Performance evaluation of solar chimney in tunnel for passive ventilation and smoke exhaustion: A numerical approach

Solar chimney applied in building ventilation can passively regulate indoor air quality without electricity cost and carbon emissions, but its application in tunnel is limited. This study conducted a numerical modelling and theoretical analysis to investigate the volumetric flow rate through multi-channel solar chimney group in tunnel under normal and fire conditions. The influences of the solar chimney arrangements on ventilation and smoke exhaustion capacity were analyzed. Results show that the solar chimney group can afford natural ventilation in tunnel without compromising the performance of smoke exhaustion through shaft. With absorbed more solar energy, increasing cavity amount and cavity width can effectively improve the ventilation performance but limited effect on smoke exhaustion. The volumetric flow rate increases with cavity height and cavity depth that is proportional to hc1/3 and L2/3 under natural ventilation. The volumetric flow rate under natural ventilation and smoke exhaustion both increase with total chimney channel area. A theoretical model considering horizontally semi-parabolic temperature distribution inside each channel was developed to correlate the volumetric flow rate, the predictions agree reasonably with numerical results under normal and fire conditions. This study contributes to the application of solar chimney group in urban tunnels and guides extraction design

Enhancing solar chimney performance in urban tunnels: Investigating the impact factors through experimental and theoretical model analysis

Efficient and sustainable ventilation in urban tunnels is crucial for combating air pollution and safeguarding human health. This study investigates the design factors impacting solar chimney performance in urban tunnels to optimize ventilation efficiency. Experimental trials analyzed the effects of blockage ratio, chimney height, and solar radiation on temperature distribution and ventilation rate. The results demonstrate that increased chimney height and solar radiation positively influence airflow velocity at the chimney outlet, enhancing ventilation. The temperature rise near absorber is higher than that closed to glazing wall. Temperature distribution within the chimney follows a distinctive horizontal two-piecewise semi-parabolic decay pattern, enabling accurate prediction of temperature profiles along the cavity depth. Novel analytical models predict temperature distribution, airflow velocity, and ventilation rate within the solar chimney system, aiding precise design and optimization. Remarkably, the blockage ratio has limited impact on ventilation rate, allowing for disregarding vehicle blockage effects in solar chimney design for urban tunnels. Matching chimney width to tunnel width and ensuring a relatively high chimney height are emphasized for optimal functionality. The study holds substantial implications for ventilation system design in urban environments, promoting healthier and more sustainable cities

Theoretical models for predicting ventilation performance of vertical solar chimneys in tunnels

Solar chimney as a reliable renewable energy system has been primarily utilized for building ventilation, but its application in the tunnel is rarely explored. This study develops theoretical models to predict the ventilation performance of vertical solar chimney in urban tunnel. Five temperature distribution types within the chimney cavity are analyzed, including uniform, vertically linear, horizontally semi-parabolic, two piecewise semi-parabolic in the depth direction, and three-dimensional parabolic profiles. The theoretical models consider the effect of chimney configuration, tunnel geometry, glazing materials, and solar radiation intensity on airflow rate through solar chimney. Validation against experimental data and numerical simulation shows that considering three-dimensional temperature distributions results in an average 11 % deviation from validation data, outperforming assumptions of uniform (29.3 % deviation) or lower-dimensional profiles. The volumetric flow rate through solar chimney exponentially decreased with h/w and h/d that the optimum ratio of h/d is 10. The airflow rate linearly increased with 0.14 power of glazing absorptivity. This analysis provides technical guidance for optimizing solar chimney design in tunnels, enhancing natural ventilation, and reducing energy consumption for mechanical ventilation systems

GRB 120729A: External Shock Origin for Both the Prompt Gamma-Ray Emission and Afterglow

Gamma-ray burst (GRB) 120729A was detected by Swift/BAT and Fermi/GBM, and then rapidly observed by Swift/XRT, Swift/UVOT, and ground-based telescopes. It had a single long and smooth \gamma-ray emission pulse, which extends continuously to the X-rays. We report Lick/KAIT observations of the source, and make temporal and spectral joint fits of the multiwavelength light curves of GRB 120729A. It exhibits achromatic light-curve behavior, consistent with the predictions of the external shock model. The light curves are decomposed into four typical phases: onset bump (Phase I), normal decay (Phase II), shallow decay (Phase III), and post-jet break (Phase IV). The spectral energy distribution (SED) evolves from prompt \gamma-ray emission to the afterglow with photon index from Γγ=1.36 to Γ≈1.75. There is no obvious evolution of the SED during the afterglow. ...(Please see article full tet for complete abstract.