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SUESFALL2008FINALTESTBANSWER

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SUESFALL2008FINALTESTBANSWER

    ,勤奋、求是、创新、奉献(

    2008 2009学年第1学期考试试卷

    主考教师,____ Thomas A. Hamade____

    学院 _ 汽车工程学院__ 班级 姓名 _________ 学号 _________

    《先进制造工艺,美(》课程试卷A答案

    ,本卷考试时间120分钟(

    题号 总分

    题分 8 7 15 16 54 100

    得分

?. Fill in the blank1 point each, 8 points total(

    1. A water vapor at temperature and pressure higher than the saturation point is known as ___superheated__

    steam.

    2. The enthalpy is H = U + PV and the internal energy for a closed system is given as dU = δQ – δW.

    3. Thermal Science is the science of energy transformation in thermodynamics, fluid flow and heat transfer.

    4. The ideal gas law (PV=nRT) is used to approximate P, T, V relationship for many gases.

    5. The Bernoulli equation is used to predict flow conditions of a fluid along the streamlines.

    6. One British thermal unit (BTU) is equal __252____ calories and each calorie is equal __4.187___ Joules.

    07. 273 K is equal __32 F__ and 0 K is equal to __460 R__.

    8. The weight of matter on the moon is much than that on earth because of the ___gravitational___ constant is

    much lower.

    ?. Choose the right answers:1 point each, 7 points total)

    1. Which one of the following devices is used to compress fluids: (a)Nozzle __X__(b)Compressor (c)Turbine

    (d) None mentioned

    2. Which one of the following is a open system: (c)

    a. Gas inside cylinder exchanges heat with surrounding but no mass enters the system.

    b. Gas isolated so matters from surrounding do not enter the system.

    c. Fluid flows in and out of the system from surrounding.

    d. Gas doing work on surrounding, however no matter enters the system.

    e. None of the above.

    2008~2009学年第1学期《先进制造工艺,美(》课程试卷B答案 1 6

3. At what temperature water evaporates when the pressure is 0 kPa:

    oa. 0 C c. 0 K d.. 0 R __X__e. All mentioned

    4. Metals thermal conductivity is: a. same as gases __X__b. Greater than non-metals c. Same as

    insulators d. None mentioned.

    5. The Bernouli Equation is valid for: (a)

     a. Steady state, incompressible flow where net frictional forces are negligible.

     b. Unsteady state heat transfer.

     c. Steady state compressible flow.

     d. None above.

    6. The mechanisms for heat transfer are: (a)

    a. conduction, convection & radiation

    b. Work and heat addition

    c. Internal energy changes

    d. Vibration and rotation of atoms.

    7. Which one of the equations used in fluid flow: (c)

    a. Einstein Equation

    b. E = mgh

    c. Bernoulli Equation.

    d. PV = nRT

    ?. Answer the following questions with True or False1 point each, 15 points total(

    1. Volume and density and specific heat are extensive properties while volume, and dimensions are intensive

    properties. _____TRUE __X___FALSE

    2. Convection is the transfer of energy between energetic hot object and less energetic cold object.

     __X__TRUE ______FALSE

     3. The potential energy of moving objects is equal to (mgh)which is different than the kinetic energy.

    __X___TRUE _____FALSE

    4. Saturated liquid-vapor mixtures co-exist when liquid and vapor phases are at equilibrium. __X___TRUE

    _____FALSE

    5. Air can be compressed adiabatically without changing its temperature. ____TRUE ___X__FALSE 6. Latent heat of fusion is the amount of energy lost during solidification of ice. ___X___TRUE

    ____FALSE

    7. Heat is added or removed from system and work is obtained by or done on a system. Both can not cause any

    changes in the internal energy and enthalpy of the system. _____TRUE __X___FALSE

    2008~2009学年第1学期《先进制造工艺,美(》课程试卷B答案 2 6

    8. Convection is the energy emitted by matter in the form of electromagnetic waves. ____TRUE

    __X___FALSE

    9. For fluids the volumetric flow rate is the same as the mass flow rate. ____TRUE ___X__FALSE 10. Van der Waals Equation of State was proposed to improve prediction of pressure, temperature and specific

    volumes relationship for ideal gases instead of using the real gases. _____TRUE

    ___X___FALSE

    11. An open system when matter flows in and out of system from surrounding. __X__TRUE

    ______FALSE

    12. Specific heat is the energy required to raise the temperature of a unit mass of substance one degree, either at

    constant pressure (C) or at a constant volume (C). __X__TRUE ______FALSE pv

    13. There can be heat transfer between two bodies that are at the same temperature (regardless of pressure) since

    the driving force for heat transfer is temperature independent. _____TRUE ___X___FALSE 14. Isothermal system is the same as adiabatic system. ____TRUE __X___FALSE

