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conceptests in chemical engineering thermodynamics note: slides marked with jlf were adapted from the conceptests of jo

1.3 What causes an azeotrope?. . . . The components can't be distilled.The components have similar boiling temperatures.The components like each other in the extreme.The components dislike each other in the extreme.. Day1 Review. 1.4 What's the difference between a chemist and a chemical engineer?.

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conceptests in chemical engineering thermodynamics note: slides marked with jlf were adapted from the conceptests of jo

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    1. ConcepTests in Chemical Engineering Thermodynamics

    3. 1.4 Whats the difference between a chemist and a chemical engineer?

    4. 1.1 What is temperature?

    5. 1.2 The picture below represents hard spheres colliding in a planar box (like an air hockey table). Which represents the area of the box that should be used to compute density? 3/16 picked A on 1st try. 3/16 picked A on 1st try.

    6. 2.1. Which of the following represents an ideal gas?

    7. 2.2 Which is characteristic of a liquid relative to a vapor?

    8. 2.3 For water at 375?C and 10 MPa, find the internal energy (kJ/kg).

    9. 2.4 The outlet from a turbine consists of steam at 100C and an entropy (S) of 7 kJ/kg-K. What is its quality?

    10. 3.1 When running a turbine, you want to recover as much energy as work as possible. If the efficiency is, say, 75% then 25% of the possible work must be lost. The lost work must show up in the turbine outlet stream somehow, but how? Note: if the exhaust is at q < 100%, the temperature might not increase, but the enthalpy does.Note: if the exhaust is at q < 100%, the temperature might not increase, but the enthalpy does.

    11. 3.2 What causes the efficiency of a turbine to be less than 100%?

    12. 4.1 Two molecules are bouncing in 2D with molecular weight of 16g/mole. Their velocities (m/s) are given by:<555, -432>, < -555,432>. Estimate the temperature in the box (K).

    15. 4.4 High pressure steam flows through an adiabatic turbine to steadily produce work. Which is the best energy balance for solving this problem?

    16. 4.5 High pressure steam flows into a piston-cylinder to produce work. Which is the most appropriate energy balance for solving this problem?

    17. 6.1 Steam at 200 bars and 600?C flows through a valve and out to the atmosphere. What will be the temperature after the expansion? H(20,600)=3539.0, H(0.1,550)=3596.3, H(0.1,500)=3488.7H(20,600)=3539.0, H(0.1,550)=3596.3, H(0.1,500)=3488.7

    18. 6.2 A gas is filling a rigid tank from a supply line. Which of the following represents the most appropriate energy balance? H=const for fillingH=const for filling

    19. 6.3 A gas is leaking from a rigid tank into the air. Which of the following represents the most appropriate energy balance?

    20. 6.4 An ideal gas (Cp=3.5R) is adiabatically and reversibly compressed in a steady state process from 25C and 1bar to 10bar. What is the exit temperature (C)? 298*(10)^(1/3.5)=575 NOTE: ANS in degC. 575-273=302!!!!!!!!!298*(10)^(1/3.5)=575 NOTE: ANS in degC. 575-273=302!!!!!!!!!

    21. 6.5 A ideal gas (Cp=3.5R) is adiabatically and reversibly compressed in a steady state process from 25C and 1bar to 10bar. What is the work requirement (J/mol)? 8.314*3.5*(575-298)=80608.314*3.5*(575-298)=8060

    22. 7.1 Two exit streams leave a turbine. One stream is given, the other can be inferred from the throttle. The turbine produces 100kW. Estimate the heat loss (kW). I outlined the solution for this problem in class and assigned its completion as hw. Lets see if anybody did.I outlined the solution for this problem in class and assigned its completion as hw. Lets see if anybody did.

