Ground Heat Transfer From a Varying Line Source With Seasonal Temperature Fluctuations

In this paper, transient heat conduction between a line heat source and a semi-infinite medium (representing a foundation of a power transmission tower and the surrounding ground) is analyzed numerically and experimentally. The tower foundation is represented by a metal rod buried in a semi-infinite medium. Using an experimental test cell with a data acquisition system, heat transfer and temperature measurements within the domain are collected. The experimental studies are first applied to unidirectional heat conduction, wherein the analytical solutions are compared against measured temperature responses. Then two transient heat transfer cases are studied: one case with a steady heat input provided by an electrical heater and another with sinusoidal temperature variations achieved by temperature-controlled fluid in a heat exchanger. The analysis shows that a metal tower footing has significant thermal effects on the temperature response of the local half-space around the footing in the foundation. This thermal effect varies with time, as well as spatially at different positions around the tower footing. In particular, measured results from the case of sinusoidal temperature variations show that the tower footing introduces additional temperature increases in the “summer” periods and temperature decreases in the “winter” periods.