Burning rate distributions for boundary layer flow combustion of a PMMA plate in forced flow
Burning rate distributions for boundary layer flow combustion of a PMMA plate in forced flow
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DOI：
10.1016/s0010-2180(03)00143-3
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发表时间：
2003-10
影响因子：
4.4
通讯作者：
R. Ananth;C. C. Ndubizu-C.;P. Tatem
中科院分区：
文献类型：
--
作者：
R. Ananth;C. C. Ndubizu-C.;P. Tatem
使用迭代方法在表面施加稳态热解动力学，获得了平坦 PMMA 板的燃烧速率 Nu 和温度分布的纳维-斯托克斯 (NS) 方程的解。 NS 解表明，Nu 取决于雷诺数 Re 和空气速度 U，这与包含边界层 (BL) 近似的经典解不同。然而，在 Re (Re >1000) 和 U (U >120 cm/s) 较大的情况下，NS 解可以表示为 Nu = ε +0.1 Re1/2，其中截距 ε 随着 U 的增加而增加，斜率与经典 BL 解给出的斜率相同。 NS 解决方案与实验进行了比较，其中短（10 厘米）PMMA 板被均匀点燃并燃烧不同的时间长度。比较表明，稳态表面热解近似在热解区的中部区域成立，其中 NS 解与 Nu 的数据一致。在热反馈较高的前缘附近，NS 解决方案会过度预测测量结果，因为最初平坦的表面会因边界移动而变得弯曲（凹入）并形成山谷。随着谷值随时间的推移而增加，NS 解和数据之间的偏差也会增加，并延伸到距前沿的距离不断增加。远离热反馈较低的前沿，NS 解决方案也会由于深度热解引起的瞬态效应而过度预测数据。当熔体接近热解温度时，数据接近 NS 解，燃烧时间增加。因此，热解区内的曲率和深度传热/热解效应分别在大燃烧时间和小燃烧时间下显着。
Solutions of Navier-Stokes (NS) equations were obtained for burning rate Nu and temperature distributions for a flat, PMMA plate using an iterative method to impose steady-state, pyrolysis kinetics at the surface. The NS solutions show that Nu depends on both Reynolds number Re and air velocity U unlike the classical solutions, which include the boundary layer (BL) approximations. However, at large values of Re (Re >1000) and U (U >120 cm/s), the NS solutions can be represented by Nu = ε +0.1 Re1/2, where the intercept ε increases with U and the slope is identical to that given by the classical BL solutions. The NS solutions are compared with experiments, in which short (10 cm) PMMA plates were ignited uniformly and burnt for different lengths of time. The comparisons show that the steady-state surface pyrolysis approximation holds in the middle region of the pyrolysis zone, where the NS solutions agree with the data for Nu. Near the leading edge, where the heat feedback is high, the NS solutions over-predict the measurements as the initially flat surface becomes curved (concave) and forms a valley due to the moving boundary. As the valley size increases with time, the deviations between the NS solutions and data increase and extend to increasing distance from the leading edge. Far from the leading edge, where the heat feed back is low, NS solutions also over-predict the data due to transient effects caused by in-depth pyrolysis. As the melt approaches the pyrolysis temperature, the data approach NS solutions with increased burn times. Therefore, the curvature and in-depth heat transfer/pyrolysis effects are significant within the pyrolysis zone at large and small burn times, respectively.