Experimental study on solar heating system based on heat pipe technology for mitigating subgrade frost heave

Subgrade frost heave is the main reason that affects the safe operation and comfort of trains during the cold season. Solar heating system based on heat pipe technology is a promising method to mitigate the frost heave by raising the subgrade temperature. In this paper, a field experiment was conducted to evaluate the heating performance of the solar heating system based on heat pipe technology in the cold season. In addition, the heat collection performance and stability of the system are compared with other solar heating systems. Finally, its applicability is discussed. Experimental results revealed that the solar heating system based on heat pipe technology can effectively raising the soil temperature and mitigate the frost heave of subgrade. During the experiment period, the soil temperature at the depth of -0.5 m in the experiment site was 5 degrees C higher than that of the comparison site, and the maximum freezing depth was 0.4 m, which was 56 % lower than that of the comparison site. The mean daily temperature of heat collection units (HCUs)fluctuated around 30 degrees C, and the mean daily temperature of the two-phase closed thermosyphons (TPCTs) fluctuated between 15 degrees C and 30 degrees C. The heat transfer efficiency of System 1 and System 2 is greater than 0.5, and the total effective heat transfer during the experiment period is 512 MJ and 283 MJ, respectively, and the heat transfer difference is about 2 times. Compared with other solar heating systems, the system proposed in this paper has good heat collection performance and more superior system stability. The mean daily heat transfer of System 1 and System 2 is 6.4 MJ and 3.71 MJ, respectively, which is 62.9 % higher and 5.6 % lower than the mean daily heat loss of subgrade of 3.93 MJ, respectively. The system has the application prospect of low maintenance cost and good long-term antifrost heave effect.