Elsevier

Powder Technology

Volume 381, March 2021, Pages 110-121
Powder Technology

Experimental and numerical studies on rebound characteristics of non-spherical particles impacting on stainless-steel at high temperature

https://doi.org/10.1016/j.powtec.2020.12.004Get rights and content

Highlights

  • Conducted experimental and numerical studies on the rebound characteristics of the particles.

  • Studied the effects of particle parameters and accelerated airflow.

  • Revealed relationship between particle rebound behavior and erosion behavior.

  • Established rebound models for different non-spherical particles.

Abstract

In this paper, innovative test methods including aerodynamic acceleration, PIV measurement, separate statistics of incidence and rebound information were used to systematically investigate the rebound characteristics of flaky oxide particles and angular quartz sand impacting stainless steel at high temperature. Through the statistical analysis of a large number of experimental results and the measurement of the microscopic erosion morphology of the target surface, combined with the numerical simulation of the gas-solid two-phase flow of the test section, the intrinsic relationship between the rebound behavior of the particles and their erosion behavior was systematically explored for the first time. Meanwhile, the effects of the incident parameters, particle size and accelerated airflow on the rebound characteristics of the particles were revealed. The results have important guiding significance for further understanding the physical properties of particle-wall interaction and predicting the particle erosion characteristics and erosion distribution of industrial equipment components.

Introduction

The erosion damage caused by fine particles is a common issue in the industries, which has a great impact on the life of equipment and operational safety [[1], [2], [3]]. In the aerospace industry, dust and sand particles in the air may severely erode compressor and turbine blades after entering the aircraft engine. In the dust environment, the service life of the engine is only 1/8 of that in the ordinary environment [4,5]. In fossil power plants, the pipeline damage caused by flake oxide particles eroding the inner wall and fly ash scouring the outer wall accounts for more than 1/3 of boiler tube explosion [6]. Oxide particles entering the steam turbine may erode key components, such as the main shut-off valve, control valve and cascade [7], resulting in valve control failure and reduced cascade service life. The actual life of some cascades is only 10% of the design life [8]. In addition, for the fluidized bed boilers using fossil fuels, the erosion of the fan blades by fly ash and coal powder may reduce the efficiency by more than 10% [9,10]. In the pneumatic transportation of metallurgy, chemical industry and other industries, the erosion damage of the elbow by fine particles makes its life only 1/50 of the straight pipe section [11]. There are numerous similar cases, involving various aspects of the national economic development and resulting in serious economic losses. Therefore, how to reduce the erosion damage of fine particles to the wall is a key scientific problem to be solved urgently and has broad application prospects.

In the process of solid particles hitting the target wall at high speed, the particles first briefly slide and roll on the wall, and then leave the wall at a certain rebound speed, while the target wall may generate elastic deformation, plastic deformation, crack or even erosion. The rebound characteristic of the particles refers to the change law of the velocity and direction of the particles before and after they hit the target wall. Under the same conditions, the more energy the particles bounce back, the less the energy involved in the target erosion. Therefore, Tabakoff regarded the rebound characteristics of particles as an important parameter of the material erosion model [12]. Moreover, after impinging the flow channel, the rebound characteristics of the particles have an important influence on the position, velocity and angle of the particles of next impingement [13]. Therefore, the rebound characteristics of particles are the basis for studying the erosion characteristics and distribution of materials.

The velocity restitution coefficient is defined as the ratio of the relative velocity of the particle after and before a collision event. In order to further characterize the interaction between the particles and the target, the velocity restitution coefficient e can be decomposed into normal and tangential velocity restitution coefficients, as shown in Fig. 1. Sommerfeld et al. [14] used a CCD camera and a pulsed laser light sheet to analyze the particle-wall collision process between glass beads and quartz particles, which have different sizes and targets with different roughness. It was found that the wall roughness and shape of particles have a considerable influence on the wall collision process and the rebound properties of the particles. Drücker et al. [15] analyzed the rebound characteristics between a single glass particle and a stainless-steel substrate by a high-speed camera. It was noted that for particles with a diameter of 1 mm to 4 mm, the velocity restitution coefficient remains nearly constant. Xie et al. [16] studied the rebound characteristics between fly ash with a diameter of 0.07 mm and 316 stainless steel. The results showed that the normal restitution coefficient first increased, then slowed down, and finally decreased with the increase of normal impact velocity. The reason is that different forces occupy different proportions at different stages. Haider et al. [17] modeled the rebound characteristics between the sieved sand particles and 316 stainless steel. It was found that as the impact angle increased, the normal and tangential velocity restitution coefficients of the particles first decreased and then increased. The above researches have focused on the impact rebound characteristics of particles with different shapes and revealed the rebound behavior of the particles to a certain extent. However, the particle velocity is less than 30 m/s, and the experimental environment is at normal temperature, which is far from the actual particle erosion velocity and ambient temperature of the power equipment.

