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Transcript of Fluid Mechanics
Study of fluid motion
Fluid Flow Basics Types of Flow Laminar Turbulent Low velocity flow
Fluid travels smoothly and in regular paths
Reynolds number is low (less than 2100)
Eg. Waterslide High velocity flow
Fluid travels in random, chaotic paths
Reynolds number is high (greater than 4000)
Eg. White water rafting Reynolds Number (Re) is a dimensionless parameter which is
used to measure the ratio of inertial to viscous forces Reynolds number is used to determine the type of flows. Fluid Flow Applications It is important to calculate Reynolds Number of specific types of flow so that appropriate models can be used when designing flow systems Airplane Wings Airplane wings are designed to retain a thin sheet of air on the surface that slides smoothly in a laminar flow
The developing turbulent flow across the wing results in a loss of the necessary lift Pipe Networks Pipe systems must be designed accordingly for the flows they will endure over a given period of time.
Turbulent fluids can behave unpredictably and cause large pressure differences over short areas, leading to reduced life times and potential pipe failures. Static Study of fluids at rest
Law of Conservation of Mass Law of Conservation of Energy Laws and Equations Continuum Assumption Industrial Applications
Flow Measurement It assumes that individual ‘molecules don’t exist’ and that they are not separated by space.
It allows fluids to be treated as a continuous 'bulk' flow instead of small separate particles.
This law tells that in a continuous flow, that the amount of matter that passes through a system stays the same
The conservation of mass are applied in washing machines
Accumulation= dirty clothes
Mass in= water + detergent
Mass out= dirty water including detergent
Momentum is a measure of how difficult it is to stop a moving object
The law tells that the momentum is constant when no other force acts
Law of Conservation of Momentum the momentum equation
Forces= Accumulation + Momentum In + Momentum Out
the continuity equation Accumulation + Mass in - Mass out=O It can be used to determine the force needed to hold the nozzle attached at the end of a sink faucet
nozzle This law tells that energy can not be destroyed or created, it can only be transformed or transferred to another
Energy can also be stored and to be use later
the energy balance equation Change in Kinetic Energy + Change in Potential Energy + Change in Internal Energy= Heat absorbed or released + Work input or output due to motion due to height due to stored molecular energy due to temperature difference due to external source of energy Fluid Energy Everywhere! In a waterfall, the water at the top has potential energy
This energy is gradually transformed to kinetic energy as it falls
Some of the energy is also transformed to mechanical work via the watermill Sulphuric acid and water both contain internal energy but when mixed, some energy is lost as heat
Body Energy Equations Mechanical Energy Equation Bernoulli's Energy Equation It is an expanded version of the general energy balance equation
It is used in pipe flow calculations such as finding the pipe size and velocity of fluid It is a shorter version of the general balance equation
It assumes steady, incompressible, frictionless flow and no work input and output
It is used for calculations in simple flows like drinking from a straw
Manometers measure pressure difference.
Sphygmomanometers are 'manometers in disguise', they are commonly known as blood pressure meters.
They are used by doctors to measure blood pressure Fluid Properties Types of Fluid Compressible A fluid in which its density is not constant (most gases) Incompressible A fluid with approximately constant density (most liquids) Newtonian Pipe flow in countercurrent heat exchanger is used to cool down or heat up fluids .
A fluid that does not change its thickness with force or time Non-Newtonian A fluid that change its thickness with force or time Fluid dynamics is used to aerodynamically design a car or airplane jets to help reduce drag force and hence increase speed Viscosity Density Describes how dense a fluid is and it is used to determine if an object would float 'Pipe-like' flow in heat exchangers also occur naturally like the ones found in ducks' feet. Fluid dynamics is used to calculate flow rate or pressure of fluids. A property of a fluid that
measures its resistance to flow
Describes the fluid's thickness http://www.aerospaceweb.org/question/aerodynamics/q0092.shtml http://www.fareastgizmos.com/this_washing_machine_carries_out_a_full_wash.php http://en.wikipedia.org/Newtons_cradle_animation_book_2.gif
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http://www.youtube.com/watch?v=QEcTRos http://www.youtube.com/watch?v=QEcTRos Viscosity of fluid flow, viewed 21 October 2011 http://i1-scripts.softpedia/Moody-Diagram.png Moody Diagram, viewed 21 October 2011 A continuous substance whose molecules move freely past one another and has a tendency to assume the shape of its container.
