The steady-state rate of heat loss from a horizontal insulated hot pipe (with a surface temperature Th) enclosed in a relatively cold rectangular trench (with a surface temperature Tc), filled with a single size of one of three different sizes of hollow plastic spheres, was examined for constant values of (Th - Tc). The procedure was repeated successively with each of the other sizes Of spheres. This arrangement was chosen to simulate a district-heating pipeline in an insulated, filled trench. By employing spheres having a diameter of 10 mm (0.4 in), the optimal configuration of the pipe (i.e., with the least rate of thermal losses) located at a displacement ratio of 0.01 (i.e., with the pipe in the upper region of the trench). By adopting such an arrangement, an improvement of ~ 4% in the overall thermal resistance of the system was achieved compared with that for the pipe at the center of the trench. Such an improvement can be gained with no extra constructional costs, and the savings should be significant over the lifetime of the district heating system.

Units: Dual