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Kohyu Satoh - One of the best experts on this subject based on the ideXlab platform.
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Temperature velocity and air entrainment of fire whirl plume a comprehensive experimental investigation
Combustion and Flame, 2015Co-Authors: Linhe Zhang, Kohyu SatohAbstract:Abstract Comprehensive measurements were performed to examine the Temperature, velocity (in axial and tangential directions) and air entrainment of propane fire whirl plume in a medium-scale fixed-frame facility. It is found that the radial profile of Excess Temperature varies consistently with the continuous flame shape and the radial decay rate of Excess Temperature decreases in the intermittent flame and plume. The centerline axial velocity depends on both the buoyancy and the axial pressure gradient related to the tangential velocity. A weak annular reverse flow is found outside the upward core at z / D ⩽ 1.0 , while the absolute axial velocity slightly increases with fire size. The growth of axial velocity core is found to be constrained by the reverse flow. The mean axial velocity radius is confirmed to be greater than the mean Excess Temperature radius in the continuous flame. The radial profile of tangential velocity varies steadily with height, and is little affected by heat release rate. The radial swirl flow consists of the vortex core, the quasi-free vortex and the near wall region, and the active reaction occurs in the vortex core. The plume growth rate increases with decreasing RiB (Richardson number) and three distinct regions are identified in different RiB ranges. The air entrainment is strong at the bottom inflow boundary layer, while the mass flow rate increases slowly with height as compared to buoyant pool fires. The suppression of air entrainment may be attributable to the radial force balance and stable stratification in the centrifugal acceleration filed. The entrainment coefficient in the continuous flame is about one to two orders of magnitude lower than that in a buoyant pool fire, and it generally increases with height in the plume of fire whirl, approaching the value for pure buoyant plume. The mean entrainment coefficient depends on the mean RiB by −1 power law for z ⩽ H f .
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effect of flow circulation on combustion dynamics of fire whirl
Proceedings of the Combustion Institute, 2013Co-Authors: Kuibin Zhou, Naian Liu, Jesse S Lozano, Yanlong Shan, Bin Yao, Kohyu SatohAbstract:In this paper, the effect of flow circulation on the combustion dynamics of fire whirl is systematically investigated by experiments. New correlations for the burning rate, flame height, radial Temperature and mass flow rate are established for fire whirl. It is clarified that flow circulation helps increase both the fuel-flame contact area and the actual fuel surface area, which in turn increases both the heat feedback to the fuel surface and the radial velocity in the ground boundary layer, leading to increase of burning rate. A novel idea for correlation of fire whirl flame height is proposed by assuming that the ratio of the fire whirl flame height to the flame height without circulation solely characterizes the effect of circulation. This idea is fully verified, thereby a new formulation for flame height is established, which successfully decouples the burning rate and the circulation. It is indicated that the fuel-rich core in the flame body of fire whirl significantly affects the radial Temperature distribution in the continuous flame region, and the flame body can be described by the combination of a cylinder and a cone. The flow circulation significantly suppresses fire plume radius and thus decreases its increasing rate with vertical distance. It is also demonstrated that the fire whirl flame involves laminarized regions in its lower section, coexisting with turbulent regions in the upper portion. The flow circulation enhances the air entrainment in the ground layer by altering the radial velocity profile and increasing the radial velocity. In the low section of flaming region, the significant decrease of mixture between the combustion products and surrounding air dominates the pure aerodynamic effect of flow circulation on the flame height. Finally, it is clarified that fire whirls maintain higher centerline Excess Temperature than general pool fires due to the effect of less air entrainment.
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experimental research on combustion dynamics of medium scale fire whirl
Proceedings of the Combustion Institute, 2011Co-Authors: Jiao Lei, Linhe Zhang, Kohyu Satoh, Naian Liu, Haixiang Chen, Lifu Shu, Pu Chen, Zhihua Deng, Jiping Zhu, John L De RisAbstract:Abstract The medium-scale fire whirl was extensively investigated by experimental means, in order to establish correlations of the burning rate, flame height and flame Temperature of fire whirl, and to clarify the difference between fire whirls and general pool fires. Experimental observations and data confirmed that a free burning fire whirl is a highly stable burning phenomenon with large quasi-steady periods. Burning rates of fire whirls depend on pool diameter similarly to those of general pool fires; however the transition turbulent burning occurs sooner as the pool diameter increases. The lip height seems to have little effect on the burning rate of fire whirls. The correlation H ∗ = K · ( Q ˙ ∗ · Γ ∗ 2 ) m was proposed to couple the height of fire whirl to the fire release rate and ambient circulation. It correlates the data from both this work and the literature. Radial Temperature profiles in the continuous region of the fire whirl were confirmed to be hump-type, implying the existence of fuel-rich inner core. The pool diameter and heat release rate do not significantly affect the radial Temperature profiles in non-dimensional radial coordinates. It was found that the fire plume of fire whirl involves three distinct zones just like that of pool fire, but with different normalized ranges. Fire whirls maintain a higher ratio of continuous flame height to the overall flame height, and also higher maximum centerline Excess Temperature in continuous flame region, as compared to general pool fires. It was further demonstrated that the fire whirl plume at its origin behaves like a turbulent jet with moderate swirling, and then tends to become buoyancy dominated downstream, with slight swirling. With an increase in dimensionless height adjusted by the plume origin, the plume centerline Excess Temperature decays rapidly and approaches the theoretical value of −5/3 for free buoyancy plume.