What is a Fluid? http://img.ehowcdn.com/calculate-density-viscosity.jpg Eg of Non-Newtonian Fluid http://www.robotvsbadger.com/wp-content.png The fluid on the LEFT has a greater viscocity (it is moving more slowly) Uglyblackjohn, 2009, Coke bottle figure, Blogspot, viewed 23 Ocotber 2011,
http://uglyblackjohn.blogspot.com/2009/06/coke-bottle-figure.html Latex Party Balloons, Balloons & Party Supplies, viewed 23 October 2011,
http://www.partycraze.com.au/kids_party_balloons_party_supplies_online Flow measurement has both industrial and everyday purpose.
E.g. When a tap is turned on the flow is measured allowing the water company to determine your water usage.
In a process plant pipes are the most common source of fluid transfer and these are measured by flow meter devices Water tap, Australian Action to end water flouridation, viewed 23 October 2011, http://australianfluorideaction.com/ Sick, Flow Meter, Power-Technology.com, viewed 23 October 2011, http://www.power-technology.com/contractors/environmental/sick-process-automation/sick-process-automation3.html Water Meter, Aimei Water Meter,viewed 23 October 2011, http://www.allwatermeter.com/ Flow Meter Devices Orifice Plates Venturi Tubes constricts the diameter of the pipe Diameter restriction occurs gradually Expensive*$$$$!!!* Sudden diameter restriction Cheap
*Save!!!!* Ventruri Tube, The Engineering Toolbox, viewed 23 October 2011, http://www.engineeringtoolbox.com/flow-meters-d_493.html Orifice Plate, The Engineering Toolbox, viewed 23 October 2011,
http://www.engineeringtoolbox.com/flow-meters-d_493.html pressure change across this constriction is used to measure the flow rate http://www.youtube.com/watch?v=gBzJGckMYO4 (Munson et al., 2009) (Munson et al., 2009) (Munson et al., 2009) (Munson et al., 2009) (Lower, 2011) (University of Sydney, 2005) (Munson et al., 2009) (Munson et al., 2009) (Skogestad, 2009) (Munson et al, 2009) (Munson et al, 2009) (Oleniscky, 2005) (Munson et al., 2009) (Perry, 2007) (Perry, 2007) (Munson et al, 2009) (Munson et al, 2009) Munson, B, Young, D, Okiishi T & Huebsch, W, 2009, Fundamentals of Fluid Mechanics, 6th edn, John Wiley & Sons, Inc., Hoboken, NJ, USA Honey has a high kinematic viscosity, 2011, eHow, viewed 26 October 2011, http://www.ehow.com/how_6697521_calculate-density-viscosity.html Floating Bowling Balls, 2011, Steven Spangler Science, viewed 26 October 2011, http://www.stevespanglerscience.com/experiment/00000067 Lower S, 2009, Liquids and their Interfaces, last date modified 23 June 2011, viewed by 26 Ocotber 2011,
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Perry, R & Green, D, 2007, Perry’s Chemical Engineers’ Handbook, 8th edn, The McGraw Hill Companies, New York, NY
Airflow over airplane wings Visual Demonstration of how fluid is distributed over wing Application of Fluid Properties Age Fotostock, 2011, Fire prevention system pipe detail, superstock, viewed 21 October 2011, http://www.superstock.co.uk/stock-photos-images/1566-059802 http://www.partycraze.com.au/kids_party_balloons_online http://uglyblackjohn.blogspot.com/coke-bottle-figure http://www.stevespanglerscience.com/experiment/00000067 http://www.superstock.co.uk/stock-photos-images/1566-059802 http://www.allwatermeter.com/ http://www.power-technology.com/contractors/environmental