RAC Lecture 6 - Lesson 6 Review of fundamentals Fluid flow...

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Lesson 6 Review of fundamentals: Fluid flow Version 1 ME, IIT Kharagpur
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The specific objective of this lesson is to conduct a brief review of the fundamentals of fluid flow and present: 1. A general equation for conservation of mass and specific equations for steady and incompressible flows 2. A general equation for conservation of momentum in integral form and discuss simplifications 3. Bernoulli equation and introduce the concepts of total, static and velocity pressures 4. Modified Bernoulli equation and introduce expression for head loss and fan/pump power 5. Methods for evaluating friction pressure drops with suitable correlations for friction factor 6. The concept of minor losses At the end of the lesson, the student should be able to: 1. Write the general equation of mass transfer and be able to reduce it for incompressible and steady flows 2. Write the general equation of momentum transfer and reduce it to incompressible, steady flows 3. Apply equations of conservation of mass and momentum to simple problems 4. Write Bernoulli equation and define static, velocity and datum pressures and heads 5. Write modified Bernoulli equation to account for frictional losses and presence of fan/pump 6. Apply Bernoulli and modified Bernoulli equations to simple fluid flow problems relevant to refrigeration and air conditioning 7. Estimate friction pressure drops and minor losses 6.1. Fluid flow In refrigeration and air-conditioning systems various fluids such as air, water and refrigerants flow through pipes and ducts. The flow of these fluids is subjected to certain fundamental laws. The subject of “Fluid Mechanics” deals with these aspects. In the present lesson, fundamentals of fluid flow relevant to refrigeration and air conditioning is discussed. Fluid flow in general can be compressible, i.e., the density of the fluid may vary along the flow direction. However in most of the refrigeration and air conditioning applications the density variations may be assumed to be negligible. Hence, the fluid flow for such systems is treated as incompressible. This assumption simplifies the fluid flow problem considerably. This assumption is valid as long as the velocity fluid is considerably less than the velocity of sound (Mach number, ratio of fluid velocity to sonic velocity less than 0.3). To analyze the fluid flow problems, in addition to energy conservation (1 st law of thermodynamics), one has to consider the conservation of mass and momentum. Version 1 ME, IIT Kharagpur
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6.1.1. Conservation of mass: As the name implies, this law states that mass is a conserved parameter, i.e., it can neither be generated nor destroyed; it can only be transferred. Mathematically, the equation of conservation of mass for a control volume is given by: 0 = + CS CV A d V d t G G ρρ (6.1) The first term on the left represents the rate of change of mass within the control volume, while the second term represents the net rate of mass flux through the control surface. The above equation is also known as continuity equation .
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RAC Lecture 6 - Lesson 6 Review of fundamentals Fluid flow...

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