低Reynolds数下水平管降膜滴状流动的实验研究

doi:10.11949/0438-1157.20190658

摘要/Abstract

摘要：

为了充分了解水平管降膜滴状流动现象，以水为实验流体，采用高速高清摄像仪对不同管距下水平管降膜滴状流动进行了可视化的实验研究。实验观察了低Reynolds数Re≤200、管间距s≤40 mm 范围内的管间滴状流动过程。根据流动形态的特征，将滴状流动划分为堆积滴状流、不完全滴状流、吊坠滴状流、完全滴状流和不完全回缩滴状流。依据实验结果，绘制了滴状流动形态分区图。提出了分离长度的概念，并讨论了流量对分离长度的影响。研究了低Reynolds数下液滴流动的滴落点间距与流量的关系。结果表明，滴状流的管间流动形态不仅受流量的影响，同时也受管间距的影响。分离长度随着Re的增大呈两段式线性增大。液滴流动的滴落点间距在Re≤100范围内随Re增大而减小，在100<Re≤200范围内趋于平稳。此外，分别建立了分离长度和滴落点间距与Re的关系式。

关键词: 水平管降膜, 滴状流动形态, 分离长度, 滴落点间距

Abstract:

To fully understand the drop-like flow phenomenon of the horizontal tube falling film, this paper uses water as the experimental fluid, and uses a high-speed high-definition camera to visualize the drop-shaped flow of the horizontal tube under different pipe spacings. The droplet flow in low Reynolds number Re≤200 and tube spacing s≤40 mm is observed. Based on the different flow characteristic, the droplet flow can be divided into accumulation droplet flow, incomplete droplet flow, pendant droplet flow, complete droplet flow and incomplete retracting droplet flow. According to the experimental results, the partition map of droplet flow is presented. The concept of separation length is proposed, and the effect of flow rate on separation length is discussed. The relationship between dropping site spacing and flow rate in droplet flow at low Reynolds number was studied. The results show that the flow pattern of droplet flow is influenced not only by flow rate but also by tube spacing. With the increase of tube spacing in Re≤120, the flow patterns between tubes are converted from accumulation droplet flow to incomplete droplet flow to pendant droplet flow, and to complete droplet flow. When 25 mm≤s≤40 mm, as the flow rate increases, the flow patterns are successively converted from incomplete droplet flow to pendant droplet flow, and to incomplete retracting droplet flow. The separation length increases linearly in two stages with the increase of Re. The growth rate in Re≤60 is smaller than it in 60<Re≤140. The correlation of separation length with Re is established in this paper. In addition, the dropping site spacing of droplet flow is investigated. The dropping site spacing decreases with the increase of flow rate in Re≤100, and remains stable in the range of 100<Re≤200. Meanwhile, the dropping site spacing of droplet flow with Re is established.

Key words: horizontal tube falling film, droplet flow pattern, separation length, dropping site spacing

中图分类号:

TK 124

柳山林, 牟兴森, 沈胜强, 梁斌, 包天杰, 倪兵. 低Reynolds数下水平管降膜滴状流动的实验研究[J]. 化工学报, 2019, 70(12): 4565-4574.

Shanlin LIU, Xingsen MU, Shengqiang SHEN, Bin LIANG, Tianjie BAO, Bing NI. Experimental study on droplet flow pattern of horizontal tube falling film flow with low Reynolds number[J]. CIESC Journal, 2019, 70(12): 4565-4574.

图/表 14

图1 降膜水循环系统

Fig.1 Diagram of falling film water circulation system

图2 布液器结构

Fig.2 Structure of liquid distributor

图3 Re=120、s=38 mm时完全滴状流的演化过程

Fig.3 Progression of complete droplet flow when Re=120 and s=38 mm

图5 Re=120、s=8 mm时不完全滴状流的演化过程

Fig.5 Progression of incomplete droplet flow when Re=120 and s=8 mm

图4 Re=120、s=23 mm时吊坠滴状流的演化过程

Fig.4 Progression of pendant droplet flow when Re=120 and s=23 mm

图6 Re=80、s=5 mm时堆积滴状流的演化过程

Fig.6 Progression of accumulative droplet flow when Re=80 and s=5 mm

图7 Re=180、s=38 mm时不完全回缩滴状流的演化过程

Fig.7 Progression of incomplete retracting droplet flow when Re=180 and s=38 mm

图8 40℃水的滴状流动模式分区图（Ⅰ—堆积滴状流；Ⅱ—不完全滴状流；Ⅲ—吊坠滴状流；Ⅳ—完全滴状流；Ⅴ—不完全回缩滴状流；Ⅵ—滴-柱状流；Ⅶ—假性柱状流；Ⅷ—柱状流）

