Practice Test 2 Solutions - Thermodynamics I | MET 3401, Exams of Thermodynamics

Download Practice Test 2 Solutions - Thermodynamics I | MET 3401 and more Exams Thermodynamics in PDF only on Docsity! . 3 ve 2ZogS_ Shree PFACTIAL-~ MET3401 KEY Test #2 Spring 2004 DDH Present complete answers with symbols, magnitude, units; in /out, etc. @oe) 1. An adiabatic, insulated vane type positive displacement compressor is used to compress air from 1 bar to 2 bar. The inlet temperature and velocity is 25°C and 15 i/s respectively. The exit temperature and velocity is 360 °C and 90 m/sec. The air mass flow rate is 45 kg/min. 5 a) Draw and label the symbolic system and P-v, T-s diagrams. LO) b) Find the specific work required to compress the air. ‘= 347 = Ne £O)c) Calculate the change in enthalpy, Ah, using average specific heat constants. Ah = 245 4% An=345 oy ASP 40) d) What is the change in enthalpy, Ah in specif inits, using the "air table"? z S e) Find the volumetric flow rate in m/sec at the discharge. ¥ Q=e a ps Fe EC) Calculate the change in entropy, As in specific units, using the “air table" ° <<< "45° EC g) Calculate the As for the process using average specific heat constants. “ e5)2. You have been hired by the Russians to work on the Siberian rail system. Steam turbines are in use. Steam flows through a heavily insulated throttling valve. The valvéis used in Aplin. Tenee nae es turbine. The turbine heat loss is kg. Ignore piping losses. (S) Draw the systems and Pv diagrams. } h 'b) Derive the specific energy equation eee hs=hz 7% What is the turbine inlet enthalpy? = 332Z/k2 = 408) Caloniate the output of the turbingin kW. Wi= 3. eexlo ee +S &c f FindAs for the turbine process steam. =,*7@5— 2 : 45 &e g) Ifthe turbine housing surface temperdinre is steady at 4 518000, fi find the entropy en ae AS = Lela trp GaAs PROCETIN EAB AE AV at Peo oe ra=20 x 10°kg/hr T=4899C TSP Zl Aoianes, i ‘Yat - 2S” 3. Aton of refrigeration is defined as a heat absorption rate of 214 kd/min froma cold source. : It is desired to operate a reversed Carnot cycle between temperature limits of —23 °C and +27 °C sothat 8 tons of refrigeration are produced. S a) Draw and label the Carnot system diagram. WwW = = 20,000 k> 7 >) Find theCOP. = S— ke He 7/2 © Calculate the power required to drive the Carnot compressor. wy = 337. a +/0 EC: ~- a) Draw and label the Carnot system, Pv, and T's diagrams for an air Carnot cycle. b) Describe the processes involved. © What is the total change in entropy for a carnot cycle? Viel D> Bleep ~ | pou 2 Looe, B40/ Yor otins ae - eS 0 PAG? METS19 Pre-Test woek Ei te = 2H Ee ye fete Mb ELLs pies ™", )—sfelod Winter 98 DDH This pre-test is ngt all inclusive. h al = jy gr 1. An adiabatic condenser for a plant power system receives/10-Kg/sec of steam from the turbine. The steam side of the condenser f 0 Pa. The quality of steam entering the condenser is 95 %. The steam condensate is 45 °C. Cooling water is pumped from a near by pond at 20 °C. The cooling water temperature increase is 15 °C. foe oe) Sketch and label system and pv,tv,ts,hs, and or ph process diagrams 4 )) Find the mass flow rate for the cooling water. (ea Find the heat loss from the steam in kJ/kg. —e y? x 2. Aheat engine is used to drive a refrigerator compressor. The units are both ideal machines i 5 "y "a0 9 ator is the same atmosphere at 80 OF. Therefrigerator maintains a cold space at 0 OF ing energy at the rate of 1000 Btwhr. To is 80 OF. The “dead zone” is 80 OF. a) Sketch and label system and pv,tv,ts,hs, and or ph process diagrams. b) Find the energy supply rate for the engine. © What is the cooling tonnage for the refrigerator? @ What assumption did you make about the drive line of engine/compressor? 6) What is the Carnot efficiency for the engine? f) What is the COP for the Carnot refrigerator? gear box has cooling fins which radiate 12 kJ/sec to the atmosphere. The atmosphere is a) Sketch and label system and pv,tv,ts,hs, and or ph process diagrams. b) What is the entropy production rate for the gearbox and the atmosphere? c) Find the entropy change rate for the gearbox if the system includes the gears bearings and oil in the box plus the housing, if the housing temp is 332 °K. The fins are a nominal 332 OK. @ Discuss the increase of Entropy Principle with regards to the gear box. ee le 4. An adiabatic air turbine operating between 3 bars and lbar develops 74 kJ/kg of turbine work. The inlet air temp is 390 °K. (Goa) Sketch and label system and pv,tv,ts,hs, and/or ph process diagrams v b) Find the efficiency using the “air tables” © Find the efficiency. Use the isentropic process equations to find properties. d) Find the efficiency. Use average specific heat information to find properties. v “ & 5. An air compressor operating at a pressure ratio of 1:6 is 82% efficient. The inlet air temp and pressure are 22 OC and .95 bar. The units are well insulated. ~ a) Sketch and label system and pv,tv,ts,hs, and or ph process diagrams ae b) Assuming a vane type compressor (open system), calculate the actual specific work a using average specific heat data from tables. © Assuming a piston cylinder compressor, calculate the actual specific work using average specific heat data from tables. @ Find the actual discharge temp. for the open system compressor. e) Find the actual discharge temp. for the closed system compressor.