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Research Papers: Energy Systems Analysis

Effect of Evaporation Temperature on the Performance of Organic Rankine Cycle in Near-Critical Condition

[+] Author and Article Information
Yuping Wang

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Minhang District,
Shanghai 200240, China
e-mail: linerw@sjtu.edu.cn

Xiaoyi Ding

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Minhang District,
Shanghai 200240, China
e-mail: dingxiaoyi_frank@126.com

Lei Tang

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Minhang District,
Shanghai 200240, China
e-mail: tangleisjtu@163.com

Yiwu Weng

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Minhang District,
Shanghai 200240, China
e-mail: ywweng@sjtu.edu.cn

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received September 9, 2015; final manuscript received December 9, 2015; published online January 5, 2016. Assoc. Editor: Kau-Fui Wong.

J. Energy Resour. Technol 138(3), 032001 (Jan 05, 2016) (8 pages) Paper No: JERT-15-1341; doi: 10.1115/1.4032238 History: Received September 09, 2015; Revised December 09, 2015

Considering the large variations of working fluid's properties in near-critical region, this paper presents a thermodynamic analysis of the performance of organic Rankine cycle in near-critical condition (NORC) subjected to the influence of evaporation temperature. Three typical organic fluids are selected as working fluids. They are dry R236fa, isentropic R142b, and wet R152a, which are suited for heat source temperature from 395 to 445 K. An iteration calculation method is proposed to calculate the performance parameters of organic Rankine cycle (ORC). The variations of superheat degree, specific absorbed heat, expander inlet pressure, thermal efficiency, and specific net power of these fluids with evaporation temperature are analyzed. It is found that the working fluids in NORC should be superheated because of the large slope variation of the saturated vapor curve in near-critical region. However, the use of dry R236fa or isentropic R142b in NORC can be accepted because of the small superheat degree. The results also indicate that a small variation of evaporation temperature requires a large variation of expander inlet pressure, which may make the system more stable. In addition, due to the large decrease of latent heat in near-critical region, the variation of specific absorbed heat with evaporation temperature is small for NORC. Both specific net power and thermal efficiency for the fluids in NORC increase slightly with the rise of the evaporation temperature, especially for R236fa and R142b. Among the three types of fluids, dry R236fa and isentropic R142b are better suited for NORC. The results are useful for the design and optimization of ORC system in near-critical condition.

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Figures

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Fig. 5

T–s diagrams of SORC (a) and NORC (b)

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Fig. 4

Schematic diagram of ORC system

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Fig. 3

Schematic diagram of sub- and near-critical region of R142b

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Fig. 2

T–s diagrams of R236fa, R142b, and R152b

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Fig. 1

Variations of physical properties of R142b in sub- and near-critical region

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Fig. 6

h–s diagram of the expansion process in the expander

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Fig. 8

Variation of minimum superheat degree with evaporation temperature

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Fig. 7

Calculation of the performance parameters for a given evaporation temperature

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Fig. 13

Variation of thermal efficiency with evaporation temperature

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Fig. 9

Variation of expander inlet pressure (a) and its slope (b) with evaporation temperature

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Fig. 10

Variation of specific absorbed heat with evaporation temperature

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Fig. 11

Variations of qevp (a) and q1, q2, and q3 (b) of R142b with evaporation temperature

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Fig. 12

Variation of specific net power with evaporation temperature

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