    23. 7.2 Which of the following represents the value for the following integral? 3^2/2 1^2/2 = 43^2/2 1^2/2 = 4

    24. 7.3 Which of the following represents the value for the following integral? Ln(1)=0; ln(3)*(1+3+9/2)=9.34Ln(1)=0; ln(3)*(1+3+9/2)=9.34

    25. 7.4 (Ex2.15) An insulated tank initially contains 500 kg of steam and water at 2.0 MPa. Half of the tank volume is occupied by liquid and half by vapor. The temperature (C) of the tank initially is closest to:

    26. 7.5 Steam at 150 bars and 600 C passes through a heater expander and emerges at 100 bars and 700 C. There is no flow of work into or out of the heater-expander, but heat is supplied. Using the steam tables, compute the flow of heat (kJ/kg) into the heater expander per mole of steam.

    27. 7.6 Steam at 150 bars and 600 C passes through a heater expander. Compute the (dimensionless) value of [H(150,600)-H(1,600)]/RT for steam at the inlet conditions.

    28. QQ1.1.1 What is the relationship for the force vs. distance, F(r), between two molecules according to the Lennard-Jones potential model?

    29. QQ1.1.2 Molecules A and B can be represented by the square-well potential. For molecule A, ? = 0.4 nm and ? = 20e-22 J. For molecule B, ? = 0.8 nm and ? = 10e-22 J. Which molecule would you expect to have the higher boiling temperature?

    30. QQ1.1.3 Steam initially at 20 MPa, T = 366?C, and H = 2421.6 kJ/kg is throttled to 1.0 MPa. What % of the expanded stream is liquid? HL=762; HV=2777; dH=2030; HL=762; HV=2777; dH=2030;

    31. QQ1.1.4 Write the most appropriate energy balance for the following: A compressor is filling the Goodyear blimp. System: the blimp and its contents The pressure entering from the pump will increase, causing Hin to change with time.The pressure entering from the pump will increase, causing Hin to change with time.

    32. 8.1 An insulated tank initially contains 500 kg of steam and water at 2.0 MPa. Half of the tank volume is occupied by liquid and half by vapor. 25 kg of moisture free vapor is vented from the tank so that the pressure and temperature are always uniform throughout the tank. Analyze the situation carefully and calculate the final pressure in the tank. E-bal? Despite vle, no heat means Hvap required so Tsys decreases.Despite vle, no heat means Hvap required so Tsys decreases.

    33. 8.2 In an old-fashioned locomotive an insulated piston+ cylinder is connected through a valve to a steam supply line at 3MPa and 300C. The back side of the piston is vented to the atmosphere at the right side of the cylinder. The volume of the cylinder is 70 liters. When the valve opens the piston is touching the left side of the cylinder. As the piston moves to the right it accomplishes 108 kJ of work before it touches the right side of the cylinder. Then, the cylinder contains 0.5 kg of steam and the temperature remains at 300C.

    34. 8.3 Megan is half Kevins age. In six more years, shell be four-fifths Kevins age. In 10 years, shell be six-sevenths Kevins age. Neither is a teenager. How old is Megan now? M=0.5K; M+6=0.8(K+6); m+10=6K/7; 0.6M + 0.8*6=6; M=6*0.2/0.6 = 0.2*10=2; K=4M=0.5K; M+6=0.8(K+6); m+10=6K/7; 0.6M + 0.8*6=6; M=6*0.2/0.6 = 0.2*10=2; K=4

    35. 8.4 Identify the engineer based on the following: Engineers like #sEngineers like #s

    36. 8.5 Two coins are tossed once each. If heads, the coin is placed in boxA. If tails, the coin is placed in boxB. What is the probability that one coin is in each box? 2/4 ways to get 1 head and 1 tail2/4 ways to get 1 head and 1 tail

    37. 8.6 Five coins are tossed once each. If heads, the coin is placed in boxA. If tails, the coin is placed in boxB. What is the probability that one coin is in boxA?

    38. 9.1 Five coins are tossed once each. If heads, the coin is placed in boxA. If tails, the coin is placed in boxB. What is the probability that one coin is in boxA?

