Analysis of the transient performance of coaxial and u-tube borehole heat exchangers
Bibliographic record
Abstract
While coaxial borehole heat exchangers often have lower borehole thermal resistances than u-tubes, studies in the literature have mixed results as to whether the coaxial design always outperforms the u-tube. This study contributes a systematic comparison between the two designs, accomplished using a custom numerical model in OpenFOAM that provides detailed predictions of the heat transfer within the ground heat exchangers . The modelling and subsequent analysis of system thermal resistances demonstrated that the u-tube and coaxial heat exchanger performances differed the most during the early, transient phase of operation. Furthermore, modelling showed that the coaxial design does not necessarily exceed the u-tube performance long term; testing of coaxial heat exchangers with polyethylene piping showed small differences in outlet temperature compared to the u-tube after 72 h. Additional testing showed that using a steel coaxial outer tube could provide a 22% improvement to performance over the u-tube design. These findings are used to compare predictions of thermal resistance with available analytical models. The impact of the results on the potential for length reductions is also discussed.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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".