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Research Papers: Radiative Heat Transfer

Modeling of Heat Transfer in Intumescent Fire-Retardant Coating Under High Radiant Heat Source and Parametric Study on Coating Thermal Response

[+] Author and Article Information
Sheng-Yen Hsu

Department of Mechanical and
Electro-Mechanical Engineering,
National Sun Yat-sen University,
No. 70, Leinhai Road, Gushan District,
Kaohsiung 80424, Taiwan
e-mail: syhsu@mail.nsysu.edu.tw

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received March 6, 2017; final manuscript received July 17, 2017; published online October 10, 2017. Assoc. Editor: Laurent Pilon.

J. Heat Transfer 140(3), 032701 (Oct 10, 2017) (11 pages) Paper No: HT-17-1122; doi: 10.1115/1.4037823 History: Received March 06, 2017; Revised July 17, 2017

In this study, a new model for intumescent coatings is developed including the radiation transfer equation. So, one of the important features of this model is to give the insight of the radiative heat transfer in intumescent coating during expansion. In addition, the model equations are derived into a new coordinate system by introducing the expansion effect into the corresponding parameters. Consequently, the numerical results can be carried out by using a fixed grid system. The numerical results show that the radiative heat transfer near the exposed coating surface cannot be well simulated by the model of thermal radiation conductivity, which is widely used in the previous studies. So, it is suggested that the radiative heat transfer in the expanded char region should be formulated by a more considerate model. In addition, several parameters of coating thermal properties (thermal conductivity, extinction coefficient, and albedo) are tested and investigated under a radiant heat source. In addition to the transient response, the effects of these coating properties on the quasi steady results are also discussed. It is found that the thermal conductivity and the extinction coefficient in the expanded char region both dominate the coating performance. For the thermal properties of virgin coating, the thermal conductivity may have significant effect when the coating has large incomplete pyrolysis (expansion) region, while the extinction coefficient has little influence. Besides, the thermal conductivity and the albedo of virgin coating both alter the heating time to initial expansion but in different mechanisms.

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References

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Figures

Grahic Jump Location
Fig. 1

The one-dimensional model configuration for the intumescent coating

Grahic Jump Location
Fig. 2

The grid-dependency test on the expansion ratio as a function of time

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Fig. 3

The comparison between the model results and the experimental data [3] for two coating thicknesses (0.127 and 0.508 cm) under three different radiant heat sources (2.5, 5, and 7.5 W/cm2). (a) The expansion ratio and (b) HBE.

Grahic Jump Location
Fig. 4

The numerical results of the reference case. (a) The local temperatures and the expansion ratio as a function of time. (b) The distributions of the coating temperature and the expansion level at 3600 s. (c) The distributions of the conductive and radiative heat fluxes at 3600 s. (d) The distributions of the thermal conductivity (kc), the equivalent radiation conductivity (kr), the modeled radiation conductivity (kR), and the apparent thermal conductivity (kc + kr) at 3600 s.

Grahic Jump Location
Fig. 5

The comparison between the model results (the reference case) and the experimental data (Sample 14 data in Ref. [3]) as a function of time. (a) The local temperatures in the expanding coating. (b) The coating thickness (xL). (Solid line: experiment data; dashed line: model results.)

Grahic Jump Location
Fig. 6

The test results for kv. (a) The substrate temperature and the expansion ratio as a function of time. (b) The distributions of the coating temperature and the expansion level at 3600 s. (c) The distributions of the conductive and radiative heat fluxes at 3600 s.

Grahic Jump Location
Fig. 7

The test results for kp. (a) The substrate temperature and the expansion ratio as a function of time. (b) The distributions of the coating temperature and the expansion level at 3600 s. (c) The distributions of the conductive and radiative heat fluxes at 3600 s.

Grahic Jump Location
Fig. 8

The test results for βv. (a) The substrate temperature and the expansion ratio as a function of time. (b) The distributions of the coating temperature and the expansion level at 3600 s. (c) The distributions of the conductive and radiative heat fluxes at 3600 s.

Grahic Jump Location
Fig. 9

The test results for βp. (a) The substrate temperature and the expansion ratio as a function of time. (b) The distributions of the coating temperature and the expansion level at 3600 s. (c) The distributions of the conductive and radiative heat fluxes at 3600 s.

Grahic Jump Location
Fig. 10

The test results for ω. (a) The substrate temperature and the expansion ratio as a function of time. (b) The distributions of the coating temperature and the expansion level at 3600 s. (c) The distributions of the conductive and radiative heat fluxes at 3600 s.

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