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Zhirong Wang - One of the best experts on this subject based on the ideXlab platform.
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experimental analytical and numerical investigation on auto Ignition of thermally intermediate pmma imposed to linear Time increasing heat flux
Applied Thermal Engineering, 2020Co-Authors: Junhui Gong, Chunjie Zhai, Yang Zhou, Lizhong Yang, Mingrui Zhang, Zhirong WangAbstract:Abstract Auto-Ignition of finite thick PMMA (polymethyl methacrylate) subjected to linear Time-increasing heat flux (HF) is experimentally investigated utilizing a heating apparatus capable of freely controlling the variation of the exposure. Ignition Times, surface and in-depth temperatures of samples were recorded. Theoretical analysis, using critical temperature, and numerical simulations considering pyrolysis and thermal insulation layer were implemented to estimate the corresponding measurements. Approximate correlations are obtained based on the analysis and they are related to the ones in thermally thick cases. Results show that the thermal insulation layer and the pyrolysis in solid have limited and significant effects on surface temperature, respectively. 1 mm PMMA cannot be treated as thermally thin due to the large temperature gradient in solid. Appreciable sample distortion and thickness regression observed in thin sample tests are responsible for the large uncertainty of Ignition Time and non-Ignition phenomenon. Thinner sample and larger increasing rate of HF would lead to higher surface temperature and shorter Ignition Time. Two stages separated by pyrolysis temperature are identified before Ignition. The measured critical temperature is 695 ± 14.5 K, and a more reasonable uncertainty range, ±30 K, is suggested by numerically fitting the measured Ignition Times.
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effect of radiation absorption modes on Ignition Time of translucent polymers subjected to Time dependent heat flux
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Yixuan Chen, Junhui Gong, Xuan Wang, Juncheng Jiang, Shunbing Zhu, Yang Zhou, Zhirong WangAbstract:Majority of previous solid Ignition models, including numerical and analytical ones, considered only surface absorption of incident heat flux for simplification. However, the influence of in-depth absorption on pyrolysis and subsequent Ignition cannot be ignored for infrared translucent polymers. This work addresses this problem and focuses on Time-dependent heat flux to establish an analytical model for Ignition behaviors prediction by means of theoretical analysis. Ignition temperature was utilized as the Ignition criterion, and both surface and in-depth absorption scenarios were considered. Thermally thick polymethyl methacrylate and polyamide 6 were selected as reference materials to verify the reliability and applicability of the proposed model by comparing the analysis results with experimental data as well as numerical simulations. A method for determining the approximation parameters of the theoretical analysis was presented to derive the relationship between Ignition Time and the coefficients in heat flux expressions. The results show that the higher surface temperature owing to surface absorption accelerates the pyrolysis rate and results in a shorter Ignition Time, while in-depth absorption affects the Ignition Time inversely. The effect of surface heat loss was also evaluated quantitatively through both analytical and numerical models. The uncertainty of the proposed model is mainly caused by the selection of the approximation parameters. Nevertheless, it provides an alternative approach to estimate the Ignition Time of translucent polymers besides numerical simulation.
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analytical prediction of pyrolysis and Ignition Time of translucent fuel considering both Time dependent heat flux and in depth absorption
Fuel, 2019Co-Authors: Junhui Gong, Long Shi, Shunbing Zhu, Yang Zhou, Stanislav I. Stoliarov, Zhirong WangAbstract:This contribution reports an approximate analytical model to predict transient mass flux and Ignition Time of translucent fuel, black poly(methyl methacrylate) (PMMA), subjected to a Time-dependent incident heat flux, atb, where t is Time and a and b are constants. The model can be easily extended to other non-charring translucent solids. The model takes into account in-depth absorption of thermal radiation in the condensed phase, which is typically ignored in the analytical formulations. Both critical temperature and critical mass flux were employed as the Ignition criteria to examine their effects on the predictions. The model was validated using exact numerical solutions and experimental data, and compared with earlier analytical models based on the assumption of surface absorption. Linear and quadratic heat fluxes were considered for validation and discussion. The results show that surface absorption accelerates the pyrolysis process and leads to higher mass flux and shorter Ignition Time with respect to the in-depth absorption case. The discrepancy between the predicted transient mass fluxes of these two absorption modes increases with increasing a. The Ignition heat flux increases with increasing a and decreases with increasing b for both surface and in-depth absorption cases. However, the critical energy is independent of heat flux in in-depth absorption scenario. Furthermore, parametric studies of in-depth absorption coefficient and critical mass flux were conducted to investigate their effects on the quality of the model predictions. Also, the equivalent Ignition temperature was calculated and compared with the experimental values. It is expected that the developed model will find its use in performance-based design applications.
