The FSV (Falling Sphere Viscometer) consists of a large glass tube which is filled with water. A smaller glass tube which is marked at two distances by the help of rubber bands is positioned in the large glass tube and is filled with the testing fluid. A funnel is placed on the top of the smaller tube. A thermometer is placed inside the larger tube to measure the temperature of water. The purpose of the water is to keep the system constant in temperature. A stir rod is placed in the water to aid this process. The funnel is used to guide the ball bearing into the smaller tube. Description
Stoke’s Law • From Stoke’s law we have, • Where, • g = acceleration due to gravity • a = radius of spherical ball bearing • v = terminal velocity of the ball bearing • delta p = difference between the density of the testing fluid and ball bearing.
Let us assume that we know the value of variables g, a, v, and delta p except for terminal velocity v. To calculate the velocity v we use the FSV and the following procedures. • Fill smaller tube with fluid being tested. • The thoroughly cleaned ball bearing is placed into the funnel and falls through the tube of the funnel and along the axis of the smaller tube. • Time the ball as it passes from the first rubber band to the second. • Measure the distance between the two rubber marks
Calculations The velocity of the ball bearing is calculated from the measured distance between two marks of the rubber bands and the time taken by the ball bearing to travel between the two rubber band marks. Then from Stoke’s Law, we can calculate the viscosity.
Budget $200. Price depends on the quality of materials. This costs approximately