Investigation of a Combined Inverted Brayton and Rankine Cycle
Bibliographic record
Abstract
Abstract Waste heat recovery is a vitally important technology to address increasingly stringent emissions legislation and environmental concerns over CO2. One such means of recovering thermal energy is the inverted Brayton cycle (IBC). This paper presents an experimental study of a novel combination of the IBC with a Rankine cycle for the first time. The IBC requires cooling of the exhaust gases after expansion. If the gases contain water vapour, as is the case for hydrocarbon combustion, and cold enough coolant is available, the water can be condensed, pressurized and re-boiled for expansion in a Rankine cycle. The steam produced from the cycle can be utilized in a number of ways. In this study, steam is injected through a series of de Laval nozzles directed into the main turbine to produce additional shaft power in a compact arrangement. To minimize the size of the system, additive manufacturing was used for the heat exchangers, giving high performance per unit volume. The study demonstrates the feasibility of the cycle in producing power from waste heat using humid gas that already is present in most applications. The experimental results show that the system is able to generate power at very low exhaust temperatures where the standard IBC would cease to operate. With an IBC inlet temperature of 370 °C, approximately 5 kJ/kg of specific shaft work was produced with 5 g/s of steam flow rate. At higher exhaust temperatures, the IBC and the Rankine cycle started to work together to increase the shaft power resulting in much higher specific work. At 620 °C, a specific shaft work of 41 kJ/kg was generated at a steam flow of 9 g/s. For the present turbomachinery sizes, this corresponded to 1933 W of power at 47 g/s of main exhaust flow. A model of the thermodynamic system was created in order to study the sensitivity of the system to parameters such as the steam expander pressure ratio and efficiency. Higher steam pressure and higher steam expander efficiency both led to greater power generated for the same operating point, particularly at high IBC turbine inlet temperatures. The peak specific work for the range of parameters explored in the paper was 68 kJ/kg with a steam expander efficiency of 70% and exhaust conditions of 600 °C and 50 g/s. The plots produced in this study can be used as a guide for others considering this system to understand the expected power generated under a range of conditions.
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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".