A model is presented for heat transfer from a fluid in laminar flow in
side a buried horizontal pipe. The top surface of the soil in which th
e pipe is buried is horizontal and flat and is kept at a temperature l
ower than the soil and the fluid temperatures. The problem is modelled
as a transient three-dimensional process in cylindrical geometry. The
solution is obtained using a string-intersected-boundary formulation
and a three-level alternating-direction implicit finite difference met
hod. The resulting equations were solved on a CDC Cyber 205 supercompu
ter. The validity of the numerical scheme has been verified by compari
son with an analytical solution for a simplified problem.