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ABSTRACT
A novel two-stage refrigeration cycle with deep intercooling and series-parallel integration of thermal and mechanical compression is proposed. Its mechanical energy consumption can be reduced by supplementing it with low-grade non-large-scale heat sources. Firstly, to show the advantages of the proposed cycle, the comparison with a two-stage refrigeration cycle with series integration of thermal and mechanical compression as well as the cascade system driven by heat and power is implemented. Secondly, the effects of the major operating parameters affecting the performance such as inter-stage pressure, inlet quality of high-pressure stage mechanical compressor and thermal compressor flow rate are analyzed. Finally, the near-optimal operating parameters for different working conditions are proposed. It is exhibited that the ECOP of the proposed layout increases by 19.4–43.7% as compared to the traditional system layouts. It is recommended that the inlet quality of 0.9 in the high-pressure mechanical compressor serves as a good guide for different operational conditions. The results show that the proposed system has a clear potential of lowering the energy consumption of cold storage refrigeration systems by supplementing with available low-grade heat. It is believed that the proposed cycle promotes a more sustainable development of fresh produce e-commerce logistics.
Highlights
The proposed layout is efficient and reliable for small and moderate heat sources.
The proposed layout is compared with the others thermodynamically.
The effect of critical parameters is analyzed in detail.
The near-optimal critical parameter for different conditions is obtained.
Nomenclature
| Symbols | = |
|
| COP | = | coefficient of performance |
| ECOP | = | exergy efficiency |
| ES | = | energy savings (kW) |
| Ex | = | exergy rate (kW) |
| ex | = | unit exergy of each point (kJ kg−1) |
| GAX | = | generator-absorber-heat exchanger |
| h | = | specific enthalpy (kJ kg−1) |
| HPCOP | = | heat powered coefficient of performance |
| k | = | normalized inter-stage pressure |
| m | = | mass flow rate (kg s−1) |
| Q | = | energy (kW) |
| q | = | inlet quality of high-pressure stage mechanical compressor |
| r | = | thermal compression flow rate fraction |
| R | = | regression value |
| s | = | specific entropy (kJ kg−1 K−1) |
| T | = | temperature (°C) |
| W | = | compressor work (kW) |
| x | = | concentration |
| ƞ | = | efficiency |
Subscripts
| abs | = | absorber, absorption |
| ca | = | chilled air |
| com | = | mechanical compressor |
| con | = | condenser |
| cw | = | cooling water |
| de | = | degrade |
| dis | = | discharge |
| ele | = | electricity |
| eva | = | evaporator |
| g | = | global |
| gen | = | generator |
| high | = | high-pressure stage |
| hw | = | hot water |
| i | = | inlet |
| int | = | inter-stage |
| low | = | low-pressure stage |
| o | = | outlet |
| opt | = | optimal |
| poor | = | poor solution |
| proposed | = | proposed layout |
| rc | = | recooling |
| rec | = | rectifier |
| ref | = | reference |
| rich | = | rich solution |
| sc | = | subcooling |
| sh | = | superheating |
| series | = | two-stage refrigeration cycle with series integration of thermal and mechanical compression |
| shx | = | solution heat exchanger |
| tot | = | total |
Acknowledgements
This work is supported by: (1) National Foreign Expert Project under the contract No. G2022163009L (2) Zhuhai Industry-University-Research Cooperation Project under the contract No. ZH22017001210017PWC; (3) Natural Science Foundation of Guangdong Province under the contract No. 2020B1515120035 and No. 2021A1515010265; (4) Key Laboratory of Efficient and Clean Energy Utilization of Guangdong Higher Education Institutes under the contract No. KLB10004.
Disclosure statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.