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Simulated effects of main properties and heat flux on first dripping behaviors of polymers impinged by small flames
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DOI：10.1016/j.firesaf.2024.104115.png)
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Abstract
En 中文
Dripping plays a significant role in understanding the UL-94 vertical test. In this study, the dripping of polymers impinged by small flames was simulated using the volume of fluid method and the enthalpy-porosity technique. The UL-94 flame was approximated using a 2026K gas flow with a velocity of 0.9 m/s, meeting with ASTMD5207. The small-size drop and the large-size drop were characterized by aspect ratios of no more than 1.1 and greater than 3.1, respectively. Decreasing surface tension (a), viscosity (mu), thermal conductivity (k), or increasing the heat flux tends to result in small-size drops. When a <= 0.04 N/m, the first drop is small-size, and the equivalent radius of the first drop follows a power-law relationship with a. As a varies from 0.03 N/m to 0.07 N/m, the critical value of mu decreases from 0.30 Pa s to 0.02 Pa s. If a = 0.07 N/m and k <= 0.1W/m & sdot;K, the first drop tends to be small-size. When a is 0.03 N/m, the size of the first drop is independent of k, and the critical heat flux is approximately 48 kW/m2. The first dripping time increases with mu, and the large-size dripping time is linear with the product of viscosity and characteristic length divided by drop mass.
Keywords:
Dripping behavior
Heat flux
Melt viscosity
Surface tension coefficient
Heat conductivity
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