would you kindly walk me through the workings of a viscometer?

  • In the first post of this series, "What" and "Why" of Viscometers, we discussed the "what" and "why" of viscometers, or what they are and why they are helpful. In this article, we will discuss the "how," in other words, the operation of each of the six different kinds of viscometers. This list is in no way exhaustive; there are other types of viscometers out there, but not all of them are useful for industrial processes. This list does not include any of those viscometers.

    #1 — Orifice viscometers

    A cup with a hole in it is typically what makes up an orifice viscometer. This hole is for the fluid to flow through. Viscosity is measured in cup seconds, which is determined by timing how long it takes the cup to empty. Orifice viscometers are well-liked in the painting industry because of their user-friendliness and the fact that they only require a brief immersion in the fluid they are measuring, making them ideal for manual use. There are Zahn Cups, Ford Cups, and a few others among them.

    #2 — Capillary viscometers

    Capillary viscometers, which can also be referred to as U-tube viscometers, include both the Ostwald and the Ubbelohde variations. They are straightforward and easy to use, consisting of a glass tube in the shape of a U that holds two bulbs, one positioned higher and one positioned lower. A capillary is used to transport fluid from a higher bulb to a lower bulb, and viscosity is determined by timing how long it takes the fluid to travel through the tube.


    #3 — Falling piston viscometers


    1. The falling piston digital viscometer was reportedly invented by Austin Norcross, which is why these instruments are also referred to as Norcross viscometers, as stated by Wikipedia

    2.  They function by drawing the fluid being measured into the piston cylinder while the piston is raised; the amount of time it takes for the piston to fall (measured in time-of-fall seconds) due to the resistance of the fluid is used to determine viscosity

    3.  Viscometers with a falling piston are not only easy to use and simple to maintain, but they also have a long product life

    #4 — Rotational viscometers

    Viscosity can be measured with a rotational  by submerging a spindle that is turning in a fluid that is being evaluated. Because rotational viscometers do not rely on gravity for their operation, the readings they produce are based on the shear stress that is present within the fluid being measured. The amount of power (torque) that is needed to turn the spindle is an indication of the viscosity of the fluid.

    #5 — Falling ball viscometers

    Viscometers that use falling balls rather than falling pistons achieve the same results as their counterparts. In this particular kind of viscometer, a ball is put into a sample of the fluid that is being measured before the reading is taken. Assuming that the dimensions of the ball are already established, the viscosity can be calculated by timing how long it takes the ball (again, in terms of time-of-fall seconds) to fall through the fluid under the influence of gravity.

    #6 — Vibrational viscometers

    For the purpose of measuring viscosity, vibrational viscometers make use of a powered vibrating rod. Depending on the viscosity of the fluid, different types of fluids offer varying degrees of resistance to vibrations. Therefore, viscosity can be determined either by measuring the dampening of the vibration or by measuring how quickly the vibration of the digital viscosity meter degrades. Both of these measurements are related to the same concept. The fact that vibrational viscometers provide high sensitivity without requiring the use of any moving parts has contributed to their widespread adoption.

    After the upper bulb has been filled with the fluid, these instruments are typically operated in a thermally-stabilized bath. Following this step, the amount of time required for the fluid to pass through the marks is measured, and this time is then multiplied by an instrument constant in order to determine the kinematic viscosity of the fluid. The dynamic viscosity of the fluid has a direct correlation with the amount of time it takes for the fluid to move through the capillary tube, while the density of the fluid has an inverse correlation with this time. Figure 2B illustrates a flow cup or orifice type viscometer, which is yet another straightforward configuration for a capillary viscometer. The operation of this apparatus involves measuring the amount of time required for a fluid to travel through an orifice or capillary while the apparatus itself consists of a reservoir and an orifice or capillary. Although these instruments are inexpensive, user-friendly, and versatile, their lack of accuracy stems from the fact that they do not maintain a constant pressure on the orifice.

    Pressurized versions of the capillary and flow cup viscometers can be used in order to maintain constant pressure during the measurement and to operate under high pressures, which enables their utilization for highly viscous fluids. Pressurized versions of these viscometers are also able to operate under high pressures. When this occurs, the movement of the fluid is caused either by the pressure of the gas or by a piston that is activated by either a weight or a driving motor.

    When determining viscosity, tube viscometers, which belong to the same category as capillary viscometers, make use of a horizontal tube that is fed by a pressurized tank.2In these instruments, the pressure is measured at various points along the tube.