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analytical prediction of heat transfer and Ignition Time of solids exposed to Time dependent thermal radiation
International Journal of Thermal Sciences, 2018Co-Authors: Junhui Gong, Long Shi, Xuan Wang, Supan Wang, Juncheng Jiang, Zhirong WangAbstract:Abstract An analytical model was developed in this study to predict the heat transfer and Ignition Time of solids subjected to Time-dependent thermal radiation (HF=atb). Both surface and in-depth absorptions, corresponding to opaque and translucent materials, were considered in the model and critical temperature was employed. The predictions of the new model fit well with the experimental and numerical results. The results show that for surface absorption the Ignition Time to the power of −(b+0.5) is proportional to a, and the reciprocal of square root of Ignition Time is linearly correlated with Ignition HF. Furthermore, a critical Ignition HF was found to represent the lower limit of Ignition HF range, which is different with the critical HF at constant HF. While for in-depth absorption, the Ignition Time to the power of −(b+1) and −1 were linearly proportional to a/(b+1) and Ignition HF, respectively. For translucent solids, the analytical model cannot be applied to constant HF but can provide relatively high accuracy in predicting Ignition Time under variable HF. Also, the effect of in-depth absorption coefficient on Ignition Time were addressed, and it was found that this important parameter exerts its influence on Ignition process following the similar mechanism with that of constant HF.
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approximate analytical solutions for transient mass flux and Ignition Time of solid combustibles exposed to Time varying heat flux
Fuel, 2018Co-Authors: Junhui Gong, Xuan Wang, Juncheng Jiang, Zhirong Wang, Yixuan Chen, Jinghong WangAbstract:Abstract An approximate analytical model was established in this study to predict the transient mass flux and Ignition Time of solid combustibles exposed to Time-dependent exponentially increasing heat flux. Critical mass flux was employed as the Ignition criterion in the developed model. A new approximation strategy was used to simplify the complicated exact solution and to derive explicit correlations between Ignition Time and heat flux. Linear and quadratic heat fluxes were focused and the conclusions under other heat fluxes can be extended through analogy. An equivalent Ignition temperature, involving critical mass flux, thermodynamics and chemical kinetics, was found in this study. The negative square root of Ignition Time is linearly proportional to the heat flux at Ignition Time. Under linear and quadratic heat fluxes, the Ignition heat flux increases with a 1/3 and a 1/5 ( a is a constant in the heat flux expression), respectively, whereas the total heat absorbed by the solid before Ignition is proportional to a −1/3 and a −1/5 , respectively. The capability of the proposed model was validated by another analytical model, numerical simulations and experimental data of black PMMA (Polymethyl Methacrylate) and pine wood. Furthermore, the effect of surface heat loss on the predictions of the proposed model was estimated and parametric study based on critical mass flux was implemented.
Junhui Gong - One of the best experts on this subject based on the ideXlab platform.
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experimental analytical and numerical investigation on auto Ignition of thermally intermediate pmma imposed to linear Time increasing heat flux
Applied Thermal Engineering, 2020Co-Authors: Junhui Gong, Chunjie Zhai, Yang Zhou, Lizhong Yang, Mingrui Zhang, Zhirong WangAbstract:Abstract Auto-Ignition of finite thick PMMA (polymethyl methacrylate) subjected to linear Time-increasing heat flux (HF) is experimentally investigated utilizing a heating apparatus capable of freely controlling the variation of the exposure. Ignition Times, surface and in-depth temperatures of samples were recorded. Theoretical analysis, using critical temperature, and numerical simulations considering pyrolysis and thermal insulation layer were implemented to estimate the corresponding measurements. Approximate correlations are obtained based on the analysis and they are related to the ones in thermally thick cases. Results show that the thermal insulation layer and the pyrolysis in solid have limited and significant effects on surface temperature, respectively. 1 mm PMMA cannot be treated as thermally thin due to the large temperature gradient in solid. Appreciable sample distortion and thickness regression observed in thin sample tests are responsible for the large uncertainty of Ignition Time and non-Ignition phenomenon. Thinner sample and larger increasing rate of HF would lead to higher surface temperature and shorter Ignition Time. Two stages separated by pyrolysis temperature are identified before Ignition. The measured critical temperature is 695 ± 14.5 K, and a more reasonable uncertainty range, ±30 K, is suggested by numerically fitting the measured Ignition Times.
