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脉冲热激励对液滴蒸发特性影响的实验研究
周心远,李军伟,陈新建,王宁飞
北京理工大学 宇航学院,北京 100081
摘要:
为了研究脉冲热激励条件下的液体燃料的蒸发特性,采用脉冲电源作为外部热激励加热微尺度燃烧器,通过连续供给液体正庚烷在微尺度燃烧器中形成悬挂单液滴,并对液滴在脉冲热激励下的非稳态蒸发特性进行了研究。通过示波器采集了脉冲电源的输出信号,同时测量来流空气温度和管口火焰温度,得到了二者对脉冲信号的响应规律,通过图像处理方法得到了液滴直径随时间的振荡规律,计算了液滴的蒸发速率以探究液滴振荡的原因。结果表明,液滴蒸发速率始终围绕燃料供给速率振荡,二者间差值是液滴振荡的根本原因。脉冲热激励首先引发空气温度的振荡,并导致火焰温度,液滴直径和蒸发速率以相同频率振荡,但均滞后于空气温度。提高加热频率或减少加热功率都能加速火焰温度对空气温度振荡的响应,但延迟了液滴直径和蒸发速率对空气温度振荡的响应。加热功率会显著影响液滴直径,当功率低于16.0W时,液滴直径超出临界直径2.6mm,液滴将坠落形成液膜。
关键词:  脉冲加热  温度振荡  热激励  动态响应  非稳态蒸发
DOI:10.13675/j.cnki.tjjs.210586
分类号:V19
基金项目:
Experimental Study on Effects of Pulsed Thermal Excitation on Droplet Evaporation Characteristics
ZHOU Xin-yuan, LI Jun-wei, CHEN Xin-jian, WANG Ning-fei
School of Aerospace,Beijing Institute of Technology,Beijing 100081,China
Abstract:
In order to investigate effects of pulsed thermal excitation on evaporation characteristics of liquid fuel, a pulse power is used as an external thermal excitation to heat a microscale burner, where a suspended droplet is formed by continuously supplying liquid n-heptane, and unsteady evaporation characteristics of the droplet under pulsed thermal excitation are studied. Firstly, output signal of the pulse power is obtained by oscilloscope, and the air temperature and flame temperature are measured to obtain response of the temperature to the pulse power. Secondly, oscillation of the droplet diameter with time is obtained by the image processing method. Finally, the droplet evaporation rate is calculated to explain the droplet oscillation. The results show that, the droplet evaporation rate always oscillates around the fuel supply rate, and the difference between them leads to the droplet oscillation. The pulsed thermal excitation first induces the air temperature oscillation, and causes the flame temperature, droplet diameter and evaporation rate to oscillate at the same frequency, but all of them lag behind the air temperature. Increasing the heating frequency or reducing the heating power can accelerate response of the flame temperature to the air temperature oscillation, but delay response of the droplet diameter and evaporation rate to the air temperature oscillation. The heating power significantly affects the average droplet diameter. When the power is lower than 16.0W, the droplet diameter exceeds the critical diameter of 2.6mm, and the droplet falls to form a liquid film.
Key words:  Pulse heating  Temperature oscillation  Thermal excitation  Dynamic response  Unsteady evaporation