Momentum, energy and scalar transport in polydisperse gas-solid flows using particle-resolved direct numerical simulations

Gas-solid flows are commonly encountered in Nature and in several industrial applications. Emerging carbon-neutral or carbon negative technologies such as chemical looping combustion and CO2 capture are examples of gas-solid flows in power generation industry. Computational fluid dynamics (CFD) simulations are increasingly being seen as a cost-effective tool in the design of technological applications in power generation industry. Device-scale CFD calculations that involve gas-solid flow are based on statistical descriptions that require closure models for the exchange of mass, momentum, energy and heat transfer between the dispersed solid phase and the gas phase. The predictive capability of multiphase flow CFD simulations strongly depends on the accuracy of the models used for the interphase exchange terms. Particle-resolved direct numerical simulation (PR-DNS) is a first-principles approach to develop accurate models for interphase momentum, energy and heat transfer in gas-solid flow. The primary objective of this work is the development of accurate models for the interphase exchange of momentum, kinetic energy and heat transfer in polydisperse gas-solid flows using PR-DNS. A novel computational tool named Particle-resolved Uncontaminated-fluid Reconcilable Immersed Boundary Method (PUReIBM) has been developed as a part of this work to perform PR-DNS of flow past fixed and freely moving spherical particles. We designed the appropriate numerical experiment that can be used to develop closure models for interphase momentum transfer and formally established the connection between PR-DNS and statistical theory of multiphase flow for which the models are intended. Using PUReIBM we developed an improved drag correlation to model interphase momentum transfer in gas-solid flow. The solution fields obtained from PUReIBM PR-DNS have been used to quantify the velocity fluctuations in the gas-phase and a simple eddy viscosity model for the gas-phase pseudo-turbulent kinetic energy has been developed. A novel PR-DNS methodology to study heat transfer in gas-solid flow has been developed. These results provide insight into the role of fluid heating in gas-solid flow and motivate the development of better models for gas-solid flow heat transfer. From PR-DNS of freely evolving gas-solid suspensions we developed a stochastic model for particle acceleration that accounts for the particle velocity distribution. In addition to model development, the implementation of a parallel algorithm that enables PR-DNS of gas-solid flow on petascale supercomputers is also discussed

Design of Auto Mix Single Stage Anaerobic Digester and Aspen Plus Simulation for Biogas Production

Bio fuels have been considered to be the viable alternatives and the supportive sources for the depleting fossil fuels under the objective of satisfying the energy demand. The work explored the possibility of biogas production in various operational scales. The present work can be categorized into two parts. In the first part, the work has surveyed various digester designs under operation and focused on the mixing and intermittent aeration that are not under light in the regular practice. The digester gas collector configuration that could promote the mixing and intermittent aeration was designed. The setup was run on 20 L scale with an objective of observing the gas production phenomenon. The recommended operational solutions were modified and implemented in the form of a 50 L digester setup to observe the performance improvements in attaining self-buffering capacity and sensitivity to the acidic feed stocks. Further suggested modifications lead to the final design that could promote intermittent aeration and mix the digester constituents without the use of impeller and with minimal or no power consumption depending on the amount of gas produced. An advanced design called compartmental digester design was next presented for the medium to large scale applications which was run on 200 L scale in a semi continuous mode using cow dung as substrate and was tested for the feasibility. The second part of our work focused on simulation of a two stage anaerobic digester configuration for studying the kinetics of hydrolysis, acidogenesis and acetogenesis and methanogenesis in three different reactors. In this study, kitchen waste stream were analysed for biogas production which was compared with the results of NISARGRUNA biogas plant (BARC) for the validation of the model and the model with same kinetics was then used to analyse the gas production from poultry manur

