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In this study, the effect of the vent area ratio on vent flow characteristics and temperature distribution in a compartment during a fire in the compartment with two ceiling vents was examined. The area ratio (A1/A2) between ceiling vent 1 (CV1), with a duct height of 0.19 m, and ceiling vent 2 (CV2), with a duct height of 0.05 m, was varied from 0.052 to 0.542, 1, 5.587, and 19.36, and numerical simulation was performed under these conditions. As the A1/A2 ratio increased, the flow pattern changed from unidirectional inflow to bidirectional flow for CV1 and from bidirectional flow to unidirectional inflow for CV2. When the A1/A2 ratio was 0.542, the outflow and inflow mass flow rates for CV1 and CV2 were found to be nearly equal. The outflow and inflow mass flow rates at CV1 were higher than those at CV2 when the A1/A2 ratio was high, while the outflow and inflow mass flow rates at CV2 were higher than those at CV1 when the A1/A2 ratio was low. Furthermore, it was observed that the temperature was lower and the temperature difference between the higher and lower regions in the upper part of the measurement position decreased near the lower part of the vent with a larger area compared to the vent with a smaller area. This was probably because the mixing effect increased near the vent with a larger area due to the occurrence of the active bidirectional flow pattern. When the flow pattern at CV1 was bidirectional, the previous correlation for predicting mass flow rate was examined. It was found that the previous correlation underestimated the mass flow rate of the numerical simulation conducted in this study.

The effects of duct height (DH) and fire location (FL) in an enclosure on the mass flow rate and flow pattern of horizontal vent (HV) flow and temperature distribution in the enclosure were investigated through numerical simulations under the condition that two HVs were installed on the ceiling of the enclosure. To evaluate the effect of DH, DHs of HV1 were set to 0.19 m (HV1_DH0.19) and 0.05 m (HV1_DH0.05) under the condition that DH of HV2 was 0.05 m (HV2_DH0.05). The effect of FL was evaluated in three cases where the fire sources were located in the center of the floor (F LC), below HV1 (F L1), and below HV2 (F L2). With respect to the DH effect, the total mass flow rate of the vent flow was slightly higher and temperature was slightly lower in the case of HV1_DH0.19 than that in the case of HV1_DH0.05. However, considering the error bars, the effect of DH in this numerical simulation condition was considered to be insignificant. Furthermore, bidirectional flow patterns appeared in HV1 and HV2 in both DH conditions. Meanwhile, with respect to the FL effect, a bidirectional flow dominated by the mass flow rate of outflow occurred in the HV where the fire source was located, and a unidirectional inflow dominated by the mass flow rate of inflow occurred in the HV where the fire source was not located. The total mass flow rates of FL1 and FL2 conditions were similar, which were higher than those of FLC condition. The temperature was higher in FLC than those in FL1 and FL2. This was due to the small mass flow rate through the HV in the FLC. Meanwhile, an increasing trend of the temperature with the rising measurement height from the floor was observed at most of the temperature measurement points. However, when the fire source was located below HV1 and HV2, as the height from the floor increased, the temperature decreased and the overall temperature was low at the temperature measurement points below the vent where the fire source was not located. This trend was attributed to the occurrence of a strong unidirectional inflow wherein a large volume of low-temperature air flowed into the enclosure from the HV where the fire source was not located.

In this experimental study, the effect of installation conditions of a water mist nozzle on thermal radiation attenuation performance was investigated. Two types of nozzles (Small_nozzle and Large_nozzle) were used. Experiments were conducted under conditions in which the nozzle was installed near the heater and heat flux sensor (Position_NH and Position_NS, respectively), and water mist was discharged from one and two nozzles (Case_ID and Case_SD, respectively). To characterize the water mist spray, the water supply pressure and droplet size were measured, and visualization of the sprayed water mist was performed. The thermal radiation attenuation performance improved with an increase in the water flow rate, and Small_nozzle showed higher thermal radiation attenuation performance than Large_nozzle. Moreover, Case_SD showed lower thermal radiation attenuation performance than Case_ID_Sum (that is, the Sum of Case_ID & Position_NS and Case_ID & Position_NH) and the difference in thermal radiation attenuation performance between Case_SD and Case_ID_Sum at a higher water flow rate was more significant than that at a lower water flow rate. These might be attributed to the wide overlapping area of water mist discharged from two nozzles in Case_SD and at a higher water flow rate, narrowing the overall width of the water mist.

