Vertical Falling Ball Viscometer

Many methods can be used to measure the viscosity of a fluid. These phenomena are usually based on one of three phenomena - a moving surface in contact with the fluid, an object moving through the fluid, and the fluid flowing through a resistive component. These phenomena utilize the three main viscometers in the industry, namely rotational and falling ball viscometers and capillary viscometers. Falling ball viscometers are commonly used to measure the viscosity of Newtonian liquids and gases. This method applies Newton's laws of motion under force equilibrium when the falling ball reaches its final velocity. According to Newton's laws of motion for a falling ball, there are buoyancy, gravity and drag, and these three forces arrive at a net force of zero. The drag force can be obtained from Stokes' law, which is valid for Reynolds numbers less than 1.

Falling ball viscometers are well suited for measuring the viscosity of fluids, and the method is described in international standards. In the G international standard, the method differs from the principles described in Ref. These standards describe an inclined tube method in which the drop ball tube is inclined 10° from the vertical. In addition, for different dynamic viscosity measurement ranges, six balls with different diameters are used, and the appropriate ball can be selected when the falling time of the ball is not less than the minimum falling time recorded during the test. The rolling and sliding motion of the ball through the sample liquid is sometimes located in an inclined cylindrical measuring tube. The viscosity of the sample is related to the time it takes for the ball to fall a specific distance, and the test results are given as dynamic viscosity.

Although the falling ball method is well established and described in international standards, operating this type of viscometer is somewhat inconvenient. For example, a viscometer requires six balls of different diameters to measure different viscosity ranges, and the user must run tests to select the appropriate balls. Furthermore, it is difficult to determine where the falling ball reaches its end velocity, i.e. whether the distance between the starting recording line and the initial drop position is sufficient. In addition, the inclined tube viscometer is 10° from the vertical; therefore the ball that hits the ground not only falls, but also rolls. This phenomenon is different from the derivation conditions of the falling ball method. Therefore, the purpose of this study is to develop a new method based on the traditional falling ball method while deriving the dynamic equations describing the behavior of falling balls in vertical tubes. Since this type of viscometer is perpendicular to the ground, it is referred to here as a vertical falling ball viscometer.