Solutions to Exam 3

# Solutions to Exam 3 - Please! Be neat, write out equations...

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Unformatted text preview: Please! Be neat, write out equations before inserting numbers, and circle your answers. If you cannot ﬁgure out one part, assume an answer and carry it through the other parts. 32, A vow . . . . . 1. ( A) AW at 1000 pSIa, and 900°F enters an adiabatic throttle valve With a mass ﬂow rate of 30 lbm/s and undergoes a throttling process to 900 psia. After the valve 15% of the ﬂow is withdrawn and passes through an adiabatic nozzle. The exit conditions from the nozzle are 30 psia and GT. The rest of the ﬂuid enters a turbine, through which it expands adiabatically. At the exit of the turbine, the ﬂuid pressure is 200 psia. The turbine efﬁciency is 85%. Consider potential and kinetic energy effects to be negligible. a) WWW determine the power output of the turbine (BTU/s). b) What is the change in speciﬁc entropy across the nozzle for the argon (BTU/Ibm °R) and the rate of entropy generation for the entire system? c) Qualitativer sketch the process from before the valve through the turbine on a T-s diagram (no numbers needed). ' C/a’o IN" 1 9607.— 2 Turbine K- r d (,3, I. _,, (/ —. "'(( L W “y 14 / Ojngfk; iji' L“ (9: ‘27 Tut/1’ A“: "T n1?) 35 H L j 2/ ’ 9+ i I 7; Ii 5 ./5/30)[Cr1» it ~21 ;;]+,gs(3y[c,,11ff,¢, F] T. 30 835 _ zro : Jamm .0501" ,2; mst '22? [xi /"/—' 5 : "5W'M’J’rts/S/aoM-oz‘j a) v, a W 302*: 2. (33%) The piston/c inder device sh wn below contains 1.5 kg of water and is connected to a source of high temperat e heat which c be considered a reversible heat transfer reservoir. It can also lose heat to the surroundings whic are at 20°C, 101 kPa, also a reversible heat transfer reservoir. The pist% NO frictio less; it tends to stick to the walls of the cylinder, but moves if the pressure is kPa The w ter starts out at State 1 at 150°C and a quality of 0.90. There is then heat transfer su h that A 0 M of heat are transferred to the cylinder from the high temperature reservoir which is t 1000°C. At the same time 200 kJ of heat is lost to the surroundings. During this process k] of rk is done. If the piston is raised far enough it hits stops at which point the volume would 3. The drawing is not to scale in terms of volumes. a) Does the piston hit the stops? What is the ﬁnal pressure (kPa)? b) What is the ﬁnal temperatureWnd if it is saturated, the quality? c) Find the entropy generation for the processw/ #7 o q y 777/1ij (1) Draw a qualitative P-V diagram for the process. 'Aeb-Draw‘a—quahtatrve-Fs-chagram—fer—thepmcess. w‘ i if 1000°C (May) enJWL‘ :33? H‘T'Resew- 3 Surroundings at ' ' 20°C,]01kPa j 75 ’7 77 , : . +« qugq/‘g v ' 3 § [4* a) ’24” 7/L+X‘UW .oo/oq q! : (,{Lf X, (1“): é3/.?+.7{/4279}: 2355315: Problem 2 continued 5y5+€mi Hz (7 W17) Won-d) = C? ~1A/ /,5{u2~ 2366.?) < 7193—2491, — X0 LZC‘M} jw/oor/sza/ L ———- 5: S r x 5W; A2347” .7/"4ﬂ‘76c7J': Q. 332/ Hm I L I ' - Tabl. /Z§ : "I 19’ ’ In 5: £3543? W 4, WW Jrfz' ’ baﬁdid/um ___/._— 5%; [3/6153 4,33? - mg 273 3/7' g on [730% Aaqul/O/Ume Co/CW/éfrm , L 5 P C X‘ W“ p ‘1’, ‘ ax) L Loo , J 1/; w , a / imﬁ'a/ rzWa/ a! 2’53 I“ 50 I 50°C 6‘ Z) 3 5%) A car tire contains 0.5 kg of pure nitrogen N2. Initially the N2 has a temperatéreof /5 7“ ﬁnd a gauge pressure of 200 kPa. Sitting in the sun, the N2 in the tire warms tQQV/fhe \ me of the tire can be considered constant. Some of the N2 is then quickly bled frOm the tire though its valve until the gauge pressure is 100 kPa; again, the tire volume can be considered co . This ha ns fast enou that the rocess can be considered adi bat' . The nitro en kn Jamar}; ppe gh p K [5: g ,1) t , 'can be considered to have variable specific heat. Aft ' ‘ ﬁﬁ 1" / IL, ‘ A a) What is pressure in the tire aﬁer the heating (kPa)? ‘ 7 ,1 a b) How much heat was transferred to the N2 (km/yo [1,44 (V f _” c) What is the temperature of the N2 after the bleeding process (k1)? d) /W hat is the difference in total entropy of the N2 between the initial (State 1) and ﬁnal {state (StateQ)? > 514.1: I L <) 4% I) (Xi—alitatively sketch a T-s diagram. Show and label the State end points (1, 2 & 3). [elm/(24% L‘W 4a) 9 z? a?" a f:- a“ F: :‘_ =7 J'ZE I l a E : 32mm 7 /)/\;¥fM'/U’L # L ., ) ;)1/L/;M,)= ‘W (3/ 74K)‘ 72/4) : \‘ :/ - ' 5/," A {g 4 _ a [deal 90 I 1 5w“ “PW/f l< 15 ﬁrm/Wm : V 7L0 ’ \[rm ZIr/ aria/M k? 0" f) ﬁlmy) .> DWI Pg s+ 4/ -1 :v‘VOB / ’ {6.724; 43405 ' {2’3" X” 2/ K 2e 6 a»; 5':[§7"5o)~3_755) “M £7] Problem 3 continued 5 0 T 50 25 7 ...
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## This note was uploaded on 01/27/2012 for the course ME 326 taught by Professor Schmidt during the Fall '07 term at University of Texas at Austin.

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Solutions to Exam 3 - Please! Be neat, write out equations...

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