Testing the Charge Residence Time on Acoustically Levitated Particles Open Access

Huang, Tianshu (Spring 2020)

Permanent URL: https://etd.library.emory.edu/concern/etds/fb494942v?locale=en


Triboelectric charging on moving particles is widely observed in nature. Studies have discovered the effects of both size and material type on the polarity and charge density of charged particles, and the mechanisms by which the particles get charged. Meanwhile, little is known about the stability of charge on the particle. One main issue for testing a particle's discharge behavior comes from the difficulty in controlling the potential influencing factors. Getting into contact with other objects can cause charge variation on the particle. Many charge measurement methods may also provide additional pathways for charge transfer.

In our thesis, we use a charge-sensing acoustic levitator to explore the discharge behavior of polystyrene bead. We test the levitation performance on pumice and polystyrene bead in different air pressure conditions. We find that, for a spherical particle of a given size, the acoustic radiation force required to levitate the particle is proportional to the particle's density and air density. Using polystyrene bead as test particles, we measure the discharge process in different relative humidities. We discover that the charge can be retained for weeks at low humidity, but decays in a few hours at high humidity. The charge loss follows a logistic behavior, which indicates that there may exist a two-step charge loss process. We also perform the measurement on gold bead and discover that the composition of the particle doesn't play a major role in the discharge behavior. Future investigation focuses on taking measurements under different pressure condition and gas compositions.

Table of Contents

1 Introduction 9

1.1 Acoustic radiation force 11

2 Experiment 16

2.1 Design 16

2.1.1 Acoustic Levitator 16

2.1.2 Charge Measurement Setup 17

2.2 Procedures 18

2.2.1 Charge measurements 18

3 Results 20

3.1 Pressure variation 20

3.2 Charge measurements 22

3.2.1 Sample measurement 22

3.2.2 Charge measurement as a function of humidity 23

4 Discussion 29

4.1 Pressure variation 29

4.2 Charge measurement 30

4.2.1 Discharge behavior at high humidities 31

4.2.2 Discharge behavior at low humidities 32

4.2.3 Effect of particle composition on discharge behavior 33

5 Conclusions and Future Work 35

Bibliography 37

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