When a cold slab travels at speed U through a liquid metal bath, it freezes out metal at the rate of V. It is shown that the problem of determining the heat-transfer coefficient h at the interface of the liquid and solid phases is equivalent—under certain simplifying assumptions—to solving the (time-independent) wave equation in a sector. For the case of α ≡ arctan V/U < π/4, treated in the present paper, the problem is reduced, through suitable changes of variables and a Fourier sine transform, to the solution of Dirichlet’s problem for the Laplace equation. The temperature field T(X, Y) is expressed as an inverse sine transform, involving a single integration (in the transform variable). One finds that at the entrance cross section to the bath, X = 0, the heat-transfer coefficient is zero, then it rapidly approaches the asymptotic (“fully developed”) value h = γcV cos α. The heat-transfer coefficient is determined in closed form for α = π/6, π/4, and asymptotic expressions of it are derived for very small and very large distances from the origin when α is arbitrary (0 < α < π/4). Numerical evaluation of the heat-transfer coefficient at the solid-liquid interface is carried out for α = π/36, π/12, π/4. Plots of the temperature field T for these angles are also shown, along rays ϑ = π/6, π/3, π/2 to the horizontal.