Heat Transfer to Supercritical Water Flowing in Short Vertical Bare Tubes
Bibliographic record
Abstract
Abstract It is well known that water-cooled nuclear-power reactors / Nuclear Power Plants (NPPs) equipped with light- and heavy-water-cooled reactors have relatively low thermal efficiencies within the range of 26–38% compared to those of thermal power plants – combined-cycle up to 62.5% and supercritical-pressure Rankine cycle up to 55%. Therefore, increasing thermal efficiency of next generation NPPs / nuclear reactors is a very important task. For water-cooled reactors / NPPs the conventional approach for increasing thermal efficiency is to move to supercritical pressures, as it was done more than 60 years ago in the thermal-power industry. Currently, together with large-capacity SuperCritical Water-cooled Reactors (SCWRs) SC-Pressure Small Modular Reactors (SCP SMRs) are also being developed. Therefore, solid knowledge of heat-transfer specifics at supercritical pressures is required. Usually, hydraulic-equivalent diameters of modern bundle flow geometries are within 5–10 mm and heated lengths are up to 4 m for SCWRs and can be shorter for SCP SMRs. Also, first SCWRs as test, experimental, or pilot reactors will be with relatively small installed capacities within 100–300 MWel. Due to that it is important to investigate supercritical heat transfer in small diameters tubes as a first and preliminary step instead of bundle geometries and bundle simulators. Usually, heat transfer in bare tubes is considered as the conservative approach compared to bundle tests, because heat transfer in bundle geometries will be higher compared to that in bare tubes due to additional turbulization from various appendages inside sub-channels. The paper presents experimental data obtained in relatively short vertical bare tubes mainly with upward flow of SCW. The experiments have been performed by Dr. V. Razumovskiy1 at the National Technical University of Ukraine. The data were obtained at the pressure of 23.5 MPa, mass fluxes of 2193 kg/m2s (main set of data) and 509 and 248 kg/m2s, and heat fluxes within 104–2660 kW/m2. The experimental data were compared to a well-known subcritical-pressure heat-transfer correlation developed by Dittus and Boelter. The heat-transfer-coefficient data were predicted quite reasonably with this correlation within the normal heat-transfer regime, but were significantly higher those within the deteriorated heat-transfer regime and within the pseudocritical region.
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How this classification was reachedexpand
Direct model labels (unvalidated)
Per-model category and study-design labels from the labeling rounds. They are machine output, unvalidated, and the disagreement between models ships as data. No study design here is MEDLINE-validated yet.
| Model arm | Categories | Study design | Confidence |
|---|---|---|---|
| gemma | no category Domain: not available · Genre: Empirical About the Canadian research system: no · About a Canadian topic: no | Bench or experimental | high |
| gpt | no category Domain: not available · Genre: Empirical About the Canadian research system: no · About a Canadian topic: no | Bench or experimental | high |
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| 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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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, unvalidatedLabeled directly by 2 models reading the full record.
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".