This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: MEEN 315—Summer 2010, Exam 2 Name K E 2 Section Number 1. Please put your name on e_ve_ry page. 2. RELAX, this is only an exam. Read over the whole exam, then decide which problems to
work ﬁrst. 3. The exam is closed book and notes. Tables are provided. No collaboration with others! 4. Include a sketch, and clearly state assumptions and equations used on problems requiring
detailed analysis. 5. If you get stuck on a problem, go to the next one. 6. Problems must be worked in the unit system in which they are speciﬁed. Failure to do so
will result in a lower score. 7. Assure that you have 12 different pages, including the formula sheet as the last page. AN AGGIE DOES NOT LIE, CHEAT, OR STEAL OR TOLERATE THOSE WHO DO 
_

_
_
—  MEEN 315—Summer 2010, Exam 2 Name Section Number Multiple choice problems worth 2 pts each. Circle the answer that is the most appropriate or
closest (numerically) to your answer. 1. An oven preheating is an example of what type of process? a. Steady State, Steady Flow
b: Isochoric “TevaiCpemture iS chm/19mg
Transient l (J, «,6
® Throttling LU h 2. To increase the COP of a Carnot refrigerator operating between the temperature range TH and
TL you can: ‘
/
W 7 P .. TL 7 H. {z TL I‘
b. Increase Wln C 0 f
.   a ‘ T” I TL
< 3. For steady state, steady ﬂow process: dEcv/dtzo, dmcv/dt:0
b, dEcv/dtCV750, dmcv/dtséO
c. dECV/dt=dw/dt, dmcv/dt=0
d. dECV/dt=0, dmcv/dt=d\y/dt 4. The enthalpy of a substance undergoing a throttling process:
a. Decreases
b. Increases
Q Does not change
(1. Increases by a factor proportional to the kinetic energy gained 5. The following is one of the Carnot principles: a. The efﬁciency of an irreversible heat engine is always more than the efﬁciency of a
reversible one operating between any two reservoirs. b. The efﬁciency of an irreversible heat engine is always more than the efﬁciency of a
reversible one operating between the same two reservoirs. ® The efﬁciency of an irreversible heat engine is always less than the efﬁciency of a H reversible one operating between the same two reservoirs. d. The efﬁciency of an irreversible heat engine is always less than the efficiency of a
reversible one operating between any two reservoirs. 6. A (a) is a device that increases the velocity of a fluid at the
expense of pressure. A (b) is a device that increases the pressure of
a fluid by slowing it down. What words belong in the blanks?
. (a) Compressor (b) Diffuser
{$1 (a) Nozzle (b) Diffuser
(a) Turbine (b) Compressor
d. (a) Nozzle (b) Compressor MEEN 315—Summer 2010, Exam 2 Name Section Number 7. The entropy of steam will (a) as it ﬂows through an actual adiabatic turbine, and the entropy of the working ﬂuid of the ideal Carnot cycle (b) during the isothermal heat addition process. What words belong in the blanks? .T. a g Q (a) Increase (b) Increases 6‘ T b. (a) Decrease (b) Remains the same
c. (a) Remain the same (b) Decreases
d. (a) Increase (b) Decreases {If m s a») 5
8. An ideal gas is contained in a rigid container. The gas undergoes an isothermal process. What
is the entropy change (kJ/K) of the process? 6%? AU’;O 47:0 #9 A510
c. 1.40
d.oo 9. The polytropic constant of an air experiencing an isentropic process is:
a. 0 $140 Pu’K: Constant“
d. 00 
K: 1.11 10. A heat pump absorbs heat from the cold outdoors at 3°C and supplies heat to a house at 20°C
at a rate of 4 kW. If the power consumed by the heat pump is 3kW, the COP of the heat pump IS: a. 0.33 \ @133 L q KM/ 97‘ MEEN 315—Summer 2010, Exam 2 Name Section Number
1. R134a expands in a reversible adiabatic turbine from 200 psi and 200 °F to 10 psia at a rate
of 12 lbm/s. Determine: a. The power output (hp) of the turbine (6 pts).
b. The exit temperature (°F) of the R134a (6 pts).
c. The entropy change (Btu/R) of the process (4 pts)
d. Draw the process on a Ts diagram. Include the numbers found in (b) and (c) (4 pts). \
. I I ' . ‘ I .
Corn rnp:Me=Mw CoEaMﬁM(hriw)
Enifo Pt} Balantel Sf: 56 §{a{‘(’ 5L
" _ b . \
P:_)ooP m " ’11:: 19:9200 P914
376‘ ° '_  O
T: 100°}: 0 W 7" 2‘ 00 F 8f“
= I 3 8 ‘74 ——,6 m ,
') — A ‘
Mom 3’ 01%35 ,% \Vzm (him he) K B‘I‘H «1&6 I AP
( 2 “$83? Isak :( Mg; (139 (W 108 mfgﬂ um; owes W: 5.22 K75 hp MEEN 315—Summer 2010, Exam 2 Name Section Number 2. Air at a pressure of 1.4 MPa, 300 0C is ﬂowing in a pipe. The pipe is connected to a rigid
evacuated tank by a threaded globe valve. The valve is opened and the tank ﬁlls with air until
the pressure in the tank reaches a ﬁnal pressure. Assuming the process takes place
adiabatically, kinetic and potential energies are negligible, and speciﬁc heats are constant,
determine: a. The appropriate simpliﬁcation of conservation of mass (7 pts).
