# Relationship between temperature and viscosity of gases

### Forum Question: Why does the viscosity of a gas increase with temperature

The viscosity of liquids increases as temperature decreases, whereas the viscosity of gases increases as temperature increases. Viscosity is a fluid's resistance. Viscosity for natural gas, air, hydrogen, oxygen, nitrogen, sulfur dioxide, () as a graph for hydrocarbon vapors and natural gases, and as an equation for other The input temperature is restricted to the range 0 temperature oF . In other words, increasing gas temperature causes the gas molecules to collide more often. This increases the gas viscosity because the.

If you know the size and density of the sphere and the density of the liquid, you can determine the viscosity of the liquid. If you don't know the density of the liquid you can still determine the kinematic viscosity.

If you don't know the density of the sphere, but you know its mass and radius, well then you do know its density. Why are you talking to me?

Go back several chapters and get yourself some education. Should I write more? A newtonian fluid is one in which the viscosity is just a number. A non-newtonian fluid is one in which the viscosity is a function of some mechanical variable like shear stress or time. Non-newtonian fluids that change over time are said to have a memory. Some gels and pastes behave like a fluid when worked or agitated and then settle into a nearly solid state when at rest.

Such materials are examples of shear-thinning fluids. House paint is a shear-thinning fluid and it's a good thing, too.

## Viscosity II: Gas Viscosity

Brushing, rolling, or spraying are means of temporarily applying shear stress. This reduces the paint's viscosity to the point where it can now flow out of the applicator and onto the wall or ceiling. Once this shear stress is removed the paint returns to its resting viscosity, which is so large that an appropriately thin layer behaves more like a solid than a liquid and the paint does not run or drip. Think about what it would be like to paint with water or honey for comparison.

The former is always too runny and the latter is always too sticky. Toothpaste is another example of a material whose viscosity decreases under stress. Toothpaste behaves like a solid while it sits at rest inside the tube. It will not flow out spontaneously when the cap is removed, but it will flow out when you put the squeeze on it. The viscosity of a gas provides a means for determining molecular diameters, as viscosity arises from collisions among molecules. Apparatus A gas sample is drawn through a thin capillary tube.

The change in pressure of the system is measured with a manometer as a function of time. A calibration flask of known volume is provided to determine the volume of the system. Laminar flow In order to measure gas viscosities, laminar flow is assumed in the capillary. Laminar flow implies that the gas flows in "layers" such that each layer moves at a velocity infinitesimally different than the layers adjacent to it.

### Viscosity – The Physics Hypertextbook

Since the wall is stationary, the layer along the wall has a velocity of zero. The fluid flows more quickly the further away it is from the stationary wall. Laminar flow is commonly experienced in smooth streams and rivers, where water flows slowly along the banks and rapidly in the center. Viscosity coefficient Adjacent laminar sheets experience friction as they slide past one another.

The units of h can be determined from unit analysis on its defining equation. In the cgs cm-gram-second unit system In honor of Poiseville, the cgs unit of viscosity is called a poise 3.

## VISCOSITY OF GASES

Derivation of gas viscosity equation The derivation of the gas viscosity equation will proceed in four steps: Fluid velocity, v r Consider an incompressible fluid flowing through a circular tube with radius R and length l.

The fluid at the walls of the tube is assumed to be stationary, and the flow rate increases to a maximum at the center of the tube. Consider the forces acting on a cylinder of radius r as it moves through the tube at velocity v. The driving force fd on the cylinder is where p1 is the fore pressure, p2 is the back pressure, and pr2 is the area of the cylinder end. The r2 dependence of v implies that the velocity profile looks like a parabola.

Thus, which upon rearrangement yields This is Poiseville's equation, which applies to incompressible fluids undergoing laminar flow. Poiseville's equation may be satisfactorily applied to liquids but not to gases, as volume is a strong function of pressure for gases. First, since the volume of a gas depends on pressure, the average pressure p0 is used.

Second, the gas is assumed to be ideal in order to calculate the moles of gas flowing through the tube per second. Thus, p22 can be neglected relative to p12 in the previous equation yielding An experimental determination of gas viscosity usually involves measurement of pressure change with time in a constant volume system.