Numerical and experimental studies of a double-pipe helical heat exchanger
Bibliographic record
Abstract
A double-pipe helical heat exchanger was studied numerically and experimentally for both heat transfer and hydrodynamic characteristics. Results from the numerical trials show that the inner Nusselt numbers in the heat exchanger were similar to literature data, despite the different boundary conditions. Nusselt numbers in the annulus were correlated to a modified Dean number. It was shown that the thermal resistance in the annulus to be the greatest limiting factor for the heat transfer, and heat transfer rates could be increased by increasing the inner tube diameter. The Prandtl number was shown to affect the inner Nusselt number; however the effects were much greater at low Dean numbers. These differences were attributed to the difference in the developing thermal and hydrodynamic boundary layers. The studies with the thermally dependent thermal conductivities showed that the Nusselt number correlated well with a modified Graetz number. Thermally dependent viscosity had little effect on the heat transfer; however it affected the pressure drop. Furthermore, it was shown that by keeping the flow rate in the inner tube or the annulus constant, the pressure drop in that section can be affected by changes in the flow rate in the opposite section, due to the change in the heat transfer rate and hence the average temperature and viscosity of the fluid. Non-Newtonian fluids showed little effect on the heat transfer rates, though they significantly affected the pressure drop relations. The uniformity of the residence time and the temperature distribution were both increased in the inner tube with increasing flow rates. It was shown that a smaller gap size in the annulus resulted in more uniform residence times. Temperature distributions in the inner tube and the annulus were affected by changes in the flow velocity in the opposite section, with lower flow rates resulting in more uniform temperature distributions. Implications of using parallel flow versus counterflow, heating versus cooling, and flow rate are discussed. Overall heat transfer coefficients and Nusselt numbers were calculated for the experimental data. The inner and annulus heat transfer coefficients were determined using Wilson plots. The results were compared to the numerical data and literature values and showed reasonable agreement. (Abstract shortened by UMI.)
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".