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.
This research effort involved experimentally testing an advanced-cycle, ammonia-water absorption chiller with a cooling capacity of 17.6 kW (5 refrigeration tons (RT)). The system was a generator-absorber heat exchange (GAX) cycle and was sized for residential and light commercial use, where very little absorption equipment is currently used. The components of the cycle were assembled with instrumentation, including flow meters, pressure transducers, and thermocouples. The findings of the research were cycle cooling load and coefficient of performance (COP), as well as many component heat duties and working fluid state points throughout the cycle. The COP of the chiller at essentially full load was measured at 0.68. A simulation of the GAX cycle was performed with a computer program that predicted the heat duties of each component and the cooling load of the cycle. The simulation of the GAX cycle and experimental testing compared closely. Existing market research shows that significant business opportunities exist for a GAX heat pump or chiller with a cooling COP of 0.70 or greater. The work performed in this study consisted of testing a GAX cycle with a COP that approached the target value of 0.70 and identified improvements that must be made to reach the target COP value.
The main objective of this study was to investigate the high-pressure oxidation rates of large (6-9 mm diameter) char particles for a wide range of five experimental conditions, with particular focus on the role of the ratio of the carbon-oxide combustion products at the reaction surface and on its analytical consequences on the Stefan flow (BLD) behavior. The char particles were obtained by pyrolytic heating of a Pittsburgh HV bituminous coal in nitrogen. The experimental conditions and ranges were gas temperature (825-1200 K), gas (oxidizer) velocity (0.08-1.28 m/s), particle mass (0.056-0.16 g), oxygen mole fraction (0.04-0.21), and total pressure (1-5 atm). This allowed for a suite of 13 different permutations of operating conditions, with each repeated five times for a total of 65 experiments, generating about 1000 experimental data points. The experiments were conducted in a high-pressure, controlled-profile (HPCP) laboratory reactor with a cantilever balance attachment. The particles were suspended from the balance attachment in a wire basket for continuous weighing to obtain the oxidation rates. The reaction was found to be mostly governed (controlled or dominated) by boundary layer diffusion (BLD), as broadly expected and predicted for particles of this size from the Stefan flow BLD analysis, but results also showed numerical variabilities in the carbon oxides ratio (CO/CO 2 ) that are believed to be original in this work. In sum, reaction rate increased with increasing temperature, oxygen concentration, and ambient velocity, in agreement with past work. Burn-out time was found to be independent of total pressure, in agreement with prediction where the reaction rate is controlled or dominated by boundary layer oxidizer diffusion. The particles burned in two stages: stage I extended through 85% to 90% of the char mass loss at which point there was a temperature drop or (nominal) "extinction" accompanied by slower reaction in the subsequent stage II. The primary focus in this study was on the stage I where comparison with rigorous theory established that the reaction was diffusion-controlled for nine of the 13 sets of experimental conditions. In the remaining four sets (high velocity, low pressure, and low oxygen concentration), there was a measurable chemical reaction resistance; however, diffusion, though not controlling, was still dominant. For eight of the 13 sets of test conditions, analysis indicated full conversion of CO to CO 2 at the particle surface. For the other five sets of test conditions (low oxygen, low temperature, and low velocity), however, CO accounted for 14% to 79% of the product gas leaving the surface, with the balance being CO 2 . The effects of the test variables were quantitatively accounted for by incorporating Stefan flow behavior in a rigorous theory of particle burning. IntroductionIn this paper, we report results of experimental and analytical studies on high-pressure oxidation rates of large char particles, obtained from a bituminous coal,
This research effort involved experimentally testing an advanced-cycle, ammonia-water absorption chiller with a cooling capacity of 17.6 kW (5 refrigeration tons (RT)). The system was a Generator-Absorber Heat Exchange (GAX) cycle and was sized for residential and light commercial use, where very little absorption equipment is currently used. The components of the cycle were assembled with instrumentation, including flow meters, pressure transducers, and thermocouples. The findings of the research were cycle cooling load and Coefficient of Performance (COP), as well as many component heat duties and working fluid state points throughout the cycle. The COP of the chiller at essentially full load was 0.68. Existing market research shows that significant business opportunities exist for a GAX heat pump or chiller with a cooling COP of 0.70 or greater. The work performed in this study provides a breadboard cycle with performance approaching the target value and identifies improvements that must be made to achieve a packaged unit operating with a cooling COP of 0.70.
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