what is the mathematical equation to calculate a viscosity index

We shall examine this kinetic picture of a gas in much more detail later (relatively) a long way between collisions. Times more room than they do in the liquid state, so the molecules go Simple kinetic picture of the gas: remember the molecules have about a thousand In fact, this rate of momentum flow can be calculated from a Momentum flow is for a given velocity gradient. Steady rate, and the coefficient of viscosity tells us what this rate of

Pattern, the x-direction speed at height zĪs explained above, the moving plate is feeding x-direction momentum into the gas at a rate F / A = η v 0 / d , this momentum moves down through the gas at a The moving top plate maintains a steady horizontal flow Rate of z-direction (downward) transfer of x -momentum, as explained in the previous The way to find the viscosity of a gas is to calculate the Estimating the Coefficient of Viscosity for a Gas: Momentum Transfer and Microscopic kinetic energy of the individual molecules moving in randomĭirections within the gas, in other words, into the random molecular kineticĮnergy we call heat. How can that be? Isn’t energy conserved? Yes, total energy is conserved, what happens is that some of the macroscopic kineticĮnergy of the gas moving as a smooth substance has been transferred into the Layers of gas decreases overall (see the exercise in the preceding section). We’re ignoring for the moment excitation of internal modes of the molecules) That kinetic energy is conserved in each individual molecular collision (so At the same time, some slower molecules fly Molecules from the fast layer fly into the slow layer, whereĪfter a collision or two they are slowed to go along with the rest. So where does the gas viscosity come from? Think of two adjacent layers of gas moving atĭifferent speeds. Meters per second, the molecules have diameter around 0.35 nm, are around 3 orĤ nm apart on average, and travel of order 70 nm between collisions with other The previous picture of crowded molecules jostling each other is completelyĭetail later, the molecules of air at room temperature fly around at about 500 The first thing to realize is that at atmospheric pressure Returning to the two plates, and picturing the gas betweenĪs made up of layers moving at different speeds as before. Note first that, in contrast to the liquid case, gasĮven more surprising, it is found experimentally that over a very wide range of Liquids (not counting liquid helium -a special Maintain steady motion, but, not surprisingly, for gases anywhere nearĪtmospheric pressure the coefficient of viscosity is far lower than that for It is found experimentally that the equation F / A = η v / d still describes the force necessary to Suggested experiment, the two parallel plates with one at rest the other moving Michael Fowler Gas Between Parallel Plates Previous index next Viscosity II: Gas Viscosity

What is the mathematical equation to calculate a viscosity index