化工学报 ›› 2022, Vol. 73 ›› Issue (7): 3251-3261.doi: 10.11949/0438-1157.20220017

• 能源和环境工程 • 上一篇    下一篇

蒸汽在含有不可溶核和可溶无机盐的细颗粒物表面的核化特性

赵庆杰1(),胡晓红1,2,张超1,2,凡凤仙1,2()   

  1. 1.上海理工大学能源与动力工程学院，上海 200093
    2.上海理工大学上海市动力工程多相流动与传热重点实验室，上海 200093
  • 收稿日期:2022-01-05 修回日期:2022-04-01 出版日期:2022-07-05 发布日期:2022-08-01
  • 通讯作者: 凡凤仙 E-mail:1907725343@qq.com;fanfengxian@usst.edu.cn
  • 作者简介:赵庆杰（1995—），男，硕士研究生，1907725343@qq.com
  • 基金资助:
    国家自然科学基金项目(51976130);上海市科委科研计划项目(13DZ2260900)

Nucleation behavior of water vapor on fine particle containing insoluble core and soluble inorganic salt

Qingjie ZHAO1(),Xiaohong HU1,2,Chao ZHANG1,2,Fengxian FAN1,2()   

  1. 1.School of Energy and Power Engineering，University of Shanghai for Science and Technology，Shanghai 200093，China
    2.Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering，University of Shanghai for Science and Technology，Shanghai 200093，China
  • Received:2022-01-05 Revised:2022-04-01 Published:2022-07-05 Online:2022-08-01
  • Contact: Fengxian FAN E-mail:1907725343@qq.com;fanfengxian@usst.edu.cn

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摘要：

鉴于生物质直接燃烧和生物质与煤混合燃烧发电过程排放细颗粒物表面通常含有一定量的可溶无机盐，基于经典异质核化理论，综合考虑晶核生长的表面扩散和直接沉积机制建立了改进的蒸汽在包含球形不可溶核和可溶无机盐的细颗粒物表面的异质核化模型，利用数值模拟方法，对4种组分颗粒(不可溶颗粒以及3种含可溶无机盐的颗粒)的异质核化特性进行对比分析。结果表明，在中等接触角条件下，不可溶颗粒的临界晶核形成自由能和临界晶核半径最大，含KCl颗粒次之，含NaCl颗粒再次之，含CaCl2颗粒最小；临界晶核条件下，表面扩散机制与直接沉积机制引起的水分子添加速率之比随颗粒半径的增大先略有增加而后保持不变，随接触角的增大而单调下降。研究还发现，当接触角较小时，含可溶无机盐颗粒的成核临界饱和度低于不可溶颗粒；当接触角较大时，含KCl和NaCl颗粒的成核临界饱和度先后超过不可溶颗粒。

关键词: 颗粒, 成核, 凝结, 不可溶核, 可溶无机盐, 数值模拟

Abstract:

The surfaces of fine particles that emitted from power generation processes with the direct combustion of biomass and with the co-combustion of biomass and coal usually contain a certain amount of soluble inorganic salt. Based on the classical heterogeneous nucleation theory, an improved model for vapor heterogeneous nucleation on the surfaces of particles containing a spherical insoluble core and soluble inorganic salt was developed, taking into account the embryo growth mechanisms of surface diffusion and direct deposition. Using the numerical simulation method, the nucleation behaviors of four types of particles (insoluble particle and three types of particle containing soluble inorganic salt) were compared and analyzed. The results show that in cases of medium contact angles, the critical free energy of embryo formation and the critical embryo radius of an insoluble particle are the largest, followed by the particles containing KCl, NaCl and CaCl2, respectively. Under the condition with critical embryo radii, the ratio of water molecule addition rates due to mechanisms of surface diffusion and direct deposition increases slightly at first and then keeps constant with increasing particle radius, and decreases monotonically with increasing contact angle. It is also found that when the contact angle is small, the critical saturation ratio for nucleation of a particle containing soluble inorganic salt is lower than that of the insoluble particle, whereas when the contact angle is larger, the critical saturation for nucleation of particles containing KCl and NaCl exceeds that of insoluble particles successively.

Key words: particle, nucleation, condensation, insoluble core, soluble inorganic salt, numerical simulation

中图分类号: 

  • X 513

图1

颗粒及蒸汽在颗粒表面异质核化形成晶核示意图"

图2

常温常压下无机盐溶液中水的活度和溶液的气-液界面自由能"

表1

常温常压下无机盐溶液中水的活度和溶液的气-液界面自由能计算系数"

参数符号NaClKClCaCl2
活度a1-0.5286-0.3818-0.5507
a2-1.0298-0.77881.3166
a3-1.73300-17.9406
a40021.6473
气-液界面自由能B/(N·kg/(m·mol))1.6200×10-31.4923×10-33.4372×10-3

表2

数值模拟采用的计算参数"

参数符号单位数值
温度TK298.15
压力pPa101325
颗粒中不可溶核的密度ρpkg/m32400
可溶无机盐质量分数fs%20
单个水分子的质量mwkg2.99×10-26
单个水分子的体积Vwm32.99×10-29
水分子的平均跳跃距离δm3.2×10-10
水分子的振动频率υHz1×1013
单个水分子的表面扩散能ΔGdiffJ2.9×10-21
单个水分子的吸附能ΔGdesJ2.9×10-20

图3

无量纲晶核形成自由能随晶核半径的变化关系"

图4

直接沉积和表面扩散机制引起的分子添加速率之比"

图5

成核临界饱和度"

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