Midterm Exam 2 Solutions | Thermodynamics | AREN 2110, Exams of Thermodynamics

Download Midterm Exam 2 Solutions | Thermodynamics | AREN 2110 and more Exams Thermodynamics in PDF only on Docsity! AREN 2110 THERMODYNAMICS Midterm Examination I 9 November 2006 Name, Nom, Nombre. PRINT Examination Time is 75 minutes. This examination is open book and open notes Point value for each problem is written next to the problem label in parentheses (e.g. (3)). SCORE 1. (25) 2. (25) 3. (25) 4. (25) x. (100) Ihave read, understand, and agree to abide by the University of Colorado honor code in this test context: Lhave neither given nor received unauthorized assistance during this examination. Signed: AREN 2110 - FALL, 2006 THERMODYNAMICS Midterm Examination I Page I 1. (25 points.) Answer the following by circling the BEST answer. 1) (5) The boundary work associated with a constant volume process is always (a) negative (d) equal to the heat transfer pero (e) equal to the change in internal energy (d) positive (f) equal to the change in enthalpy 2) (5) For an open system, “steady-state” is associated with which unique condition? (a) Mass is conserved (d) The process is adiabatic (b) Energy is conserved (e) Inlet velocity = outlet velocity Coprerey of the control volume does not change with time (f) Inlet temperature = outlet temperature 3) (5) Boundary work can be done by an ideal gas in a closed system in an isothermal process if, and only if (@yine process is not adiabatic (d) the process is adiabatic (b) the process is isobaric (e) the process is isochoric (c) the process is polytropic (f) isothermal process cannot have boundary work 4) (5) The purpose of an adiabatic turbine is to (a) produce work from heat transfer to fluid (d) increase pressure from enthalpy decrease of fluid {b) produce work from evaporation of fluid (@)produce work from enthalpy decrease of fluid {c) reduce the pressure and temperature of fluid (f) produce work from enthalpy increase of fluid 5) (5) An_ideal gas flows through a steady-state adiabatic diffuser. The temperature of the gas MUST (a) remain constant (b) decrease (e) depend on heat loss from the system (c) depend on work done by the system (f} cannot tell from information given AREN 2110 - Fy 2006 THERMODYNAMICS Midterm Examination II Page 4 3. (continued) d) (3) What is the mass of liquid at the end of the process in kg? M=(- x) mM, = 05 (35-44) [INT ky | e) (5) If this process were carried out at constant volume, how much heat (kJ) would have to be removed to condense half the R- 1344? 47 eM = 0, O4IOF “hy Q- i = AUF m (u,- -4) Pouch thet; (A-tz if ee igs “ per) a — (utas-ws7\iy = Upt Y= 0.0282/ mika U = 256.374%, dks oe. Cen kea, Wi Bt * 20. cutee 02731) | W = —35 106 k3s7 = 0602921 My tg 0+ Sg FUE )aopy n= BrS(ISH 0B) 1154 = leh “h, 4, (25 points) The pressure of air is increased froft 150KkPa to 600 kPa in an adiabatic compressor operating at steady state with 25 kw power from the motor. The inlet air flow rate is 6 n?/min and inlet air temperature is 40 °C. a) (10) What is the temperature of the air at the compressor outlet? Neglect kinetic energy change. free ZY B-hambch)=n a7) m=/50h% OM, . —(-25 bn 2 O16 Tky h00sks (7 ¥0 eat (23) Wty Oty ’ 3 bk CF d) ote / 17184 E\EM2k) b) (5) What is the volumetric flowrate at the compressor outlet? V, eM = “RE = 0.1oTk, oeerkr (York 2 “ZF 2 G00 Ke. Min min =| 0.037 xs =)2.2 m? jo" 3 AREN 2110 — FALL, 2006 THERMODYNAMICS Midterm Examination Il Page 5 4. (continued) The compressed air now flows into an adiabatic nozzle where the velocity is increased from 4 m/s at the inlet to 100 m/s at the outlet and the pressure decreases from 600 kPa to 250 kPa. ce) (5) What is the temperature of the air as it exits the nozzle? | g ¥: TH (Nah * ©) Gt Gar") - On (ET) Ve ) =/. So ee 2000 se OO, - = G1) S508 Io -/0000 — /,02 (7, 189) 2Zooo T, = 184 & = A5TK d) (5) What is the ratio of the inlet area to the outlet area for the nozzle (Ay/A2)? PUA Hp UAL (of Avopa\e hrm fe |X EN \ =< | os) 7 AT