Search

Water and latent heat can be efficiently recycled from flue gas by using a porous membrane technology, and both the mechanism of water vapor condensation in nanopores and effects of surface properties are critically important to the performance of porous membranes. In this present study, the molecular dynamics simulation was employed to explore the mechanism of water vapor condensation and infiltration in nanopores with tunable surface wettability. Non-equilibrium molecular dynamics simulations of water vapor condensation in a single nanopore with tunable surface wettability were carried out, and then characteristics and dynamic behaviors of water vapor adsorption and condensation in hydrophobic and hydrophilic nanopores were examined in detail. Simulation results indicated that hydrophilic nanopores had high adsorption capacity, and the capillary pressure was the key for the infiltration or rebound progress of condensate in the hydrophobic nanopore. Based on the semi-infiltrated hydrophobic nanopore-liquid water system, furthermore, capillary pressures of hydrophobic nanopores with different sizes and tunable surface wettability were calculated quantitatively by molecular dynamics simulations.

Rigid polyurethane (PUR) foam, a sustainable thermosetting building facade porous polymer material, has been widely applied in the construction industry for energy conservation. Additional knowledge of the fire safety performance of PUR foam at different altitudes and sample widths is required. Comparative lab-scale experiments were conducted in the Lhasa plateau (66.5 kPa) and the Hefei plain (99.8 kPa) in China. Flame propagation characteristics (average flame spread rate and flame height) were measured at different widths and atmospheric pressures of the test locations. Experimental results show that the dependence of dimensionless flame heights on sample width shows negative power law relationships with index of -w / 5.4 - -w / 5.8. Both flame height and flame spread rate were lower under low ambient pressure conditions as Hf ∝ P0.26~0.33 and Vf ∝ P0.057~0.568 Flame spread rate decreased with increasing sample width in the convection regime before a critical width of 4 cm – 8 cm, after which the flame spread rate increased in the radiation regime. Results of this study contribute to the science of combustion, fire safety and energy conservation, and provide a basis for fire safety protocols for historical heritage buildings in the Lhasa plateau.

Experimental and theoretical investigations are conducted to analyze the influences of low atmospheric pressure on burning behavior of building facade insulation material flexible polyurethane (FPU). Comparison experiments for downward flame spread process over FPU under various facade inclined structures were performed at Hefei (99.8 kPa) and Lhasa (66.5 kPa), respectively. Characteristic parameters including burning rate (i.e. mass loss rate), flame spread velocity and flame height were studied in this paper. Firstly, morphological experimental results exhibited that the combustion was slower in reduced pressure condition and wider specimens showed more gradual flame spreading. Secondly, an inverted V-shaped spreading pyrolysis front was observed, and a “two-terminal” combustion behavior was found for narrow FPU board by partial molten flow combustion, which is critical to practical fire rescue techniques. Thirdly, power-law progressions of burning rate vs. pressure was proposed with an exponent ranging from 0.61 to 1.39, which can be illustrated by utilizing classical theory for sub-atmospheric pressure pool fire. Further, the increasing facade inclination angle significantly enhanced the flame spreading velocity, which suppressed the effect of pressure at high inclination angles. The flame temperature was measured to be increased at the lower pressure causing faster flame puffing. Finally, a linear relationship was determined between the pressure index values obtained by flame height vs. pressure and the inclination angle.

The fire risk associated with the use of rigid polyurethane foam (PUR) as thermal insulation material in building facades was investigated. To assess the effect of ambient pressure, the combustion ...

This study investigated the factors affecting the fire safety analysis of the common construction material flexible polyurethane foam, based on combustion at various inclination angles and the ambient pressures at the altitudes of the cities of Hefei (99.8 kPa) and Lhasa (66.5 kPa). The effects of ambient air pressure, specimen width and inclination angle on the burning rate (as determined by mass loss), average flame spreading velocity, flame temperature and flame length were examined. The combustion rate was lower at 66.5 kPa and the wider specimens exhibited gradual spreading of the flame front in conjunction with melting and dripping. The burning rates at various inclinations were found to correlate with the pressure according to the expression m ∝ p n , 0.67 n 1.36 , and this result can be explained based on pool fire theory. The average flame spreading velocity was found to correlate with pressure at various inclinations according to the relationship V a ∝ p n , 2 / 3 n 1 . The flame temperature was also observed to increase somewhat at the lower pressure, leading to an increase in the flame puffing frequency. Finally, a power law was used to describe the relationship between flame height and pressure, while a linear relationship was obtained between the index and the angle of inclination.

We report the synthesis and photoelectrochemical (PEC) studies of a novel CdSe/BiVO4 planar heterojunction photoelectrodes for photoelectrochemical water splitting fabricated by chemical bath deposition of CdSe on the spin-coated BiVO4 layers. Temperature and time of chemical bath deposition were investigated to obtain the optimal deposition condition. The optimized CdSe/BiVO4 with enhanced photo absorption yielded a maximum photocurrent density of 2.48 mA under the irradiation of AM 1.5 G (100 mW/cm2) simulated solar light illumination, which is enhanced by 3.87 times compared to bare BiVO4.

