Analysis of Phase Change Materials (PCMs) Used for Borehole Fill Materials

Abstract

PCMs used as borehole fill materials were selected and freeze curve, fusion temperature as well as latent heat of fusion of each material were obtained according to Differential scanning calorimetry (DSC) test. One-dimensional solidification and melting of a circular tube with uniform volumetric energy generation is examined analytically. Analytic solutions are obtained using a quasi-steady approximation. Phase change time of mixed backfill materials are 7.97 h (in summer) and 9.64 h (in winter), restoration time of which are 8.30 h (in summer) and 8.80 h ( in winter) respectively, results indicated phase changing process would accomplish completely during system operating. Therefore, Heat/ cold output for a single borehole would increase 33.6% / 19.7% after PCMs are added to backfill materials, which helps to decrease borehole number for the fixed energy demand.