    15. A tank that has a mixture of propane gas and propane liquid is considered a pure substance. __X__TRUE

    ______FALSE

    IV. Answer the following questions (6 questions, 6 points each, 36 points total(

    1. When piping losses are negligible, there is negligible dissipation of mechanical energy into thermal energy.

    Then when there are no mechanical devices such as fans, turbines, pumps, the Bernoulli Equation reduces to

    degenerate form of the energy equation. The Bernoulli equation then between any two points along the

    streamline of a flow is written as:

2. Write down Newton’s Law for cooling at constant heat transfer coefficient (h):

3. Write down the radiation heat transfer between two-surface enclosures in terms (εζ) time the difference

    between their body temperatures to a known power.

    4. Define internal energy and express its SI and English units. Internal energy is the sum of all the microscopic

    forms of energy of a substance. Units: SI Joules or calories, & BTU(English)

    5. Define potential energy and give its equation: potential energy is the energy of a system as a result of its

    elevation in a gravitational field. PE = mgh

    2008~2009学年第1学期《先进制造工艺,美(》课程试卷B答案 3 6

    6. Give three examples of steady state system. (a) water flowing at a constant velocity. (b) Car moving at a

    constant speed. (c) Temperature of water is constant during boiling at one atmosphere. The pressure of a

    closed tank is constant at a constant temperature. Any process function independent of time. 7. Give three examples of unsteady state system. (a) hot water is cooling to room temperature. (b)The pressure

    rise in a piston during compression. (c)The volume of a conical container changes with time during filling. (d)

    a pump is started to pump water. Any process that is time dependent.

    8. Can you calculate the volume of liquid water using PV=nRT? Why not.? No because the Ideal Gas Law

    PV=nRT is only valid for gases and not liquids. If the calculation is attempted then the answer is much

    much greater than real and becomes erroneous answer.

V. Solve the following problems8 problems POINTS SHOWN54 points total(

    1. (5POINTS) A car weighs 1200kg is accelerated from rest to 85 km/hour speed. Calculate the work

    2obtained by the car in BTU. Use KE = (1/2) mν.

    22KE = (1/2)(1200Kg)((85km/hr)(1hr/3600s)(1000m/km)) (1N/kgm/s) (1J/N.m)(1cal/4.187J)(1BTU/252cal) mm

    KE = 317BTU

    22. (5POINTS) A 4500 pounds rock is falling vertically at an acceleration of 32.174 ft/s. Find the amount

    of potential energy loss (in BTU) when it hits the ground 150 feet below.

    PE = mgh

    22= 4500# x (0454Kg/#)(32.174ft/s)(150ft)((12in/ft x 2.54cm/in x1m/100cm)(1J/N.m)(1cal/4.187J)(1BTU/252cal) m

    PE = 868.1BTU

    3. (9POINTS) Steam flows at steady state through an adiabatic turbine at 15kg/s. It enters the

    oturbine at P = 10Mpa, T = 450C and ν = 80m/s. The exit conditions are P = 1MPa, T = 11122o400C, ν = 50m/s. After one hour of operation determine: (a) the change in enthalpy, (b) the 2

    change in kinetic energy and (c) the work output by the turbine. (hint use superheated steam

    2tables). Work output = - m [h h + (ν ν )/2]. 2121

    Steam expands in a turbine. The change in kinetic energy, the power output, and the turbine inlet area are to be determined.

    Assumptions 1 This is a steady-flow process since there is no change with time. 2 Potential energy changes are

    negligible. 3 The device is adiabatic and thus heat transfer is negligible.

    (a) Properties From the steam tables (Tables A-4 through 6)

    P10 MPa?1 P = 10 MPa 1h3242.4 kJ/kgT450C11?T = 450C 1

    V = 80 m/s and 1

    P1 MPa?2 STEAM h22828.3 kJ/kgT2200C??

    m = 15kg/s ? W The change of Enthalpy = 3242.4 2828.3 = -414.10kJ/kg

    (b) The change in kinetic energy is determined from

     P = 10 kPa 2

    x = 0.92 2008~2009学年第1学期《先进制造工艺,美(》课程试卷B答案 4 6 2

    V = 50 m/s 2

    2222??VV50 m/s(80 m/s)1 kJ/kg;;21?( ke1.95 kJ/kg22?(221000 m/s?)

    ;;;(c) There is only one inlet and one exit, and thus . We take the turbine ,,mmm12

    as the system, which is a control volume since mass crosses the boundary. The energy balance for this steady-flow system can be expressed in the rate form as

    0 (steady);;;;EEE0inoutsystem,?,?,?,?Rate of net energy transferRate of change in internal, kinetic, by heat, work, and mass potential, etc. energies

    ;;EEinout

    22;;;;(/2)(+/2) (since Qpe0)mhVWmhV11out22

    22 ??VV21;?(;Wmhhout21?(2?)