Both experimental and theoretical methods were proposed to assess the effects of adjacent, parallel, and symmetric exterior wall structures on the combustion and flame spreading characteristics of rigid polyurethane (PUR) foam insulation. During the combustion of PUR specimens, the flame leading edge was found to transfer from a unique inverted &lsquo, W&rsquo, shape to an inverted &lsquo, V&rsquo, during flame propagation. This phenomenon is attributed to edge effects related to boundary layer theory. The effects of the adjacent fa&ccedil, ade angle on flame spreading rate and flame height were shown to be nonlinear, as a result of the combined influences of heat transfer, radiation angle, and the chimney restriction effects. A critical angle around 90 degree with maximum thermal hazards outwards by parallel fire was observed and consistent with the mass loss rate and flame height tendencies. For narrow spacing configurations or angles (e.g., 60 and 90 degrees), phenomenological two-pass processing in conjunction showed that increased preheating lengths were associated with enhanced heat transfer. The results of this study have implications concerning the design of safe fa&ccedil, ade structures for high-rise buildings, and provide a better understanding of downward flame spreading over PUR.

Downward flame spread over polymer materials is one of the typical hazardous scenarios in building fires, and also an important feature for fire safety research. This work was motivated to study the coupling effects of ambient pressure and orientation on downward fire propagation with a widely used thermal insulation polymer, flexible polyurethane (FPU). Comparative experiments were conducted under 3 different pressures (75 kPa, 80 kPa and 100 kPa) and 4 angles of inclination (0°, 30°, 60°, 90°) respectively, to investigate the variation of fire characteristics including flame tilt, length, spread velocity, burning rate, and related heat transfer mechanisms. The results showed non-monotonic tendencies of these parameters with enlarged inclination angle, and more complicated relationships by coupling pressure effect. Flame tilt was found be determined by the asymmetric entrainment induced, and also a key factor controlling heat preheating mechanism. Variation of spread velocity and consequent burning rate and flame length were discussed theoretically based on different preheating heat fluxes including convection, radiation and conduction from fire and solid phase. Particularly, a semi-quantitative correlation for coupling effects of pressure and inclination on flame spread velocity was proposed, which could help to improve the understanding of fire evaluation under low pressures.

Research on building-integrated photovoltaic/thermal (BiPV/T) technology has been conducted for years because the system can provide electric power and thermal energy simultaneously. A façade-integrated tri-functional PV/T collector system is presented and studied in this paper. The collector can work in PV/water-heating mode or PV/air-heating mode. Besides, it can also work in the composite mode that air and water be heated simultaneously. So optimum work mode of the collecor can be chosen for different energy demands. The collector can be combined with the southern wall of building, then it operates as PV-Trombe wall for passive room heating and electricity generation in winter, and for domestic water heating and electricity generation in other seasons. For the different working modes, theoretical research is carried out and dynamic model of the collector and building are developed. Based on the models, the performance of collector and the thermal behavior of the room are investigated under different climates conditions.

The output power of the solar photovoltaic panel decreases as the operating temperature increases. The use of photovoltaic/photothermal (PV/T) collectors not only effectively cools the operating temperature of the battery, increases photovoltaic power, but also produces hot water. Therefore, the PV/T collector improves the annual utilization efficiency of solar energy, and can meet the user's demand for different energies. This paper builds an experimental platform to compare the PV/T collector photovoltaic/photothermal performance and experimental comparison with traditional PV. The results show that the PV/T collector has a thermal efficiency of 31.5% and a photovoltaic efficiency of 17.82% at a flow rate of 0.023 Kg/s to achieve high efficiency in solar energy utilization.

The effects of the initial preheating perturbation on the dynamical behaviors of FGC wave propagation instability for low-velocity FGC in packed bed are studied numerically. The behaviors of the flame front inclination, break, and shrinking instabilities are always observed in experiments. Based on the experimental phenomena, an initial thermal perturbation model is numerically proposed as to predict the deformation behaviors of the flame front instabilities. The typical flame shapes are obtained depending on filtration velocity, equivalence ratio, and initial preheating temperature difference. It is demonstrated that the development of flame front inclination instability is proportional to the magnitude of initial preheating perturbation. At a lower equivalence ratio, the initial thermal perturbation of 300 K leads to the evolution of flame front break. Increasing filtration velocity leads to the appearance of flame front break, due to the intensification of the hydrodynamic instability. In addition, a perculiar instability of flame front shifting is also confirmed with the initial thermal perturbation of 400 K, which results in a fuel leakage of incomplete combustion.

