136879 research outputs found
Sort by
An Investigation and Proof of Concept for Subcritical Ultra-Low Temperature Organic Rankine Cycle
No full textIn support of a major push towards a greener world using renewable energy, the Organic Rankine Cycle (ORC) is a promising area of exploration for generating power from low grade thermal sources. An ORC is able to operate at lower temperatures and at reduced temperature differentials due to its use of alternative working fluids, rather than conventional water. This study seeks to prove the viability of an ultra-low grade ORC operating with a 10 degree temperature differential between the high to low temperature reservoirs. To accomplish this task, a carbon dioxide Organic Rankine Cycle was operated at a steady state marked by twenty minutes of unchanging states, thus achieving the correct test conditions for the chosen working fluid. A wide assortment of experimental data was then captured and used for analysis and modeling. The Engineering Equation Solver (EES) software was utilized to model the behavior of a Rankine Power Cycle that is capable of using different working fluids (i.e. an ORC with carbon dioxide) operating with a 10 degrees Fahrenheit temperature differential between 40 degrees Fahrenheit and 50 degrees Fahrenheit (i.e. temperature reservoirs). After comparing multiple refrigerants using the cycle model under idealized conditions, carbon dioxide was chosen with a theoretical net work production of 1.73 Btu/lbm and a 1.91% thermal efficiency. This latter value is comparable to the Carnot efficiency of 1.96% since the modeled pumps and turbine assumed a 100% isentropic efficiency, and heat transfer in the heat exchangers was assumed to occur over a 0 degrees Fahrenheit temperature difference.
The test facility used in this study was designed and constructed based on the results of the simulation from the aforementioned cycle model. Even so, it was necessary to make numerous system modifications to overcome unforeseen problems once components and parts were procured (i.e. delivered to REEL) and assembled. Specifically, modifications had to be made to the condenser and chillers in order to achieve consistent liquid conversions in the heat exchangers. Furthermore, the original experimental system was assembled with a throttle valve to replace and simulate the pressure drop across a Tesla turbine, to be incorporated in the system at a later date. The results from the throttle valve testing indicated that if a turbine had been installed then the ORC test rig could achieve a power output of 1.91 Btu/lbm and a power draw of 6.05 Btu/lbm. However, the carbon dioxide test facility assembled and operated had mismatched carbon dioxide circulating pumps with the isentropic efficiency measured to be 4.46% and with an excessive power draw of 6.05 BTU/lbm. Even though these pumps will be switched out in the future, in terms of this study, the net work of -4.14 BTU/lbm is less important than the simulated 1.91 Btu/lbm power output achieved. The heat exchangers were analyzed and determined to have efficiencies of 19.2% and 24.5% for the evaporator and condenser, respectively. In summary, evaluating and testing additional working fluids, along with modifying the pumps to have increased efficiencies for low viscosity fluids, such as carbon dioxide, should allow for increased overall cycle efficiency and the potential to generate net positive power in the future
Developmental Outcomes of Prenatal E-cig Aerosol Vaping
Get PDFElectronic cigarettes (e-cigs) are tobacco products that have become popular among youth and young adults due to targeted advertising and misconceptions about their safety. The unfounded perception that e-cigs are less harmful than traditional cigarettes may result in the use of e-cigs during pregnancy. There are limited studies evaluating the effects of e-cig aerosol exposure on pregnancy in animal models and only a single report of gestational e-cig exposure in humans. To examine the impact of prenatal e-cig aerosol exposure on pregnancy and development we utilized a pregnant Sprague-Dawley rat model combined with a chronic, whole-body, environmental exposure to e-cig aerosols generated by commercially available e-cig atomizers. We found that exposure to e-cig aerosols containing nicotine significantly reduced fetal and neonatal growth, but aerosols without nicotine did not. Growth restriction was accompanied by reduced blood flow in the maternal uterine artery and fetal umbilical artery. Analysis of signature amino acid profile revealed altered concentrations in maternal and fetal plasma of animals exposed to e-cig aerosols with nicotine. Amino acid concentrations in the fetal lungs were altered by e-cig aerosols regardless of nicotine. RNA sequencing of fetal lung transcriptome showed altered expression after exposure to e-cig aerosols with and without nicotine. E-cig aerosols containing nicotine altered neonatal lung morphology and produced trends in respiratory mechanics that may increase the workload of breathing. Interestingly, e-cig aerosols with and without nicotine reduced the area of the pressure-volume loop during forced oscillation techniques which may indicate increased atelectasis in neonatal lungs. The effects of prenatal e-cig aerosol exposure were more pronounced in animals exposed to aerosols containing nicotine, however, e-cig aerosols without nicotine were also found to effect the physiology of pregnancy. Further studies will be required to identify molecular mechanisms of e-cig aerosol induced alterations to pregnancy and development. The data presented in these studies lay a foundation for our understanding of prenatal exposure to e-cig aerosols by providing evidence that e-cig vaping during pregnancy can have deleterious outcomes for the developing offspring
