Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 21 for “"Transcritical"”.
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Dynamic Model and Adaptive Control of a Transcritical Organic Rankine Cycle
The Transcritical Organic Rankine Cycle (TORC) is a non-linear time-varying heat recovery system for small-scale power generation. It is similar to a boiler-turbine system but uses organic fluid as the primary heat carrier instead of H2O and works in both subcritical and supercritical regions. The …
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An investigation of transcritical effects for fuel injection and mixing applications
… a numerical framework for characterizing transcritical effects on droplet evaporation at ambient conditions typical of modern combustors. The approach combines scaling analysis with a first-principles model to describe droplet evaporation behavior in fluid-independent, non-dimensional …
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Design and Lab Implementation of an Air Source Transcritical CO2 Heat Pump
<p>A laboratory-scale air-source transcritical CO2 heat pump (TCHP) was developed to evaluate the performance of low-global-warming-potential (GWP) refrigerants for cold climate applications. A custom climate chamber was also constructed to simulate winter weather conditions typical of the …
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Primary refrigeration system commissioning based on a transcritical 2- stage R744 cycle
This report gives a brief background into the use of carbon dioxide as a refrigerant (R744) and describes the development of a two-stage trans-critical cooling system that is intended to be used as a chiller for the detectors at CERN's Large Hadron Collider (LHC). It then goes on to describe the …
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Second law analysis of a waste heat recovery combined power cycle using transcritical carbon dioxide
… To maximize heat exchanger effectiveness, a transcritical working fluid is used in the Rankine bottoming cycle to better match the heating curve of the sensible heat source. Carbon dioxide is selected as the working fluid because it possesses a relatively low critical temperature which makes …
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Dynamic modeling and control of transcritical vapor compression system for battery electric vehicle thermal management
… However, these vapor compression systems operate transcritical, thus requiring novel control techniques. This thesis develops a framework for architecture and control design of BEV subsystems. The foundation of this process is the development of multi-domain models. Models for the transcritical …
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Experimental and Analytical Investigation of a Two-Phase Ejector Used for Expansion Work Recovery in a Transcritical R744 Air-Conditioning System
… represent an inherent drawback of the transcritical carbon dioxide (CO2, R744) refrigeration cycle, the supercritical heat rejection pressure can be used to maximize the system performance. In addition, large throttling losses make R744 a suitable fluid for expansion work recovery. This …
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Experimental and numerical investigation of the design and control of vapor-compression systems with integration of two-phase ejectors for performance enhancement through expansion work recovery
… with inherently high throttling loss, such as transcritical CO2 (R744) systems, should use the ejector to directly supplement compressor power using the pressure increase provided by the ejector, while systems using lower-pressure refrigerants should use the ejector to improve the performance …
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Potentials for COP increase in vapor compression systems
… and numerically investigated for R410A and transcritical R744. Experiments were carried out in a limited range of operating conditions but an experimentally validated model was used to extrapolate trends. As the relative size of the HXs was increased, a maximum COP of 9.5 (without fans …
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Hamiltonian bifurcations in Schrodinger trimers
… change due to Hamiltonian Hopf bifurcations and transcritical bifurcations. The Hamiltonian Hopf bifurcation occurs when eigenvalues on the imaginary axis collide and split and has two types: elliptic and hyperbolic. These two types arise in the DNLS problem, and the families of periodic orbits …
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Bifurcation Analysis of Endogenous Growth Models
… versions of the model and locate Hopf and transcritical bifurcation boundaries. In an extended analysis, we investigate the existence of Andronov-Hopf bifurcation, branch point bifurcation, limit point cycle bifurcation, and period doubling bifurcations. While these all are local …
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Integrate-and-fire modelling of neuronal systems with modulatory properties
… model around its organising centre, that is, the transcritical singularity. The proposed methods allow the study of neural dynamics and modulation in an efficient and interpretable manner. This is shown for modulation both via a change of intrinsic conductances and via a change of mean applied …
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Dynamic Analysis of an Inflatable Dam Subjected to a Flood
… flow regimes were identified: subcritical, transcritical and supercritical. When breaking occurs it may be of any type: spilling, plunging or surging. In addition, for values of the Froude number close to 1, the upstream solitary waves break. A systematic study was undertaken, to define the …
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Vortex control of two-phase refrigerant flow in nozzles and its application in ejector vapor compression cycles
… Finally, the influence of vortex control on transcritical R744 ejector and cycle performance has been experimentally investigated. Vortex control was applied to ejectors with different geometric parameters. The performance of ejector and ejector cycle with vortex control was compared with …
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Commercial Electric Vehicle Cabin Heating System Modelling and Optimization
… a complete system redesign to accommodate transcritical operation. Optimization of the orifice diameter yielded an average system COP improvement of approximately 2 %, and the inclusion of an internal heat exchanger enhanced system performance by up to 10% in certain conditions. Across most …
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Rate-induced tipping in a moving habitat
… dies out. In the monostable Logistic Model, a transcritical bifurcation occurs between its travelling pulse solution and its zero (extinction) solution, which gives rate-induced tipping that can be reversed with a clear indication of an eventual local extinction as this critical speed is …
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Thermoacoustic Oscillations in Supercritical Fluid Flows
Pressure oscillations in supercritical Jet-A fuel flowing through four parallel, heated tubes connected to common manifolds have been observed in this study. Tests were performed with fuel inlet temperatures ranging from 70F to 700F, and fuel pressures ranging from 360-700 psi. Total fuel flow rate …
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Problems in nonlinear dynamics
… change the pitchfork bifurcation to a transcritical bifurcation. Cyclic-fold bifurcations, Hopf bifurcations of the nontrivial constant solutions, and period-doubling sequences leading to chaos are induced by these quadratic terms. The effects of quadratic nonlinearities for the case of …
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Low temperature glide cycles for energy storage applications: Thermodynamic and capital cost analysis
… energy conversion, including the Joule-Brayton, transcritical, and glide (also known as Kalina) cycles. The latter has not been extensively studied yet for PTES and is the focus of the present work. Akin to a Rankine cycle, it differs by employing a zeotropic mixture for the working fluid. As a …
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Design, Testing And Controls For Air Source Heat Pump System In Cold Climates Using Natural & Conventional Refrigerants
<p>Fossil-fuel based heating systems used in the residential buildings in northeastern U.S region are not only inefficient but also largely responsible for the greenhouse gas emissions in U.S. Electrification of the buildings has been proved to be the most efficient way to reduce the greenhouse gas …
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