A two-region model combing numerical simulation and analytical solution for U tube ground heat exchanger

A new model combing numerical simulation and analytical solution is proposed for U tube ground heat exchanger with varied heat flux boundary. The calculation area is divided into two parts by the boundary of the borehole wall. For the area in the borehole and the surrounding soil area, the calculation method is steady analytical solution and finite volume method respectively. In the borehole, steady heat transfer model is established based on energy conservation. During the calculation, the first variables should be obtained are the exiting fluid temperature and heat flux per unit length which are calculated by steady analytical method with the known borehole temperature at the start time, and then the borehole temperature and the surrounding soil temperature profile in the very time step are simultaneously calculated by solving the transient heat conduction equation with varied heat flux boundary, the following work is circularly calculating exiting fluid temperature, heat flux per length which was considered as the heat flux boundary for the next time step. The simulation agrees well with the corresponding experiment data which demonstrate the accuracy of the numerical simulation in present work.