Fras Leszek J, Dziekonski Cezary, Dera Wojciech, Jarząbek Dariusz M
Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland.
Rev Sci Instrum. 2018 Oct;89(10):105111. doi: 10.1063/1.5025123.
In this paper, we present a device which is very sensitive for small changes in the viscosity of the investigated fluid. The main part of the device is a piezo-electric bimorph which consists of the brass shim with two piezo-ceramic layers on the opposite sides. One of them is responsible for generating vibrations, whereas the second one is meant to measure system response which is produced by the damping properties of the surrounding fluid. During the experiment, the cylindrical bar is forced to move by the series of sinusoidal waves with different frequencies and at constant amplitudes. The probe is immersed in the fluid and then the amplitude vs frequency and phase vs frequency curves are obtained. Next, one can determine the viscosity according to a proper mathematical model. The resonant frequency is related to the damping coefficient which depends on the viscosity of the surrender fluid and immersion depth of the probe. The coefficients necessary for calculating viscosity are obtained by fitting the resonance curve to the amplitude vs frequency data obtained from the experiment. The device has been applied to study the anisotropy of magnetorheological fluids. The weak anisotropy of viscosity has been observed. The highest value of viscosity was observed in the case of viscosity measurement in the direction orthogonal to the magnetic field and the lowest in the direction parallel to the magnetic field.
在本文中，我们展示了一种对所研究流体粘度的微小变化非常敏感的装置。该装置的主要部分是一个压电双晶片，它由一个黄铜垫片和两侧的两个压电陶瓷层组成。其中一个负责产生振动，而另一个用于测量由周围流体的阻尼特性产生的系统响应。在实验过程中，圆柱形杆受到一系列不同频率且振幅恒定的正弦波的作用而被迫移动。探头浸入流体中，然后获得振幅与频率以及相位与频率的曲线。接下来，可以根据适当的数学模型确定粘度。共振频率与阻尼系数相关，阻尼系数取决于周围流体的粘度和探头的浸入深度。通过将共振曲线与从实验中获得的振幅与频率数据进行拟合，得到计算粘度所需的系数。该装置已被用于研究磁流变流体的各向异性。观察到了粘度的弱各向异性。在垂直于磁场方向测量粘度时观察到最高粘度值，而在平行于磁场方向测量时观察到最低粘度值。
