Experimental study on evolution of waterfilm height during static flash of pure water

doi:10.11949/j.issn.0438-1157.20180991

Abstract

Abstract:

Experimental study on evolution of waterfilm height during static flash of pure water was carried out with superheat varying between 7.0 K and 32.5 K, orifice diameter at 5, 10, 20 mm, and flash speed between 0.004 s^-1 and 0.073 s^-1. Results indicated that the maximum expansion rate of waterfilm increased with rising superheat or orifice diameter. At given orifice diameter, the flash speed decreased with rising superheat, however, the maximum expansion rate of waterfilm increased with it. At given superheat, both flash speed and the maximum expansion rate increased with increasing orifice diameter. At last, an experimental correlation was set up between maximum expansion rate and superheat, flash speed. The calculated results matched well with experimental data. These results provided a technical support for the miniaturization, compactness and finely control of industrial flash system.

Key words: static flash, superheat, orifice diameter, flash speed, maximum expansion rate

摘要：

设计搭建了静态闪蒸实验台，利用高速摄影对不同过热度、节流孔板直径和闪蒸速率下纯水静态闪蒸过程中液膜高度的演变规律进行了实验研究。实验中过热度为7.0~32.5 K，节流孔板直径为5、10、20 mm，闪蒸速率为0.004~0.073 s^-1。通过液膜膨胀率来衡量和比较液膜高度的变化，液膜膨胀率是指闪蒸过程中液膜实时液位与初始液位的比值。结果表明：最大膨胀率随过热度或节流孔板直径的增大而增大；节流孔板直径一定时，闪蒸速率可通过改变过热度来调节，此时最大膨胀率随闪蒸速率的增大而减小；当过热度一定时，闪蒸速率可通过改变节流孔板直径来调节，此时最大膨胀率随闪蒸速率的增大而增大。最后，根据实验结果拟合得到过热度、闪蒸速率与最大膨胀率的实验关联式，其计算值与实验值吻合良好。本文研究结果对工业闪蒸设备小型化、紧凑化和精细控制提供了重要的实验依据。

关键词: 静态闪蒸, 过热度, 节流孔板直径, 闪蒸速率, 最大膨胀率

CLC Number:

TK 124

Huihui WANG, Dan ZHANG, Qingzhong YANG, Zhaocheng NIU. Experimental study on evolution of waterfilm height during static flash of pure water[J]. CIESC Journal, 2019, 70(S1): 54-60.

王辉辉, 张丹, 杨庆忠, 牛照程. 纯水静态闪蒸中液膜高度演变的实验研究[J]. 化工学报, 2019, 70(S1): 54-60.

Figures/Tables 11

Fig.1 Experiment system of static flash

Table 1 Uncertainty analyses of experiment parameters

参数	绝对不确定度,dx	最小测量值,x_min	最大相对不确定度,dx/x_min
T/K	0.2	66.2	3.0×10^-3
H_fc/m	5.0×10^-4	0.1	5.0×10^-3
τ/s	0.025	2	0.0125
ΔT/K	—	—	4.2×10^-3
H_r	—	—	7.1×10^-3
NET	—	—	5.9×10^-3
FS/s^-1	—	—	0.0138

Fig.2 Typical evolution of waterfilm height

Fig.3 Evolutions of waterfilm height under different superheats

Fig. 4 Comparison of expansion rate of waterfilm under different superheats

Fig. 5 Evolutions of waterfilm height under different orifice diameters

Fig.6 Comparison of expansion rate of waterfilm under different orifice diameters

Fig.7 Definition of turning instant between fast and gradual evaporation stages

Fig.8 Maximum expansion rate versus flash speed at given orifice diameter

Fig.9 Maximum expansion rate versus flash speed at given superheat

Fig.10 Relative error between calculated and experimental maximum expansion rate

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