Numerical Modeling and Experimentation on Evaporator Coils for Refrigeration in Dry and Frosting Operational Conditions
Bibliographic record
Abstract
The drive to improve energy efficiency in refrigeration and heat pump systems necessarily leads to a continuous reassessment of the current heat transfer surface design and analysis techniques. The process of heat exchange between two fluids at different temperatures, separated by a solid wall occurs in many engineering applications and heat exchangers are the devices used to implement this operation. If improved heat exchanger designs are used as evaporators and condensers in refrigerators and heat pumps, these can considerably benefit from improved cycle efficiency. Air coolers or coils are heat exchangers applied extensively in cold stores, the food industry and air conditioning as evaporators. In these devices, heat transfer enhancement is used to achieve high heat transfer coefficients in small volumes, and extended surfaces or fins, classified as a passive method, are the most frequently encountered. Almost all forced convection air coolers use finned tubes. Coils have in this way become established as the heat transfer workhorse of the refrigeration industry, because of their high area density, their relatively low cost, and the excellent thermo physical properties of copper and aluminum, which are their principal construction materials. Compact coils are needed to facilitate the repackaging of a number of types of air conditioning and refrigeration equipment: a reduced volume effectively enables a new approach to be made to the modular design and a route towards improving performance and size is through appropriate selection of refrigerants, heat transfer enhancement of primary and secondary surfaces through advanced fin design and circuit configurations. Circuiting, although practically used on an empirical basis, has not yet received sufficient attention despite its potential for performance improvement, flow and heat transfer distribution, cost and operational efficiency. In the specific case of refrigeration and air conditioning, a confined phase changing refrigerant exchanges heat in evaporators with the cold room, giving up its heat. The design and operation of refrigeration coils is adapted to these particular conditions. Geometrically they generally consist of copper tubing to which aluminum fins are attached to increase their external surface area over which air is flowing, in order to compensate for this latter poor convection heat transfer. Coils generally achieve relatively high heat transfer area per unit volume by having dense arrays of finned tubes and the fins are generally corrugated or occasionally louvered plates with variable spacing and number of passes. Internal heat transfer of phase changing refrigerant is high and varies www.intechopen.com Two Phase Flow, Phase Change and Numerical Modeling 28 with flow regimes occurring along the tube passes. Flow on the secondary surfaces (outside of tubes and fins) in cooling, refrigeration or deep freezing, becomes rapidly complicated by the mass transfer during the commonly occurring processes of condensation and frost deposition, depending on the air prevailing conditions. Overall, geometric and operational considerations make these components very complex to design and analyse theoretically.
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How this classification was reachedexpand
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) | 0.000 | 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 teacher head, 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".