b. The appropriate simpliﬁcation of conservation of energy (7 pts).
c. The ﬁnal temperature (K) of the air in the tank (6 pts). aim; hi 2 ’47th mi i’li :n’lzdL ”7;: W); b; r Li). LPL": J; 71: KT: =(/.4)(573)/< MEEN 315—Summer 2010, Exam 2 Name Section Number 1 3. An uninsulated mixing chamber has two streams of water entering. Steam ¢MPa, 500 °C)
enters at inlet lwith a mass flow rate of 2.0 kg/s. 0.5 kg/s of water (2 MPa, 30 °C) enters at
inlet 2. A single flow exits at point 3. The mixing chamber has a heat loss of300 kW.
Determine: a. A sketch of the system described. Include given information (5 pts). b. The mass flow rate (kg/s) of the exiting stream (5 pts). c. The state of the exiting stream. [If the stream exits as a super heated vapor, use
temperature (°C) and pressure (MPa) to describe the state. If the stream exits as a 2 M 2 2 B phase mixture, use temperature (°C) and quality (%) to describe the state. If the stream
' exits as a subcooled liquid, use temperature (°C) to describe the state.] (10 pts). _ 4:»
[email protected]:300Kw COM: ml+iiflLeﬁq320
930°C . . State! $156.: Pg; rm PS; MEG . :§00°C 7—2300 , KT
. J’ .v : ,. h=39é83 52; h—Iv—vél‘r W77" r9 MEEN BIS—Summer 2010, Exam 2 Name Section Number 4. A power cycle receives 1000 kl of energy by heat transfer from a reservoir at 1200 0C and
discharges energy by heat transfer to a reservoir at 30 0C. Determine:
a. The minimum amount of heat transfer (kJ) to the cold reservoir. (5 pts).
b. The maximum amount of work (kJ) that can be produced by the cycle. (5 pts).
0. The maximum efﬁciency (%) of the cycle (5 pts).
d. The entropy change (kJ/K) of the cold reservoir (5 pts). Q/L _ ’TH ,— [000/57; [#73 K / M/nfE QC TC QC 3 O 3 F QC: 105,70 kr
E) WM: lGOOvQOSJO : 7941,30 KT
c) ’7), Wne‘i' V ,_ 7QLI,30 *loo 5 / QM ’ IOOO f4! 10 MEEN 315—Summer 2010, Exam 2 Name Section Number AP=pgh Pv = RT PV = mRT Pv:([email protected] Weed =V1212R W: [W W=m1Pdv dh=deT 2'71 _ Z ".1” = d121, vx= Vf + x(vgvf) ux = Uf + x(ug — Uf) hx = hf + x(hg — hf) micIx mule/x W 2 If . d5 F = kx (linearspring) SG=p/pH20 du = cvdT h=u+PV X: mvnpur AKEZ‘l—m(V22—Vlz) APEngZZ—Zl)
Inliquirl + mvapar 2 cp =cv +R Q—W+ 282,111,. +V,2/2+gz,) — 27710010 +V02/2+gzo) = dE/dt inlets Guile/s qWZAU+Ake+Ape Q _ W ___:_t(U + KE + PE) Q'WZAU+ AKE+APE fﬁg g 0 Clausius Inequality dS : 5Q/T'"> TdS : du + PdV TdS = dh — VdP
T reversible
V — V V
AS=S§—s§’—I'\’Inp—2 szufornﬂ W=p1V1In—2—forn=1
p1 _ ’7 V1
AS=CPln(T2/T.)Rln(P2/P1)]. P1 _ P11 V1 _ Vrl isentropic, variable
ideal gas,constprop ————— ——— . _
AS=CV In(Tz/T1)+Rln(V1/V1) P2 Prz V2 Vrz properties, ideal gas
As=Cp1n(T2/T1) incompressible p v k
—2 = —1 isentropic, ideal gas
p1 V2
W : QH ' QL Q . 1 (k—1)/k k—l
AS = — heat reserv01r 12 [P2] [V1] 1. . .
— = — = — senlro 1c,1dea] as
T T, p1 v2 P g (QH/QL)rev = TH/TL
COP = QH/Win (heat Tl = Wnet/QH (heat engine, power COP = QL/Win (refrig. systems)
pump) cycle) p V2 Pz'R+I/22’V2 E =ri1e 6mm“ : — + 7 + g2  Aemechw p 2 l +g(ZZ ‘Zl mech mech
onedimensionalﬂow :rh = pVA
IDEAL GAS CONSTANT: Ru: 0.08314 barm3/(kmolK) Ru= 8.314 kJ/(kmolK) Ru= 1.986 Btu/(lbmol°R)
Ru: 1545 ﬁlbf/(lbmol°R) 5Q W W (ke) (ke)
AS = — + S = S ; = a ; = a ; = ‘
ll T l, “c W1“ w “n (ket “d (ket
dSm, Q  . . 
dz : Zi— + iggmmsm — Ugly/smmsau, + ng AS = ($va forresewoir 12 ...
View
Full Document
 Fall '07
 RAMUSSEN

Click to edit the document details