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effect of radiation absorption modes on Ignition Time of translucent polymers subjected to Time dependent heat flux
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Yixuan Chen, Junhui Gong, Xuan Wang, Juncheng Jiang, Shunbing Zhu, Yang Zhou, Zhirong WangAbstract:Majority of previous solid Ignition models, including numerical and analytical ones, considered only surface absorption of incident heat flux for simplification. However, the influence of in-depth absorption on pyrolysis and subsequent Ignition cannot be ignored for infrared translucent polymers. This work addresses this problem and focuses on Time-dependent heat flux to establish an analytical model for Ignition behaviors prediction by means of theoretical analysis. Ignition temperature was utilized as the Ignition criterion, and both surface and in-depth absorption scenarios were considered. Thermally thick polymethyl methacrylate and polyamide 6 were selected as reference materials to verify the reliability and applicability of the proposed model by comparing the analysis results with experimental data as well as numerical simulations. A method for determining the approximation parameters of the theoretical analysis was presented to derive the relationship between Ignition Time and the coefficients in heat flux expressions. The results show that the higher surface temperature owing to surface absorption accelerates the pyrolysis rate and results in a shorter Ignition Time, while in-depth absorption affects the Ignition Time inversely. The effect of surface heat loss was also evaluated quantitatively through both analytical and numerical models. The uncertainty of the proposed model is mainly caused by the selection of the approximation parameters. Nevertheless, it provides an alternative approach to estimate the Ignition Time of translucent polymers besides numerical simulation.
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analytical prediction of pyrolysis and Ignition Time of translucent fuel considering both Time dependent heat flux and in depth absorption
Fuel, 2019Co-Authors: Junhui Gong, Long Shi, Shunbing Zhu, Yang Zhou, Stanislav I. Stoliarov, Zhirong WangAbstract:This contribution reports an approximate analytical model to predict transient mass flux and Ignition Time of translucent fuel, black poly(methyl methacrylate) (PMMA), subjected to a Time-dependent incident heat flux, atb, where t is Time and a and b are constants. The model can be easily extended to other non-charring translucent solids. The model takes into account in-depth absorption of thermal radiation in the condensed phase, which is typically ignored in the analytical formulations. Both critical temperature and critical mass flux were employed as the Ignition criteria to examine their effects on the predictions. The model was validated using exact numerical solutions and experimental data, and compared with earlier analytical models based on the assumption of surface absorption. Linear and quadratic heat fluxes were considered for validation and discussion. The results show that surface absorption accelerates the pyrolysis process and leads to higher mass flux and shorter Ignition Time with respect to the in-depth absorption case. The discrepancy between the predicted transient mass fluxes of these two absorption modes increases with increasing a. The Ignition heat flux increases with increasing a and decreases with increasing b for both surface and in-depth absorption cases. However, the critical energy is independent of heat flux in in-depth absorption scenario. Furthermore, parametric studies of in-depth absorption coefficient and critical mass flux were conducted to investigate their effects on the quality of the model predictions. Also, the equivalent Ignition temperature was calculated and compared with the experimental values. It is expected that the developed model will find its use in performance-based design applications.
