PENG Deqi¹， LIU Jian¹， FU Weng¹， YU Tianlan²， TAN Zhuowei¹， WU Shuying¹， LI Fang¹ 

1. School of Mechanical Engineering and Mechanics， Xiangtan University， Xiangtan 411105， China； 2. School of Mechanical Engineering， Hunan University of Technology， Zhuzhou 412007， China

Abstract

Objective　To optimize the design of the converging-diverging tube liquid-solid two-phase flow heat exchanger， a visual experimental platform was constructed. Particle image velocimetry （PIV） was employed to investigate the two-dimensional flow field characteristics within a vertical upward converging-diverging tube liquid-solid two-phase flow heat exchanger. The study analyzed the influence of inlet fluid velocity， particle size， and particle volume fraction on the radial velocity and vorticity of the fluid， aiming to elucidate the mechanisms of enhanced mass and heat transfer in the liquid-solid two-phase flow within the converging-diverging tube.

Methods　A visual experimental platform was established， utilizing tap water as the circulating liquid medium， spherical acrylic particles as the solid phase material， and quartz glass as the converging-diverging tube structure. Based on the general principles of particle settling velocity in engineering applications and considering the constraints of experimental conditions， three key parameters were selected， i. e. ， inlet fluid velocity， particle size， and particle volume fraction. Each parameter was set at five gradient levels. Two-dimensional PIV technology was employed to systematically investigate the flow field characteristics within a vertical upward converging-diverging tube liquid-solid two-phase flow heat exchanger. The influence of inlet fluid velocity， particle size， and particle volume fraction on the radial velocity and vorticity of the fluid was explored， and the optimal combination of operating conditions was determined.

Results and Discussion　The increase in the average radial velocity of the liquid-solid two-phase flow indicated enhanced radial fluid motion， which strengthened fluid exchange between different regions and promoted heat and mass transfer among these regions. Within a single pitch of the converging-diverging tube， the radial velocity of the liquid-solid two-phase flow at various radial positions exhibited positive and negative fluctuations as the axial height increased. The peak radial velocity occurred at axial heights of approximately 0， 6， and 24 mm， aligning with the junctions between the expanding and contracting sections of the tube. Along the radial direction， the radial velocity gradually increased from the tube center to the tube wall. The average radial velocity increased with higher inlet fluid velocity and volume fraction but decreased with larger particle sizes. The vorticity of the liquid-solid two-phase flow showed a symmetric positive-negative distribution along the radial direction， with larger vorticity values near the wall and lower values in the central region. Both the overall average vorticity and the near-wall average vorticity increased with higher inlet fluid velocity and volume fraction but decreased with larger particle size. At an inlet fluid velocity of 1. 0 m/s， the overall average vorticity was 80. 7 s^⁻¹， and the near-wall average vorticity was 126. 4 s⁻¹. When the volume fraction ranged from 1% to 5%， the near-wall average vorticity was approximately 56. 6% to 69. 4% higher than the overall average vorticity. Under the conditions of an inlet fluid velocity of 1. 0 m/s， a volume fraction of 5%， and a particle size of 1. 5 mm，the fluid motion within the converging-diverging tube liquid-solid two-phase flow heat exchanger was the most intense， effectively enhancing mass and heat transfer within the tube.

Conclusion　The factors influencing the average radial velocity of the liquid-solid two-phase flow， in descending order of impact， are inlet fluid velocity， volume fraction， and particle size. Similarly， the factors affecting the average vorticity in the near-wall region， in descending order of influence， are inlet fluid velocity， volume fraction， and particle size.

Keywords： converging-diverging tube； liquid-solid two-phase flow； flow field characteristics； particle image velocimetry；heat exchanger

Get Citation: PENG Deqi， LIU Jian， FU Weng， et al. Influencing factors of flow field characteristics of liquid-solid two-phase flow in converging-diverging tube heat exchangers［J］. China Powder Science and Technology， 2025， 31（3）： 1−11.

Received: 2024-08-06.Revised: 2025-03-03,Online: 2025-03-26.

Funding Project: 国家自然科学基金项目， 编号： 5217525； 湖南省自然科学基金项目， 编号： 2024JJ7546。

Corresponding Author: 谭卓伟（1990—），男，讲师，博士，硕士生导师，研究方向为动态流程下的强化传质过程研究。E-mail：tanzhuowei1990@126.com 。

CLC No: TB4； TK124；                Type Code: A

Serial No: 1008-5548（2025）03-0001-11