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### Engineering Approach to Solving Problems

Course: ME 2124, Spring 2011
School: Virginia Tech
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Word Count: 181

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Approach Engineering to Solving Problems Problem description: After some study, state what is known about the problem. What to find: State in own words what is to be found. Draw diagrams Identify system boundary. Closed system or control volume? of the system: Include relevant info such as forces, motions, inputs and outputs acting on the system. Given info: Write down known property values and other given...

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Approach Engineering to Solving Problems Problem description: After some study, state what is known about the problem. What to find: State in own words what is to be found. Draw diagrams Identify system boundary. Closed system or control volume? of the system: Include relevant info such as forces, motions, inputs and outputs acting on the system. Given info: Write down known property values and other given info. Sketch property diagrams e.g. v-T, p-T diagrams etc. Simplifying assumptions: List assumptions, e.g. effects that can be neglected, (Engineering model) approximations. etc. down Write operating conditions, interactions, e.g. steady state, no friction etc. Analysis : Write down governing equations, simplify them as per assumptions. Identify needed tables, charts, property relations. Add, revise diagrams, other info as needed. Do the number of equations equal the number of unknowns? Solve problem in symbolic form first, then plug in numbers along with units. Check solution: Have in mind a reasonable "ball park" estimate for the solution. Do a sanity check of the magnitudes and algebraic signs. Check that the units of the solution are correct.
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Virginia Tech - ME - 2124
The Ideal Gas and Incompressible Substance Equations of State Equations of state that accurately describe substance behavior over a wide range of pressures, temperatures, and specific volumes are quite complicated. For a limited range of conditions, howev
Virginia Tech - ME - 2124
Pressure-Volume Work for Closed Systems Pressure-volume work done on the environment by a system going from state 1 to state 2 is defined byW12 = PdV .1 2This definition gives work out of the system as positive. It is only valid when the process is qua
Virginia Tech - ME - 2124
Typical Thermodynamics Units under the SI and British Systems Dimension Mass Moles SI Unit kg (kilogram) kgmol or kmol (kilomol) units of molec. wt. are kg/kgmol Length m (meter) Time s (second) Force N (Newton) 1 N = 1 kg m / s2 Absolute K (Kelvin) Tempe
Virginia Tech - ME - 2124
Thermal Conductivities of Various MaterialsThermal Conductivity 25C / 77F W/m/K Acetone Acrylic Air Alcohol Aluminum, Pure Aluminum, Alloy Aluminum Oxide Ammonia Antimony Argon Asbestos mill board Asbestos, loosely packed Asbestos-cement Asbestos-cement
Virginia Tech - ME - 2124
The air in piston-cylinder device initially has a temperature of T=70C and a pressure of 200 kPa (gage). What is the gage pressure after the air has cooled to T=25C and the volume has been decreased by the piston to only 1/3 of the original volume?
Virginia Tech - ME - 2124
Virginia Tech - ME - 2124
ex 5b For a power cycle Qin = 60 kJ and Qout = 38 kJ. Determine the net work of the cycle and the thermal efficiency.
Virginia Tech - ME - 2124
ex 5b For a power cycle Qin = 60 kJ and Qout = 38 kJ. Determine the net work of the cycle and the thermal efficiency.