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analytical prediction of heat transfer and Ignition Time of solids exposed to Time dependent thermal radiation
International Journal of Thermal Sciences, 2018Co-Authors: Junhui Gong, Long Shi, Xuan Wang, Supan Wang, Juncheng Jiang, Zhirong WangAbstract:Abstract An analytical model was developed in this study to predict the heat transfer and Ignition Time of solids subjected to Time-dependent thermal radiation (HF=atb). Both surface and in-depth absorptions, corresponding to opaque and translucent materials, were considered in the model and critical temperature was employed. The predictions of the new model fit well with the experimental and numerical results. The results show that for surface absorption the Ignition Time to the power of −(b+0.5) is proportional to a, and the reciprocal of square root of Ignition Time is linearly correlated with Ignition HF. Furthermore, a critical Ignition HF was found to represent the lower limit of Ignition HF range, which is different with the critical HF at constant HF. While for in-depth absorption, the Ignition Time to the power of −(b+1) and −1 were linearly proportional to a/(b+1) and Ignition HF, respectively. For translucent solids, the analytical model cannot be applied to constant HF but can provide relatively high accuracy in predicting Ignition Time under variable HF. Also, the effect of in-depth absorption coefficient on Ignition Time were addressed, and it was found that this important parameter exerts its influence on Ignition process following the similar mechanism with that of constant HF.
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approximate analytical solutions for transient mass flux and Ignition Time of solid combustibles exposed to Time varying heat flux
Fuel, 2018Co-Authors: Junhui Gong, Xuan Wang, Juncheng Jiang, Zhirong Wang, Yixuan Chen, Jinghong WangAbstract:Abstract An approximate analytical model was established in this study to predict the transient mass flux and Ignition Time of solid combustibles exposed to Time-dependent exponentially increasing heat flux. Critical mass flux was employed as the Ignition criterion in the developed model. A new approximation strategy was used to simplify the complicated exact solution and to derive explicit correlations between Ignition Time and heat flux. Linear and quadratic heat fluxes were focused and the conclusions under other heat fluxes can be extended through analogy. An equivalent Ignition temperature, involving critical mass flux, thermodynamics and chemical kinetics, was found in this study. The negative square root of Ignition Time is linearly proportional to the heat flux at Ignition Time. Under linear and quadratic heat fluxes, the Ignition heat flux increases with a 1/3 and a 1/5 ( a is a constant in the heat flux expression), respectively, whereas the total heat absorbed by the solid before Ignition is proportional to a −1/3 and a −1/5 , respectively. The capability of the proposed model was validated by another analytical model, numerical simulations and experimental data of black PMMA (Polymethyl Methacrylate) and pine wood. Furthermore, the effect of surface heat loss on the predictions of the proposed model was estimated and parametric study based on critical mass flux was implemented.
Matthew A Oehlschlaeger - One of the best experts on this subject based on the ideXlab platform.
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Ignition Time measurements for methylcylcohexane and ethylcyclohexane air mixtures at elevated pressures
International Journal of Chemical Kinetics, 2009Co-Authors: Jeremy Vanderover, Matthew A OehlschlaegerAbstract:The Ignition of methylcyclohexane (MCH)/air and ethylcyclohexane (ECH)/air mixtures has been studied in a shock tube at temperatures and pressures ranging from 881 to 1319 K and 10.8 to 69.5 atm, respectively, for equivalence ratios of 0.25, 0.5, and 1.0. Endwall OH* emission and sidewall pressure measurements were used to determine Ignition delay Times. The influence of temperature, pressure, and equivalence ratio on Ignition has been characterized. Negative temperature coefficient behavior was observed for temperatures below 1000 K. These measurements greatly extend the database of kinetic targets for MCH and provide, to our knowledge, the first Ignition measurements for ECH. The combination of the MCH measurements with previous shock tube and rapid compression machine measurements provides kinetic targets over a large temperature range, 680–1650 K, for the validation of kinetic mechanisms. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 82–91, 2009
