No abstract is provided for this article.
The combustion and flame spread behaviors of discrete fuels often depend on the distribution of the fuel arrays, including the fuel bed width and the spacing of the fuel arrays. In this study, scenarios with six different numbers of columns (n, 1–11 with an interval of 2) and nine different spacings (S, 1–9 mm) were designed. By varying n and S, 54 groups of experimental scenarios over thermally thick birch rod arrays were studied to determine the effects of fuel bed width and spacing. The experimental results showed that the critical spacing for multi-column arrays was larger than that for single-column arrays. Moreover, flame extinction was found when n > 1 and S = 1 mm . The value of S had a limited influence on the mass loss rate when S > 2 mm , but restrained the mass loss rate when S ≤ 2 mm . A piecewise correlation between a newly defined dimensionless mass loss rate and the exposed area ratio was proposed. Moreover, a prediction model of the mass loss rate was developed, which agreed reasonably well with the experimental data. With increasing spacing, the flame height showed three stages: increasing, relatively stable, and decreasing, which were dominated by the balance between air entrainment and radiant heat feedback. The three processes were further described by a piecewise correlation between the dimensionless flame height and fuel bed width. Based on the assumption of a constant incident heat flux, a prediction model of the global flame spread rate was built, which presented better predicted results than the previous models. In addition, it was found that the newly defined dimensionless global flame spread rate linearly increased with increasing porosity.
Full-scale compartment fire experiment initiated by a corner gasoline pool fire was conducted to investigate the enhancement effect of polyethylene (PE) slabs attached on the internal walls on fire development and smoke evolution. An open door and an initially closed window served as the openings to provide natural ventilation condition. Corresponding numerical simulations, employing a CFD tool Fire Dynamics Simulation (FDS), were carried out as well to study the fire growth, smoke temperature, smoke layer height, and indoor visibility. Both PE and non-PE compartment fire circumstances were simulated to examine the intensifying mechanism of burning PE slabs. The results show that the attached PE slabs on the walls would greatly intensify the compartment fire and result in a much higher smoke temperature by about 325 °C, which could significantly facilitate the potential occurrence of flashover. The molten PE generated a considerable pool fire on the floor and resulted in a secondary peak in smoke temperature curve after the burnout of gasoline. However, this secondary peak is not found in the simulation results due to the neglect of melting and flowing process in numerical model. Some random ignition incidents in test, such as the splash of pool fire and collapse of furniture, contributed to the deviation between experimental and numerical results. Smoke layer height was empirically estimated to be 1.8 m and compared with numerical predictions. The empirical model predicted the smoke layer height well after the break of window at the steady state.
No abstract is provided for this article.
This paper deduces the quantitative relationship between the flux vectors and the power of power winding (PW) in brushless doubly‐fed reluctance generator (BDFRG). On this basis, the direct power control (DPC) theory of BDFRG is established, which makes up the deficiency that the DPC theory of BDFRG is only based on qualitative analysis in the existing literature. The power derivative expression is derived for accurately analyzing the effect of voltage vector of control winding (CW) on the power of PW, concluding that the control effect of DPC is related to the operation point of a BDFRG. The number of basic voltage vectors of CW connected with two‐level converter is limited, resulting that under some operation conditions, a BDFRG controlled by DPC could present a time interval where the power cannot be controlled satisfactorily. Therefore, the space vector modulation‐based direct power control (SVM‐DPC) strategy of BDFRG is proposed, which can solve the above problem and fix the switching frequency. Experimental results prove the correctness of the elaboration and the proposed method. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.
No abstract is provided for this article.
The role of tensor force is investigated by using the time-dependent Hartree-Fock (TDHF) theory in the collision 16O+40Ca. The full tensor force is incorporated in our TDHF implementation. The calculations are performed in three-dimensional Cartesian coordinate without any symmetry restrictions. We study the effect of tensor force on Coulomb barrier, upper fusion threshold energy, and energy contribution of the time-odd and tensor terms in Skyrme energy functional. The Coulomb barrier obtained from the energy functional with frozen density approximation is compared with the available experimental data. We find that the tensor force may change the upper fusion threshold energy in the order of a few MeV for the collision 16O+40Ca. The tensor force has a non-negligible effect in heavy-ion collisions.
Incorporating phase change material (PCM) into construction materials is an effective method for modifying building energy regulations throughout their service life. However, the effectiveness of PCM is constrained by its low thermal conductivity, highlighting the need for efficient enhancement methods. This study introduces thermally conductive carbon-based additions at both the nano-scale and meso-scale with different shapes, including carbon nano-tube (CNT), carbon black nano-particle (CB), and carbon fibre (CF) in PCM mortar. The mixed hydrated inorganic salt serves as the core PCM, while expanded perlite acts as the supporting material for the stable PCM composite, based on the presented research. The multi-scale additions establish thermal conduction pathways that improve temperature regulation performance. The modified samples exhibited a temperature difference of 2.2 °C and a time lag of up to 20 min under natural cooling conditions. Notably, CB positively influenced thermal conductivity, while CNT demonstrated an unexpected minor reduction. The enhancement in thermal conductivity increased with the content of CB, reaching an optimal enhancement of 18 %, except at a CNT content of 0.5 %. Conversely, both CB and CNT consistently improved thermal diffusivity. Furthermore, the compressive strength of the modified samples was significantly enhanced by up to 24 % compared to PCM mortar without carbon modifications. The modification method proposed in this study significantly improves both the thermal and mechanical properties of PCM mortar.
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.
In this paper, the intellectual nondestructive testing (NDT) instrument for largesize geotechnical engineering and its application are presented. The instrument consists of large power rare earth magnetostrictive transducer, which has focused energy and good repetition, DB16 digital acquisition system that communicates with personal computer (PC) or notebook PC by parallel interface and high sensitive (PZT) transducer with low frequency. The data is dealt with computerized tomography (CT) technology and the results are color contour map. The manipulations of parameter setting, data acquisition and save, CT calculation and contour map are completed with one special program.
Solar chimney is a reliable system totally based on solar energy to enhance natural ventilation in buildings, but challenge still exists to optimize its performance with the lowest cost. In this study, three designing factors, including configuration, installation conditions, and material usages, were reviewed to provide a technical guide for engineering applications. Regarding the configuration, the performance of solar chimney can be enhanced with a high cavity, an appropriate cavity gap (usually 0.2-0.3 m), equivalent inlet and outlet area, and height/gap ratio of 10-15. Regarding installation conditions, an optimum inclination angle of 45° was usually suggested, and large openings can enhance the performance while the increasing rate keeps decreasing. The principles of material usage are to maximum the heat absorption and reduce the heat losses, considering properties such as thermal conductivity, absorptivity, emissivity, transmissvity, and reflectivity.
This study experimentally investigates fire behaviors of double fires with asymmetric heat release rates in a naturally ventilated tunnel including flame merging and longitudinal ceiling gas temperature distribution. The comparison between double fires with symmetric and asymmetric heat release rates was also made. The results show that the flame merging possibility increases as the heat release rate on one side increases. The ratio of heat release rates between double fire sources still influences the flame merging possibility under a given total heat release rate. The ceiling gas temperature distribution is related to the flame merging state. As the fire separation distance increases from zero, the position of peak temperature is closer to the fire source with a larger heat release rate due to a smaller flame tilt angle. For scenarios with mean flame merged, the ceiling gas temperature distribution on both sides is equal. For scenarios with mean flame not merged, the ceiling gas temperature on the side with a larger heat release rate is much higher. Finally, different empirical models are established to predict the excess ceiling gas temperature attenuation, considering different flame merging states and smoke spread regions.