Virginia Tech - ME - 2124
Ex 6a A piston cylinder contains 2 lbs of air that is being compressed. Initial state: T1=540R, p1=1atm. Final state: T2=840R, p2=6atm. During the compression 30 Btu is transferred to the environment via heat interaction. The value of cv for air can be ta
Virginia Tech - ME - 2124
Virginia Tech - ME - 2124
2. Systems, Interactions, Properties, States, ProcessesSystem Bounded region of interest defined by us for our convenience. Specification of the boundary is crucial and must be consistent throughout a process. Choose system boundaries according to: 1) Kn
Virginia Tech - ME - 2124
Phases, Ideal Gases, p-v-T DiagramsPhase - Matter that is homogeneous in chemical composition and physical structure. Examples:Pure Substance - Matter that is uniform and invariable in chemical composition. Is air a pure substance?Simple Compressible S
Virginia Tech - ME - 2124
Work Interactions, Heat InteractionsMechanics definition of work:r r W = F dss2 s1Examples: 1. Constant force field, e.g. earth's gravityF = mg2. A springW= W= W=F = kx3. Friction (dry)F = mgThermodynamic definition of Work Interaction: A work
Virginia Tech - ME - 2124
Lect 51st Law of Thermodynamics, Energy, CyclesKinetic Energy - The energy of mechanical motionKE = 1 mV 22KE = KE2 - KE1 = 1 m V22 - V12 2()Potential Energy &quot;Stored&quot; mechanical energy e.g. gravitational potential energyPE = mgzPE = PE 2 - PE1 =
Virginia Tech - ME - 2124
Lec 6Internal Energy, Enthalpy, h and u and Specific Heats cv and cpIn many applications the quantity, Internal Energy U added to the product PV appears so often it has been given its own symbol H that is called enthalpy. H = U + pV H on a unit mass bas
Virginia Tech - ME - 2124
Lec 7Control Volumes and Mass BalancesControl Volume A prescribed, bounded region under study. The boundary may be fixed or may move and deform. Mass may cross the control volume boundary.Mass Rate Balance Conservation of mass requiresdm cv &amp; &amp; = mi -
Virginia Tech - ME - 2124
Lec 8Mass Balances, Energy Balances and Applications to Conversion Devices.Review of mass balanceConservation of energy for a control volumeEnergy balance can be expressed in terms of beginning and end states or in terms of flow ratesWork for a contr
Virginia Tech - ME - 2124
Lec 9Mass and Energy Balances for Devices Cont.Turbines - Devices which produce power as a result of a gas or liquid passing through a set of vanes attached to a freely rotating shaft. Ex. Hydropower Steam and gas turbines V12 - V22 &amp; + W + m (h - h )
Virginia Tech - ME - 2124
lec 10Introduction to Fluid MechanicsFluid Mechanics The discipline within applied mechanics that is concerned with the behavior of liquids and gases at rest or in motion. Topics: e.g. fluid pressure, viscosity, fluid flow, turbulence Fluid A substance
Virginia Tech - ME - 2124
Virginia Tech - ME - 2124
Heat Transfer Homework Answers ME 2124 Fall 2011Problem Answer(s)&amp; a) dT/dx = -280 K/m, Q = 14,000 W/m2 &amp; b) dT/dx = 80 K/m, Q = -4,000 W/m2HT1&amp; c) T2 = 110C, Q = -8,000 W/m2 &amp; d) T1 = 60C, Q = 4,000 W/m2 &amp; e) T1 = -20C, Q = -10,000 W/m2HT2 3.5 3.7 3
Virginia Tech - ME - 2124
Fluid Mechanics Homework Answers ME 2124 Fall 2011Problem FL1 Answer(s) 1000 N/m2 (a) diagram (b) F = mgsin (c) sketch (d) F = Av/h (e) v = mghsin / A (f) 31.7 cm/s, lower (a) 265 kPa (b) 196.2 Pa 3.43104 lbfFL2FL3 1.67 1.70(a)2Ri l = Ro - Ri(a) 0.60
Virginia Tech - ME - 2124
Thermodynamics Homework Answers ME 2124 Fall 2011Problem TD1 TD2 1.7 1.16 TD3 TD4 TD5 TD6 1.42 TD7 TD8 TD9 TD10 3.105 TD11 TD12 2.30 2.33 2.42 TD13 TD14 TD15 2.68 2.72 Answer(s) 34.4 furlongs/fortnight 4.21108 yen/day (a) 30.9 ft/s2; (b) 150 lbf - 25.8 f
Virginia Tech - ME - 2124