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a shock tube study of iso octane Ignition at elevated pressures the influence of diluent gases
Combustion and Flame, 2008Co-Authors: Hsiping S Shen, Jeremy Vanderover, Matthew A OehlschlaegerAbstract:The Ignition of iso-octane/air and iso-octane/O{sub 2}/Ar ({proportional_to}20% O{sub 2}) mixtures was studied in a shock tube at temperatures of 868-1300 K, pressures of 7-58 atm, and equivalence ratios {phi}=1.0, 0.5, and 0.25. Ignition Times were determined using endwall OH* emission and sidewall piezoelectric pressure measurements. Measured iso-octane/air Ignition Times agreed well with the previously published results. Mixtures with argon as the diluent exhibited Ignition Times 20% shorter, for most conditions, than those with nitrogen as the diluent (iso-octane/air mixtures). The difference in measured Ignition Times for mixtures containing argon and nitrogen as the diluent gas can be attributed to the differing heat capacities of the two diluent species and the level of induction period heat release prior to Ignition. Kinetic model predictions of Ignition Time from three mechanisms are compared to the experimental data. The mechanisms overpredict the Ignition Times but accurately capture the influence of diluent gas on iso-octane Ignition Time, indicating that the mechanisms predict an appropriate amount of induction period heat release. (author)
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a shock tube study of cyclopentane and cyclohexane Ignition at elevated pressures
International Journal of Chemical Kinetics, 2008Co-Authors: Shane M Daley, Andrew M Berkowitz, Matthew A OehlschlaegerAbstract:Ignition delay Times for cyclopentane/air and cyclohexane/air mixtures were measured in a shock tube at temperatures of 847–1379 K, pressures of 11–61 atm, and equivalence ratios of ϕ = 1.0, 0.5, and 0.25. Ignition Times were determined using electronically excited OH emission monitored through the shock tube endwall and piezoelectric pressure measurements made in the shock tube sidewall. The dependence of Ignition Time on pressure, temperature, and equivalence ratio is quantified and correlations for Ignition Time formulated. Measured Ignition Times are compared to kinetic modeling predictions from four recently published mechanisms. The data presented provide a database for the validation of cycloalkane kinetic mechanisms at the elevated pressures found in practical combustion engines. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 624–634, 2008
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shock tube measurements of iso octane Ignition Times and oh concentration Time histories
Proceedings of the Combustion Institute, 2002Co-Authors: David F Davidson, Matthew A Oehlschlaeger, John T Herbon, Ronald K HansonAbstract:Abstract Ignition delay Times and OH radical concentration profiles were measured in toluene/O 2 /Ar mixtures behind reflected shock waves. Initial reflected shock conditions spanned 1400–2000 K and 1.5–5.0 atm, with equivalence ratios of 0.5–1.875 and toluene concentrations of 0.025–0.5%. OH Time histories were monitored using narrow-linewidth ring dye laser absorption of the well-characterized R 1 (5) line of the OH A–X (0, 0) band at 306.7 nm. Ignition Time data were extracted from the OH traces and were found to compare very well with measurements using sidewall pressure. These new data are in agreement with the recent measurements of Burcat et al. [NASA TM-87312, 1986], but not with the measurements of Pitz et al. [Second Joint Meeting, US Sections of the Combustion Institute, Paper 253, 2001] or Burcat et al. [Combust. Flame 36 (1979)]. The results of this study were compared to three detailed kinetic models: Pitz et al. [Second Joint Meeting, US Sections of the Combustion Institute, Paper 253, 2001], Dagaut et al.[Phys. Chem. Chem. Phys. 4 (2002)], and Lindstedt and Maurice [Combust. Sci. Technol. 120 (1996)]. The ability of the mechanisms to predict the measured Ignition Time data and OH concentration profiles was analyzed. Suggestions to improve model performance have been made, and key reactions that need to be studied further have been identified. This work has yielded the first quantitative measurements of OH Time histories during toluene oxidation, and hence provides a critical data set useful for evaluating and refining comprehensive mechanisms on toluene oxidation.
Juncheng Jiang - One of the best experts on this subject based on the ideXlab platform.
