q2_soln - ME 2124 — Introduction to Thermal-Fluid...

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Unformatted text preview: ME 2124 — Introduction to Thermal-Fluid Engineering Name: Quiz 2 ~ Sept 22, 2011 Piedged: This quiz consists of 3 problems worth 30 or 35 points each for a total of 100 points. The quiz is closed book and closed notes. Some usequ information. is given below. You will have 50 minutes to complete this quiz. PLEASE DO NOT OPEN THE QUIZ UNTIL YOU ARE ASKED TO DO SO. Units/Conversions: “019; 273.15 to 0°12 :- 459.67 R Ta=12in iN=1kg*m/sz 1 lbf 232.174 mire/s1 1 Pa :5 firmwareWWW-Wan 1 mi = 5280 a " “ET m r @3333“; 000 kg*m2/s:)' 1 ft3 = 7.481 gallons rrrrfifimttjbo liters ““““ "WWW lininfléos Ihr=60 min Si Prefixes: Mega 1,009,000 K110 1000 Centi 1/100 Milli 1/1000 m “"er W “(367’ ' {W 5 Erie-“~15; Constants, properties, and formulas: Earth gravity g 2 = 32.17 ft/s2 AmuM—w wmw‘wih Universal gas constantly—2 1545 ft*lbf/(lbrnol*R) m 1.986 Btu/(Ibmol*R) RAWWMWWM P 2 FM PABS : Pyiiiiwflmr TABS m T SCALE ZERO + TRELA TIME“ 12 : Wm : 1/ p m : nM if MMMM WW _ g _ M Ideal gas: {Efigm 1:23;: HRT 2.3 m R f M Incompressible: v = coagmm Newwww g _ ,_MK m#iiMu““w'_'_'m"”'m-—‘A‘Hum—-MH"....mHm_m~“nWW-Mwwnmw'wmw'm " wvah--_...M Molar masses M: CO 1“ 28 kg/kmol, H2 2 2kg/kméll In“, My ‘ w w “M WNWMWW “mm-mm mWN—MM,WWMM.M.«u.u: WW“ 4 v “w MM wwmmuwm. w—WWMM—lmm - v-W-m- W“ m x I Work for a polytropic process (pi/1 = constant) W = (P; V; — P1V1)/(l— n); : mR(T3 — T1)/(1m 1:) Work for a constant-temperature process in an ideal gas W: P1 V; 111(V2/V1) 2 --b j; V132 -— 451C Forax +bx+c=0, XZT Please ask the instructor for any other constants, properties, or conversionfactors you need. Problem 1. {35 pts.) // / _/ Two closed, rigid tanks containing carbon monoxide (CO) and g H 335K hydrogen (H2) respectively and are in contact so that energy may L be exchanged Except at the interface, the tanks are well I” insulated from the environment. The tank of CO has an initial a", V = 2m3 temperature of 600K, pressure of 200 kPa and voiurne of 2.0 m3. ‘ t The hydrogen tank has an initiai temperature of 400K, pressure f of 300 kPa and volume of 1.0 In}. The two tanks eventualiy reach a” mutual stable equilibrium. .2” Lb pt: zaokPa a) Write an energy balance that includes the initial and final states of the tanks b) Find the finai temperature of the gas in the tanks The attached table may provide useful information. AH relevant values should be taken at TESOOK and are considered to be constant over the temperature range of interest. f t i ‘ r4 “7' .[ibl W2 ft with"? i anoint" qggumfitlm; 2 Miami gas I w was"? fit {TIME woe} (2'2ng item's: P” Hi“ J TE ) " {ital : (M55? ‘ {3 mile, at F l 0 flex a \ . ‘. ' i“ ' mg) Lian-65g mgrgk..&fi J i J; 4;" t: it or .. ‘_ i 3 n I l giggmgfi mg, sifgiECieEgywfig' will)“; swath“ Angeli”? the gangé’; tit/tav- g: n; EM F- arm. ma. MEL Wig; Quilt-“t itti i [will mi’sé'w‘iiit a (rm “we {if :fii} % fig}? 53.1,; K Wit" ‘le fit like Wt- fi EQ’: r; mg rant -- (“if We; Mr; :13: 1,1 S if L Milw- Jr ML '2 I {/7 fat; grim R a 91k 3‘03 s.) M um [at fwlmf'h' at?“ 3 iii Wit. WW i t \ g} 4: f K F r 78% r w 2 . at * Jean w} tafitmt i - QST’SC “ gyijéé'gfiy'wiwi {in} a M”, M}: “we-"WW 9 —_~ “““““““““““““““““““““ " [@333 Ta x i1 an W 5 a; If“ a; r it 9 is; The; (E hm: : (1 téifl}: it} 8% 5g Problem 2 {30 fits.) A thermodynamic machine operates on the ogrele 1—>2—>3—>4—>1 shown below. Process Work Out {— Heat Transfer In 1—>2 0 - 0 Decreasing, L100 _> 550 R 4->1 0 Constant, 550 R a) What is the work for process 3—)4? b) is the machine a heat engine or a refrigeration machine? Explain your answer. (2) If the machine is a heat engine, what is its thermal efficiency? If it is a refrigerator, what is its Coefficient of Performance? i}:- fifijjfir k! 51;) a i 1; L156.” £15.25 ‘1: M . ‘ I “I m “at ”"" Vt} ' » 1:1: he} v ’23 (t 5‘ “““ " We rig r “a a a hi . .. «A v A: Ekifiiwfi 01.)