Experimental investigation on the efficiency of the phase change materials for enhancing the thermal performance of energy piles in sandy soils

Abstract

The application of phase change materials (PCMs) is an efficient technique for enhancing the thermal properties of energy piles. In most previously applied studies, paraffin-based materials with low melting temperatures were implemented as PCM to improve energy piles in cold climate conditions. This study explored the efficiency of using lauric acid as a PCM in energy piles by performing small-scale physical model tests under warm climate conditions. Two concrete energy piles with the same diameter of 58 mm and length of 830 mm with PCM and without it were placed in the center of a tank filled with silica sand. The energy piles went through a series of heating tests with the loading temperature (corresponding to the initial temperature) of +10 to +40 °C. To analyze the effect of implementing lauric acid on temperature, and pore water pressure (PWP) distributions in sandy soil, digital thermometers and pore pressure transducers were used in different parts of the inlet side of the model. Results were compared between the two piles with and without PCM in dry and saturated media. The achieved results demonstrate that by adding 1.5% of lauric acid to the energy pile, temperature changes along the pile can be reduced up to 13% in the dry and 10% in the saturated condition. Also, the temperature changes in the soil media could be decreased by up to 5% in dry media. Additionally, the induced excess pore water pressure around the modified energy pile with lauric acid was about 2.14 times lower than the conventional pile. Besides the reduction in the temperature and PWP, the extracted power had an upward trend by increasing the thermal loading. The results revealed that due to the phase transition process, applying a small amount of lauric acid in the energy piles reduces the temperature fluctuations-related responses and could improve the thermal performance of the heat exchange system.