    39. 9.2 Four coins are tossed once each. If heads, the coin is placed in boxA. If tails, the coin is placed in boxB. What is the probability that one coin is in boxA?

    40. 9.3 Do not use a calculator to solve the following. Compute: log10(8000)-log10(4)-log10(2)=

    41. 9.4 Nitrogen at 300K and 10bar is adiabatically and reversibly expanded to 1bar. What is the final temperature (K)?

    42. 9.5 Nitrogen at 300K and 10bar is throttled to 1bar. What is the final temperature(K)?

    43. 9.6 Suppose two boxes but the one with NA particles is three times as large as the empty box. Then what is the change in entropy?

    44. 10.1 Three moles of N2 at 2 bars and 300K are expanded into a box that is 33.33% larger. Then what is the DS?

    45. 10.2 One mole of O2 at 2 bars and 300K is expanded into a box that is four times larger. Then what is the DS?

    46. 10.3 One mole of O2 is mixed with 3 moles of N2 at 2 bars and 300K. Then what is the final pressure (bar)?

    47. 10.4 One mole of O2 is mixed with 3 moles of N2 at 2 bars and 300K. Then what is the DS?

    48. 10.5 One mole of O2 is mixed with 3 moles of N2 at 2 bars and 300K. Then what is the DS/R?

    49. 10.6 (Closed book) Estimate Cv/R for He.

    50. 10.7 (Closed book) Estimate Cv/R for N2.

    51. QQ1.2.1 Identify the most appropriate energy balance for the following situation. A pot of water brought to a boil from initially cold water in a pressure cooker on the oven with the pressure relief valve operating perfectly. System: the pot and its contents. C. Because need Q to boil and Hvap is constant for sat vap at const P.C. Because need Q to boil and Hvap is constant for sat vap at const P.

    52. QQ1.2.1b A disk is initially at the position (0.2,0.2)nm in a box that is 5nm on a side with its lower left corner at the origin in Cartesian coordinates. The disk is 0.4 nm in diameter. The velocity of the disk is (543,456)m/s. Compute the time (ns) when the disk collides with the east wall. B. 5-0.2 = 0.2+543*tB. 5-0.2 = 0.2+543*t

    53. QQ1.2.2 If I fill an empty helium cylinder adiabatically to 1800 psia from a line at 300K, then seal it and allow it to equilibrate with the surrounding air on a 300K day, what will be the final pressure in the cylinder (psia)? Cp/R=5/3=>T1=500K. 3*1800/5=1080Cp/R=5/3=>T1=500K. 3*1800/5=1080

    54. QQ1.2.3 For a system of 6 particles distributed between two boxes, what is the % of distinguishable microstates corresponding to the macrostate with 4 particles in Box A and 2 particles in Box B? Pi=6!/(4!*2!)=6*5/2 = 15. M^N=2^6=64. 15/64=23%Pi=6!/(4!*2!)=6*5/2 = 15. M^N=2^6=64. 15/64=23%

    55. QQ1.2.4 One mole of O2 is mixed with 4 moles of N2 at 2 bars and 300K. Then what is the DS/R?

    56. 12.1 Charlie was cleaning his living room. He lifted a sofa cushion and found an equal number of pennies, nickels, and dimes totaling $1.28. How many of each coin did he find?

    57. 12.2 A steam engine is to operate between 500C and 50C. Estimate its thermodynamic efficiency(%) according to the Carnot guideline.

    58. 12.3 A heat pump converts work into heat, extracting heat from a colder source and supplying it to the higher temperature sink. Suppose 30kW of heat is to be pumped to 80 from 30F. Estimate how much work (kW) is required if Carnot efficiency is achieved.

    59. 12.4 Steam is supplied to a steady state turbine at 10 MPa and 600C. The discharge from the adiabatic, reversible turbine is at 25C. Determine the quality of the outlet steam (%).