The simulation model of buildingEXODUS is applied to simulate occupant evacuation in a high-rise dormitory building. Three cases are simulated to analyze the influence of the route selection on evacuation efficiency. The result of buildingEXODUS is compared with those of Japan's empirical formula and Pauls' empirical formula. The evacuation time calculated by Pauls' formula is the shortest because route selection and different use ratio of each staircase are not taken into account. The result simulated by buildingEXODUS is the longest because the details of human behavior, occupant property, building structure, and environment are all taken into account. Shorter evacuation time can be obtained by assigning some occupants to less occupied areas instead of taking the shortest routes and balancing the use ratio of each staircase and exit.

Pt and Pd co-doped TiO2 nanoparticles were synthesized using modified sol-gel processes and characterized by BET surface area, SEM, TEM, XRD, EDX, FT-IR, and UV-Vis spectroscopy. The results showed that the Pt/Pd-TiO2 nanoparticles possess high surface area and small particles size compared with individual Pt or Pd doped TiO2. The significantly high photocatalytic activity can be ascribed to the simultaneous effects of doped Pt and Pd by cascadal electron transfer from TiO2 to Pd to Pt and reach surface excitation state. And the optimum molar ratio of Pt/Pd at 1.5 can effectively reduce the electron–hole recombination rate.

The influence of exit's position changes on evacuation was studied in unit rooms by Pathfinder Software simulation. Using three different structural forms of unit rooms as the research objects, the effect of two exits' position changes on the total evacuation time and the evacuation efficiency was researched. The results show that when the two exits are arranged in the homonymy and the distance between them is the minimum value 0, the evacuation efficiency can achieve the greatest value, which facilitates evacuation. When the distance between the two exits cannot take the minimum value 0, the two exits should be arranged in the homonymy symmetrically or in the offside just as in case 3, the distance between the two exits has little effect on evacuation efficiency at this time. The study results have guidance for the design of exits' position and occupants' safe evacuation in buildings.

As the flat form of a "return" shape building for example, the effects of staircase design on evacuation in architectural plane design was studied using Pathfinder numerical simulation method. The staircase layout effects on evacuation time was the mainly research content. The results indicate that in addition to considering the distance between two adjacent stairs, the distribution of occupants in building plane is also an important factor which needs to be considered on the layout of staircase. The changes of staircase plane positions have a great impact on the total evacuation time in the case of the same total stair exit width. It is favored for evacuation when the evacuation time differences of staircase exits are small. The study results have some guidance on the plane design of staircases and evacuation.

The evacuation process under emergency is studied by means of experiments and simulations, focusing on the influence of the environment information. A revised cellular automaton model in which environment information is considered as "static information" (building structure, spatial distance, etc.) and "dynamic information" (sounds of fire alarm, etc.) is introduced. Two scenarios, including evacuation with and without visibility in a classroom, are studied to investigate the different influence of the two kinds of information on human behavior. The experimental and simulation results demonstrate that: (1) to intensify the spatial distance information can reduce the evacuation time; (2) the spatial distance is not the only decisive factor especially in evacuation without visibility because the sound information, which is ignorable in evacuation with visibility, is playing a more important role under this condition; (3) the intensity of static information can reflect evacuees' familiarity of the environment; (4) the model can reproduce the experiments well, and the simulation method is useful for further study of the crowd movement simulation.

An existing cellular automaton evacuation model is modified to simulate an evacuation experiment conducted in a classroom with obstacles. In the modified model, the impact of the occupant density around exits on human behavior in evacuation is considered. The simulation and experimental results prove that this improvement makes sense, because besides the spatial distance to exits, people may also choose the exit according to the occupant density around exits. The distribution of individual evacuation times as a function of initial positions and the dynamics of the evacuation process are studied. Comparison between the experimental and simulation results shows that the model can reproduce the experiment well. The improvement of the CA model is useful for further study.

Individual behavior of occupants, which is quite complex, greatly affects the route choice, the evacuation time and the efficiency. The phenomenon of the kin behavior often occurs during evacuation. In this paper, a two-dimensional Cellular Automata model is applied to simulate the process of evacuation with respect to the kin behavior. Many interesting phenomena during real evacuation, such as incoherence, jamming, gathering, backtracking and waiting, are simulated by the variation of the building structure, the occupants' arrangement, the kin attraction and the route selection. We conclude that the psychology of going with the crowd is not always harmful; the conclusions about the kin behavior in one-exit case are the same as those in two-exits case; the number of the sub-groups and the members in each sub-group influence the evacuation efficiency a lot; the typical phenomena of waiting and backtracking in real evacuation do reduce the evacuation efficiency. We have preliminarily found that the proper kin behavior is beneficial to improve the evacuation efficiency.

Experiment study on the influence of visibility on occupant evacuation in classroom is carried out. Different visibility conditions can be achieved by wearing different sunglasses or different daylight with curtains open or close. Occupant walking speed decreases with low visibility. And it is difficult to judge the evacuation routes and exit locations with low visibility. Especially when the visibility is zero, evacuation time is prolonged a lot and some special phenomenon can be found. A 2D cellular automata random model of occupant evacuation developed by our research group is used to simulate this evacuation process. Simulation results are almost consistent with the experiments.