In this study, the effects of water mist characteristics according to the axial position on thermal radiation attenuation performance were experimentally investigated using the single-fluid nozzle. Under the water flow rate conditions of 200∼350 g/min, the thermal radiation attenuation performance was measured at the axial position (i.e., downstream direction of water mist from nozzle exit) of 200∼1000 mm. In addition, during the discharge of water mist, the water supply pressure and droplet size of water mist were measured and the water mist was visualized. As a result, with an increase in the water flow rate, the thermal radiation attenuation performance was improved. Overall, the attenuation rate was measured to be 12.4∼30.1%. In the axial position of 200∼400 mm, with an increase in the axial distance from the nozzle exit, the thermal radiation attenuation performance was improved. This may be because the effect of improvement of the thermal radiation attenuation performance by an increase in the spray width is predominant over the effect of reduction in it by an increase in the droplet size. In addition, in the axial position of 400∼1000 mm, with an increase in the axial distance from the nozzle exit, the thermal radiation attenuation performance was reduced. This is because the droplet size of water mist increases and spray width is narrowed. Based on this study, it was confirmed that the water mist characteristics according to the axial position and thermal radiation attenuation performance are closely correlated.

In this study, the effect of ceiling vent location on the fire phenomena in the enclosure with side and ceiling vents was numerically investigated. As the ceiling vent location, Case F, Case F-M, Case M, Case M-B, and Case B were tested, and their distances from the side vent to the center of each vent were 0.265, 0.525, 0.750, 0.975, and 1.235 m, respectively. Among these cases, Case M-B showed the lowest temperature distribution in the enclosure and smoke layer temperature, the thinnest smoke layer, and the highest mass flow rate of outflow through the ceiling vent. One of possible reasons for these results is owing to the fact that the behavior of fire plume is changed by the inflow through the side vent. As the visualization result of temperature distribution, to determine the ceiling vent location for the improvement of smoke ventilation performance, it can be important to predict the amount of fire plume inclination by inflow through the side vent and the height of inclined fire plume region. To predict the amount of fire plume inclination by inflow through the side vent, the previous correlations of flame angle were assessed, which under-estimated the fire plume inclination of present numerical simulation.

The scaling law was examined using numerical simulation for fire phenomena in a compartment with a horizontal natural opening in this study. The results of the large-scale conversion of the scaled model numerical simulation results ([Small-scale] condition) from the earlier studies obtained by applying the scaling law were compared to those of the large-scale numerical simulation performed in this study ([Large-scale] condition). The overall trends for the effects of horizontal natural opening area and fire source location on the discharge mass flow rate through the horizontal natural opening, temperature distribution in the compartment, and flow velocity through the horizontal opening were found to be identical under the [Small-scale] and [Large-scale] conditions. A complex bidirectional flow was observed through the horizontal natural opening under the conditions of this study and the accuracy in predicting the average W-velocity value based on the scaling law was low; however, the accuracy in predicting the range of velocity fluctuation was higher than the average value under certain conditions. Based on the standard deviation of the numerical simulation results, the percentages of the data within ± 30% of the difference between the [Small-scale] and [Large-scale] conditions relative to the total number of data were 100, 75, and 88% for the discharge mass flow rate, temperature, and flow velocity through the horizontal natural opening, respectively. The accuracy of the scaling law was found to be high for the discharge mass flow rate under the conditions considered in this study.

