دانلود رایگان مقاله اثر کشش سطحی و زبری سطح چوب در تاثیر چلپ چلوپ یک قطره آب خالص

abstract

Concerning the deeper understanding of the mechanisms on fire suppression with multicomponent water mist/spray, the dynamical process of a water drop with or without additives impacting upon wood surfaces is preliminarily studied. The initial diameters of the pure water drop and the water drop with NaCl additive are about 2.470.1 mm, and the diameter of the water drop with AFFF (Aqueous Film-Forming Foam) additive is about 1.870.1 mm. The drop impact velocities are varied from 1.13 m/s to 2.80 m/s. A Photorn FASTCAM high-speed video camera coupled with a Nikon 200 mm micro-lens is used to record the dynamical process of the drop impacting. The results show that the critical impact Weber number of the water drop with additives is obviously larger than that without additives, and the critical impact Weber number increases with decrease of the wood surface roughness. In addition, the current empirical models both on predicting the critical Weber number and the maximum spread factor just partially agree with the experimental results. The current results are limited to the interaction of a single water drop impacting upon a horizontal wood surface.

4. Conclusions

The experimental study on the impact of a water drop with additives on different wood surfaces has been performed. Following conclusions can be drawn: 1) The additives being considered obviously affect the critical Weber number for drop splash when it impacts upon wood surfaces, the smaller the drop surface tension is, the larger the critical Weber number will be. 2) The impact splash of a water drop with additives is obviously influenced by the roughness of the wood surfaces, i.e., Wec increases as Ra decreases. 3) The empirical models on predicting the critical Weber number and maximum spread factor just partially agree with the experimental results of a pure water drop and the water drop with 5% NaCl additive. The current results are limited to the interaction of a single water drop impacting upon a horizontal wood surface, and future study would be focused on improving the model by considering the effects of not only the drop liquid properties, but the surface roughness, wettability, temperature and basic density of the wood surfaces, etc.