Predicting radiative characteristics of hydrogen and hydrogen/methane jet fires using FireFOAM C.J. Wang a,c , J.X. Wen b, *, Z.B. Chen c , S. Dembele c a State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, China b Warwick FIRE, School of Engineering, University of Warwick, Coventry CV4 7AL, UK c The Centre for Fire and Explosion Studies, Kingston University, London SW15 3DW, UK article info Article history: Received 30 December 2013 Received in revised form 4 April 2014 Accepted 7 April 2014 Available online 1 May 2014 Keywords: Hydrogen jet fire Hydrogen/methane jet fire FireFOAM Multi-component fuel abstract A possible consequence of pressurized hydrogen release is an under-expanded jet fire. Knowledge of the flame length, radiative heat flux as well as the effects of variations in ground reflectance is important for safety assessment. The present study applies an open source CFD code FireFOAM to study the radiation characteristics of hydrogen and hydrogen/methane jet fires. For combustion, the eddy dissipation concept for multi- component fuels recently developed by the authors in the large eddy simulation (LES) framework is used. The radiative heat is computed with the finite volume discrete ordi- nates model in conjunction with the weighted sum of grey gas model for the absorption/ emission coefficient. The pseudo-diameter approach is used in which the corresponding parameters are calculated using the formulations of Birch et al. [24] with the thermody- namic properties corrected by the Able-Noble equation of state. The predicted flame length and radiant fraction are in good agreement with the measurements of Schefer et al. [2], Studer et al. [3] and Ekoto et al. [6]. In order to account for the effects of variation in ground surface reflectance, the emissivity of hydrogen flames was modified following Ekoto et al. [6]. Four cases with different ground reflectance are computed. The predictions show that the ground surface reflectance only has minor effect on the surface emissive power of the smaller hydrogen jet fire of Ekoto et al. [6]. The radiant fractions fluctuate from 0.168 to 0.176 close to the suggested value of 0.16 by Ekoto et al. [6] based on the analysis of their measurements. Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction Hydrogen is regarded as an important clean energy carrier in the future energy landscape. However, safety issues related to pressurized hydrogen release are of concern and are being incorporated in the development of hydrogen safety Codes and Standards. A related particular hazard which needs to be addressed is hydrogen jet fires. If the pressure in storage tanks or transportation systems is more than 1.9 times the ambient pressure, the release is choked with the resulting jet being under-expanded and has sonic speed at the leak/rupture point. The resulting radiative jet fire extends to several metres and even more than ten metres. Direct impingement, convective or radiative heat from such jet fires can cause human casualties and damages to the directly affected and * Corresponding author. E-mail addresses: [email protected], [email protected](J.X. Wen). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 20560 e20569 http://dx.doi.org/10.1016/j.ijhydene.2014.04.062 0360-3199/Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 2 0 5 6 0e2 0 5 6 9
Available online at w
ScienceDirect
journal homepage: www.elsevier .com/locate/he
Predicting radiative characteristics of hydrogen andhydrogen/methane jet fires using FireFOAM
C.J. Wang a,c, J.X. Wen b,*, Z.B. Chen c, S. Dembele c
aState Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, ChinabWarwick FIRE, School of Engineering, University of Warwick, Coventry CV4 7AL, UKcThe Centre for Fire and Explosion Studies, Kingston University, London SW15 3DW, UK
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 2 0 5 6 0e2 0 5 6 920568
Rr ¼ SEP$Af
Q(31)
where Af and Q are fire surface area and total fire heat release
rate. Normally, Q is constant for a given fire. The radiant frac-
tion hence changes with the SEP as Af is kept almost constant.
This is further illustrated in Fig. 5, where the radiant fraction
has similar trend as the surface emissive power and ranges
from 0.168 to 0.176. The discrepancy is about 5%, much larger
than that of surface emissive power. That is, the radiant frac-
tion exhibits more sensitive to the ground surface reflectance.
Conclusions
Six cases of under-expanded hydrogen and hydrogen/
methane jet fires are simulated using open source CFD code
FireFOAM in the LES frame. Combustion and radiative heat
transfer are computed using the eddy dissipation concept for
multi-component fuels recently developed by the authors and
the finite volume discrete ordinates model. The predictions
are found to be in very good quantitative agreement for flame
length and radiant fraction with themeasurements of Schefer
et al. [2], Studer et al. [3] and Ekoto et al. [6]. These results have
demonstrated that the FireFOAM code can be used as a reli-
able predictive tool for hazard analysis of hydrogen and
hydrogen/methane jet fires.
In order to investigate the effects of ground surface reflec-
tance on the radiant fraction, four cases with different ground
surface reflectance are simulated with one having the same as
the experimental condition of Ekoto et al. [6]. The predictions
show that the ground surface reflectance only hasminor effect
on the surface emissive power of the jet fire. The radiant frac-
tions fluctuate from 0.168 to 0.176 close to the suggested value
of 0.16 by Ekoto et al. [6] based on the analysis of their mea-
surements. Moreover, they seem are more sensitive to the
ground surface reflectance than surface emissive power. The
increaseof groundsurface reflectancedoesnot result ina linear
increase in thesurfaceemissivepowerand the radiant fraction.
Acknowledgement
The authors would like to acknowledge the funding from the
European Commission FP7-IIF Project (Grant No. 909658), the
National Natural Science Foundation of China (Grant No.
51276177), the National Basic Research Program of China (973
Program, Grant No. 2012CB719704) and the Fundamental
Research Funds for the Central Universities.
We are grateful to Etienne Studer, from the Heat Transfer
and Fluid Mechanics Laboratory, France, for providing details
of their hydrogen/methane jet fire measurements.
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