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Sanjivani Rural Education Society's Sanjivani College of Engineering, Kopargaon, 423603. An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune Subject: Fluid Mechanics T.¥.B. Tech (CIVIL) Unit-l: (A) Fluid Properties By Prof. V. S. Chaudhari (Assistant Professor) Department of Civil Engineering Sanjivani College of Engineering, Kopargaon-423603 Introduction to Fluid Mechanics According to the molecular spacing, matter may be classified as 1, Solids - molecular spacing is almost zero 2. Fluids a) Liquids - molecular spacing is larger than Solids b) Gases - molecular spacing is larger than Liquids What is Fluid? A Fluid is a substance that deforms continuously in the face of tangential or shear stress, irrespective of the magnitude of shear stress. This continuous deformation under the application of shear stress. What is Fluid? > Fluid may be defined as a substance which is capable of flowing, > It has no definite shape of its own but occupy/conforms to the shape of the containing vessel. » Further even small amount of shear force exerted on a fluid will cause it to undergo a deformation which continues as long as force continues to apply » Distinction between a solid and a fluid is made on the basis of the substance’s ability to resist an applied shear (or tangential) stress that tends to change its shape. > A solid can resist an applied shear stress by deforming, whereas a fluid deforms continuously under the influence of shear stress, no matter how small. » In solids stress is proportional to strain, but in fluids stress is proportional to strain rate. When a constant shear force is applied, a solid eventually stops deforming, at some fixed strain angle, whereas a fluid never stops deforming and approaches a certain rate of strain, Fluid : - Tendency to flow Ideal Fluids (Viscosity, Surface Tension & it is incompressible) 6 Sr Real Fluids (Viscosity, Surface Tension and possess Compressibility) Difference between Slid, Liquid and Gas Solid liquid Gas Do not have a definite shape; Donot havea definite shape; Have definite shape ‘they take the shape of the ‘they take the shape of the container container h : Haveadefinitesizeorvolume | Have adefinite size or volume coho eve CoE ems Negligible compressibility Slightly compressible Highly compressible Cannotfiow Canflow Canflow ‘ Particles move freely but are e Particles do not move freely confined within botndary Particles can move freely Force of attraction between the Force of attraction betweenthe | particlesis less than that in Force of attraction between the particles is the maximum solids, butis morethan thatin | particlesis the least. gases Introduction to Fluid Mechanics Fluid mechanics itself is also divided into several categories. The study of = Hydrodynamics: the mation of fluids that are practically incompressible (such as Haules, especially water, and gases at low speeds) is usually referred to as. @ A subcategory of hydrodynamics is hydraulics, which deals with liquid flows in pipes and open channels. = Gas dynamics deals with the flow of fluids that undergo significant density changes, such as the flow of gases through nozzles at high speeds. @ Aerodynamics deals with the flow of gases (especially air) over bodies such as aircraft, rockets, and automobiles at high or low speeds. @ Some other specialized categories such as meteorology, oceanography, and hydrology deal with naturally occurring flows. Application Areas Fluid Mechanics Mechanics of Fluid is extremely important in many areas of Engineering, and Science as below Biomechanics * Blood flow through arteries and veins * Airflow in lungs Household + Piping system for cold water, natural gas, sewage * Piping and ducting network for heating and air conditioning system Refrigerator, Vacuum cleaner, dish washer etc. Meteorology and Ocean Engineering * Movement of air currents and water currents Applications Aircraft and Spacecraft PROPERTIES OF FLUIDS 1. Density or Mass Density. > The ratio of the mass of a fluid to its volume. It is denoted the symbol (rho). > In Sl unit is kg per cubic meter, ie, kg/ms. (The value of density of water is 1 gm/cms or 1000 kg/m3.) = wearin al ~ valume of fluid Pry Note- O With the increase in temperature volume of fluid increases and hence mass density decreases. Incase of fluids as the pressure increases volume decreases and hence mass density increases. © Density of Water is 1000 kg/m: at temperature of 4¢C 3. Specific Volume > Specific volume of a fluid is defined as the volume of a fluid occupied by a unit mass or volume per unit mass of a fluid is called specific volume. » Mathematically, it is expressed as >» Thus specific volume is the reciprocal of mass density. > Itis expressed as m*/kg. It is commonly applied to gases. 4. Specific Gravity » Specific gravity is defined as the ratio of the weight density (or density) of a fluid to the weight density (or density) of a standard fluid. > For liquids, the standard fluid is taken water and for gases, the standard fluid is taken air. ® Specific gravity is also called relative density. It is dimensionless quantity and is denoted by the symbol S. set OR S=+ P Me Ww + Incase of liquids water at 4°C is considered as standard liquid = Pemar = 1000 kgira? Standard Liquic: Water Standard Gas: Air (at #23 Kira) O When two layers of a fluid, a distance ' dy' apart, move one over the other at different velocities, say u and u + du as shown in Fig,, the viscosity together with relative velocity causes a shear stress acting between the fluid layers, where [1 (called mu) is the constant of proportionality and is known as the co-efficient of dynamic viscosity cr only visrsty. represents the mie of scar strain orate of scar deformation or vekoiy grades. \y Rewton-scc Ny | It CGS system unit of dynamic viscosity is called poise (P). ST unit of viscosity = “2 aaalc + m mm I the value of jis given in poise, multiply it by 0.1 10 get it in x. ‘Thus viscosity is also defined as the shear stress required to produce unit rate of shear strain. le MKS system, force is represented by kgf and length by mete (m). in COS system, force bs by dyne and length by cm and in SI system force is represcntcd by Newton (N) and length bby motre (ma). MKS unit of viscosty = “21° CGS unit of viscosity = = In the above expression N/m? is also known as Pascal which is represented by Pa. Hence N/m? = Pa = Pascal 2 SI ait of viscosity = Nate? = Pas, SI unit of viscosity ~ Senate ‘The unit of viscosity Is COS Is alw ealled Poise which Is equal te aeee-sce Or Poise om 