The characteristics of HIV patients who are long-term responders to nevirapine

Objective: To define Nevirapine long term responders (NLTRs) and identify the characteristics of patients who stay on the drug for long periods of time without adverse effects and maintain suppression of HIV replication without development of resistance.Methodology: Demographic and clinical data was collected for all the patients >18 years old from Department of Clinical Immunology, Royal Perth Hospital, Western Australia. All the patients included in the study received Nevirapine as part of their first regimen of anti-retroviral therapy. Data collection and analysis were divided in three groups based on their length of stay on Nevirapine; short-term, medium and long-term responders. Patients who stayed on Nevirapine continuously for more than five years were considered long-term responders (60+ months). Patients who withdraw before six months of therapy due to the drug’s side effects or any other reason are considered short-term responders (0-6 months). Patients whose length of stay on the drug is intermediate between these two groups are considered as medium responders (6-60 months). Investigation of the possible genetic influence on response to Nevirapine was made by analysis of genetic markers like HLA-B35+C4, HLA-DR1, and HLA-B14.Results: We found no difference in the frequencies of HLA-DR1 or HLA- B14 in the three groups. However, we found that HLA-B35+HLA-C4 did not occur in any of the Nevirapine long term responders (NLTRs). This was not described in previous studies. Furthermore, when a survival analysis was performed, carriage of HLA-B35+HLA-C4 identified patients who were not NLTRs.Conclusion: This study was carried out to determine whether or not factors like age, gender, baseline CD4+ count, baseline RNA, and HLA alleles would predict the length of stay on Nevirapine. Although the factors considered for the study have previously been associated with hyper-sensitivity reactions, they do not predict how long a patient would stay on the drug. However, it can be understood from the study that patients who had a combination of HLA alleles B35+HLA-C4 would not continue on Nevirapine use for a prolonged time

Galaxy Shapes and Intrinsic Alignments in The MassiveBlack-II Simulation

The intrinsic alignment of galaxy shapes with the large-scale density field is a contaminant to weak lensing measurements, as well as being an interesting signature of galaxy formation and evolution (albeit one that is difficult to predict theoretically). Here we investigate the shapes and relative orientations of the stars and dark matter of halos and subhalos (central and satellite) extracted from the MassiveBlack-II simulation, a state-of-the-art high resolution hydrodynamical cosmological simulation which includes stellar and AGN feedback in a volume of $(100{h^{-1}\mathrm{Mpc}})^3$. We consider redshift evolution from $z=1$ to $0.06$ and mass evolution within the range of subhalo masses, $10^{10} -6.0 \times 10^{14.0}{h^{-1}M_{\odot}}$. The shapes of the dark matter distributions are generally more round than the shapes defined by stellar matter. The projected root-mean-square (RMS) ellipticity per component for stellar matter is measured to be $e_\text{rms} = 0.28$ at $z=0.3$ for $M_{subhalo}> 10^{12.0}{h^{-1}M_{\odot}}$, which compares favourably with observational measurements. We find that the shapes of stellar and dark matter are more round for less massive subhalos and at lower redshifts. By directly measuring the relative orientation of the stellar matter and dark matter of subgroups, we find that, on average, the misalignment between the two components is larger for less massive subhalos. The mean misalignment angle varies from $\sim 30^{\circ}-10^{\circ}$ for $M \sim 10^{10} - 10^{14} {h^{-1}M_{\odot}}$ and shows a weak dependence on redshift. We also compare the misalignment angles in central and satellite subhalos at fixed subhalo mass, and find that centrals are more misaligned than satellites. We present fitting formulae for the shapes of dark and stellar matter in subhalos and also the probability distributions of misalignment angles.Comment: 18 pages, 18 figures, submitted to MNRA

Intrinsic alignments of galaxies in the MassiveBlack-II simulation: analysis of two-point statistics

The intrinsic alignment of galaxies with the large-scale density field is an important astrophysical contaminant in upcoming weak lensing surveys. We present detailed measurements of the galaxy intrinsic alignments and associated ellipticity-direction (ED) and projected shape ($w_{g+}$) correlation functions for galaxies in the cosmological hydrodynamic MassiveBlack-II (MB-II) simulation. We carefully assess the effects on galaxy shapes, misalignment of the stellar component with the dark matter shape and two-point statistics of iterative weighted (by mass and luminosity) definitions of the (reduced and unreduced) inertia tensor. We find that iterative procedures must be adopted for a reliable measurement of the reduced tensor but that luminosity versus mass weighting has only negligible effects. Both ED and $w_{g+}$ correlations increase in amplitude with subhalo mass (in the range of $10^{10} - 6.0\times 10^{14}h^{-1}M_{\odot}$), with a weak redshift dependence (from $z=1$ to $z=0.06$) at fixed mass. At $z \sim 0.3$, we predict a $w_{g+}$ that is in reasonable agreement with SDSS LRG measurements and that decreases in amplitude by a factor of $\sim 5$--18 for galaxies in the LSST survey. We also compared the intrinsic alignments of centrals and satellites, with clear detection of satellite radial alignments within their host halos. Finally, we show that $w_{g+}$ (using subhalos as tracers of density) and $w_{\delta+}$ (using dark matter density) predictions from the simulations agree with that of non-linear alignment models (NLA) at scales where the 2-halo term dominates in the correlations (and tabulate associated NLA fitting parameters). The 1-halo term induces a scale dependent bias at small scales which is not modeled in the NLA model.Comment: 25 pages, 27 figures, revised after referee comments, accepted for publication in MNRA