Study on anti-fouling characteristics of particulate fouling using built-in self-rotating rotors

doi:10.11949/0438-1157.20221419

Abstract

Abstract:

Dirt on the surface of heat transfer tubes not only hinders heat transfer, but also increases fluid flow resistance, resulting in reduced service life of heat transfer tubes and economic losses. By inserting the rotor into a heat transfer tube, the heat transfer enhancement, antifouling and descaling can be realized simultaneously. In this paper, the flow field and particle fouling characteristics in the heat transfer tube with built-in rotors were studied under different inlet velocities. Using multiple reference frame model (MRF) to show the rotation of rotors, particle fouling characteristics were obtained based on Euler-Euler liquid-solid two-phase flow model and user defined functions (UDF) plug-in program. The results show that the spiral flow appears by installing a rotor to the heat transfer tube, and the circumferential velocity and radial velocity of the fluid can be increased, so the heat transfer performance of the tube wall is enhanced. With the flow rate increasing from 0.15 m/s to 0.35 m/s, the stable value of particle deposition rate in the tube with the self-rotating rotor increases by 136.5%, and the increasement gradually becomes larger. However, the asymptotic value of fouling resistance decreases by 48.3%, and the time required to reach asymptotic value decreases with increasing inlet velocity. On this basis, compared with the fixed rotor, it is found that when the flow rate is 0.15—0.25 m/s, the fouling resistance is smaller when the rotor is fixed, and when the flow rate is 0.30—0.35 m/s, the fouling resistance is smaller when the rotor is rotating. Therefore, the study of particle fouling characteristics at different inlet velocities provides an important basis for the selection and design of the built-in rotor.

Key words: heat transfer tube, rotor, two-phase flow, fouling, particle, numerical simulation

摘要：

传热管表面的污垢不仅阻碍热量传递，还会增加流体流动阻力，导致传热管使用寿命缩短和经济损失。通过在传热管内插入转子可有效实现传热强化和在线除垢抑垢，研究了不同流速下自转式内置转子圆管内的流场和颗粒污垢特性，采用多重参考系模型（MRF）模拟转子在不同流速下的转动，基于欧拉-欧拉液固两相流模型加载UDF得到管内的颗粒污垢特性。结果表明，内置转子传热管内呈螺旋流动，周向速度和径向速度提高，从而增强管壁的换热性能。随着流速从0.15 m/s增加到0.35 m/s，自转式内置转子圆管内颗粒稳定沉积率增加了136.5%，且增加的幅度逐渐变大；但污垢热阻渐近值减少了48.3%，且达到污垢渐近值所需的时间缩短。在此基础上对比固定转子发现，当流速为0.15~0.25 m/s，转子固定时的污垢热阻更小，而当流速为0.30~0.35 m/s，转子转动时的污垢热阻更小。研究可为内置转子的选型和设计提供参考。

关键词: 传热管, 转子, 两相流, 结垢, 颗粒, 数值模拟

CLC Number:

TK 172

Guangshuo XIE, Siliang ZHANG, Jiarui WANG, Juan XIAO, Simin WANG. Study on anti-fouling characteristics of particulate fouling using built-in self-rotating rotors[J]. CIESC Journal, 2022, 73(12): 5384-5393.

谢广烁, 张斯亮, 王家瑞, 肖娟, 王斯民. 自转式内置转子颗粒污垢抑制特性研究[J]. 化工学报, 2022, 73(12): 5384-5393.

Figures/Tables 15

Fig.1 Geometric model

Table 1 Physical parameters of the medium

物性	密度/ (kg/m³)	比热容/ (J/(kg·K))	热导率/ (W/(m·K))	动力黏度/(Pa·s)
水	998.2	4182	0.6	0.001003
氧化镁	1740	873	25.0	—
铝	2719	871	202.4	—
钢	8030	502.48	16.3	—

Fig.2 Schematic diagram of experimental process

Fig.3 Arrangement diagram of experimental setup

Table 2 Grid independence verification

固定区域网格尺寸/mm	旋转区域网格尺寸/mm	网格数量/个	稳定沉积率×10⁴/ (kg/(m²·s))	相对变化/%
5.0	1.6	344134	2.83	—
5.0	1.0	1728899	2.30	18.7
5.0	0.8	2034997	1.94	15.7
5.0	0.6	3203782	1.75	9.8
5.0	0.5	4923102	1.69	3.4

Fig.4 Comparison curves of fouling resistance between simulated values and experimental data

Fig.5 Velocity contour on z=0 section of heat transfer tube

Fig.6 Pathlines of heat transfer tube

Fig.7 Temperature contour on z=0 section of heat transfer tube

Fig.8 Pressure contour on z=0 section of heat transfer tube

Fig.9 The curve of deposition rate with time

Fig.10 The curve of removal rate with time

Fig.11 The curve of fouling thermal resistance with time

Fig.12 The curve of stable value of deposition rate under different flow velocity

Fig.13 The curve of stationary fouling resistance under different flow velocity

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