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Research Papers: Fuel Combustion

# Experimental Testing of Gerotor and Scroll Expanders Used in, and Energetic and Exergetic Modeling of, an Organic Rankine Cycle

[+] Author and Article Information
James A. Mathias

Department of Mechanical Engineering and Energy Processes, Southern Illinois University-Carbondale, Mailcode 6603, Carbondale, IL 62901mathias@engr.siu.edu

Jon R. Johnston1

Department of Mechanical Engineering, Ohio State University, 206 West 18th Avenue, Columbus, OH 43210

Jiming Cao2

Department of Mechanical Engineering, Ohio State University, 206 West 18th Avenue, Columbus, OH 43210

Douglas K. Priedeman3

Department of Mechanical Engineering, Ohio State University, 206 West 18th Avenue, Columbus, OH 43210

Richard N. Christensen

Department of Mechanical Engineering, Ohio State University, 206 West 18th Avenue, Columbus, OH 43210

1

Also at General Motors.

2

Also at Verizon.

3

Also at ExxonMobil.

J. Energy Resour. Technol 131(1), 012201 (Feb 05, 2009) (9 pages) doi:10.1115/1.3066345 History: Received November 27, 2007; Revised September 04, 2008; Published February 05, 2009

## Abstract

This paper presents the experimental testing of relatively cost-effective expanders in an organic Rankine cycle (ORC) to produce power from low-grade energy. Gerotor and scroll expanders were the two types of expanders tested to determine their applicability in producing power from low-grade energy. The results of the experimental testing showed that both types of expanders were good candidates to be used in an ORC. The gerotor and scroll expanders tested produced 2.07 kW and 2.96 kW, and had isentropic efficiencies of 0.85 and 0.83, respectively. Also the paper presents results of an analytical model produced that predicted improved cycle efficiency with certain changes. One change was the flow rate of the working fluid in the cycle was properly matched with the inlet pocket volume and rotational speed of the expander. Also, the volumetric expansion ratio of the expander was matched to the specific volume ratio of the working fluid (R-123) across the expander. The model incorporated the efficiencies of the expanders and pump obtained during experimental testing, and combined two expanders in series to match the specific volume ratio of the working fluid. The model determined the power produced by the expanders, and subtracted the power required by the working fluid pump and the condenser fan. From that, the model calculated the net power produced to be 6271 W and the overall energy efficiency of the cycle to be 7.7%. When the ORC was simulated to be integrated with the exhaust of a stationary engine, the exergetic efficiency, exergy destroyed, and reduction in diesel fuel while still producing the same amount of power during 2500 h of operation were 22.1%, 22,169 W, and 4,012 L (1060 U.S. gal), respectively. Consequently, the model presents a very realistic design based on results from experimental testing to cost-effectively use low-grade energy.

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## Figures

Figure 1

Expansion process of a gerotor expander

Figure 2

Expansion process of a scroll expander

Figure 3

Experimental test setup

Figure 4

Isentropic efficiency versus EMratio for Gerotor C and Scroll C tests

Figure 5

State points of the entire ORC including working fluid, exhaust, and air

Figure 6

Temperature versus entropy graph of R-123 in ORC

Figure 7

Exergy destruction and shaft power produced (W) of the components of the ORC

Figure 8

Sensitivity analysis of energy efficiency with respect to temperatures and pressures of expander and condenser

Figure 9

Sensitivity analysis of exergy efficiency with respect to temperatures and pressures of expander and condenser

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