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

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.

Analysis of a scroll machine for micro ORC applications by means of a RE/CFD methodology

“…This value resulted equal to 0.29, as a consequence of the imposed flank gap between the fixed and the moving profiles. This value is comparable to similar results found in literature [24].…”

Numeryczna analiza przecieków osiowych w bezolejowej sprężarce spiralnej w stanie nieustalonym

“…Sprawia to, Ŝe świetnie nadają się do zastosowania w układach chłodniczych, klimatyzacyjnych (takŜe w klimatyzatorach samochodowych), jak równieŜ w obiegach pomp ciepła. Dodatkowo, nowym polem zastosowań jest wykorzystywanie maszyn spiralnych jako rozpręŜarek w układach ORC [3,4]. Zasada działania spręŜarki spiralnej (rys.…”

Dynamic simulation and experimental validation of an Organic Rankine Cycle model

“…Oliveira (2007) provides an example layout of a combined heat and power solar thermal system which utilises a Rankine cycle to produce work from solar heat, and recovers useful heat from the condenser. Mathias et al (2009) uses a simple non-regenerative ORC with a scroll expander to produce an isentropic efficiency as high as 83%. It is demonstrated that the highest isentropic efficiency is attained when both the specific volume ratio of the fluid undergoing expansion is matched to the built-in volume ratio of the expander, and when the volume flow rate is matched to the rotational speed.…”

“…The expander performs at between 57% and 59% isentropic efficiency for all months of the year. This is a respectable efficiency for a power expander, however, isentropic efficiencies of up to 83% have been reported in the literature (Clemente et al, 2011;Mathias et al, 2009;Oudkerk et al, 2011). Greater isentropic, and therefore system, efficiency might be achieved by using a similar sized scroll expander that has been purpose-built for expansion.…”

“…Greater isentropic, and therefore system, efficiency might be achieved by using a similar sized scroll expander that has been purpose-built for expansion. Modifications to inlet and exit nozzles as in Mathias et al (2009) and improved lubrication as in Wang et al (2009) might help toward this goal.…”