4.3. Temperature Effect on Coefficient of Viscosity

If you look at this molecular levels, when you talk about the liquids, they will have a molecular bonding forces between two molecules okay. But that is much weaker when talk about the gases. So gas is at more random motions as compared to the molecules are more random motion as compared to the liquids.

At a molecular level, the interactions between molecules in liquids are due to stronger bonding forces than in gases. As a result, gas molecules move more freely and randomly than liquid molecules. When we increase the temperature of a fluid, it affects these molecular motions significantly, causing them to become more energetic and increase the rate of collisions between them.

Think of the way people behave in a crowded room. At a cooler temperature (or lower energy), people might stand close together and talk quietly. As the temperature increases, they get more energetic, move around more, and talk louder, resembling the increased kinetic energy and movement of molecules in a heated fluid.

If you look at experimental findings, if you let it is this now having one atmospheric pressure. This is the if I increase to the 50 atmospheric pressure the coefficient of the viscosity on this room will not change that high. That may change it less than 0.5% of the at the one atmospheric value.

While increasing temperature has a considerable effect on molecular motion and, consequently, the viscosity of a fluid, increasing pressure does not result in significant changes in viscosity for most liquids. Experiments show that even a substantial increase in pressure from 1 to 50 atmospheres results in a viscosity change of less than 0.5%, indicating that pressure has a negligible impact on viscosity compared to temperature.

Imagine trying to compress a sponge underwater. If you push down hard (add pressure), the sponge becomes denser, but its ability to absorb water (likened to viscosity) doesn’t change much. In contrast, as you warm the sponge (increase the temperature), it expands and absorbs water more readily.

When you increase this the temperatures, it definitely you increase the random motions of these molecules. For liquids, the temperature increase reduces the binding force, the intermolecular binding force between two molecules. Because of that, there will be a decreasing trend of coefficient of viscosity.

As temperature rises, the kinetic energy of liquid molecules increases, resulting in more random motion. This increased motion weakens the intermolecular forces that hold the molecules together. With these forces diminished, molecules can slide past one another more easily, leading to a decrease in viscosity—the measure of a fluid's resistance to flow.

Think about honey. If you store it in the fridge, it becomes thick and gloopy (high viscosity). However, when you heat it slightly, it flows much more easily (low viscosity) because the heat reduces the internal forces between the honey molecules.

When we increase temperature like from 20º to 40º or the 40º to 100º C temperatures then there will be a increases the random motions of the molecules. Because of that, you will see that in a gas as is given here, the viscosity and temperatures, the viscosity increases as the temperatures increases.

For gases, as the temperature increases, the velocity and energy of the gas molecules increase significantly. This leads to more frequent and more forceful collisions between the molecules, which results in an increase in viscosity. Therefore, unlike liquids, for gases, viscosity tends to rise with temperature due to the greater molecular activity and movement.

Imagine a busy highway with cars (gas molecules) moving faster as the temperature rises. Initially, in cooler weather, traffic is manageable and less congested. However, as it gets warmer and more cars get on the road (representing increased molecular motion), congestion (viscosity) increases because the cars are moving more vigorously—and collisions become more frequent.

Now, if you look at this for the gases already established by with standard of atmospheres that for the Sutherland correlation technique, which gives a relationship between the dynamic viscosity and the temperatures.

The Sutherland correlation provides a mathematical relationship between the viscosity of a gas and its temperature. It is essential for understanding how gases behave under varying thermal conditions. The equation includes constants specific to each gas, thus allowing for accurate predictions of viscosity at different temperatures, highlighting the difference in behavior from liquids.

Consider a cookbook that suggests how thick or thin to make a sauce at different cooking temperatures. Similarly, the Sutherland correlation acts like a cookbook for predicting how the viscosity of gases changes with temperature, but with scientific adjustments for each type of gas.

Similar way for the liquids if you look at that, it will have the 10 to the power functions and b and the c will be the constants and these things what we can compute get it from experimental or any reference book and textbook.

Different types of fluids, whether gases or liquids, have different coefficients of viscosity values that can vary significantly based on temperature. Experimental determination or reference data in textbooks can provide exact coefficients for various fluids, showing that each has a unique behavior under temperature changes.

Think of different kinds of batters, like thick pancake batter versus runny cake batter. Each will behave differently when heated, just like different fluids respond uniquely to temperature changes when it comes to their viscosity.

So the coefficient of viscosity, which is a directly proportionality constant, that does not vary as the rate of deformations are, or the time is changing. Most of the common fluid flow problems also follow Newtonian fluids but some of the cases it does not follow the Newtonian fluids.

The coefficient of viscosity plays a crucial role in fluid mechanics, serving as a proportionality constant. In fluids classified as Newtonian, viscosity remains constant, regardless of the rate of flow or deformation. However, non-Newtonian fluids exhibit changing viscosity depending on flow conditions, suggesting that understanding these differences is vital for fluid dynamics.

Think of water as a predictable friend who behaves the same way no matter how hard you push; this is like a Newtonian fluid. On the other hand, consider a reluctant friend who needs a gentle push to get going but becomes exceptionally active when pushed harder; this represents non-Newtonian fluids.

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