Heat Transfer in Double U-Tube Boreholes With Two Independent Circuits
Bibliographic record
Abstract
This study presents the development of an analytical model to predict steady-state heat transfer in double U-tube geothermal boreholes equipped with two independent circuits. Such boreholes can be used for heat extraction in one circuit, combined with a heat pump, for example, and simultaneous thermal recharging in the other circuit. The model accounts for a thermal interaction among pipes, and it predicts the fluid temperature profiles in both circuits along the borehole depth, including the exit fluid temperature. Different circuit configurations are assessed under typical borehole operating conditions. For a typical borehole geometry, results show that double U-tube boreholes with two independent circuits connected to a relatively low temperature heat source are superior to single U-tube and regular (one circuit) double U-tube boreholes. The axial variation in fluid temperature and the heat exchange among pipes show that most of the heat transfer occurs in the downward legs. Furthermore, in some cases, the fluid in the heat extraction leg gets cooled as it flows upward, which is contrary to the desired effect.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".