Whitaker et al. [18] applied the high-speed particle shadow velocity method to analyze the rebound characteristics of quartz sand particles hitting an aluminum plate. It was found that the velocity restitution coefficient varies drastically with changes in particle velocity and angle. Delimont et al. [19] explored the rebound characteristics of 0.02–0.04 mm sand impacting Ni-based superalloy at different temperatures, and pointed out that the increase in particle velocity is the root cause of the decrease in velocity restitution coefficient, and the influence of environmental temperature increase on the particle restitution coefficient is negligible. Lawrence et al. [20] used the PIV to study the impact rebound characteristics of fly ash particles in a gas turbine environment, and pointed out that an increase in particle velocity and size may cause a decrease in the velocity restitution coefficient. Tabakoff et al. [21,22] used high-speed photography and Laser Doppler Velocimeter (LDV) to study the rebound behavior of quartz sand and fly ash particles impacting 2024 aluminum alloy and stainless steel at high temperature, and established the corresponding particle rebound model. Forder et al. [23] focused on the erosion damage of oil field control valves by sand particles in the petroleum industry, and established an expression of the velocity restitution coefficient of quartz sand particles impacting AISI4130 steel through experimental research. In the above-mentioned literature, experimental studies have been conducted on particle rebound characteristics for different applications, and the relationship between the particle restitution coefficient and the impact angle was obtained through statistical analysis, which can predict the erosion damage of key components of industrial equipment. However, based on the above studies, only macroscopic statistical results of particle impact and rebound parameters were obtained, and the internal relationship between particle rebound behavior and particle erosion behavior have not been deeply analyzed. Therefore, the influences of particle impact parameters, particle size, shape and other related factors on the particle rebound behavior have not been revealed.

In this paper, through experimental studies and numerical simulations, the rebound characteristics of flake iron oxide particles and angular quartz particles impacting a typical martensitic stainless steel were investigated systematically. Based on the statistical analysis of a large number of experimental results, the micro erosion morphology analysis of the target surface and the gas-solid two-phase flow numerical simulation analysis of the test section, the relationship between the particle impact rebound behavior and the particle erosion behavior was systematically explored for the first time. Besides, the effects of particle impact parameters, particle size accelerated air flow and other factors on the particle velocity restitution coefficient were also revealed. The results have important guiding significance for further understanding the physical properties of particle-wall impact and rebound, and predicting the particle erosion characteristics and the erosion distribution of industrial equipment components.

Section snippets

Experimental setup and measurement technique

Fig. 2 shows the high-temperature high-speed gas-solid two-phase flow and particle erosion test platform applied in this study. The test platform includes four parts: high-temperature gas system, particle feeding system, erosion testing system and exhaust gas treatment system. The basic working principle of the test platform is as follows: the particle feeding system uses dry compressed air to transport the solid particles output by the particle feeder to the particle disperser. The

Particle velocity vector field

The original images of the particles impacting the target are shown in Fig. 5. The incident direction of the particles is from top to bottom, and the thin white lines in the figure can be regarded as the boundary of the particle incident and rebound regions. Fig. 6, Fig. 7 are the velocity vector fields of iron oxide particles and quartz sand particles impacting the stainless-steel target under typical working conditions after being processed by Davis 8.0 software. The velocity vector field of

Conclusions

In this paper, a systematic experimental study on the rebound characteristics of flake iron oxide particles and angular quartz sand particles impacting martensitic stainless steel by the pneumatic acceleration method was carried out on a high-temperature and high-speed gas-solid two-phase flow and particle erosion testbed. Through the statistical analysis of a large number of test results and the measurement of the micro-erosion morphology of the target surface, combined with the numerical

Declaration of Competing Interest

None.

Acknowledgement

The authors would like to thank for the support of National Natural Science Foundation of China (NSFC) (No. 51606152) and the Fundamental Research Funds for the Central Universities (No. sxxj032020009).

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