[논문]Dynamic Responses of Electrorheological Fluid in Steady Pressure Flow

Nam, Yun-Joo; Park, Myeong-Kwan

Dynamic Responses of Electrorheological Fluid in Steady Pressure Flow
정상압력 유동 하에서 전기유변유체의 동적 응답 원문보기

Nam, Yun-Joo (부산대학교 대학원 지능기계공학과) , Park, Myeong-Kwan (부산대학교 기계공학부 및 기계기술연구소)

Dynamic responses of electrorheological (ER) fluids in steady pressure flow to stepwise electric field excitations are investigated experimentally. The transient periods under various applied electric fields and flow velocities were determined from the pressure behavior of the ER fluid in the flow channel with two parallel-plate electrodes. The pressure response times were exponentially decreased with the increase of the flow velocity, but increased with the increase of the applied electric field strength. In order to investigate the cluster structure formation of the ER particles, it was verified using the flow visualization technique that the transient response of ER fluids in the flow mode is assigned to the densification process in the competition of the electric field-induced particle attractive interaction forces and the hydrodynamic forces, unlike that in the shear mode determined by the aggregation process.

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문제 정의

The pressure response of ER fluids in the flow mode is of significant importance for effective design and control of such devices. Consequently, the main purpose of this work is to investigate the dynamic response of ER fluids in steady pressure flow to stepwise electric field excitations.

가설 설정

4. While the rising response time is determined in the competition of the field-induced particle interaction forces and the hydrodynamic forces, the decaying response time is determined only by the hydrodynamic force. Therefore, the decaying response time is much shorter than the rising response time.

제안 방법

The dynamic responses of the ER fluid were obtained from the time-varying pressure behaviors as a function of the flow velocity and the applied electric field strength. In the flow visualization, the cluster structure formation of the ER particles between the electrodes was recorded using a digital video camera at the sampling speed of 40Hz, and the results were analyzed using a personal computer. All experiments were done at room temperature (25℃)
Numerous experimental and theoretical researches have been carried out on the transient process of ER fluids in sheared state. In these researches, the relationship between the field-induced interaction force and the hydrodynamic force were taken on account of the transient process, and the relations of the transient times with respect to shear rate, electric field strength, and particulate volume fraction were presented. The inverse relationship between the transient time and shear rate was similar to that between the pressure response time and flow velocity, although the experiments in this investigation were carried out in the flow mode.
Therefore, in order to investigate the dependence of the pressure response of ER fluids on the flow velocity and electric field strength and to clarify the difference of the cluster structure formation mechanisms between in the shear and flow modes, the transient behavior of the particle structure between the two parallel-plate electrodes should be examined. For the purpose, the flow visualization technique is introduced in the present investigation.

대상 데이터

2(a) shows a schematic configuration of the flow channel used for the investigation of the rheological properties under steady pressure flow. The test section is a rectangular channel with two parallel-plate electrodes at its top and bottom. The flow channel except of the two electrodes is made of acetal resin.

성능/효과

1. The pressure response of ER fluids and the structure response of ER particles in steady pressure flow are determined mainly by the densification process in the competition of the field-induced particle interaction forces and the hydrodynamic forces, unlike that in steady shear determined by the aggregation process.
2. When the flow velocity is increased under the same electric field, the densification process is promoted and the average size of the clusters in steady state is decreased. Therefore, the dynamic response time of ER fluids in steady pressure flow is exponentially decreased due to the densification period shortened with the increase of the flow velocity.
3. When the electric field strength is increased under the same flow field, the hydrodynamic effect on the transient behavior of the particle structure is relatively decreased and the average size of the clusters in steady state is increased. Therefore, the dynamic response time of ER fluids in steady pressure flow is increased due to the densification period increased with the electric field strength.
^(5-7) The flow visualizations using various optical techniques have been also conducted to study the electric field-induced structure formation of ER particles.^(8-10) In these studies, the effects of various electric fields and shear rates on the cluster structure behavior of the ER fluids in two electrodes were investigated, and it was verified that the response time of ER fluids is determined in the interrelation between the electric field-induced particle attractive interactions and the hydrodynamic forces.

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Dynamic Responses of Electrorheological Fluid in Steady Pressure Flow
정상압력 유동 하에서 전기유변유체의 동적 응답 원문보기

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Dynamic Responses of Electrorheological Fluid in Steady Pressure Flow 정상압력 유동 하에서 전기유변유체의 동적 응답 원문보기

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Dynamic Responses of Electrorheological Fluid in Steady Pressure Flow
정상압력 유동 하에서 전기유변유체의 동적 응답 원문보기

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