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effect of radiation absorption modes on Ignition Time of translucent polymers subjected to Time dependent heat flux
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Yixuan Chen, Junhui Gong, Xuan Wang, Juncheng Jiang, Shunbing Zhu, Yang Zhou, Zhirong WangAbstract:Majority of previous solid Ignition models, including numerical and analytical ones, considered only surface absorption of incident heat flux for simplification. However, the influence of in-depth absorption on pyrolysis and subsequent Ignition cannot be ignored for infrared translucent polymers. This work addresses this problem and focuses on Time-dependent heat flux to establish an analytical model for Ignition behaviors prediction by means of theoretical analysis. Ignition temperature was utilized as the Ignition criterion, and both surface and in-depth absorption scenarios were considered. Thermally thick polymethyl methacrylate and polyamide 6 were selected as reference materials to verify the reliability and applicability of the proposed model by comparing the analysis results with experimental data as well as numerical simulations. A method for determining the approximation parameters of the theoretical analysis was presented to derive the relationship between Ignition Time and the coefficients in heat flux expressions. The results show that the higher surface temperature owing to surface absorption accelerates the pyrolysis rate and results in a shorter Ignition Time, while in-depth absorption affects the Ignition Time inversely. The effect of surface heat loss was also evaluated quantitatively through both analytical and numerical models. The uncertainty of the proposed model is mainly caused by the selection of the approximation parameters. Nevertheless, it provides an alternative approach to estimate the Ignition Time of translucent polymers besides numerical simulation.
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analytical prediction of heat transfer and Ignition Time of solids exposed to Time dependent thermal radiation
International Journal of Thermal Sciences, 2018Co-Authors: Junhui Gong, Long Shi, Xuan Wang, Supan Wang, Juncheng Jiang, Zhirong WangAbstract:Abstract An analytical model was developed in this study to predict the heat transfer and Ignition Time of solids subjected to Time-dependent thermal radiation (HF=atb). Both surface and in-depth absorptions, corresponding to opaque and translucent materials, were considered in the model and critical temperature was employed. The predictions of the new model fit well with the experimental and numerical results. The results show that for surface absorption the Ignition Time to the power of −(b+0.5) is proportional to a, and the reciprocal of square root of Ignition Time is linearly correlated with Ignition HF. Furthermore, a critical Ignition HF was found to represent the lower limit of Ignition HF range, which is different with the critical HF at constant HF. While for in-depth absorption, the Ignition Time to the power of −(b+1) and −1 were linearly proportional to a/(b+1) and Ignition HF, respectively. For translucent solids, the analytical model cannot be applied to constant HF but can provide relatively high accuracy in predicting Ignition Time under variable HF. Also, the effect of in-depth absorption coefficient on Ignition Time were addressed, and it was found that this important parameter exerts its influence on Ignition process following the similar mechanism with that of constant HF.
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approximate analytical solutions for transient mass flux and Ignition Time of solid combustibles exposed to Time varying heat flux
Fuel, 2018Co-Authors: Junhui Gong, Xuan Wang, Juncheng Jiang, Zhirong Wang, Yixuan Chen, Jinghong WangAbstract:Abstract An approximate analytical model was established in this study to predict the transient mass flux and Ignition Time of solid combustibles exposed to Time-dependent exponentially increasing heat flux. Critical mass flux was employed as the Ignition criterion in the developed model. A new approximation strategy was used to simplify the complicated exact solution and to derive explicit correlations between Ignition Time and heat flux. Linear and quadratic heat fluxes were focused and the conclusions under other heat fluxes can be extended through analogy. An equivalent Ignition temperature, involving critical mass flux, thermodynamics and chemical kinetics, was found in this study. The negative square root of Ignition Time is linearly proportional to the heat flux at Ignition Time. Under linear and quadratic heat fluxes, the Ignition heat flux increases with a 1/3 and a 1/5 ( a is a constant in the heat flux expression), respectively, whereas the total heat absorbed by the solid before Ignition is proportional to a −1/3 and a −1/5 , respectively. The capability of the proposed model was validated by another analytical model, numerical simulations and experimental data of black PMMA (Polymethyl Methacrylate) and pine wood. Furthermore, the effect of surface heat loss on the predictions of the proposed model was estimated and parametric study based on critical mass flux was implemented.