Shijie Zhong - One of the best experts on this subject based on the ideXlab platform.
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Controls on plume heat flux and plume Excess Temperature
Journal of Geophysical Research, 2008Co-Authors: Wei Leng, Shijie ZhongAbstract:[1] Plume heat flux and plume Excess Temperature in the upper mantle inferred from surface observations may pose important constraints on the heat flux from the core and mantle internal heating rate. This study examined the relationship between plume heat flux Qp, core-mantle boundary (CMB) heat flux Qcmb and plume Excess Temperature ΔTplume in thermal convection using both numerical modeling and theoretical analysis. 3-D regional spherical models of mantle convection were computed with high resolution and for different Rayleigh number, internal heat generation rate, viscosity structures and dissipation number. An analytic model was developed for variations in Qp and ΔTplume with depth. The results can be summarized as following. (1) Mantle plumes immediately above the CMB carry nearly 80%–90% of the CMB heat flux. (2) Qp and ΔTplume decrease by approximately a factor of two for plumes to ascend from near the CMB to the upper mantle depth. (3) Our analytic model indicates that the decrease in Qp and ΔTplume is mainly controlled by the steeper adiabatic gradient of plumes compared with the ambient mantle and the reduction ratios for Qp and ΔTplume due to this effect depend upon the dissipation number and the distance over which plumes ascend. (4) The subadiabatic Temperature also contributes to the reduction of Qp and ΔTplume, but its contribution is only 20% to 30%. Subadiabatic Temperature from our models with >50% internal heating rate ranges from 35 K to 170 K for CMB Temperature of 3400°C. (5) Our results confirms that ∼70% internal heating rate for the mantle or Qcmb of ∼11 TW is required to reproduce the plume-related observations.
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constraints on thermochemical convection of the mantle from plume heat flux plume Excess Temperature and upper mantle Temperature
Journal of Geophysical Research, 2006Co-Authors: Shijie ZhongAbstract:[1] Seismic and geochemical observations indicate a compositionally heterogeneous mantle in the lower mantle, suggesting a layered mantle. The volume and composition of each layer, however, remain poorly constrained. This study seeks to constrain the layered mantle model from observed plume Excess Temperature, plume heat flux, and upper mantle Temperature. Three-dimensional spherical models of whole mantle and layered mantle convection are computed for different Rayleigh number, internal heat generation, buoyancy number, and bottom layer thickness for layered mantle models. The model results show that these observations are controlled by internal heating rate in the layer overlying the thermal boundary layer from which mantle plumes are originated. To reproduce the observations, internal heating rate needs ∼65% for whole mantle convection, but for layered mantle models, the internal heating rate for the top layer is ∼60–65% for averaged bottom layer thicknesses 2520 km) and has radiogenic heat generation rate >2.82 × 10−12 W/kg that is >3 times of that for the depleted mantle source for mid-ocean ridge basalts (DMM). For the top layer to have the radiogenic heat generation of the DMM, mantle secular cooling rate needs to exceed 145 K/Ga. The current study also shows that plume Temperature in the upper mantle is about half of the CMB Temperature for whole mantle convection or ∼0.6 of Temperature at compositional boundary for a layered mantle, independent of internal heating rate and Rayleigh number. Finally, the model calculations confirm that mantle plumes accounts for the majority (∼80%) of CMB heat flux in whole mantle convection models. However, plume heat flux decreases significantly by as much as a factor of 3, as plumes ascend through the mantle to the upper mantle, owing to the adiabatic and possibly diffusive cooling of the plumes and owing to slight (∼180 K) subadiabaticity in mantle geotherm.
Linhe Zhang - One of the best experts on this subject based on the ideXlab platform.
