to three solid layers between two fluids. Number layers from side 1 toward side 2; set unused layer thicknesses to zero and retain positive conductivity inputs.
2. R″ = 1/h₁ + Σ(Lᵢ/kᵢ) + 1/h₂; U = 1/R″. Each term uses the same wall area.
3. q″ = U(T₁ − T₂); Q = Aq″. Positive heat flow is from side 1 toward side 2.
4. Subtract q″ times each successive resistance to obtain surface and interface temperatures. Zero-thickness layers have no temperature drop.
5. Assumes steady one-dimensional heat flow, constant properties and perfect layer contact, without heat generation, radiation, air gaps, thermal bridges or phase change. Supply coefficients and conductivities appropriate to the operating conditions.
6. Illustrative inputs are not specified material properties or regulatory U-values. At the defaults, R″ = 1.49 m²·K/W and Q = 134.2282 W.

Sources

• US DOE Fundamentals Handbook: conduction and convection, HT-02 pages 9–10 and 20–22 ↗