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approximate analytical solutions for temperature based transient mass flux and Ignition Time of a translucent solid at high radiant heat flux considering in depth absorption
Combustion and Flame, 2017Co-Authors: Junhui Gong, Juncheng Jiang, Yixuan Chen, Jinghong Wang, Yabo Li, Jing Li, Zhirong WangAbstract:Abstract Most studies, employing Ignition temperature as the Ignition criterion, utilized surface absorption of radiant incident heat flux in analytical models when investigating the Ignition mechanism of solid combustibles. However, in-depth absorption exerts its influence on Ignition Time significantly for translucent solid, especially at high radiant heat flux. In this work, we extend the previous researches from surface absorption to in-depth absorption to develop an approximate analytical Ignition model using critical mass flux instead of critical temperature. An approximation methodology is proposed during derivation to study the in-depth absorption scenario. The comparison among this model, available experimental data of black PMMA in the literature and previous numerical simulations indicates that the proposed model provides relatively high accuracy in predicting Ignition Time. Furthermore, the pure surface absorption circumstance is also reexamined and compared with the classical Ignition theory. The results show that surface absorption hypothesis accelerates the total mass flux, which consequently shortens the Ignition Time. However, in-depth absorption assumption eliminates the heat accumulation on surface and results in good prediction for Ignition Time at high heat flux. For in-depth absorption, the absorption coefficient affects the heat penetration depth and temperature distribution in this layer which consequently affects the thermal degradation reaction rate, mass flux and finally Ignition Time. Meanwhile, the Ignition Time considering both surface and in-depth absorption is discussed, and the relationship with pure surface and in-depth absorption conditions is obtained.
Jinghong Wang - One of the best experts on this subject based on the ideXlab platform.
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approximate analytical solutions for transient mass flux and Ignition Time of solid combustibles exposed to Time varying heat flux
Fuel, 2018Co-Authors: Junhui Gong, Xuan Wang, Juncheng Jiang, Zhirong Wang, Yixuan Chen, Jinghong WangAbstract:Abstract An approximate analytical model was established in this study to predict the transient mass flux and Ignition Time of solid combustibles exposed to Time-dependent exponentially increasing heat flux. Critical mass flux was employed as the Ignition criterion in the developed model. A new approximation strategy was used to simplify the complicated exact solution and to derive explicit correlations between Ignition Time and heat flux. Linear and quadratic heat fluxes were focused and the conclusions under other heat fluxes can be extended through analogy. An equivalent Ignition temperature, involving critical mass flux, thermodynamics and chemical kinetics, was found in this study. The negative square root of Ignition Time is linearly proportional to the heat flux at Ignition Time. Under linear and quadratic heat fluxes, the Ignition heat flux increases with a 1/3 and a 1/5 ( a is a constant in the heat flux expression), respectively, whereas the total heat absorbed by the solid before Ignition is proportional to a −1/3 and a −1/5 , respectively. The capability of the proposed model was validated by another analytical model, numerical simulations and experimental data of black PMMA (Polymethyl Methacrylate) and pine wood. Furthermore, the effect of surface heat loss on the predictions of the proposed model was estimated and parametric study based on critical mass flux was implemented.
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approximate analytical solutions for temperature based transient mass flux and Ignition Time of a translucent solid at high radiant heat flux considering in depth absorption
Combustion and Flame, 2017Co-Authors: Junhui Gong, Juncheng Jiang, Yixuan Chen, Jinghong Wang, Yabo Li, Jing Li, Zhirong WangAbstract:Abstract Most studies, employing Ignition temperature as the Ignition criterion, utilized surface absorption of radiant incident heat flux in analytical models when investigating the Ignition mechanism of solid combustibles. However, in-depth absorption exerts its influence on Ignition Time significantly for translucent solid, especially at high radiant heat flux. In this work, we extend the previous researches from surface absorption to in-depth absorption to develop an approximate analytical Ignition model using critical mass flux instead of critical temperature. An approximation methodology is proposed during derivation to study the in-depth absorption scenario. The comparison among this model, available experimental data of black PMMA in the literature and previous numerical simulations indicates that the proposed model provides relatively high accuracy in predicting Ignition Time. Furthermore, the pure surface absorption circumstance is also reexamined and compared with the classical Ignition theory. The results show that surface absorption hypothesis accelerates the total mass flux, which consequently shortens the Ignition Time. However, in-depth absorption assumption eliminates the heat accumulation on surface and results in good prediction for Ignition Time at high heat flux. For in-depth absorption, the absorption coefficient affects the heat penetration depth and temperature distribution in this layer which consequently affects the thermal degradation reaction rate, mass flux and finally Ignition Time. Meanwhile, the Ignition Time considering both surface and in-depth absorption is discussed, and the relationship with pure surface and in-depth absorption conditions is obtained.
