288 publications from this institution
Flame spread over wire surface is different from other solid fires as it is usually accompanied by melting and dripping processes. Although the related behaviors at reduced pressure (20–100 kPa) are significant to those fire risk evaluations, very few studies have been undertaken on this matter. Therefore, the thermoplastic dripping and flame spread behaviors of energized polyethylene insulated copper wires were investigated experimentally at reduced pressure. It was known from experimental results that the dripping frequency increases, showing a relatively smooth (linear) and rapid (power) increasing trends under high and low electrical currents, respectively. A short-period flame disappearance was observed during the dripping process, which is unique for the energized wire at reduced pressure. The bright flame can disappear for several seconds and then show again after the dripping. While at 20 kPa or lower, the wire flame would turn to a completed extinguishment after the dripping. A critical dripping point was proposed to show the minimal required electrical current to sustain the flame spearing. The critical current changes smoothly during 100–80 kPa and decreases rapidly at 80–60 kPa. Additionally, the dripping phenomenon can stop or delay the flame spread, partly because of the short-term flame disappearance.
This study presents the world-first design of solar chimney for a real building considering both energy-saving and fire safety. Typical designing factors on both functions were investigated by a numerical tool after it was validated by experiments. It was obtained that solar chimney can be adopted for both functions with 7.42 air changes per hour natural ventilation under normal conditions and at least 6.52 times extension of available safe egress time for occupants under typical fire conditions. It was also known that the previously obtained optimized cavity gap of 0.2–0.3 m is no longer applicable for a big space, where the optimum gap is 1.2 m considering both functions for a big space. A consistency coefficient is also proposed here that a positive consistency coefficient means the increased parameter can enhance the performance of both functions, while a negative coefficient represents the performance enhancement of one function will compromise the other. The consistency coefficient of those designing parameters are: cavity gap (30.91) > air supply area through top vent (12.47) > air supply area through bottom door (5.4) > cavity height (3.09) > 0 > solar radiation (-0.47) > cavity height below the roof (-40.04). The parameters with negative consistency such as cavity height below the roof should be considered carefully when both functions are planned.
No abstract is provided for this article.
No abstract is provided for this article.
The thermal performance of a ground heat exchanger (GHE) largely depends on the heat transfer fluid circulating in the system. In this study, a laboratory test apparatus for a horizontal spiral-coil ground heat exchanger (HSGHE) was designed and constructed to investigate the effects of different volume fractions of CuO/water nanofluid on the energy efficiency of the HSGHE. The results showed that, at a volumetric fraction of 1%, the CuO/water nanofluid led to a 9.4% increase in the heat exchange rate of the HSGHE, compared to water. In addition, the heat transfer enhancement effect at a lower volume fraction of the CuO/water nanofluid was greater than the effect of its viscosity on the performance of the HSGHE. The CuO/water nanofluid with a volumetric fraction of 1% was not recommended for use in the HSGHE owing to its performance efficiency coefficient (PEC) of less than 1. The optimal volume fraction was 0.5%, at which the PEC was the highest (1.025). Therefore, it was determined that the utilization of a low volume fraction of CuO/water nanofluid in HSGHE provides energy efficiency enhancements independent of the GHE design.
No abstract is provided for this article.
The use of recycled concrete is a significant step to reduce the need for natural resources and the demand on landfill sites for disposing the waste. Previous studies have mainly focused on its behaviours under ambient temperature although the characteristics of recycled concrete after high temperature exposures is important in many practical applications such as fire resistance. Also, the effect of elevated temperature on the mechanical and porosity behaviours of recycled concrete aggregate (RCA) containing rubber for pavement base/subbase applications has never been studied. In this study, the effects of high-temperature environment on the mechanical properties of recycled concrete aggregate (RCA) mixed with crumb rubber (CR) in a range of 0.5–2% were investigated both experimentally and theoretically. Unconfined compression strength (UCS) and X-ray micro-tomograph tests were undertaken on the mixed samples which were heated to different temperatures ranging from 20 °C to 600 °C. It was observed from the experimental results that UCS increased under a higher temperature up to 300 °C. At an ambient temperature of 20 °C, RCA samples without any addition of CR exhibited the highest UCS value while under high temperature, RCA samples with 1% CR had the highest UCS value. The strength of RCA mixed with crumb rubber showed an increasing trend under a temperature higher than 150 °C, which can be attributed to the melting processes of the crumb rubber. According to the X-ray micro-tomograph tests, the inclusion of rubber led to a decreasing porosity. It is interesting to note that porosity rises when temperature increased from 20 °C to 150 °C. This may be due to the restructuring of the shape of rubber particles into spheres as well as the excessive pore water forces generated from water evaporation. Also, when the temperature increased from 150 °C to 450 °C, the porosity decreased since the melted rubber particles flowed into the voids and filled more pores. The outcomes of this study can provide practical guidance on the application of recycling concrete.
Owing to the restriction of using Halon 1301 (CF3Br) for fire suppression, several alternatives to Halon 1301 have been developed, including C2HF5 (HFC-125), C3H2F3Br (2-BTP), and C6F12O (Novec1230). However, in the Federal Aviation Administration (FAA) Aerosol Can Explosion Test (FAA-ACET), it was found that these alternatives did not suppress lean flames at sub-inert concentrations, but promoted combustion, eventually leading to overpressure. Therefore, they have not been successfully applied in aircraft cargo compartments. Herein, different blend ratios of C3H2F3Br and C2HF5 were used to explore their inhibitory effects on combustion enhancement under lean combustion conditions. A chemical kinetic model was developed and validated using a one-dimensional free-propagation flame simulator. The laminar burning velocity predicted by the model was consistent with the experimental results. The adiabatic flame temperature and overall reaction rate were determined using thermodynamic equilibrium calculations and perfectly stirred reactor (PSR) simulations. By comparing the blend inhibitors with different blend ratios, it was found that the blend of C3H2F3Br and C2HF5 at blend ratios of 25/75 and 50/50 effectively reduced the total heat release and system reactivity. In addition, the blend inhibitor not only weakened the fuel properties of C2HF5, but also further enhanced the bromine-catalysed radical recombination cycle. Notably, a new reaction occurred when C3H2F3Br and C2HF5 were blended into the FAA-ACET chamber: Br + CHF2CF3 = HBr + CF3-CF2, indicating that the Br atoms promoted the decomposition of C2HF5.
Under the fact that previous studies have usually ignored the influences of room configuration, wall solar chimneys under both cooling and heating modes were analyzed theoretically to fill the research gap. Solar chimneys are different from solar photovoltaics which produce electricity directly, while the energy saving of the target building is realized by promoting natural ventilation and saving the electricity originally consumed by heating, cooling, and air conditioning (HVAC) systems. Solar chimney performance depends on the airflow rate and its temperature, where theoretical models were developed in this study to predict the natural ventilation with four typical types, including fresh-air cooling, fresh-air heating through chimney cavity and room, and sealed heating (without any fresh-air supply). It is known that the room configuration shows considerable influence on solar chimney performance, where a coefficient is proposed to address the impact. Different from the cooling mode, airflow rate under heating mode was found not only dependent on cavity height but also the opening height of the room. To heat a typical room, fresh-air heating through the cavity shows the highest airflow rate but with the lowest temperature, which can be applied to regularly occupied buildings under cool weather conditions. Fresh-air heating through the room shows an opposite way, which is suitable for regularly occupied buildings under cold weather conditions. The performance of sealed heating is between these two, which can be used for nonregularly occupied buildings as there is no fresh air supply.