    60. 12.5 Steam is supplied to a steady state turbine at 10 MPa and 600C. The discharge from the adiabatic, reversible turbine is at 25C. Determine the work generated (kJ/kg).

    61. 13.1 Steam undergoes a state change from 450 C and 3.5 MPa to 150?C and 0.3MPa. Determine ?S (kJ/kg-K) from (a) steam tables. HW 3.2a: 0.07HW 3.2a: 0.07

    62. 13.2 Steam undergoes a state change from 450 C and 3.5 MPa to 150?C and 0.3MPa. Determine ?S (kJ/kg-K) from (b) IG assumption. HW 3.2b: 0.13 HW 3.2b: 0.13

    63. 13.3 Steam undergoes a sudden state change from 600K and 1 MPa to double the volume. Determine Tf (C) from (b) steam tables. HW 3.6b: 594-273 = 321.HW 3.6b: 594-273 = 321.

    64. 13.4 Instead of burning gas directly to get heat, it is proposed to run a heat engine (HE) that runs a heat pump (HP). Qh =40kJ/h. TF =800K;TS =263; Th =293. HE exhausts to TS. Compute QF (kJ/h) HW3.8: QS/TS=QF/TF=> W/QF=(800-263)/800=0.67; Qh/Th=QS/TS=> W/Qh=(293-263)/293=0.102 W=4, QF=4/0.67=6HW3.8: QS/TS=QF/TF=> W/QF=(800-263)/800=0.67; Qh/Th=QS/TS=> W/Qh=(293-263)/293=0.102 W=4, QF=4/0.67=6

    65. 13.5 1mol/min air enters at 500K, 2bar and exits at 350K, 1bar. The process produces 2000J/min of work. It also exchanges heat with a reservoir at 300K. Estimate Sgen. HW3.12: dH=Q+W => Q=2000-3.5*8.314(150)=2365 ; Sgen=8.314*[3.5ln(350/500)-ln(1/2)]+2365/300=3.3HW3.12: dH=Q+W => Q=2000-3.5*8.314(150)=2365 ; Sgen=8.314*[3.5ln(350/500)-ln(1/2)]+2365/300=3.3

    66. 14.1 A process produces as much work as possible from a turbine operating between 10MPa and exhausting at 40C, sat vapor. Estimate the entropy at the outlet. 8.25558.2555

    67. 14.2 A process produces as much work as possible from a turbine operating between 10MPa and exhausting at 40C, sat vapor. Estimate the work (kJ/kg). Betw 1200-1250C, S=8.2126-8.3010=> H~halfway~5200. W=5200-2573 = 2627Betw 1200-1250C, S=8.2126-8.3010=> H~halfway~5200. W=5200-2573 = 2627

    68. 14.3 A process heats saturated liquid water from 40C to steam at 10MPa and 1225C. Estimate the heat required (kJ/kg). 5200-167.5 = 50335200-167.5 = 5033

    69. 14.4 A process produces as much work as possible from a turbine operating between 10MPa and exhausting at 40C, sat steam. The process condenses the vapor and pumps it to 10MPa (Wp~0) then reheats to steam at the turbine inlet conditions. Estimate the thermal efficiency (W/QH) of this cycle. 2627/5033=0.5222627/5033=0.522

    70. 14.5 A process produces as much work as possible from a turbine operating with a max pressure of 10MPa and exhausting at 40C, sat steam. The boiler temperature is constrained by the softening temperature of steel. If you lower the temperature entering the turbine, the quality exiting will ____. 2627/5033=0.5222627/5033=0.522

    71. 14.6 A process produces as much work as possible from a turbine operating between 10MPa and exhausting at 40C, sat steam. The process condenses the vapor and pumps it to 10MPa (Wp~0) then reheats to steam at the turbine inlet conditions. Compute the thermodynamic efficiency of a Carnot cycle operating in the same temperature range. (1225-40)/(1225+273)=0.79(1225-40)/(1225+273)=0.79

