Experimental Study on Choking Phenomenon of Gas-Powder Flow
Experimental Study on Choking Phenomenon of Gas-Powder Flow
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发表时间：
2005
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通讯作者：
Shen Feng-man
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作者：
Shen Feng-man
基于两相均相平衡模型理论，对气粉两相流动的堵塞现象进行了实验研究和理论分析。在水平等截面管道内进行了不同密度、比热容和导热系数的Al_2O_3、中空Al_2O_3粉末的实验，以了解质量流量与进口滞止压力的关系。应用堵塞原理，确定了气粉两相流动的表观临界压力比和表观声速。考虑到两相流动的热弛豫，定义了固相有效比热容(ESHC)、混合物的有效等熵指数(EIE)和相对有效比热容(RESHC)。实验结果表明，随着滞止压力的增大，质量流量在堵塞前呈三次多项式增长，在堵塞后呈线性增长。通过对比不同粉料的实验结果，得出了粉料的物理性质对气粉流动ASV的影响。当固体质量负荷量(SML)较小时，ASV主要受粉末导热系数的影响。当SML较大时，粉末的密度反而影响ASV。固相的ESHC随载荷的增加而减小。热导率是影响ESHC的主要因素，而密度对ESHC影响不大。固相的ESHC很小(0.5%)，可以忽略不计。因此，气相的等熵指数可以作为混合物的等熵指数来计算气固两相流动的ASV。
Based on the theory of two-phase homogeneous equilibrium model (HEM), the choking phenomena of gas?powder flow were experimentally studied and theoretically analyzed. Experiments were conducted in a horizontal constant cross-section duct with three kinds of powder: Al2O3, hollow Al2O3 and Al, with different densities, specific heat capacities and thermal conductivities, in order to understand the relationship between the mass flow-rate and the inlet stagnant pressure. Applying the choking principle, the apparent critical pressure ratio and apparent sonic velocity (ASV) of gas?powder flow were determined. Considering the thermal relaxation of the two-phase flow, the effective specific heat capacity (ESHC) of solid phase, the effective isoentropic exponent (EIE) of the mixture and the relative effective specific heat capacity (RESHC) were defined. The experimental results show that, with the increase of the stagnation pressure, the mass flow rate increases as a cubic polynomial function before choking and linearly after choking. The influence of the physical properties of powders on ASV of gas?powder flow is obtained by the comparison between experimental results of different powders. When solid mass loading (SML) is small, ASV is mainly affected by the thermal conductivity of the powder. When SML is large, the density of the powder affects ASV instead. ESHC of the solid phase decreases with the increase of its loading. The thermal conductivity is the main factor to affect ESHC, while density is hardly so. ESHC of the solid phase is very small (0.5%), and may be ignored. Therefore, the isoentropic exponent of the gas phase can be used as that of the mixture to calculate the ASV of gas?particle flow.