    Then the power output of the turbine is determined by substitution to be

;(10 kg/s)(2828.33242.41.95)kJ/kg6.241 MWWout

    W(out) 6.241 MW x 3600s 22,467 MJ

4. (6POINTS) Find the specific volume, internal energy and the enthalpy for superheated steam (water) at

    o10mPa and 1200 C. Use p1000 textbook for superheated steam.

    3V = 0.067938 m/kg , u = 4452.4kJ/kg , h = 5131.7

    oo5. (6POINTS) One cubic meter of mild steel is heated from 25C to 500C. Using the properties

    in Table A-3b and assuming constant heat capacity, calculate heat transferred to the steel.

    3[Density = 7.83 g/cm, and heat capacity Cp = 0.500 kJ/kg.K]

    Analysis The internal energy and enthalpy changes are equal for a solid. Then,

     HUmcT(1000 kg)(0.50 kJ/kg~K)(50025)K237,500 kJ

    6. (9POINTS) 16-6C Write down the equations for the physical laws. Identify the variables in each equation:

    a. Fouries’s Law of conduction.

    b. Newton’s Cooling Law of Convection.

    c. Stefan-Boltzman Law for Radiation emission

    dT;QkAa. Conduction is expressed by Fourier's law of conduction as where dT/dx is the temperature gradient, conddx

    k is the thermal conductivity, and A is the area which is normal to the direction of heat transfer.

    ;QhA(TT)b. Convection is expressed by Newton's law of cooling as where h is the convection heat convss

    transfer coefficient, A is the surface area through which convection heat transfer takes place, T is the surface ss

    temperature and T is the temperature of the fluid sufficiently far from the surface.

    44;Q(;A(TT)c. Radiation is expressed by Stefan-Boltzman law as where is the emissivity of (ssradsurr

    2008~2009学年第1学期《先进制造工艺,美(》课程试卷B答案 5 6

surface, A is the surface area, T is the surface temperature, T is the average surrounding surface temperature sssurr

    824and is the Stefan-Boltzman constant. 5.6710 W/m~K

    oo7. (6POINTS) The inner and outer surface of a 0.5cm thick 2mx2m window glass in winter are 10C and 3C,

    respectively. If the thermal conductivity of the glass is 0.78W/m.K, determine the amount of heat loss

    through the glass over a period of 5 hours. Use Fourier’s law for conduction.

The inner and outer surfaces of a window glass are maintained at specified temperatures. The amount of heat

    transfer through the glass in 5 h is to be determined.

    Assumptions 1 Steady operating conditions exist since the surface temperatures of the glass remain constant at the

    specified values. 2 Thermal properties of the glass are constant.

    Properties The thermal conductivity of the glass is given to be k = 0.78 W/m~C. Glass

    Analysis Under steady conditions, the rate of heat transfer through the glass by conduction is

    (103)CT2;QkA(0.78 W/m~C)(22 m)4368 W condL0.005m

    Then the amount of heat transfer over a period of 5 hrs becomes 10C 3C

    ; QQt(4.368 kJ/s)(53600 s)78,620 kJ0.5 cm cond

    o8. (8POINTS) Consider a person standing in a room maintained at 20C at all

    times. The inner surfaces of the walls, floors, and ceiling of the house are

    ooobserved to be at an average temperature of 12C in winter and 23C in

    summer. Determine the rate of radiation heat transfer between this person and the surrounding during winter and summer if exposed surface area,

    2emissivity, and the average outer surface temperature of the person are 1.6 m,

    o0.95, and 32C, respectively.

The rate of radiation heat transfer between a person and the surrounding surfaces at specified temperatures is to be

    determined in summer and winter.

    Assumptions 1 Steady operating conditions exist. 2 Heat transfer by convection is not considered. 3 The person is

    completely surrounded by the interior surfaces of the room. 4 The surrounding surfaces are at a uniform temperature.

    Properties The emissivity of a person is given to be ( = 0.95

    Analysis Noting that the person is completely enclosed by the surrounding surfaces, the net rates of radiation heat

    transfer from the body to the surrounding walls, ceiling, and the floor in both cases are: (a) Summer: T = 23+273=296 surr

    Tsurr 44;()Q(;ATTradsurrss

    8242444(0.95)(5.6710 W/m.K)(1.6 m)[(32+273)(296 K)]K

    =84.2 W

    Qrad (b) Winter: T = 12+273= 285 K surr

    44;()Q(;ATTradsurrss

    8242444(0.95)(5.6710 W/m.K)(1.6 m)[(32+273)(285 K)]K

    =177.2 W

    2008~2009学年第1学期《先进制造工艺,美(》课程试卷B答案 6 6

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