    72. 15.1 A turbine compresses Freon134a (Cp/R=10.2, MW=102) from sat vapor at 0.126MPa to 0.789MPa. Estimate the minimal work requirement (kJ/kg) assuming the ideal gas law. (Hint: p654 for Tsat) W=CpT1*[(P2/P1)^R/Cp-1]=10.2*8.314*252*(1.197-1)/102=41kJ/kg W=CpT1*[(P2/P1)^R/Cp-1]=10.2*8.314*252*(1.197-1)/102=41kJ/kg

    73. 15.2 A valve throttles Freon134a (Cp/R=10.2, MW=102) from sat Liq at 0.789MPa to 0.126MPa. Estimate the enthalpy (kJ/kg) at the outlet. (Hint: p654) SatLiq at 0.78918MPa => 242.95=HsatLiq Ebal=> dH=0 SatLiq at 0.78918MPa => 242.95=HsatLiq Ebal=> dH=0

    74. 15.3 A valve throttles Freon134a (Cp/R=10.2, MW=102) from sat Liq at 0.789MPa to 0.126MPa. The fluid from the valve is heated to saturated vapor. Estimate the ratio of this heat divided by the work of compressing the ideal gas from 0.126 to 0.789MPa (QL/W). (386-243)/41=3.5(386-243)/41=3.5

    75. 15.4 A turbine compresses Freon134a (Cp/R=10.2, MW=102) from sat vapor at 0.126MPa to 0.789MPa. Estimate the minimal work requirement (kJ/kg) using the chart on p653. W=426-386=40J/gW=426-386=40J/g

    76. 16.h1 The optimal intermediate pressure for continuous two-stage adiabatic compression of an ideal guess is: W=426-386=40J/gW=426-386=40J/g

    77. 16.h2 HW3.17. The work produced (J/g) is: 12001200

    78. 16.h2 HW3.27. The work required for compressor 1 (J/g) is: 12001200

    79. 16.h4 HW3.33. The initial can pressure (bar) is: 162bars162bars

    85. QQ1.3.1 A process produces as much work as possible from a turbine operating between 5MPa and exhausting at 45C, sat steam. The process condenses the vapor and pumps it to 5MPa (Wp~0) then reheats to steam at the turbine inlet conditions. Compute the work generated by the turbine (kJ/kg). 4628-2582=20464628-2582=2046

    86. QQ1.3.2 A process produces as much work as possible from a turbine operating between 5MPa and exhausting at 45C, sat steam. The process condenses the vapor and pumps it to 5MPa (Wp~0) then reheats to steam at the turbine inlet conditions. Compute the thermodynamic efficiency of this Rankine cycle. 2046/(4628-188)=0.792046/(4628-188)=0.79

    87. QQ1.3.3 A process produces as much work as possible from a turbine operating between 5MPa and exhausting at 45C, sat steam. The process condenses the vapor and pumps it to 5MPa (Wp~0) then reheats to steam at the turbine inlet conditions. Compute the thermodynamic efficiency of a Carnot cycle operating in the same temperature range. (1000-45)/(1000+273)=0.79(1000-45)/(1000+273)=0.79

    88. QQ1.3.4 A turbine operates between 5MPa, 550C and 45C, sat steam. Compute the efficiency of this turbine. Wact=3551-2582=969; Wlost=(45+273)*(8.1633-7.1237)=331=> Wrev=1300; eff=969/1300=75%Wact=3551-2582=969; Wlost=(45+273)*(8.1633-7.1237)=331=> Wrev=1300; eff=969/1300=75%

    89. 17.1 An adiabatic turbine is supplied with steam at 2.0 MPa and 600?C and it exhausts at 98% quality and 24?C. Compute the work output (kJ/kg).(15) Hout=101+0.98*2444=2496; W=3690.7-2496=1194.6Hout=101+0.98*2444=2496; W=3690.7-2496=1194.6

