Fluid Flow Lecture (September 16, 2024)

Application of Fluid Flows Lecture 8 - 10 am - 12 nn (Mon.) September 16, 2024 Lerjun M. Peñaflor PhD Agricultural and Biosystem Engineering Department BUCAF  A fluid is a substance that continuall...

Application of Fluid Flows Lecture 8 - 10 am - 12 nn (Mon.) September 16, 2024 Lerjun M. Peñaflor PhD Agricultural and Biosystem Engineering Department BUCAF  A fluid is a substance that continually deforms (flows) under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases. PROPERTIES OF FLUIDS Viscocity Surface Tension Compressibility  Viscosity Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid. A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion.  SURFACE TENSION - is a contractive tendency of the surface of a fluid that allows it to resist an external force. Fluids tends to attend the minimum surface area as possible. While a molecule inside the bulk fluid is pulled in each and every direction by the adjacent molecules. But, at the surface of the fluid, the case is different , the adhesive forces causes downward pull on the molecule due to coherent, so the molecule on the surface tends to move down.  Formula used to calculate surface tension gh = h= σ = F/ L  Compressibility Compressibility of the fluid is character to shrink in volume when increasing the external pressure. It is expressed by coefficient of compressibility Fluid Flow  Fluid flow may be defined as the flow of substances that do not permanently resist distortion  Identification of type of flow is important whether the flow of fluid through a pipe can be viscous or turbulent and it can Re < 2130 bewill the flow determined be laminar by Reynolds number. Re > 4000 the flow will be turbulent  The subject of fluid flow can be divided into fluid FLUID STATICS  deals with the fluids at rest in equilibrium. Examples: water in a kettle, corn syrup in a beaker, starch solution in a basin  Common to these fluids is the pressure property, unlike a rigid body a fluid does not confine its weight on a point but distributes it over the surface area of its container in the form of pressure.  Characteristic of fluid pressure is the uniformity of pressure intensity at any specified depth ofPaPfluid P Zbulk P 𝑷=𝝆 𝒁𝒈 z z z FLUID DYNAMICS  deals with the fluids in motion. Examples: materials flowing in a conduits, exchanger, pumps and other equipment , fill in a container.  Fluids can also flow outside of confinements or in the absence of boundaries, such as wind blown by an electric fan.  two important equations: Continuity and Bernoulli Equations Forms of energy in 𝑸𝟏=𝑸𝟐 moving fluids:  friction energy  kinetic energy  mechanical  pressure energy energy BERNOULLI'S THEOREM When the principals of the law of energy is applied to the flow of the fluids the resulting equation is a Bernoulli's theorem Consider a pump working under isothermal conditions between points A and B Bernoulli's theorem statement, "In a steady state the total energy per unit mass consists of pressure, kinetic and potential energies are constant" ENERGY LOSS According to the law of conservation of energy, energy balance have to be properly calculated fluids experiences energy losses in several ways while flowing through pipes, they are  Frictional losses  Losses in the fitting  Enlargement losses  Contraction losses Friction in a pipe where: = pressure difference between between the two ends of the pipe with length, L. where: f= 16/ R e for laminar flow f= 0.316 for smooth pipe f values from The Moody Diagram if the reynolds value is higher Application of BERNOULLI'S THEOREM  Used in the measurement of rate of fluid flow using flowmeters  It applied in the working of the centrifugal pump, in this kinetic energy is converted in to pressure. Assumptions pipeline is horizontal A and B at same position, therefore ZA = Z B Friction losses is neglegible, F = 0 liquid is incompressible so density remain the same ρA = ρB = ρ No work is done on liquid therefore , W = 0 Total discharge , Q = average velocity x area of cross section Thank you !!!