Ch4solutions - 4-4C Energycan be transferred o or frOO)...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
4-4C Energy can be transferred to or frOO) a control volume as heat. various fOnDS of work. and by mass transport. 4-11 The radiator of a Sleam heating system is initially filled with superheated steam. The valves are closed. and steam is allowed to cool until the pressure drops to a specified value by b"ansferring heat to the room. The amount of heat transfer is to be determined. and the process is to be shown on a P-v diagram. Assumptions 1 The tank is stationary am thus the kinetic and potential energy changes are zero. 2 There are no work interactions. Analysis We take the radiator as the sys~m. This is a closed system since no mass enters or leaves. Noting that the volume of the system is constarc and thus there is no boundary work, the energy balance for this stationary closed system can be expressed as E ill - E 0lIl = fj.E IySICID . ~~~ ~~~ ci llll~ Net ~ --- a-.e a. w.-I. kiIICtic. by hal, work,8nd mass pcxenIIaJ, clc.cnerJies '. -Q. =~U = m(u2 -uJ) (sinceW - KE - PE - 0) . -fz!ouc = DoU = m(U2 -UJ) (SmCe W = KJ:; = Pc - 0) ! QQUI=m(ul-U2) I Using data from the steam tables (Tables A-4 ! through A-6), ". some properties are determined to be p. = 300kPa } VI = O. 7964m 3~g ~ = 250.C UI =2728.7kJ~~ kP V I = 0.001043, v A' = 1.6940m3 /kg P2=100 a~ J U I = 417.3", U Ig = 2088.7kJ/kg I I Noting that VI = V2 and Vr < V2 < VI ' thejmass and the final internal en? becomes VI 0.020m3 1 p m=-= 3=Of251 kg VI 0.7964 m /kg I X2 =~~= 0.7964-0.~1043=0.470 v II 1.6940 - O. 1043 U2 =ul +X2ufg =417.36+ 0.470x2088.7)=1399.0kJ/kg I . Substituting, QOUI =m(ul -U2) = (0.0251 kg)(2728.7 - 399.0) kJ/kg Substituting, = 33.4 kJ
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
, 4-14 An insulated rigid tank is initially filled with a saturated liquid-vapor mixture of water. An electric heater in the tank is turned on, and the entire liquid in the tank is vaporized. The length of time the heater was kept on is to be determined. and the pr<x:ess is to be shown on a P-v diagram. Asswnptions 1 The tank is stationary and thus the kinetic and potential energy changes are zero. 1. The device is well-insulated and thus heat trans&r is negligible. 3 The energy stored in the resistance wires. and the heat transferred to the tank itself is negligible. Analysis We take the contents of the tank as the system. This is a closed system since no mass enters or leaves. Noting that the volume of the system is constant and thus there is no boundary work. the energy balance for this stationary closed system Ca4 be expressed as .. E in - E out = I1E System ~-~ ~-~ Net enCI'IY Ir3RSfer ChInle ia internal. kinetic. by Ileal. .-k. aIM! mass poccnlial. etc. energIeS W"ln =~U =m(u2 -u,) (sinceQ = KE = PE =0) VJJ}J =m(U2 -U,) W~ . The properties of water are (Tables A4 thr~ugh A-6) ~ PI: 100kPa } Vf =0.001043, vJ = 1.694Om3/kg xI = 0.25 U f C 417.36, u.. = 2088.7kJ/kg T vI =vf +x,vfg = 0.001043+ [0.21 x(I.6940-0.001043)]= 0.42428m3/kg UI =Uf +X'"jg = 417.36+(0.25)(2088.7)= 939.5kJ/kg /'" v2 = vI = 0.42428m3!kg } = = 25567kJ/k "2 u ~4 2428 J/k . g sat. vapor ~¥. m I Substituting, (IIOY)(8A)6I = (Skg)(2556. 7 -~9_5) kJ/I,.J~~ ~ ) '~ IkJ/s
Background image of page 2
4.18 A cylinder is initially filled with R-I ~a at a specified state. The refrigerant is cooled at constant
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/13/2011 for the course MMAE EGN3343 taught by Professor Quanfangchen during the Spring '10 term at University of Central Florida.

Page1 / 15

Ch4solutions - 4-4C Energycan be transferred o or frOO)...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online