Properties of Fluids: Temperature, Density, Pressure

Fluids are substances that have the ability or a tendency to flow. The air that we breathe and the water that we drink are all various types of fluids. Both the liquids and the gases are referred to as fluids. They are shapeless as they follow the law of inertia. Hence, they take the shape of whatever containers they are stored in. In this article, we will explore the various properties of fluids, the applications of fluid mechanics, and some related sample questions.

Key Terms: Fluid, density,Specific Weight, Specfic Volume, Pressure, Surface Tension, Gas, external forces, shear force

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What is a Fluid?

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A material capable of continually flowing and deforming under shared stress is known as a fluid. Liquids and gases are examples of fluids, which are a subset of the phases of matter. Fluids are substances that deform constantly when subjected to external forces. These are materials that cannot withstand the shear force (a force that causes a change in form) that is applied to them. Air, water, toothpaste, and molten lava are a few examples of fluids. Under the influence of force or pressure, fluid flows. Fluid mechanics is the study of forces and flow within a fluid.

Check out important questions for Mechanical Properties of Fluids. (Mechanical Properties of Fluids .pdf)

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Properties of Fluids

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Despite the fact that each fluid is unique in terms of composition and particular features, there are several characteristics that all fluids share. These characteristics can be classified as follows:

• Kinematic properties: These properties help in the comprehension of the motion of fluids. The kinematic characteristics of fluids are velocity and acceleration.
• Thermodynamic characteristics: These qualities aid in determining the fluid's thermodynamic state. The thermodynamic characteristics of fluids include temperature, density, pressure, and specific enthalpy.
• Physical properties: These characteristics, including color and odor, aid in determining the fluid's physical condition.

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Density

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The mass of the fluid divided by its volume gives the density of that fluid. Gases have varying densities depending on pressure and temperature, whereas liquids have constant densities. Water has a density of 1000 Kg/m³, while air has a density of 1.225 Kg/m³. It is denoted by ρ.

Density or ρ = Mass of fluid / Volume of fluid

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Specific Weight

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A fluid's specific weight is defined as the weight per unit volume. As it moves from place to place, specific weight is affected by gravity's acceleration. Water has a specific weight of 9.81 1000 N/m³. It is denoted by w.

Specific Weight or w = \(\frac{Weight}{Volume}\)

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Temperature

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One of the thermodynamic characteristics of fluids that affect their state of hotness or coldness is temperature. Temperatures are expressed in various units such as Celsius, Kelvin, or Fahrenheit. Because of its independence from the characteristics of the material, Kelvin is the most commonly utilized unit. The impact of temperature on fluids is seen in the graph below.

Temperature

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Pressure

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We can observe that in a fluid, there is a pressure differential between the top and bottom layers, which causes movement. In aerodynamics, this phenomenon can be observed.

The action of force on a unit area causes pressure, which is represented by the symbol P and is denoted by the unit N/m².

Pressure or P=\(\frac{Force}{Area}\)

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Specific Volume

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Specific volume is the reciprocal of density in fluid mechanics. It is defined as the volume occupied by a fluid per unit mass. It is denoted by v. Its unit is m³/Kg

Specific Volume or v =\(\frac{Volume}{Mass}\)

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Surface Tension

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Surface tension is the phenomenon that takes place when the surface of a liquid comes into contact with another phase. Water has a surface tension of 0.059 N/m at 100°C and 0.079 N/m at 0°C. It is denoted by T.

Surface Tension or T = \(\frac{Force}{Length}\)

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Applications of Fluid Mechanics

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Fluid mechanics are used in various disciplines. Some of them are:

• Geophysics
• Civil Engineering
• Mechanical Engineering
• Oceanography
• Biology
• Meteorology
• Chemical Engineering
• Astrophysics

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Things to Remember

• A material capable of continually flowing and deforming under shared stress is known as a fluid.
• Fluids include air and gases.
• Fluid mechanics is the study of forces and flow within a fluid.
• There are three ways of differentiating the properties of fluids i.e., Kinematic Properties, Thermodynamic Properties, and Physical Properties.
• Important properties include Density, Specific Weight, Pressure, Temperature, Specific weight, surface tension.
• Physical properties include color, odor, and appearance.
• Kinematic properties include velocity and acceleration.
• Thermodynamics properties include temperature, internal energy, specific weight, specific volume, etc.