A STUDY OF SOLID CO2 FORMATION FROM RAPID FLUID EXPANSION USING CFD AND MATHEMATICAL MODELLING

Rapid carbon dioxide expansion from an accidental pipeline leakage is an adiabatic process that forms solid CO2 micro-particles entrained in CO2 vapor. While the vapor is subsequently dispersed as vapor cloud, the micro-particles – at sizes larger than 100 μm – can rain out to form a solid pool. The pool will then sublimate to the atmosphere and contribute significantly to the concentration of vapor cloud. Ultimately, the effect of solid rainout pool on vapor cloud concentration and dispersion has to be taken into consideration when calculating safety distance. In order to investigate the sizes of solid micro-particles formed under varying discharge scenarios, the process of rapid fluid expansion through an orifice (leakage) is emulated using a simulation model. It involves an integration of two sub-models: (1) a 3-D Computational Fluid Dynamics (CFD) model using FLUENT 14.0, and (2) a mathematical model published by authors Hulsbosch-Dam, Spruijt, Necci & Cozzani (2012). The CFD model employs the FLUENT software to obtain temperature and velocity profiles of rapid fluid expansion. The mathematical model calculates the droplet size distribution from the point of release and size of final solid particles formed. The combination of the two models generates results and parametric trends (mainly the effect of leakage size on the size of particles formed). They are then compared with experimental data available in literatures, and validation is achieved. Finally, the model is used to simulate rapid carbon dioxide expansion from pipeline leakage at supercritical storage conditions. Conclusive evidence shows that at supercritical storage conditions (specifically at 310 K and 150 bar), a pipeline leakage will not produce solid CO2 micro-particles big enough to form a solid rainout pool

Advanced coding and modulation schemes for TDRSS

This paper describes the performance of the Ungerboeck and pragmatic 8-Phase Shift Key (PSK) Trellis Code Modulation (TCM) coding techniques with and without a (255,223) Reed-Solomon outer code as they are used for Tracking Data and Relay Satellite System (TDRSS) S-Band and Ku-Band return services. The performance of these codes at high data rates is compared to uncoded Quadrature PSK (QPSK) and rate 1/2 convolutionally coded QPSK in the presence of Radio Frequency Interference (RFI), self-interference, and hardware distortions. This paper shows that the outer Reed-Solomon code is necessary to achieve a 10(exp -5) Bit Error Rate (BER) with an acceptable level of degradation in the presence of RFI. This paper also shows that the TCM codes with or without the Reed-Solomon outer code do not perform well in the presence of self-interference. In fact, the uncoded QPSK signal performs better than the TCM coded signal in the self-interference situation considered in this analysis. Finally, this paper shows that the E(sub b)/N(sub 0) degradation due to TDRSS hardware distortions is approximately 1.3 dB with a TCM coded signal or a rate 1/2 convolutionally coded QPSK signal and is 3.2 dB with an uncoded QPSK signal

Reply to Jurdy & Stefanick comment

We disagree with virtually all of what Jurdy & Stefanick have written. Part of our disagreement stems from personal opinions about what is ‘simple’, ‘arbitrary’, ‘artificial’, ‘undesirable’, etc., but other disagreements are more profound and reveal a very different understanding of finite rotations. Jurdy & Stefanick raise two basic objections. One concerns statistical questions that were not meant to be part of Chang et al. (1990). The other addresses the main issue of our paper, the parametrization of uncertainties of rotations. They suggest that both our approach is flawed and that theirs, outlined in Jurdy & Stefanick (1987), is better. Except possibly for their opinion of what constitutes a covariance matrix, we try not to indulge the reader with long discussions of questions of personal preference, but instead to confine our response to these basic questions

A STUDY OF SOLID CO2 FORMATION FROM RAPID FLUID EXPANSION USING CFD AND MATHEMATICAL MODELLING

Rapid carbon dioxide expansion from an accidental pipeline leakage is an adiabatic process that forms solid CO2 micro-particles entrained in CO2 vapor. While the vapor is subsequently dispersed as vapor cloud, the micro-particles – at sizes larger than 100 μm – can rain out to form a solid pool. The pool will then sublimate to the atmosphere and contribute significantly to the concentration of vapor cloud. Ultimately, the effect of solid rainout pool on vapor cloud concentration and dispersion has to be taken into consideration when calculating safety distance. In order to investigate the sizes of solid micro-particles formed under varying discharge scenarios, the process of rapid fluid expansion through an orifice (leakage) is emulated using a simulation model. It involves an integration of two sub-models: (1) a 3-D Computational Fluid Dynamics (CFD) model using FLUENT 14.0, and (2) a mathematical model published by authors Hulsbosch-Dam, Spruijt, Necci & Cozzani (2012). The CFD model employs the FLUENT software to obtain temperature and velocity profiles of rapid fluid expansion. The mathematical model calculates the droplet size distribution from the point of release and size of final solid particles formed. The combination of the two models generates results and parametric trends (mainly the effect of leakage size on the size of particles formed). They are then compared with experimental data available in literatures, and validation is achieved. Finally, the model is used to simulate rapid carbon dioxide expansion from pipeline leakage at supercritical storage conditions. Conclusive evidence shows that at supercritical storage conditions (specifically at 310 K and 150 bar), a pipeline leakage will not produce solid CO2 micro-particles big enough to form a solid rainout pool

Atomic ionization by sterile-to-active neutrino conversion and constraints on dark matter sterile neutrinos with germanium detectors

The transition magnetic moment of a sterile-to-active neutrino conversion gives rise to not only radiative decay of a sterile neutrino, but also its non-standard interaction (NSI) with matter. For sterile neutrinos of keV-mass as dark matter candidates, their decay signals are actively searched for in cosmic X-ray spectra. In this work, we consider the NSI that leads to atomic ionization, which can be detected by direct dark matter experiments. It is found that this inelastic scattering process for a nonrelativistic sterile neutrino has a pronounced enhancement in the differential cross section at energy transfer about half of its mass, manifesting experimentally as peaks in the measurable energy spectra. The enhancement effects gradually smear out as the sterile neutrino becomes relativistic. Using data taken with germanium detectors that have fine energy resolution in keV and sub-keV regimes, constraints on sterile neutrino mass and its transition magnetic moment are derived and compared with those from astrophysical observations