} a flu. s ‘2: .5- W! we, a at I 049E} Ag g GEM} “i my I w W t it t- "? We? ' an; 1‘ t " km «1;. a i , . {'3 trier: r af’éwe e W {WW "M “W? new raw ‘_ s b} Wca‘ a w i ~ N W ‘ .-. 5:“? 5313 {i 1% - . m 4:- m" ageing) “ft E f" C? 57‘ :7? 16 —; WWW“- m MI W; U > M Q W1 yet 6:, t a w a»: 9 e as if eerie? g9 Q Milw- fl few we,” , 1a wig} 3 M mg? if (:2 anti Problem 3 £35 pts.! 024 The specific heat, C\. of an ideal gas (gas constant R = 0.257 kJ/(1<g*K)) is shown 1n the figure at right- How much energy does It Dtake to warm 0.22 a system containmg 3.0 kg of the gas from 25.0 C to 75.0 C? CV a. Assume that eV is constant and is determined from the average of :JiK 0.20 the cv values for the beginning and ending temperatures. 0.18 b. Take into account variations in c... Now assume that for the given temperature change, a poiytropic work interaction takes place on a system containing 3.0 kg of the gas, that is described by pV”= const, where n = 0.5. 0. Write the resulting energy balance for the system. (1. Use the result for part a. or b. and determine the vaiues of Q and W for the work and heat interactions. ;- '5 a; . 1... a" "h r “if,” . > . 9 a firm " " it? a?” “‘ W 5%. 5- mm 50%: <5. 3, i (Jitter q r} flEEMeJHB W ..:~ :5 ~ “in 5" t " " 5 . r . . .w tr“, Kw!" L 4 \3 'f - qu- . i e i . m it“ 3” ire e’i it “i W m £5 a t ‘3 ~- " f'fit.i::..;...2fi ...... f3: .... .3215 t 2:: “.Linmig its . Tables in SI Units Ideat Gas Specific Heats of Some Comman Gases (kl/kg - K) ........................... a P 5 k 5,, 0. k F 5,. 6,. k Temp " Temp. Air Nitrogen, N2 Oxygen, (:2 K 1.003 “0.716 “II-1.401 . 1.0.39 I 0.742 1.400 - 0.913 . 0.653 _ 1.398 s- ' 300 1.005 0.718 1.400 - 1.039 0.743 1.400 0.918 0.658 r1395 300 350 15.008 0.721 - 1.398 1.04-1__ .0.-744,_-1.39_9_- ' 0:928 . 0.668 -- 1.389 350- 400 1.013 0.726 I 1.395 1.044 0.747 1.397 0.941 0.681 1.382 400 450 1.020 0.733 1.391 1.049 0.752 1.395 0.956 0.696 1.373 450 500 1.029 0.742 E 1.387 1.056 0.759 1.391 0.972 0.712 g 1.365 500 550' 1940' 0753' i; 1.33.1 . 1.065 600 1.051 0.764 ;_ 1.37.6 : 1.075" ;_ 650. - 1.063 01776 _:.1.3-7'0_: _11.086-;-- '- 700 1.075 0.788 1.364 1.098 750 1.087 0.800 1.359 1.110 800 1.099 0.812 5 1.354 a 1.121 1.121. a - 13.44:: . 1.112 0-855- . . . '- 6 Temp. Carbon Carbon Temp. K Dioxide, C02 Monaxide, t0 Hydrogen, 82 K I. 250' ' 0.791" ._ 0:602 -' 1.314 _’-'-.-I-"1.03'9- . 0.743 1' 250 300 0.846 _ 0.657 1.288 11040 0.744 300 :359. 0.8.95. '. 9.709. _ 1.2.68 _.;..._1'-.043... £19746; _ . 355 400 0.939 0.750 1.252 1.047 r 0.751- 1395 14.476 10.352 1.398 a 400 450 0-978 0-790 1-239 450 500 E 1.014 0.825 1.229 .4 500 . 550 1.046 _ 0.857 1.220 550 :600 , 1.075 _: 0.886 1.213 600' ': .659 1:102. i 0.91.3 2.29.7 .650 700 A 1.126 0.937 1.202 700 750 1-148 0.959 1.197 750 800 1,169 0.980 1.193 800 900 1.204 1.015 ' 1:186 ' -' " 1' " ' ' 4 900 10.00 15.234 1.045 ' 1118.1 1000' .aaal- 1 1.5:: "1:: W Source: Adapted from K. Wark, Thermodynamics, 4th 00., McGraw-Hill, New York. 1983, as based on “Tables of Thermal Properties of Gases,” NBS Circular 564, 1955. ...
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This note was uploaded on 10/05/2011 for the course ME 2124 taught by Professor Uzgoren during the Spring '08 term at Virginia Tech.

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q2_soln - ME 2124 — Introduction to Thermal-Fluid...

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