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Temperature velocity and air entrainment of fire whirl plume a comprehensive experimental investigation
Combustion and Flame, 2015Co-Authors: Linhe Zhang, Kohyu SatohAbstract:Abstract Comprehensive measurements were performed to examine the Temperature, velocity (in axial and tangential directions) and air entrainment of propane fire whirl plume in a medium-scale fixed-frame facility. It is found that the radial profile of Excess Temperature varies consistently with the continuous flame shape and the radial decay rate of Excess Temperature decreases in the intermittent flame and plume. The centerline axial velocity depends on both the buoyancy and the axial pressure gradient related to the tangential velocity. A weak annular reverse flow is found outside the upward core at z / D ⩽ 1.0 , while the absolute axial velocity slightly increases with fire size. The growth of axial velocity core is found to be constrained by the reverse flow. The mean axial velocity radius is confirmed to be greater than the mean Excess Temperature radius in the continuous flame. The radial profile of tangential velocity varies steadily with height, and is little affected by heat release rate. The radial swirl flow consists of the vortex core, the quasi-free vortex and the near wall region, and the active reaction occurs in the vortex core. The plume growth rate increases with decreasing RiB (Richardson number) and three distinct regions are identified in different RiB ranges. The air entrainment is strong at the bottom inflow boundary layer, while the mass flow rate increases slowly with height as compared to buoyant pool fires. The suppression of air entrainment may be attributable to the radial force balance and stable stratification in the centrifugal acceleration filed. The entrainment coefficient in the continuous flame is about one to two orders of magnitude lower than that in a buoyant pool fire, and it generally increases with height in the plume of fire whirl, approaching the value for pure buoyant plume. The mean entrainment coefficient depends on the mean RiB by −1 power law for z ⩽ H f .
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experimental research on combustion dynamics of medium scale fire whirl
Proceedings of the Combustion Institute, 2011Co-Authors: Jiao Lei, Linhe Zhang, Kohyu Satoh, Naian Liu, Haixiang Chen, Lifu Shu, Pu Chen, Zhihua Deng, Jiping Zhu, John L De RisAbstract:Abstract The medium-scale fire whirl was extensively investigated by experimental means, in order to establish correlations of the burning rate, flame height and flame Temperature of fire whirl, and to clarify the difference between fire whirls and general pool fires. Experimental observations and data confirmed that a free burning fire whirl is a highly stable burning phenomenon with large quasi-steady periods. Burning rates of fire whirls depend on pool diameter similarly to those of general pool fires; however the transition turbulent burning occurs sooner as the pool diameter increases. The lip height seems to have little effect on the burning rate of fire whirls. The correlation H ∗ = K · ( Q ˙ ∗ · Γ ∗ 2 ) m was proposed to couple the height of fire whirl to the fire release rate and ambient circulation. It correlates the data from both this work and the literature. Radial Temperature profiles in the continuous region of the fire whirl were confirmed to be hump-type, implying the existence of fuel-rich inner core. The pool diameter and heat release rate do not significantly affect the radial Temperature profiles in non-dimensional radial coordinates. It was found that the fire plume of fire whirl involves three distinct zones just like that of pool fire, but with different normalized ranges. Fire whirls maintain a higher ratio of continuous flame height to the overall flame height, and also higher maximum centerline Excess Temperature in continuous flame region, as compared to general pool fires. It was further demonstrated that the fire whirl plume at its origin behaves like a turbulent jet with moderate swirling, and then tends to become buoyancy dominated downstream, with slight swirling. With an increase in dimensionless height adjusted by the plume origin, the plume centerline Excess Temperature decays rapidly and approaches the theoretical value of −5/3 for free buoyancy plume.
John L De Ris - One of the best experts on this subject based on the ideXlab platform.
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experimental research on combustion dynamics of medium scale fire whirl
Proceedings of the Combustion Institute, 2011Co-Authors: Jiao Lei, Linhe Zhang, Kohyu Satoh, Naian Liu, Haixiang Chen, Lifu Shu, Pu Chen, Zhihua Deng, Jiping Zhu, John L De RisAbstract:Abstract The medium-scale fire whirl was extensively investigated by experimental means, in order to establish correlations of the burning rate, flame height and flame Temperature of fire whirl, and to clarify the difference between fire whirls and general pool fires. Experimental observations and data confirmed that a free burning fire whirl is a highly stable burning phenomenon with large quasi-steady periods. Burning rates of fire whirls depend on pool diameter similarly to those of general pool fires; however the transition turbulent burning occurs sooner as the pool diameter increases. The lip height seems to have little effect on the burning rate of fire whirls. The correlation H ∗ = K · ( Q ˙ ∗ · Γ ∗ 2 ) m was proposed to couple the height of fire whirl to the fire release rate and ambient circulation. It correlates the data from both this work and the literature. Radial Temperature profiles in the continuous region of the fire whirl were confirmed to be hump-type, implying the existence of fuel-rich inner core. The pool diameter and heat release rate do not significantly affect the radial Temperature profiles in non-dimensional radial coordinates. It was found that the fire plume of fire whirl involves three distinct zones just like that of pool fire, but with different normalized ranges. Fire whirls maintain a higher ratio of continuous flame height to the overall flame height, and also higher maximum centerline Excess Temperature in continuous flame region, as compared to general pool fires. It was further demonstrated that the fire whirl plume at its origin behaves like a turbulent jet with moderate swirling, and then tends to become buoyancy dominated downstream, with slight swirling. With an increase in dimensionless height adjusted by the plume origin, the plume centerline Excess Temperature decays rapidly and approaches the theoretical value of −5/3 for free buoyancy plume.
