1.1. Basics of Fluid Mechanics- 1 (Contnd.)

Welcome back, this is the second lecture and we are going to study fluid properties again. So, we in the last class we studied mainly the shear stress and fluid viscosities So, today we will proceed a little further, this is for course called hydraulic engineering.

This segment introduces the continuation of the discussion on fluid mechanics, specifically revisiting the properties of fluids such as shear stress and viscosity. Understanding these properties is essential for studying hydraulic engineering as they heavily influence the behavior of fluids under different conditions.

Imagine fluids like syrup and water. Syrup has a higher viscosity than water, meaning it flows more slowly. This is similar to how different liquids behave in terms of shear stress when they are pushed or pulled.

So, as we said that viscosity and other concepts are for all fluids and gas is also a fluid. So, we will also see what a perfect gas law is you have studied that already in your class 10th and 12th but this is these first 10 lectures are going to be a revision of your basics fluid mechanics course.

The ideal gas law, represented as PV = nRT, is a fundamental equation in fluid mechanics. Here, P stands for pressure, V for volume, n for the number of moles of gas, R is the universal gas constant, and T is the temperature in Kelvin. It encapsulates how gases behave under different conditions.

Think of a balloon. When you heat it, the gas inside expands, increasing the pressure and volume according to the ideal gas law. If you squeezed the balloon, the volume decreases but the pressure might increase.

One of the important other property in terms of gases is bulk modulus of elasticity. So, what does bulk modulus elasticity do? It relates the change in volume to the change in pressure.

The bulk modulus of elasticity is a measure of a material's resistance to uniform compression. It describes how much a substance will compress under an applied pressure. The higher the bulk modulus, the less it compresses at a specific pressure.

Consider a sponge. When you press it, it compresses and changes its volume. The bulk modulus quantifies how resistant the sponge is to that compression. A denser sponge (high bulk modulus) will compress less than a soft sponge.

So, one of the phenomenon’s is isothermal, which is constant temperature. So, what happens is PV = nRT , that equation we already know So, PV = nRT. So =RT which is constant.

An isothermal process occurs when a gas undergoes compression or expansion at a constant temperature. In such cases, the relationship between pressure and volume is inversely proportional, illustrated by the equation PV = constant.

Think of a bicycle pump when you inflate a tire. As you compress air into the tire (increasing pressure), the temperature remains nearly constant if measured directly at the tire's surface, showcasing an isothermal process.

So, we are going to look at another phenomenon or process called Isentropic where no heat is exchanged.

An isentropic process is an idealized process where entropy remains constant. This often occurs in thermodynamics where no heat is added or removed from the system. The behavior of gases in isentropic processes can be analyzed using the specific heat ratio.

Consider a piston engine that compresses air without allowing heat to escape. The air heats up due to compression, but because it's an isentropic process, no energy is lost as heat, mimicking a perfect scenario.

Another important thing that we should be aware of speed of sound is speed of ‘c’ is given as this is the formula and we know that it is.

The speed of sound in a gas is a crucial property that depends on the gas's temperature and molecular composition. It can be derived from the equations discussed in fluid mechanics, linking back to pressure and density.

Think of a jet flying through the sky. When it breaks the sound barrier, it's traveling faster than the speed of sound in air, creating a sonic boom—an example of how speed of sound affects performance in aviation.

So, another concept is vapour pressure. So, this is the variation of vapour pressure along with the temperature.

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. As temperature increases, the vapor pressure rises, which affects boiling points and evaporation rates.

Imagine a pot of water on the stove. As the water heats up, more molecules escape into the air, increasing vapor pressure until it eventually boils. This illustrates how temperature influence vapor pressure.

Another such properties, the surface tension. An example here is that the pressure increases in a spherical droplet.

Surface tension is a property of liquid surfaces that makes them behave like a stretched elastic membrane. It is caused by the attraction of molecules at the surface of a liquid, resulting in a pressure difference between the inside and outside of drops or bubbles.

Think of water droplets on a leaf. The droplets bead up instead of spreading out due to surface tension, which allows small insects to walk on water without sinking.

So, normally, the revision of our fluid properties is complete and the basics that we have seen.

The section concludes the review of essential fluid properties such as viscosity, density, specific weight, and elasticity. Understanding these concepts sets the foundation for further studies in hydraulic engineering.

Consider engineers designing a dam. They need to understand the properties of water (viscosity, density) to predict how it will behave under various conditions, ensuring the dam is safe and effective.

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