In this study, the thermal radiation attenuation performance of water mist was investigated using twin-fluid atomizers. The water and air flow rates of Small atomizer were 36~105 g/min and 10~30 L/min, whereas those of Large atomizer were 37~300 g/min and 20~60 L/min, respectively. In the present experimental range, the thermal radiation attenuation of Small atomizer and Large atomizer were 6.1~11.9% and 5.2~14.6%, respectively. With the increase in water and air flow rates, the thermal radiation attenuation increased, and under similar water and air flow rate conditions, Small atomizer showed higher thermal radiation attenuation than Large atomizer. Based on the present experimental data, it was found that the air (gas) discharge area is a potentially important factor in determining the thermal radiation attenuation performance. Additionally, through the analysis of thermal radiation attenuation per unit water flow rate, it was confirmed that the twin-fluid atomizer can result in higher thermal radiation attenuation than the single-fluid atomizer under the same water flow rate condition.

In this study, the phenomena of water droplet impact on burning methanol and n-heptane pool surfaces were experimentally investigated under various size and velocity conditions of impact droplet. In the n-heptane pool, the temperature increased to the deeper location of the pool and the droplet impact velocity was slower, as compared with those in the methanol pool. These results were caused by the higher heat release rate of the n-heptane pool. However, the impact droplet sizes on the burning methanol and n-heptane pool surfaces appeared to be similar. By visualizing the droplet impact phenomena, the impact pattern maps of burning methanol and n-heptane pool surfaces were constructed and compared with the previous impact pattern maps of their unburned pool surfaces. In the burning and unburned methanol and unburned n-heptane pools, patterns of single jet and splash with secondary jet were observed. On the contrary, in the burning n-heptane pool, patterns of single jet and canopy were observed.

Water mist, which is an alternative to halon fire-extinguishing agents, can maintain the clean environments and prevent the huge fire loss in diverse industrial fields. In the present experimental study, the spray characteristics of a twin-fluid nozzle for water mist and its heptane pool fire extinguishing performance were investigated. As the spray characteristics, the SMD (Sauter Mean Diameter) of water mist, discharged water flux distribution, downward air flow velocity, and inlet pressures of fluids were measured and analyzed. Subsequently, through the fire extinguishing experiments using three different heat release rate conditions, the fire extinguishing map, extinguishing time, water consumption, and water mist effect on the mass loss rate were examined in detail. In addition, the experimental data using the twin-fluid nozzle were compared and discussed with those using the single-fluid nozzle reported in a previous study. Based on the present experimental data of fire extinguishments, particularly under high air flow rate conditions, the twin-fluid nozzle showed high fire extinguishing performance. Moreover, compared with a previous study using the single-fluid nozzle, it was found that the twin-fluid nozzle can successfully extinguish liquid pool fire with shorter fire extinguishing times, lesser water consumption, and lower inlet pressures. Based on the present results, it was found that the air flow of the twin-fluid nozzle is an important factor that determines and affects its fire extinguishing performance. Further, the twin-fluid nozzle was found to possess a significant potential to considerably improve the performance of water mist fire suppression systems.

Nitrogen-incorporated ovoid-shaped nanodiamond (NOND) film exhibits excellent electrochemical sensing properties owing to its unique characteristics. In this study, to improve the sensitivity of NO...

In this study, the effect of surfactants and liquid temperature on boiling regime transitions of high-temperature rod during quenching was examined using inverse heat transfer analysis. Liquid pools of the aqueous sodium dodecyl sulfate (SDS) and Triton X-100 solutions were used with pure water. In the present experimental range, the critical heat flux (CHF) and minimum film boiling (MFB) point for all test fluids increased as the liquid temperature decreased. On the other hand, the SDS and Triton X-100 surfactants suppressed the CHF and MFB point, which might be due to the enhancement of vapor film stability caused by reduced surface tension. Some previous experimental studies have reported that the surfactants enhance the boiling regime transitions, but their results seem to be contradictory to the present ones. Considering the present study with the previous works, the surfactants seem to have different effect on boiling phenomena depending on the boiling regime. In other words, in the aqueous surfactant solution, the boiling regime transition points seem to be markedly influenced by a path of boiling regime. In addition, boiling mode diagrams were presented for pure water and aqueous surfactant solutions.