Naian Liu - One of the best experts on this subject based on the ideXlab platform.
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effect of flow circulation on combustion dynamics of fire whirl
Proceedings of the Combustion Institute, 2013Co-Authors: Kuibin Zhou, Naian Liu, Jesse S Lozano, Yanlong Shan, Bin Yao, Kohyu SatohAbstract:In this paper, the effect of flow circulation on the combustion dynamics of fire whirl is systematically investigated by experiments. New correlations for the burning rate, flame height, radial Temperature and mass flow rate are established for fire whirl. It is clarified that flow circulation helps increase both the fuel-flame contact area and the actual fuel surface area, which in turn increases both the heat feedback to the fuel surface and the radial velocity in the ground boundary layer, leading to increase of burning rate. A novel idea for correlation of fire whirl flame height is proposed by assuming that the ratio of the fire whirl flame height to the flame height without circulation solely characterizes the effect of circulation. This idea is fully verified, thereby a new formulation for flame height is established, which successfully decouples the burning rate and the circulation. It is indicated that the fuel-rich core in the flame body of fire whirl significantly affects the radial Temperature distribution in the continuous flame region, and the flame body can be described by the combination of a cylinder and a cone. The flow circulation significantly suppresses fire plume radius and thus decreases its increasing rate with vertical distance. It is also demonstrated that the fire whirl flame involves laminarized regions in its lower section, coexisting with turbulent regions in the upper portion. The flow circulation enhances the air entrainment in the ground layer by altering the radial velocity profile and increasing the radial velocity. In the low section of flaming region, the significant decrease of mixture between the combustion products and surrounding air dominates the pure aerodynamic effect of flow circulation on the flame height. Finally, it is clarified that fire whirls maintain higher centerline Excess Temperature than general pool fires due to the effect of less air entrainment.
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experimental research on combustion dynamics of medium scale fire whirl
Proceedings of the Combustion Institute, 2011Co-Authors: Jiao Lei, Linhe Zhang, Kohyu Satoh, Naian Liu, Haixiang Chen, Lifu Shu, Pu Chen, Zhihua Deng, Jiping Zhu, John L De RisAbstract:Abstract The medium-scale fire whirl was extensively investigated by experimental means, in order to establish correlations of the burning rate, flame height and flame Temperature of fire whirl, and to clarify the difference between fire whirls and general pool fires. Experimental observations and data confirmed that a free burning fire whirl is a highly stable burning phenomenon with large quasi-steady periods. Burning rates of fire whirls depend on pool diameter similarly to those of general pool fires; however the transition turbulent burning occurs sooner as the pool diameter increases. The lip height seems to have little effect on the burning rate of fire whirls. The correlation H ∗ = K · ( Q ˙ ∗ · Γ ∗ 2 ) m was proposed to couple the height of fire whirl to the fire release rate and ambient circulation. It correlates the data from both this work and the literature. Radial Temperature profiles in the continuous region of the fire whirl were confirmed to be hump-type, implying the existence of fuel-rich inner core. The pool diameter and heat release rate do not significantly affect the radial Temperature profiles in non-dimensional radial coordinates. It was found that the fire plume of fire whirl involves three distinct zones just like that of pool fire, but with different normalized ranges. Fire whirls maintain a higher ratio of continuous flame height to the overall flame height, and also higher maximum centerline Excess Temperature in continuous flame region, as compared to general pool fires. It was further demonstrated that the fire whirl plume at its origin behaves like a turbulent jet with moderate swirling, and then tends to become buoyancy dominated downstream, with slight swirling. With an increase in dimensionless height adjusted by the plume origin, the plume centerline Excess Temperature decays rapidly and approaches the theoretical value of −5/3 for free buoyancy plume.
