High-Fidelity Modeling of Buoyancy-Driven Diffusion Flames Towards Fire Suppression

Buoyancy-driven diffusion flames have been widely studied as a canonical fire configuration due to practical and scientific interests. Numerical investigations are conducted in this dissertation to improve understandings of interactions and couplings among turbulence, chemistry, soot, and multiphase radiation in buoyancy-driven diffusion flames. A high-fidelity modeling framework based on OpenFOAM-5.x, including detailed models for chemistry, radiation, and soot, is developed to improve the numerical accuracy and the computational efficiency with scale-resolved simulations. A Monte Carlo ray tracing (MCRT) based radiation solver coupled with line-by-line databases is developed to describe gas and soot radiation. Detailed and efficient radiation models for water mists are developed and coupled with the MCRT solver. An adaptive hybrid integration chemistry solver is implemented to speed up finite-rate chemistry integration. A semi-empirical two-equation soot model is incorporated to describe soot dynamics. The developed multi-physical platform is systematically verified through a series of combustion-radiation systems including a laminar ethylene diffusion flame and four laminar methane diffusion flames with good agreement. The developed platform is subsequently employed to investigate a laboratory-scale turbulent pool fire. Good agreement with experiments on radiative heat fluxes, and with theories on flame temperature, velocity and puffing frequency, is achieved. Detailed investigations on interactions among chemistry, soot, radiation, and turbulence are performed to gain physical insights on modeling chemistry, soot and radiation. Drawn on the database from high-fidelity pool fire simulations, three physics-based reduced-order models including a flamelet model considering re-absorption, an optimized two-step mechanism for chemistry, and a simple soot model based on the laminar smoke point concept, are developed. Encouraging results are obtained using the reduced-order models with considerable savings in computational cost. Finally, to investigate radiative attenuation of water mists in fire suppression, a radiation model considering anisotropic scattering for water mists is developed and validated against theoretical values, and is adopted to obtain benchmark results for development of reduced-order radiation models

Effect of Multiphase Radiation on Coal Combustion in a Pulverized Coal jet Flame

The accurate modeling of coal combustion requires detailed radiative heat transfer models for both gaseous combustion products and solid coal particles. A multiphase Monte Carlo ray tracing (MCRT) radiation solver is developed in this work to simulate a laboratory-scale pulverized coal flame. The MCRT solver considers radiative interactions between coal particles and three major combustion products (CO2, H2O, and CO). A line-by-line spectral database for the gas phase and a size-dependent nongray correlation for the solid phase are employed to account for the nongray effects. The flame structure is significantly altered by considering nongray radiation and the lift-off height of the flame increases by approximately 35%, compared to the simulation without radiation. Radiation is also found to affect the evolution of coal particles considerably as it takes over as the dominant mode of heat transfer for medium-to-large coal particles downstream of the flame. To investigate the respective effects of spectral models for the gas and solid phases, a Planck-mean-based gray gas model and a size-independent gray particle model are applied in a frozen-field analysis of a steady-state snapshot of the flame. The gray gas approximation considerably underestimates the radiative source terms for both the gas phase and the solid phase. The gray coal approximation also leads to under-prediction of the particle emission and absorption. However, the level of under-prediction is not as significant as that resulting from the employment of the gray gas model. Finally, the effect of the spectral property of ash on radiation is also investigated and found to be insignificant for the present target flame