ME 2124 Introduction to Thermal Fluid Engineering Homework Problems Fluid Mechanics Fall 2011 1. Two plates are separated by an oil film 0.010 mm thick. Oil viscosity is oil = 0.1 N-sec/m2. The upper plate is moving at 100 mm/s. The oil flow between the p
Virginia Tech - ME - 2124
ME 2124 Introduction to Thermal-Fluid Engineering Homework Problems Heat Transfer (HT) Fall 2011 1. Consider steady-state conditions for one-dimensional conduction in the system below having a thermal conductivity k = 50 W/mK and a thickness L = 0.25 m, w
Virginia Tech - ME - 2124
ME 2124 Introduction to Thermal-Fluid Engineering Homework Problems - Thermodynamics (TD) - Fall 2011 1. An archaeologist has found a hieroglyphic inscription describing how a team of 4,000 Egyptians could move a 20-ton granite block a distance of 1.5 cub
Virginia Tech - ME - 3514
ME 3514 - System DynamicsPolicy Sheet Fall Semester, 2011CRN 94332 - MWF 8:00 AM 8:50 AM Randolph Hall 221Credit:3 credit hoursPrerequisites: MATH 2214, ESM 2304: Dynamics Of Particles And Rigid Bodies - Vector treatment of the kinematics and kinetic
Virginia Tech - ME - 3514
Virginia Tech - ME - 3514
ME3514Laplace TransformTopics Laplace transform Inverse Laplace Transform p Laplace Transform Table Solving Differential Equations Using Laplace Transform Final Value Theorem Partial Fraction Expansion (by hand and using MATLAB)M. Remillieux1ME3514L
Virginia Tech - ME - 3514
ME3514Partial Fraction ExpansionTime Domain Laplace Domain Step # 1: Take Algebraic equationSolving ODE usingDifferential equation with initial conditions We want to solve for x(t)Many times we can not find the -1 [X(s)] in the Laplace table Then, we
Virginia Tech - ME - 3514
ME3514Mechanical SystemsOutline Units Mechanical Elements Derive equations of motion (EOM) Newton's law Energy method Compute Natural Frequency Compute responseM. Remillieux1ME3514Units SI Britishsec in (or ft) lb lb/in lb.s/in lb.s2/in lb.in lb.in
Virginia Tech - ME - 3514
ME3514 Complex Numbers:Complex NumbersImaginary Partz a ibReal P R l Part Imaginary Unit, I i U iti 1Graphic Representation:Complex Plane b Imaginary Axis Complex Number zVector Representation of z a Real AxisComplex numbers also behaves as a vec
Virginia Tech - ME - 3514
ME 3514 SYSTEM DYNAMICSInstructor Ricardo A Burdisso A. 153 Durham Hall 231-7355 rburdiss@vt.eduIntroduction SYSTEMS: combination of components acting together to perform a task. Component is a single unit of a system. D Dynamic vs static system i t ti
Virginia Tech - ME - 3514
ME3514Partial Fraction Expansion Using MATLABIMPORTANT NOTE: MATLAB and book use different notation! OGATA Expansion FormX ( s) r r r B( s) 1 2 . n A( s) s p1 s p2 s pn X ( s) r r r B( s) 1 2 . n A( s) s p1 s p2 s pnMATLABPoles p1 , p2 ,., pnp1 , p
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Virginia Tech - ME - 3514
ME3514Topics Transfer Function T f F ti Block Diagram Transient Response Analysis using TF with MATLAB p y g Unit Impulse (Delta) Function Impulse Delta f function Momentum Relationship between momentum and impulse Laplace transform of an impulse Exampl
Virginia Tech - ME - 3514
ME3514State-Space To model Dynamic SystemsState-Space State Space Modeling: is a method to find the response of dynamic systems that can be easily implemented on the computer, e.g. MATLAB. State-Space equations: consists of two type of equations, e.g. &quot;
Virginia Tech - ME - 3514
ME 3514Transfer-Function ApproachObjective Use Transfer Function and Block Diagram to model and analyze mechanical systems. Explore transient response of systems using transfer function with application of MATLABTopics R. BurdissoTransfer Function Bl
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