Effect of Boundary Conditions on Propagation and Morphology of Premixed Flames in Narrow Conduits

Boundary conditions play a key role in the evolution and morphology of flame fronts, especially when combustion occurs in narrow chambers. The burning intensity and the flame-generated flow can be significantly modified by the momentum and energy transferred at the walls, which are further modified by the exothermal nature of the process. In this work, the effect of the wall roughness and thermal conditions on the flame propagation is explored. Specifically, conduits with and without obstacles, having adiabatic or isothermal walls, are investigated.;Wall friction constitutes one of the main reasons of spontaneous flame acceleration in narrow pipes. Although this phenomenon has been intensely studied, the researchers have focused on the mechanistic scenario of the combustion intensification, induced by the wall friction, putting less emphasis on the heat exchanged at the walls. In this study, besides the adiabatic condition, the surfaces have been kept at multiple constant temperatures in order to explore the wall thermal effects on the burning process, recognizing its potential to diminish or even quench the reaction.;Moreover, the inclusion of solid obstacles at the pipe walls provides a mechanism of extremely fast flame acceleration, which is driven by an intense jet-flow generated by the delayed combustion occurring between obstacles. In this work, the flame dynamics promoted in the obstructed configuration is analyzed, comparing the attained acceleration rates to other mechanisms such as that generated by the wall friction and the so-called finger flame evolution.;For this purpose, a parametric study provided by extensive fully-compressible numerical simulations of the combustion and hydrodynamic equations is performed. The geometry is primary given by 2D channels, although cylindrical \u27smooth\u27 tubes have been also considered. The wall conditions include non-slip walls and slip walls with obstacles; adiabatic and isothermal, with the fuel characterized by the thermal expansion coefficient. Four regimes of flame propagation in isothermal \u27smooth\u27 channels have been identified, for flames propagating a distance around 100-150 times the flame thickness: (i) no flame propagation or extinction; (ii) linear flame velocity; (iii) almost-constant flame propagation speed; and (iv) oscillating flame velocity. In the obstructed configuration, the developing of turbulent and laminar combustion regimes at the early stages of the process have been identified in relation to the obstacles size and spacing, including a finger flame-like limit when small enough obstacles are in place

Thermal analysis of tilted roofs composed of two separated surfaces

Due to the rising power costs and lack of nonrenewable energy sources, the cooling of houses is becoming more expensive. Looking for alternative methods applicable to this process is becoming not only an option, but also a necessity. Changes in the roof structure of buildings can be applied in order to achieve a more favorable thermal transmission behavior. The utilization of a tilted roof, composed of two separated surfaces, generates natural convection currents in the channel between them. These currents, after driving off part of the transferred heat, decrease the temperature of the lower surfaces and consequently, the heat flux through the ceiling into the living areas.;The natural convection phenomenon is treated by numerical means, and the influence of the dimensions of the proposed design on the ventilation rates is analyzed in order to determine the most efficient geometry. The comparison of thermal performances between the proposed roof and a typical unventilated design is also established in order to realize the quantitative advantage of the proposed model.;Results show that the separation between surfaces strongly influences the process within certain values; i.e. a reduction in the heat flux through the ceiling achieved by the system of 32.9% can be raised to 45.4% by increasing the width of the channel from 0.05m to 0.15m, and keeping the other dimensions constant. Moreover, higher tilt angles also improve natural ventilation rates. For example, a 32.8% reduction obtained by the system at a 30 degree tilt angle grows up to 41.6% by raising the tilt angle to 65 degrees. A vertical extension or exhaust channel on the top increases the reduction of heat flux too, but with less intensity. In this sense, the heat flux reduction achieved by the system, when the vertical exhaust length is 12.5% of the length of the roof, increases from 32.9% to 45.5% when a considerably bigger vertical extension is used, 60% of the roof length

Spitzer Space Telescope Measurements of Dust Reverberation Lags in the Seyfert 1 Galaxy NGC 6418

