Abstract
Closed-loop U-shaped geothermal wells show great potential owing to their special well-depth structure, which can provide a good flow rate and heat extraction. However, no advanced process parameter optimization method is available for U-shaped geothermal wells. To effectively describe the heat transfer processes of U-shaped geothermal wells, an analytical solution that couples transient heat conduction in the surrounding soil (or rocks) with the quasisteady heat transfer process in boreholes was developed. This modelling approach depends on many common elements, such as the thermophysical properties of the working fluid and series of resistances for various elements in the wellbore. Subsequently, based on the exergy analysis method, the optimal operating flow rate was defined and a design method for the optimal flow rate was developed. Results indicate that to obtain the maximum exergy efficiency, different optimal flow rates for the U-shaped geothermal well are achieved at different stages of the heating period. This findings of this study expand the research ideas of the process parameter optimization of U-shaped geothermal wells and provide a theoretical basis for developing an optimal circulating-flow-rate design for U-shaped geothermal wells.
Highlights
As The global warming issue becomes more prominent, the target of carbon neutral has prompted a shift in current energy systems
The mathematical model must be validated using experimental data or other calculated results to determine whether the mathematical model can accurately describe the temperature distribution and heat extraction using a U-shaped geothermal well
Based on the analysis in Section 3.2., both the outlet temperature and heat extraction will change with changes in the flow rate, and the change trend observed under different working conditions is the same
Summary
As The global warming issue becomes more prominent, the target of carbon neutral has prompted a shift in current energy systems. In the case of working condition 1in November, when the flow rate is set as 9 m3/h, the maximum outlet temperature achieved, i.e., 321.03 K (Figure 8).
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