Development of a model pile for heat transfer experiments in the centrifuge

Conventional energy piles use embedded plastic pipes to circulate a fluid through solid concrete which enables transfer of heat into, or out of, the ground as required. Such piles are relatively low efficiency owing to the poor conductivity of the concrete in which the pipes are embedded. They are also known to be susceptible to damage during construction and their adoption as a sustainable energy source has, as a result, been limited. A novel method of heat transfer, which is much less susceptible to damage during construction, and has been found in field trials to be more energy efficient, exploits the significantly higher conductivity of water in a rotary augured hollow, cast in-situ, or precast pile. In such a pile the plastic pipes are placed in the water filled central void of the pile. Such an arrangement will lead to the ground around the pile experiencing a lower range of temperature variation compared with standard energy piles and the influence of this effect on pile capacity will be explored. In order to model multiple cycles of temperature variation to which the ground around a prototype pile may be subjected it is necessary design experimental apparatus that is capable of rapid heating and cooling and with high thermal conductivity materials. The paper will describe the design of a model pile which incorporates an immersed heating element capable of bringing the pile temperature to a specific maximum value and a means of quickly purging the heated water to return the pile temperature to the desired minimum value whilst the pile carries a constant axial load in the centrifuge.