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Research Papers: Heat and Mass Transfer

The Thermal Response of Intumescent Coating Under Different Combinations of External Heat Fluxes

[+] Author and Article Information
Sheng-Yen Hsu

Department of Mechanical &
Electro-Mechanical Engineering,
National Sun Yat-sen University,
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 September 6, 2017; final manuscript received January 17, 2018; published online April 11, 2018. Assoc. Editor: Zhixiong Guo.

J. Heat Transfer 140(8), 082001 (Apr 11, 2018) (8 pages) Paper No: HT-17-1528; doi: 10.1115/1.4039220 History: Received September 06, 2017; Revised January 17, 2018

In this study, the heat-blocking performance of intumescent coating under various combinations of external radiative and convective heat fluxes is investigated numerically. The results show that the temperature distribution and heat fluxes near the coating surface are significantly affected by the heat-source combination, and consequently, the thermal responses of coating are different. For the same magnitude of convective heat source, the higher flame temperature (lower heat convection coefficient) has larger thermal effect on coating response. For the same magnitude of heat source, the radiative heat source generates more thermal response of coating than the convective one. Moreover, if the external heat flux is not intense enough to cause large expansion ratio (2 < xL/L < 11) in 3600 s, the combination of heat source can significantly affect the substrate temperature and the total heat flux at the coating surface. However, if the expansion ratio is sufficiently large (xL/L > 11) at the quasi-steady-state (3600 s), the substrate temperature and the total heat flux are independent of the combination of heat source, which only affects the temperature and the radiative and convective heat fluxes near the coating surface (∼3 mm in this study).

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References

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Figures

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Fig. 1

The one-dimensional model configuration for intumescent coating subject to external heat sources

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Fig. 2

The grid-dependency test on the expansion ratio as a function of time (Q˙r= 5 W/cm2, Tf = 1700 K, hf = 0.005 W/cm2 K)

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Fig. 3

The numerical results for convective heat source of Tf = 1700 K and hf = 0.005 W/cm2 K (Q˙r= 0 W/cm2). (a) The coating surface temperature, substrate temperature, and expansion ratio as functions of time. (b) The distributions of coating temperature and expansion level at 3600 s. (c) The distributions of conductive and radiative heat fluxes at 3600 s. (d) The distributions of thermal conductivity (kc), equivalent radiation conductivity (kr), and modeled radiation conductivity (kR) at 3600 s.

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Fig. 4

The comparison of coating responses under different combinations of Tf and hf for the same convective heat flux (Q˙c= 7 W/cm2). (a) The substrate temperatures and expansion ratios as functions of time. (b) The distributions of coating temperatures at 3600 s.

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Fig. 5

The comparison of coating responses under different combinations of Q˙c and Q˙r for the same magnitude of external source (Q˙c+Q˙r= 7 W/cm2). (a) The substrate temperatures and expansion ratios as functions of time. (b) The distributions of coating temperatures at 3600 s.

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Fig. 6

The effect of conductive heat source on coating response by varying Tf (hf = 0.005 W/cm2 K and Q˙r = 5 W/cm2). (a) The substrate temperatures and expansion ratios as functions of time for the cases of Tf = 300 K, 1000 K, and 1700 K. (b) The distributions of the coating temperatures at 3600 s for the cases of Tf = 300 K, 1000 K, and 1700 K. (c) The conductive and radiative heat fluxes on coating surfaces at 3600 s as functions of Tf. (d) The coating surface temperatures, substrate temperatures, and expansion ratios at 3600 s as functions of Tf.

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Fig. 7

The effect of radiative heat source on coating response by varying Q˙r (Tf = 1700 K and hf = 0.005 W/cm2 K). (a) The substrate temperatures and expansion ratios as functions of time for the cases of Q˙r= 0 W/cm2, 5 W/cm2, and 10 W/cm2. (b) The distributions of coating temperatures at 3600 s for the cases of Q˙r= 0 W/cm2, 5 W/cm2, and 10 W/cm2. (c) The conductive and radiative heat fluxes at coating surface at 3600 s as functions of Q˙r. (d) The coating surface temperatures, substrate temperatures, and expansion ratios at 3600 s as functions of Q˙r.

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Fig. 8

(a) The substrate temperatures and (b) the total heat fluxes at coating surface under different combinations of external heat fluxes as functions of the corresponding expansion ratios at 3600 s

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Fig. 9

The coating responses in 3600 s under different combinations of heat source for xL/L≈ 6. (a) The substrate temperatures and expansion ratios as functions of time. (b) The distributions of coating temperature and local expansion level at 3600 s.

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Fig. 10

The coating responses in 3600 s under different combinations of heat source for xL/L≈ 20. (a) The substrate temperatures and expansion ratios as functions of time. (b) The distributions of coating temperature at 3600 s.

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