We present results from a fifteen-month campaign of high-cadence (~ 3 days) mid-infrared Spitzer and optical (B and V ) monitoring of the Seyfert 1 galaxy NGC 6418, with the objective of determining the characteristic size of the dusty torus in this active galactic nucleus (AGN). We find that the 3.6 $\mu$m and 4.5 $\mu$m flux variations lag behind those of the optical continuum by $37.2^{+2.4}_{-2.2}$ days and $47.1^{+3.1}_{-3.1}$ days, respectively. We report a cross-correlation time lag between the 4.5 $\mu$m and 3.6 $\mu$m flux of $13.9^{+0.5}_{-0.1}$ days. The lags indicate that the dust emitting at 3.6 $\mu$m and 4.5 $\mu$m is located at a distance of approximately 1 light-month (~ 0.03 pc) from the source of the AGN UV-optical continuum. The reverberation radii are consistent with the inferred lower limit to the sublimation radius for pure graphite grains at 1800 K, but smaller by a factor of ~ 2 than the corresponding lower limit for silicate grains; this is similar to what has been found for near-infrared (K-band) lags in other AGN. The 3.6 and 4.5 $\mu$m reverberation radii fall above the K-band $\tau \propto L^{0.5}$ size-luminosity relationship by factors $\lesssim 2.7$ and $\lesssim 3.4$, respectively, while the 4.5 $\mu$m reverberation radius is only 27% larger than the 3.6 $\mu$m radius. This is broadly consistent with clumpy torus models, in which individual optically thick clouds emit strongly over a broad wavelength range.Comment: 13 pages, 9 figure

Dust Reverberation Mapping and Light-Curve Modelling of Zw229-015

Multiwavelength variability studies of active galactic nuclei (AGN) can be used to probe their inner regions which are not directly resolvable. Dust reverberation mapping (DRM) estimates the size of the dust emitting region by measuring the delays between the infrared (IR) response to variability in the optical light curves. We measure DRM lags of Zw229-015 between optical ground-based and Kepler light curves and concurrent IR Spitzer 3.6 and 4.5 $\mu$m light curves from 2010-2015, finding an overall mean rest-frame lag of 18.3 $\pm$ 4.5 days. Each combination of optical and IR light curve returns lags that are consistent with each other within 1$\sigma$, which implies that the different wavelengths are dominated by the same hot dust emission. The lags measured for Zw229-015 are found to be consistently smaller than predictions using the lag-luminosity relationship. Also, the overall IR response to the optical emission actually depends on the geometry and structure of the dust emitting region as well, so we use Markov chain Monte Carlo (MCMC) modelling to simulate the dust distribution to further estimate these structural and geometrical properties. We find that a large increase in flux between the 2011-2012 observation seasons, which is more dramatic in the IR light curve, is not well simulated by a single dust component. When excluding this increase in flux, the modelling consistently suggests that the dust is distributed in an extended flat disk, and finds a mean inclination angle of 49$^{+3}_{-13}$ degrees.Comment: 32 pages, 32 Figures, 7 Tables; Accepted for publication in MNRA

SNOT-22 in a Control Population

AIM: To assess SNOT-22 and its subscales in a non-rhinosinusitis UK-wide population.  METHODOLOGY/PRINCIPLE: This analysis uses data from the 'Chronic Rhinosinusitis Epidemiology Study' (CRES) which recruited from 30 centres across the UK, and the Socioeconomic Cost of ChrOnic Rhinosinusitis study' (SocCoR); 250 volunteers without CRS were recruited as part of these studies. Study-specific questionnaires including demographics, socioeconomic factors and past medical history as well as SNOT-22 and SF-36 were distributed. The control (non-CRS) population had no self-reported nasal problems in the past, no chronic conditions undergoing active treatment and no hospital admissions in the preceding 12 months.  RESULTS: The mean SNOT-22 total score overall was 12.0. The mean was 10.2 for males with a median of 6.5, and a mean of 13.2 for females with a median of 9. Females scored significantly more highly than males on the sleep/fatigue and facial domains.  CONCLUSIONS: Our data demonstrate differences in SNOT-22 amongst males and females. These data can be used in future studies for comparison with different disease populations with rhinosinusitis. This article is protected by copyright. All rights reserved

\u3cem\u3eSpitzer Space Telescope\u3c/em\u3e Measurements of Dust Reverberation Lags in the Seyfert 1 Galaxy NGC 6418

We present results from a 15 month campaign of high-cadence (~3 days) mid-infrared Spitzer and optical (B and V) monitoring of the Seyfert 1 galaxy NGC 6418, with the objective of determining the characteristic size of the dusty torus in this active galactic nucleus (AGN). . . . For the remainder of the abstract, please visit: http://dx.doi.org/10.1088/0004-637X/801/2/12