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Research Papers: Energy Systems Analysis

Organic Fluids in a Supercritical Rankine Cycle for Low Temperature Power Generation

[+] Author and Article Information
Rachana Vidhi

Clean Energy Research Center,
University of South Florida,
4202 E. Fowler Avenue,
Tampa, FL 33620
e-mail: rachana@mail.usf.edu

Sarada Kuravi

Department of Mechanical
and Aerospace Engineering,
Florida Institute of Technology,
150 W. University Boulevard,
Melbourne, FL 32901
e-mail: skuravi@fit.edu

D. Yogi Goswami

e-mail: goswami@usf.edu

Elias Stefanakos

e-mail: estefana@usf.edu
Clean Energy Research Center,
University of South Florida,
4202 E. Fowler Avenue,
Tampa, FL 33620

Adrian S. Sabau

Oak Ridge National Laboratory,
Materials Science and Technology Division,
P.O. Box 2008,
Oak Ridge, TN 37831
e-mail: sabaua@ornl.gov

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the Journal of Energy Resources Technology. Manuscript received November 6, 2012; final manuscript received January 23, 2013; published online May 27, 2013. Assoc. Editor: Kau-Fui Wong.

J. Energy Resour. Technol 135(4), 042002 (May 27, 2013) (9 pages) Paper No: JERT-12-1253; doi: 10.1115/1.4023513 History: Received November 06, 2012; Revised January 23, 2013

This paper presents a performance analysis of a supercritical organic Rankine cycle (SORC) with various working fluids with thermal energy provided from a geothermal energy source. In the present study, a number of pure fluids (R23, R32, R125, R143a, R134a, R218, and R170) are analyzed to identify the most suitable fluids for different operating conditions. The source temperature is varied between 125 °C and 200 °C, to study its effect on the efficiency of the cycle for fixed and variable pressure ratios. The energy and exergy efficiencies for each working fluid are obtained and the optimum fluid is selected. It is found that thermal efficiencies as high as 21% can be obtained with 200 °C source temperature and 10 °C cooling water temperature considered in this study. For medium source temperatures (125–150 °C), thermal efficiencies higher than 12% are obtained.

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References

Figures

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Fig. 1

A supercritical Rankine cycle on a T-S diagram

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Fig. 2

Layout of the thermodynamic cycle simulated in chemcad 6.3.0. The numbers in the square blocks indicate the fluid condition; the numbers in the circles refer to equipment unit.

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Fig. 3

T-S diagram of a supercritical cycle with the temperature profile of the hot brine

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Fig. 4

T-S diagram for R-32 at different pressures

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Fig. 5

Thermal efficiency of the SRC as a function of heat source temperature at a constant pressure ratio

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Fig. 6

Effect of (a) pressure (b) pressure ratio at 125 °C heat source temperature

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Fig. 7

Effect of (a) pressure (b) pressure ratio at 150 °C heat source temperature

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Fig. 8

Effect of (a) pressure (b) pressure ratio at 175 °C heat source temperature

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Fig. 9

Effect of (a) pressure (b) pressure ratio at 200 °C heat source temperature

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Fig. 10

Turbine work output versus pressure ratio at 200 °C heat source temperature for R134a based cycles

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Fig. 11

Pump work input versus pressure ratio at 200 °C heat source temperature for R134a based cycles

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Fig. 12

Change in turbine output and pump input as a function of pressure ratio at 200 °C heat source temperature for R134a based cycles

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Fig. 13

Optimum pressure as a function of heat source temperature for 10 °C cooling water temperature

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Fig. 14

Thermal efficiency of a SRC as a function of heat source temperature at optimum pressures

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Fig. 15

Exergy efficiency of SRC as a function of heat source temperature

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Fig. 16

Thermal efficiency for R134a as a function of cooling water temperature at a heat source temperature of 200 °C

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