Fig.8 Partition map of droplet flow of 40℃ water

图9 不同Re下液滴的分离长度

Fig.9 Separation length of droplet under different Re

表1 拟合常数a、b

Table 1 Fitting constants a and b

a	b	适用范围
9.2	7.7	Re≤60
6.6	30.3	60<Re≤140

图10 式(4)和式(5)的预测值与实验值的比较

Fig.10 Comparison of experimental data with values predicted by Eq. (4) and Eq. (5)

图11 滴落点间距

Fig.11 Dropping site spacing

图12 Reynolds数对滴状流滴落点间距的影响

Fig.12 Effect of Reynolds number on dropping site spacing of droplet flow

图13 式(8)的预测值与实验值的比较

Fig.13 Comparison of experimental data with values predicted by Eq. (8)

参考文献 31

1	Khawaji A D , Kutubkhanah I K , Wie J M . Advances in seawater desalination technologies[J]. Desalination, 2008, 221(1): 47-69.
2	Fernández-Seara J , Pardiñas Á Á . Refrigerant falling film evaporation review: description, fluid dynamics and heat transfer[J]. Appl. Therm. Eng., 2013, 64(1/2): 155.
3	何茂刚, 王小飞, 张颖 . 制冷用水平管降膜蒸发器的研究进展及新技术[J]. 化工学报, 2008, 59(S2): 23-28.
	He M G , Wang X F , Zhang Y . Review of Prior research and new technology of horizontal-tube falling-film evaporator used in refrigeration[J]. Journal of Chemical Industry and Engineering(China), 2008, 59(S2): 23-28.
4	Ribatskia G , Jacobi A M . Falling-film evaporation on horizontal tubes—a critical review[J]. Int. J. Refrig., 2005, 28(5): 635-653.
5	沈胜强, 梁刚涛, 龚路远, 等 . 水平管降膜蒸发器传热系数空间分布[J]. 化工学报, 2011, 62(12): 3381-3385.
	Shen S Q , Liang G T , Gong L Y , et al . Distribution of heat transfer coefficient in horizontal tube falling film evaporator[J]. CIESC Journal, 2011, 62(12): 3381-3385.
6	Killion J D , Garimella S . A critical review of models of coupled heat and mass transfer in falling-film absorption[J]. Int. J. Refrig., 2001, 24(8): 755-797.
7	Mu X , Shen S , Yang Y , et al . Experimental study on overall heat transfer coefficient of seawater on three tube arrangements for horizontal-tube falling film evaporator[J]. Desalin. Water Treat., 2016, 57(21): 9993-10002.
8	陈自刚, 王书冯, 来盛旺, 等 . 水平管外降膜传热性能的数值模拟及实验研究[J]. 化工机械, 2018, 45(6): 757-763.
	Chen Z G , Wang S F , Lai S W , et al . Numerical simulation and experimental study on heat transfer performance of falling film outside the horizontal tube[J]. Chem. Eng. Mach., 2018, 45(6): 757-763.
9	Hu X , Jacobi A M . The intertube falling film(1): Flow characteristics, mode transitions, and hysteresis[J]. J. Heat Transfer, 1996, 118(3): 616-625.
10	Xu L , Wang S , Wang S , et al . Studies on heat-transfer film coefficients inside a horizontal tube in falling film evaporators[J]. Desalination, 2004, 166: 215-222.
11	陈学 . 水平管外海水降膜流动与蒸发传热过程研究[D]. 大连: 大连理工大学, 2015.
	Chen X . Flow and evaporation heat transfer of seawater falling film around horizontal tube[D]. Dalian: Dalian University of Technology, 2015.
12	沈胜强, 陈学, 牟兴森, 等 . 管间距对水平管降膜蒸发流动形态和传热的影响[J]. 哈尔滨工程大学学报, 2014, (12): 1492-1496.
	Shen S Q , Chen X , Mu X S , et al . The effect of tube spacing on flow pattern and heat transfer of horizontal tube falling film evaporation[J]. Journal of Harbin Engineering University, 2014, (12): 1492-1496.
13	Chen J , Zhang R , Niu R . Numerical simulation of horizontal tube bundle falling film flow pattern transformation[J]. Renewable Energy, 2015, 73: 62-68.
