多组分液滴自然对流厚交换层蒸发模型及其检验

为发展多组分液体燃料高温蒸发模型,首先以零扩散和无限扩散概念为基础,拓展考虑自然对流的厚交换层高温蒸发模型到多组分液体燃料,提出多组分NC-TEL模型。其次,采用挂滴法对正庚烷-乙醇、正癸烷-乙醇、RP-3航空煤油-乙醇三种混合燃料的单液滴在高温静止和强迫对流条件下的蒸发特性进行实验研究。实验结果显示:混合液滴蒸发速率随温度升高而显著增大,温度越高组分构成比例对液滴蒸发率的影响越明显;本文实验条件下,对流环境对于液滴蒸发的促进作用并不明显。最后,用实验数据检验蒸发模型。模型对比结果显示:总体上,NC-TEL模型优于R-M模型,高温段预测精度平均提升了8%～35%;低温段,零扩散NC-TEL模型与实验结果吻合程度较好,而无限扩散NC-TEL模型与实验结果相比误差略大;高温段,对于正庚烷-乙醇混合燃料液滴,NC-TEL模型预测较为准确,而对于正癸烷/RP-3航空煤油-乙醇混合燃料液滴,NC-TEL模型预测值则偏低,可能的原因是微爆现象和Marangoni现象。

Thick Exchange Layer Evaporation Model withNatural Convection Effect for MulticomponentDroplet and Its Validation

In order to develop the high temperature evaporation model for multicomponent liquid fuel, based on zero-diffusion/infinite diffusion concept, thick exchange layer evaporation model with natural convection effect is expanded to multicomponent liquid fuels and multicomponent NC-TEL model is proposed. Then suspended single droplet evaporation characteristics of three kinds of blended fuel: n-heptane - ethanol, n-decane - ethanol, RP-3 aviation kerosene - ethanol were experimentally studied in high temperature air environment with and without forced convection. The experimental results show that the droplet evaporation rate value increases significantly along with the increase of ambient temperature. And the higher the temperature is, the more significant the composition ratio is to the droplet evaporation rate. The effects of forced convection on droplet evaporation are not very obvious in the condition in this paper. Finally, the model was validated by experimental data. The model comparison results show that on the whole, NC-TEL model behaves better than R-M model, and the prediction accuracy in high temperature test section is improved by 8% to 35% on average. In the lower temperature test section, the zero-diffusion NC-TEL model is in good agreement with the experimental results, while the infinite diffusion NC-TEL model has a certain error. In high temperature test section, for n-heptane - ethanol droplet, the predictions of NC-TEL model are accurate. But for n-decane/RP-3 aviation kerosene- ethanol, the prediction values of NC-TEL model are lower, and possible causes are the microexplosion phenomenon and the Marangoni phenomenon.