Measurement of the neutral plane of an internal fire whirl using the background-oriented Schlieren technique for a vertical shaft model of a high-rise building

Su, ChungHwei; Bai, JiaHong

doi:10.1016/j.measurement.2015.10.004

Cited by 12 publications

(14 citation statements)

References 27 publications

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“…In 2013, the best color mask to display the highest sensitivity for color Schlieren imaging was successfully found by Chen and Ting (Chen and Ting, 2013). Su and Bai (2016) demonstrated that the background-oriented schlieren technique can directly and immediately measure the neutral plane position of an internal fire whirl for a vertical shaft model (Su and Bai, 2016). The Schlieren technique uses the first derivative variation of the refractive index between the light and the flow field, as shown in equation (1) (Aleiferis et al , 2015; Kuehn and Goldstein, 2017): …”

Section: Methodsmentioning

confidence: 99%

Analysis of tilted neutral planes for tall space fires with unsymmetrical openings using numerical simulation and Schlieren photography technique

Su¹,

Wang²

2019

HFF

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Purpose The purpose of this paper is to analyze the variations in the neutral plane when a tall space with unsymmetrical openings is on fire. The neutral plane of the fire scene is an important index of a natural smoke exhaust system. The numerical simulation method and the Schlieren photography technique were used as analysis tools. The results of model experiments and numerical simulation were compared with each other to confirm the rationality of the conclusions. The results were to discuss the characteristics of various cases and showed that the neutral planes of the fire scene were not always horizontal. Design/methodology/approach The numerical simulation method and the Schlieren photography technique were used as analysis tools. The flow patterns of hot air in various cases were recorded using the flow visualization technique. In addition, the renowned simulation software, fire dynamics simulator (FDS), was used for case analysis. The Schlieren photography technique was used for 1/12.5 model experiments with six smokeless candles burned, and FDS was used for a numerical simulation. In terms of the case of unilateral vents, the exhaust efficiency was discussed when the exhaust vent and air inlet were located on the same side or different sides. Findings This study demonstrates that makeup air flowing in from the inlets and openings has a significant impact on the effectiveness of natural smoke exhaust systems. The results illustrated that the neutral planes were tilted in some cases. In some cases, the results showed that one side was the air inlet and the other side was the exhaust vent, even if the openings were at the same height in some cases. These phenomena have rarely been discovered or studied in the past. The exhaust efficiency was not always better when the vent was located in the rooftop. Originality/value This study analyzed the neutral plane of a fire scene using the common unsymmetrical opening spaces in the Taiwan region as an example. The phenomenon of non-horizontal neutral plane has rarely been studied in the past. The temperature of the discharged hot gas was low because of an efficient exhaust effect, which reduced the heat and smoke storage in the space. The results obtained by these two methods were consistent, and showed that the cases with the same opening area had different smoke extraction efficiencies, meaning the smoke extraction effect cannot be judged only by the opening areas.

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Section: Methodsmentioning

confidence: 99%

Analysis of tilted neutral planes for tall space fires with unsymmetrical openings using numerical simulation and Schlieren photography technique

Su¹,

Wang²

2019

HFF

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“…The relationship between the gas density, ρ, and the gas refractive index, n, can be represented by the Gladstone–Dale equation, as in Eq. ( 1 ) (Schwarz 1996 ; Martínez-González et al 2012 ; Su and Bai 2016 ): where G(λ) is defined for air by: Here in n: gas refractive index; ρ: the gas density (kg/m 3 ); G(λ): Gladstone-Dale number(m 3 /kg); Δh: the offset distance (m); f: lens focal length (m); λ: wave length (m).…”

Section: Methodsmentioning

confidence: 99%

Visualization of hot flows of tall space fires in model experiments with Schlieren Photography technique

Wang

Shih

et al. 2016

SpringerPlus

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The natural smoke exhaust system for tall spaces is more advantageous than the mechanical type of exhaust. In Taiwan, the effectiveness of natural smoke exhaust systems is inspected only by checking the vent area size. However, the air flow field in a tall space is very complicated, both at ordinary times or during fires. This study used Schlieren Photography technique, on the principle that light rays are refracted when penetrating materials of different densities, to test and simulate the dynamic measurement of hot air in tall space model. A single-mirror Schlieren system, including an 838 mm (H) × 736 mm (W) square concave mirror, as well as the focal length of 3100 mm was adopted. The experimental process of six smokeless candles were used for 1/12.5 model experiment to record the dynamic distribution and accumulation of air flow in the abovementioned space. FDS software was used to simulate various fire scenarios. The different locations of openings in some cases were studied with the maximum temperature scales of 40 and 45 °C, separately. The simulation results and experimental images showed highly similar hot air flow patterns. Schlieren Photography was proved capable of recording and visualizing the dynamic flow of hot air immediately, directly and accurately.

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“…Compared to conventional Schlieren imagin and optical interferometry, the measurement system is quite simple: it consists of only a background, camera, and light source. BOS technique has been applied to various density fields, such as gas flows [6,7,8,9,10], shock waves [4,5,11,12], flames [13,14,15,16,17], and liquid-gas interfaces [18,19]. Furthermore, it has also been applied to various length scales, from micrometers [2,11,12,20] to meters [5,21].…”

Section: Introductionmentioning

confidence: 99%

Background oriented schlieren technique with fast Fourier demodulation for measuring large density-gradient fields of fluids

Shimazaki,

Ichihara,

Tagawa

2022

Preprint

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In order to measure the large density-gradient fields of fluids such as underwater shock waves, we employed a fast Fourier demodulation called Fast Checkerboard Demodulation (FCD) method in Background Oriented Schlieren (BOS) technique. BOS is a simple image-based measurement technique that detects the apparent displacement (local distortion) of a background image caused by the density gradient of the fluid in front of the background. The cross-correlation particle image velocimetry (PIV) method, which is commonly employed in the BOS technique for detecting the apparent displacement, uses a random-dot background, whereas FCD uses a periodic pattern as the background (e.g., checkerboard pattern, lattice grid pattern (grid scale)) to detect the apparent displacement as the phase change of the pattern in the Fourier space. In this study, we measured the apparent displacement, which is proportional to density gradient of fluid, of an underwater shock wave using FCD and PIV. The results showed that FCD can measure a displacement gradient of up to 2.5 times larger than that which PIV can measure. Furthermore, we systematically investigated the measurement limit of FCD-BOS by changing several parameters of the periodic patterns, such as the grid size. Also, we explored the related parameters in the Fourier space to understand the limitations. It is worth noting that FCD-BOS with lattice grid pattern (grid scale) can measure the apparent displacement as accurately as that with a custom-made pattern, indicating that large density-gradient fields of fluids can be measured using a simple setup with a commercially available (inexpensive) pattern.

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Measurement of the neutral plane of an internal fire whirl using the background-oriented Schlieren technique for a vertical shaft model of a high-rise building

Cited by 12 publications

References 27 publications

Analysis of tilted neutral planes for tall space fires with unsymmetrical openings using numerical simulation and Schlieren photography technique

Analysis of tilted neutral planes for tall space fires with unsymmetrical openings using numerical simulation and Schlieren photography technique

Visualization of hot flows of tall space fires in model experiments with Schlieren Photography technique

Background oriented schlieren technique with fast Fourier demodulation for measuring large density-gradient fields of fluids

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