    90. 17.2. An adiabatic turbine is supplied with steam at 2.0 MPa and 600?C and it exhausts at 98% quality and 24?C. Compute the efficiency of the turbine.(20) LW=(24+273)*DS=297*(7.7043-8.4120)=210; eff=Wact/(Wact+LW)=1194.6/(1194.6+210)=0.850; Alt: q=(7.7043-.3543)/(8.5764-.3543)=0.8939; Hout=.8939*2545+.1061*101=2285.7; eff=1194.6/(3690.7-2285.7)=0.8498LW=(24+273)*DS=297*(7.7043-8.4120)=210; eff=Wact/(Wact+LW)=1194.6/(1194.6+210)=0.850; Alt: q=(7.7043-.3543)/(8.5764-.3543)=0.8939; Hout=.8939*2545+.1061*101=2285.7; eff=1194.6/(3690.7-2285.7)=0.8498

    91. 17.3. An ordinary vapor compression cycle is to be operated on R134a (Cp/R=10.2,MW=102) to cool a chamber to 260K. Heat will be rejected to air at 308K. The temperatures in the coils are 256K and 312K. Estimate the compressor work (J/g). (Hint: Use IG estimate )(10) T2=256(0.9856/0.14989)^(1/10.2) = 308; W=10.2*8.314*(308-256)/102=43 J/g Note: Chart shows W=42J/g, but T2=323K. T value of 308 is weird b/c coils are hotter.T2=256(0.9856/0.14989)^(1/10.2) = 308; W=10.2*8.314*(308-256)/102=43 J/g Note: Chart shows W=42J/g, but T2=323K. T value of 308 is weird b/c coils are hotter.

    92. 17.4. An ordinary vapor compression cycle is to be operated on R134a (Cp/R=10.2,MW=102) to cool a chamber to 260K. Heat will be rejected to air at 308K. The temperatures in the coils are 256K and 312K. Estimate the COP.(10) Wact=3551-2582=969; Wlost=(45+273)*(8.1633-7.1237)=331=> Wrev=1300; eff=969/1300=75%Wact=3551-2582=969; Wlost=(45+273)*(8.1633-7.1237)=331=> Wrev=1300; eff=969/1300=75%

    93. QQ1.4.1. An ordinary vapor compression cycle is to be operated on propane (Cp/R=8.85,MW=44) to cool a chamber to 260K. Heat will be rejected to air at 308K. The temperatures in the coils are 256K and 312K. Estimate the pressure in the condenser. Wact=3551-2582=969; Wlost=(45+273)*(8.1633-7.1237)=331=> Wrev=1300; eff=969/1300=75%Wact=3551-2582=969; Wlost=(45+273)*(8.1633-7.1237)=331=> Wrev=1300; eff=969/1300=75%

    94. QQ1.4.2. An ordinary vapor compression cycle is to be operated on propane (Cp/R=8.85,MW=44) to cool a chamber to 260K. Heat will be rejected to air at 308K. The temperatures in the coils are 256K and 312K. Estimate the work of compression (J/g). Chart=> 965-879=86; IG => T2=256*(1.335/0.2707)^(1/8.85)=306.6; W=(306.6-256)8.85*8.314/44=85Chart=> 965-879=86; IG => T2=256*(1.335/0.2707)^(1/8.85)=306.6; W=(306.6-256)8.85*8.314/44=85

    95. QQ1.4.3. An ordinary vapor compression cycle is to be operated on propane (Cp/R=8.85,MW=44) to cool a chamber to 260K. Heat will be rejected to air at 308K. The temperatures in the coils are 256K and 312K. Estimate the COP. W=(306.6-256)8.85*8.314/44=85; QL=879-624=255; QL/W=255/85=3.0W=(306.6-256)8.85*8.314/44=85; QL=879-624=255; QL/W=255/85=3.0

    96. End of File

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