Analytical g-function for vertical geothermal boreholes with effect of borehole heat capacity

作者：Nian, Yong-Le; Cheng, Wen-Long^*

来源：Applied Thermal Engineering, 2018, 140: 733-744.

DOI：10.1016/j.applthermaleng.2018.05.086

• Geothermal borehole
• Ground heat exchangers
• g-functions
• Borehole heat capacity
• Transient heat conduction

Thermal response factors, known as g-functions play an important role in design in geothermal boreholes and ground heat exchangers (GHE). In this paper, a new analytical g-function is proposed to account for the effect of borehole heat capacity (BHC) on ground thermal response; and the quantitative effect of BHC on ground and fluid temperature can be obtained by the new g-function without needing transient borehole resistance. Firstly, a cylindrical source model considering BHC effect was built to conduct the new g-function by Laplace transform method. Then, the fluid temperature models coupling with the proposed g-function were built to investigate the effect of BHC fluid temperature. By comparing new model with conventional g-functions, it was found that the new g-function agreed better with the experimental data than the conventional models during short time. The largest relative error for ground temperature prediction for U pipe GHE was about 2.9% and the mean relative error for fluid temperature prediction in coaxial GHE was less than 1%. Moreover, it was found that the BHC had an especially significant influence on ground thermal response and fluid temperature at short times and the influence weakened with time. And the larger the BHC was, the smaller the influence radius would be.

• 出版日期2018-7-25
• 单位中国科学技术大学