14	Bustamante J G , Garimella S . Dominant flow mechanisms in falling-film and droplet-mode evaporation over horizontal rectangular tube banks[J]. Int. J. Refrig., 2014, 43: 80-89.
15	Ruan B , Jacobi A M , Li L . Effects of a countercurrent gas flow on falling-film mode transitions between horizontal tubes[J]. Exp. Therm. Fluid Sci., 2009, 33(8): 1216-1225.
16	Maron-Moalem D , Sideman S , Dukler A E . Dripping characteristics in a horizontal tube film evaporator[J]. Desalination, 1978, 27(2): 117-127.
17	Sideman S , Horn H , Moalem D . Transport characteristics of films flowing over horizontal smooth tubes ☆[J]. Int. J. Heat Mass Transfer, 1978, 21(3): 285-294.
18	Hu X , Jacobi A M . The intertube falling film(2): Mode effects on sensible heat transfer to a falling liquid film[J]. J. Heat Transfer, 1996, 118(3): 626-633.
19	Yung D , Lorenz J J , Ganić E N . Vapor/liquid interaction and entrainment in falling film evaporators[J]. J. Heat Transfer, 1980, 102 (1): 20-25.
20	吕凯, 王小飞, 张颖, 等 . 水平蒸发管管间相邻液柱分离间距测量[J]. 化工学报, 2012, 63(3): 740-745.
	Lyu K , Wang X F , Zhang Y , et al . Departure-site spacing for liquid columns falling between horizontal circular tubes[J]. CIESC Journal, 2012, 63(3): 740-745.
21	Liu S , Shen S , Mu X , et al . Experimental study on droplet flow of falling film between horizontal tubes[J]. Int. J. Multiphase Flow, 2019, 118: 10-22.
22	Subramaniam V , Garimella S . Numerical study of heat and mass transfer in lithium bromide-water falling films and droplets[J]. Int. J. Refrig., 2014, 40: 211-226.
23	Killion J D , Garimella S . Gravity-driven flow of liquid films and droplets in horizontal tube banks[J]. Int. J. Refrig., 2003, 26(5): 516-526.
24	Killion J D , Garimella S . Pendant droplet motion for absorption on horizontal tube banks[J]. Int. J. Heat Mass Transfer, 2004, 47(19): 4403-4414.
25	Subramaniam V , Garimella S . From measurements of hydrodynamics to computation of species transport in falling films[J]. Int. J. Refrig., 2009, 32(4): 607-626.
26	Killion J D , Garimella S . Simulation of pendant droplets and falling films in horizontal tube absorbers[J]. J. Korean Marine Eng., 2004, 126(6): 597-607.
27	李美军, 路源, 张士杰, 等 . 水平管降膜吸收局部传热传质特性的数值模拟[J]. 化工学报, 2017, 68(4): 1364-1372.
	Li M J , Lu Y , Zhang S J , et al . Numerical study of local heat and mass transfer characteristics of falling films over horizontal tubes[J]. CIESC Journal, 2017, 68(4): 1364-1372.
28	Hu X , Jacobi A M . Departure-site spacing for liquid droplets and jets falling between horizontal circular tubes[J]. Exp. Therm. Fluid Sci., 1998, 16(4): 322-331.
29	Mu X , Shen S , Yang Y , et al . Experimental study of falling film evaporation heat transfer coefficient on horizontal tube[J]. Desalination, 2008, 220(1/2/3): 654-660.
30	Ribatski G , Thome J R . Experimental study on the onset of local dryout in an evaporating falling film on horizontal plain tubes[J]. Exp. Therm. Fluid Sci., 2007, 31(6): 483-493.
31	Eggers J , Dupont T F . Drop formation in a one-dimensional approximation of the Navier-Stokes equation[J]. J. Fluid Mech., 1994, 262: 205-221.