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Exam2_Spring2004

Exam2_Spring2004 - 1 A piston-cylinder device with a set of...

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Unformatted text preview: 1. A piston-cylinder device, with a set of stops on the top, initially contains 3 kg of air at - 200 We and 27 C which supports the piston. Heat is now transferred to the air, and the piston rises slowly until it hits the stops, at which point the volume is twice the initial volume. More heat is transferred until the pressure inside the cylinder also doubles. Determine the work done by the air and the amount of heat transfer for this process neglecting friction. Also, show the process on a P—v diagram. (36 points). Use formal problem solving procedure or lose points. vcmu:m,f,t,ec%=e,gna i t\ [FM/b: W161 FOR P205353; figurtpnam (L‘Wféfi SPEECH j awrfiawuakwo Harm 9 K: it J m At; my]; as) mfic-MMV (Aitté'r APE :0) WW Eons: Q‘W': AE': =AU+A$Z 4A}? F’V =mRT swag" fresher ‘ // HUM 1- 1 £5); W : ngdV 12PM; P/x/ PG! Sims If H'EKE WE" fv’Awm‘Zfi, ”cg—U) ~73 Hub 633 TABLE. or? L8, = Elem tarp/p? (3i 3,0“: T” PM) Lis W ”we“ E ‘; T2: Sci: 73, MW Imam: “fad/r M' a} do?) ® i ? v a P 2 V- ,i w ;;.: 3g =Zliinfic¢faswum Tl T3 T3 T‘ 2. Circle the correct answer on each of the following questions. (28 points; 7 points each). There will be no partial credit, but you must show allworkf rf ll r a. A fixed mass m of an ideal gas at a temperature T expands isothermally The amount of heat added to the gas is given by Q=£ Massive 0/ mRT(V2/V1) PTln(Vin/‘1ZZ,( ,' ) 6:91]: (:er v“ ‘ (VW T T NE? W _ , nflTlhiVWflz 1 we jay: NJ 5:, wet/97%: P(V2-V1) b. A closed system consisting of a mass of 10 kg of a substance is heated by adding 10 k] of heat to the System. The system‘s specific internal energy increases by 0.5 kJ/kg. How much work (in U) does the system per-fez? (.3 — W: [AL/4» Afgw‘l' i) -15kJ ii) -5kJ (a W”:- (.32 -5. re An iii 10 kJ xiii-i _ ' fl) 51:1 2 - '2 (0 * ”(03> ' 15k] :- grit-1‘ c. A steady flow of nitrogen gas in a constant diameter pipe experiences a decrease of temperature from 500 K to 400 K due to heat loss and a decrease of pressure from 5 bars to 4.5 bars due to fi'iction. What happens to the velocity of the nitrogen? 111) iv) A 5A2. 7/“, V, /4 591/846— fit/3e increases ,3 7r .1 ‘ . decreases he]; Ff: 535* i r. E; :3; - 41:; 3:3! remains the same 7“; 772. ?- F’. j 2. g ‘an can’ttell V 2",? .2174?) scribe if”? , Verl/r 11. Liquid water passes through a horizontal, isothermal, adiabatic nozzle What happens to the pressure of the water? 111) iv) _ 1.1:“ Ida. increases :hl [1,... L» I. decreases remains the same . it}. {3250:291- can’t tell ‘ 4'" $657- f) ’21-'09, #3) 3' V9,, , a.) F) a} [:1 T i...— 3. A homeowner has devised a humidifier that is shown below. Water is taken from the faucet and fed to a reservoir that incorporates an electric resistance heater. The reservoir is shaped like a nozzle so that a high velocity of vapor will be ejected and distributed to the room. Water enters the reservoir thmugh a hose having a diameter of 5 mm and has a temperature of 20 C, a pressure of 100 kPa, and a volume flow rate of 1 liter per hour. Saturated water vapor at 100 kPa leaves the top of the device through a 20 mm diameter circular opening. a) Estimate the electrical power input required to operate the device at these conditions and b) Calculate the ratio of the change in the fluid’s kinetic energy to its change in enthalpy. On this basis, state whether or not it is reasonable to neglect kinetic energy differences. You can neglect heat transfer between the reservoir and the room and changes . in potential energy. (36 points). Use formal problem solving procedure or lose points. ' ll '45? «II;I '9 I: ‘ In‘ @140“ V; “2‘8“??? 7’ l 1’ " A1 (3: Sem/ Saturated Vapor / 9/ _: la'aj/_ ”9r 4r M 100 kPa assess: 62:0 j @ fine.- a W, Weill/(why - .. u—ul-I-I'H-I. WSBUWat/g I SEF; Apia-0! 43:63 ; at? . ‘ Cor 8,452:— tr‘avs; may jfm ~ 1;; dd 0 we 'I :52.- 19 “3:55 ' 3m 5150 20c 100 kPa WM" . 1 ~ ‘ - . . ’ _# at r M r: M ‘ fif—W+"§M€;eé/M:d / ,? I '1' z a“ 0 " . ’4‘ ,4 -(v M, ._ f —W+m , 29+ ”1-31..” «+th . :2: _ . 2]” Edwflmf/ .4 ,, , 5%? .’ M: _’.=: __d,_..._._3_ :- _ ”r:? v: “J '3" W ' l 1": ofidiavjim’flé '2 €4.66 % / Ll ‘7‘2E92ac. 0’0“” msfl/‘j: ' 17- . Was: 4—? .,_ 9:394 + (ooomzfljamfl‘fi? [44/] : grade: Kf/ky - - l7; 1" Aymara? 2‘75”“; £447 5 V1 :1 ”:1 F2”; :' ' ._ 4—: 3 2 "2g jgfllm/EPRW Adz“? “/4; Ft; . ‘ 4% VLH-fiw Am : 0.72% [(W‘ W : “0.73m: m7 0 . 00m 215?“! .W I h V.l‘6+‘/D (ii? 575%") 4-7 . , hé’fd’i/fi/Zé ...
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