The prediction performance of design fire curves is numerically investigated for tunnel fire using the fire dynamics simulator (FDS). A large eddy simulation (LES) was adopted in the simulation of a previous 750 kW tunnel fire experiment. Based on the experimental heat release rate, t2-fire growth, quadratic and exponential design fire curves (DFCs) are mathematically constructed and adopted in the FDS simulation. The predictions of each DFCs are compared against the experimentally measured smoke temperature, smoke travel time, and carbon monoxide (CO) concentration. In addition, the prediction performance of the mixture fraction (MF) and mixing controlled fast chemistry (MCFC) combustion models, is compared. The simulation results of the MF and MCFC models are similar except for the CO concentration features. For the performance of the DFCs, t2-fire growth curve with the MF combustion model is the most effective combination, which demonstrated the most reasonable agreement with the experimental data.

Water scarcity is one of the most critical problems that humans have to face. Working toward solving this problem, we have developed a thin-film composite (TFC) membrane using the modified molecular layer-by-layer (modified mLBL) method to fabricate polyamide (PA) active layers on different substrates. Besides, it has been found that graphene oxide (GO) contains abundant functional groups such as hydroxyl and epoxide groups, which are able to improve both the physical and chemical properties of the forward osmosis (FO) membrane. Thus, we have employed graphene oxide (GO) as the substrate and used the modified mLBL method to prepare active polydopamine/graphene oxide (PDA/GO) layers to enhance the water flux of the forward osmosis (FO) membrane. PDA/GO-coated layers could enhance the hydrophilic nature of the substrate and lower its surface roughness, which would facilitate the formation of the PA layer. Moreover, the PDA/GO coating can be applied to all substrates because of the high degree of adhesion of PDA to different substrates. In this study, the highly hydrophilic poly(vinylidene fluoride) membrane is superior in FO properties, with a water flux of 17.32 LMH and a reverse solute flux of 4.34 gMH. In addition, an excellent performance of 60.15 LMH and 14.88 gMH can be achieved when the pressure-retarded osmosis (PRO) test mode with a draw solution concentration of 2.0 M is used in the test. It shows that the membrane prepared using the novel method showed excellent FO performance, which has high potential in industrial applications such as desalination.

It has been reported that bipyramidal anatase TiO2 with {101}-exposed facets (AT170) results in outstanding photocatalytic performance. However, its activity decayed significantly and comparatively lower than that of commercial P25 after 20 min. Further studies and calculations showed that the methylene blue (MB) degradation rate constants for AT170 were time dependent and decrease of k values with time. Besides, the results of XPS, EA and TEM could clearly elucidate that the active sites of catalysts were blocked by the carbon buildup and covered on the surface creating the metal–carbon bonding on the catalysts. These observation strongly implied the existence of the poisoning effect of AT170 during photocatalytic processes. Also, the surface area values of P25 and AT170 were found to be 46.83 and 3.56 m2/g respectively. It was suggested that the catalyst poisoning effect could be prevented or controlled by increasing the surface area of the catalyst. Besides of surface area, zeta potential was also found to be served as the important factor determining the photocatalytic performance toward organic dyes due to the attraction/repulsion of electrostatic interaction. The zeta potential values of P25 and AT170 were found to be − 3.8 and − 32.9 mV respectively, which can adsorb cationic MB dyes on the negative charged surface through attraction of electrostatic interaction successively enhancing the degradation performance. It strongly indicates that both surface area and zeta potential play vital roles in photocatalytic degradation toward organic dyes and affect the rate constants.

