Experimental study on heat transfer attenuation due to thermal deformation of horizontal GHEs

Abstract

In soil thermal energy storage system with high temperature (exceeds 50 °C), the pipe thermal deformation (buckling) can lead to air gap between pipe and soil. During the pipe-soil heat transfer, the gap is actually the thermal resistance. The aim of this study is to investigate the gap between pipe and clay soil, the corresponding heat transfer attenuation and the influence of the initial pipe bending degree. However, the pipe is buried in the soil, the gap is hard to measure. So, the novelty of this work is to put forward the measuring methods of the pipe-soil gap width and the heat transfer attenuation rate from pipe to soil during the heating process. By experiment, the thermal deformation of pipe, the gap width and the heat transfer attenuation rate are analysed. The results indicate that the pipe displacement and the gap width increase with the temperature rise. Correspondingly, the heat transfer attenuation can be found in the gap-side soil area. During the heating process, the heat transfer attenuation rate will decrease with the temperature rise. In comparison, larger pipe bending could get larger thermal deformation, larger gap width and larger heat transfer attenuation rate.