Detailed Modeling of a Small-Scale Turbulent Pool Fire

Turbulent pool fires have been studied as a canonical configuration in fire science with wide interest. A numerical study of a small-scale turbulent heptane pool fire is conducted in the present study to understand the interactions and coupling among turbulence, chemistry, soot, and radiation in pool fires. A Monte Carlo ray tracing based radiation solver, with line-by-line spectral models for five gaseous species and soot, is coupled with a fireFOAM-based reacting flow solver to describe the dynamics of the target fire. A 33-species skeletal mechanism is employed to describe the finite-rate chemistry. A two-equation soot model with C2H2 based inception model is incorporated to describe soot dynamics. Turbulence is resolved by the computational grid to avoid the uncertainties in modeling the sub-grid scale stress and turbulence-chemistry-radiation interactions. The computed radiative heat fluxes are directly compared with experimental signals and good agreement is observed. Rarely compared in the literature, the line-of-sight spectral distribution of the emissive power is computed and compared with experimental measurements with excellent match in the 4300 nm CO2-dominant emissive peak. A secondary emissive peak near 3300 nm is absent from the numerical results, which can be attributed to experimental uncertainties and/or insufficient representation of the C-H stretching bonds in the radiation spectral model. The instantaneous flame structures show the presence of abundant hydrocarbon molecules as fuel pyrolysis products. A detailed examination of the chemical and radiative source terms reveals the disproportionate relation between these two source terms, especially when soot is present. Soot radiation is largely optically thin while gas radiation is much thicker in optical depth, as a result of the spatial structures of the flame and the non-grey interactions between gas and soot. With the abundant information provided by the detailed simulation in this study, models for turbulence-chemistry-radiation interactions will be derived in future work

DataSheet_1_Treatment- and immune-related adverse events of immune checkpoint inhibitors in esophageal or gastroesophageal junction cancer: A network meta-analysis of randomized controlled trials.zip

ObjectiveTo systematically evaluate the safety and adverse event profiles of immune checkpoint inhibitors (ICIs) in patients with esophageal cancer (EPC) or gastroesophageal junction cancer (GEJC).MethodsPubMed, Web of Science, Cochrane Library, and major conference proceedings were systematically searched for all phase II or phase III randomized controlled trials (RCTs) in EPC or GEJC using ICIs. Safety outcomes including treatment-related adverse events (trAEs), immune-related adverse events (irAEs), and serious trAEs were evaluated by network meta-analysis or dichotomous meta-analysis based on the random-effects model.ResultsEleven RCTs involving EPC (five RCTs) and GEJC (six RCTs) were included in the final meta-analysis. NMA showed that placebo was associated with the best safety ranking for grade 3–5 trAEs (SUCRA = 96.0%), followed by avelumab (78.6%), nivolumab (73.9%), ipilimumab (57.0%), and pembrolizumab (56.6%). Conventional pairwise meta-analysis (CPM) showed that ICIs have similar grade 3–5 trAE risk compared with chemotherapy (RR = 0.764, 95% CI: 0.574 to 1.016, I2 = 95.7%, Z = 1.85, P = 0.065). NMA showed that the general safety of grade 3–5 irAEs ranked from high to low is as follows: ChT (85.1%), placebo (76.5%), ipilimumab (56.0%), nivolumab (48.5%), avelumab (48.4%), camrelizumab (41.8%), pembrolizumab (36.4%), and nivolumab + ipilimumab (21.6%). CPM showed that the rates of grade 3–5 irAEs in the ICI group and the chemotherapy group were 7.35% (154/2,095, 95% CI: [6.23%, 8.47%]) versus 2.25% (42/1,869, 95% CI: [1.58%, 2.92%]), with statistical significance (RR = 3.151, 95% CI = 2.175 to 4.563, Z = 6.07, P = 0.000). The most common irAEs in the ICI group were skin reaction (15.76%, 95% CI: [13.67%, 17.84%]), followed by hypothyroidism (9.73%, 95% CI: [8.07%, 11.39%]), infusion-related reactions (5.93%, 95% CI: [4.29%, 7.58%]), hepatitis (5.25%, 95% CI: [4.28%, 6.22%]), and pneumonitis (4.45%, 95% CI: [3.5%, 5.4%]).ConclusionDifferent ICIs had different toxicity manifestations and should not be considered as an entity. Compared with chemotherapy, ICIs were more prone to irAEs, but the overall rates remained low and acceptable. For clinicians, it is important to recognize and monitor the adverse events caused by ICIs for patients with EPC or GEJC.</p