Gas sensors based on semiconductors have outstanding sensitivity compared with the oxide-based devices; however, the high operation temperature greatly hinders its development in practical applications. Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide, and the patients with severe COPD with or without exacerbation tend to have airflow obstruction, which results in an increase of CO

Hierarchically ordered structures with low tortuosity, excellent mechanical flexibility, high optical transparency, and outstanding electrical conductivity are critically important in developing flexible transparent supercapacitor electrodes for innovative applications in electronics and displays. Here a CVD process is employed to fabricate leaf-skeleton inspired electrodes, which are reticulated monolithic networks consisting of carbon nanostructures serving as a 3D spongy core and graphene-based films as a protective/conductive shell. The network electrodes show optical transmittance of 85–88%, an electrical sheet resistance of ~1.8 Ω/sq, and an areal capacitance of 7.06 mF cm−2 (at 0.78 mA cm−2 in a three-electrode cell) in Na2SO4 aqueous electrolyte. Flexible transparent and symmetric supercapacitors, based on PVA/H3PO4 gel and the network electrodes, possess a stable working voltage of 1.6 V, energy and power density of 0.068 μWh cm−2 and 47.08 μW cm−2 at an optical transparency of ~80%, and no capacitance loss over 30,000 flat-bend-release cycles. Flexible, transparent supercapacitor electrodes are promising materials for innovative electronic and display applications. Here, the authors report a leaf-skeleton inspired core-shell network that exhibits up to 88% optical transmittance and is stable over 30000 bend-release cycles while retaining competitive electrochemical performance.

A new synthetic method to grow O-deficient rutile TiO2(s) nanorods (NRs) and nanowires (NWs) by a vapor–solid reaction growth method is developed. TiCl4(g) was employed to react with commercially supplied CaTiO3(s) (size 2–4 μm) at 973 K under atmospheric pressure to generate TiO2(s) NRs (diameters 80–120 nm, lengths 1–4 μm). The reaction employing TiCl4(g) and CaO(s) at 973 K also generated CaTiO3(s) (size 4–13 μm) as the intermediate which reacted further with TiCl4(g) to produce NWs (diameters 80–120 nm, lengths 4–15 μm). This is the first report of 1D rutile TiO2(s) nanostructure with such a high aspect ratio. Both of the NRs and the NWs, with compositions TiO1.81 and TiO1.65, respectively, were single crystals grown in the [001] direction. Their morphology was affected by the reaction temperature, the concentration of TiCl4(g), and the particle size of CaTiO3(s). The NRs and the NWs were investigated as anode materials for Li+-ion batteries. At constant current rates 1, 2, and 5 C (1 C = 170 mA g–1) for 100 cycles, the cycling (1.0–3.0 V) performance data of the NRs were 146, 123, and 104 mA h g–1, respectively. On the other hand, the cycling performance data of the NWs were 120, 80, and 52 mA h g–1, respectively. This is attributed to the high Li+ ion diffusion rate (DLi+) of the NRs (29.52 × 10–15 cm2 s–1), which exceeds that of the NWs (8.61 × 10–15 cm2 s–1). Although the [001] growth direction of the NR crystals would provide the fastest channels for the diffusion of Li+ ions and enhance the battery capacity, the extremely long channels in the NWs could hamper the diffusion of the Li+ ions. The O-deficiency in the structure would increase the conductivity of the electrode material and improve the stable cycling stability of the batteries also. The long-term cycling test at 2 C for the battery constructed from the NRs retained 121 mA h g–1 after 200 cycles and 99.2 mA h g–1 after 800 cycles. The device has an excellent long-term cycling stability with a loss of only 0.04% per cycle.

The glucose level is an important biological indicator for diabetes diagnosis. In contrast with costly and unstable enzymatic glucose sensing, oxide-based glucose sensors own the advantages of low fabrication cost, outstanding catalytic ability, and high chemical stability. Here, we fabricate a self-supporting spiky Cu x O/Cu nanowire array structure by electrochemical cycling treatment. The spiky Cu x O/Cu nanowire is identified to be a Cu core passivated by a conformal Cu2O layer with extruded CuO petals, which provides abundant active sites for electrocatalytic reaction in glucose detection. An interruptive potential sweeping experiment is presented to elucidate the growth mechanism of the spiky Cu x O/Cu nanostructure during the potential cycling treatment. The spiky Cu x O/Cu nanowire array electrode exhibits a sensitivity of 1210 ± 124 μA·mM-1·cm-2, a wide linear detection range of 0.01-7 mM, and a short response time (