Thermal Storage Characteristics of a Vertical Single U-Tube Borehole Heat Exchanger Under Fluid Quantity Constraints

Borehole thermal energy storage (BTES) can solve the mismatch between production and utilization of industrial waste heat and other energy, improve energy utilization efficiency, and reduce carbon emissions.A large body of literature has been published to study the thermal storage performance of borehole heat exchangers (BHE) under various operating conditions, but the fluid quantity limitation has not been considered in the research process.In practical projects, there is a limit to the amount of fluid that can be produced.This paper establishes a three-dimensional vertical BHE model based on project data and performs model validation to study the impact of flow velocity, temperature, and initial ground temperature on its thermal storage performance under fluid volume limitation.The results showed that the heat transfer rate and heat storage amount of BHE increased with fluid temperature and decreased with initial ground temperature.Meanwhile, the heat transfer rate of BHE increased with flow velocity, but the heat storage amount decreased with flow velocity.The ideal flow velocity under the parameters of this research is 0.1 m/s, and the continuous operating mode outperforms the intermittent operation mode.