Before revision: Infinitely long plane wall These first Heisler–Gröber charts were based upon the first term of the exact Fourier series solution for an infinite plane wall: where Ti is the initial uniform temperature of the slab, T∞ is the constant environmental temperature imposed at the boundary, x is the location in the plane wall, λn is (n + 1/2) , and α is thermal diffusivity.
After revision: Infinitely long plane wall These first Heisler–Gröber charts were based upon the first term of the exact Fourier series solution for an infinite plane wall: where Ti is the initial uniform temperature of the slab, T∞ is the constant environmental temperature imposed at the boundary, x is the location in the plane wall, λ is the root of λ * tan λ = Bi , and α is thermal diffusivity.