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Unformatted text preview: ME201 Exam 2 March 28, 2008
SO (WWW
Name: Student No. Instructions
1. There are three problems. Allocate your time and eﬂort to maximize your points.
2. Layout your work clearly and show your reasoning. 3. This is an openbook (Text Book) examination. One 8%x11 paper allowed. Problem 1 (30 points) A Carnot refrigerator operates in a kitchen in which the temperature is 25 ° C. The refrigerator consumers 600 Watts of power and has a COP of 12.0. Determine (a) the rate of heat removal from the refrigerated space, (10 points) (b) the temperature of the refrigerated space. (10 points) (0) Is it possible to develop (i) an actual and (ii) a reversible refrigeration cycle that has a
higher COP than a Carnot refrigeration cycle operating between the same temperature \Z_.\)(U'V\M‘ limits? Explain. (10 points)
T =25°° Co "
H Wi\m:éOOW
TH =25‘t27 322.98 K a} ’
i§t> \ = a“
)3" WM . WM
__ 0{L=IZ><600=7200 (Tl/S) =7\2\<%
‘Zafr‘i Lelﬂdl'd Lb ) a o g .
gimp, CQH : 51], ‘i'Wam (TM 'g‘L'WJ) 9 QH :: 7200+600 =7300[O]g);7.f 1%
SW02, +1412, l’efrtaﬂmﬁf RS 0m Fefﬁ'jem We hem/é fill a Ii gr: 7290 x27?
. _ 1,
at. ‘E 70”” (\t/l W V/o/Mc‘lmn afrw A—ecmol Wearf
Wmhfmmbs. Problem 2 (35 points) 2(a) Will the temperature of air rise as it is compressed by an adiabatic compressor? Why? (5
points) Yes, ﬁg W9$W+W We m9 Wlééé {57/ out WWW; W77699W~ 2(b) Air enters a compressor operating at steady state with a mass ﬂow rate of 0.72 kg/s at a pressure of 100 kPa, and a velocity of 6 m/s through an inlet with an area of 0.1 m2. At
the exit, the pressure is 700 kPa, the temperature is 450 K, and the velocity is 20 m/s. The
power consumed by the compressor is 125 kW. Determine (i) the air temperature at the inlet. (15 points) (ii) the rate of heat transfer during the compression process and the direction of the
v a heat transfer. (15 points) v.5 WM =123‘kv\/) R=0,287%.k «A: m é '3
VJ: L :2 _,.2L_.— ;o\&333{%?) WC 0‘72
Woﬁ ’ R 3 macaw “270 CK). \JU Tm, [ﬁlm/v 1C1” Ma CV (WM/fwssw) I 1
Cir“ 4!”th : VCA (Le—I LL: 2— T“
@m=~wM+&mww+V¥A4). ’2,» firm Twe Ail? \3 r :2 M“
T), Z€DK >A0 90‘ g
—» m __>Ae=4s~w€zg )6:
’ a . J H 629“: .425 +072 (451} ~Z‘io.le + Zﬂﬂc) = may _(¥%) Problems 3 (35 points) 3(a) A pistoncylinder device contains 2 kg saturated vapor water at 2.0 MPa. Heat is then
rejected from the cylinder at constant pressure to the surroundings until the total volume
decreases by 50 percent. The temperature of the surroundings is 20 ° C. Determine (i) the amount of the heat loss to the surroundings, (15 points)
(ii) the entropy change of the system during this process, (10 points)
(iii)the entropy change of the surroundings during this process. (5 points) 3(b) Is it possible for the entropy change of a closed system to be less than zero during an
irreversible process? Explain ([5 points). Yes, 1+ .‘s 055M163 ‘, 5 w/L M 38.
low) a ewes +m+o+vt WWW get/\P/m'i'fm 1‘s reach»; "How gee/o 3Q). KW‘ mglkgﬂ wfo—r Mirna/van:wa Proceigj @ Frm:ﬁ:2\0MPﬂ f3 h,=— 27%:‘3‘4;éj/ “5 = (1%?» “9 WWW, :>,X= (Uz’fo‘Zt/E g 0.04‘roar—0w01C77
L VEMk’wa 0°07?f&7’0\00l{77 =0+W+ Lm: AW; TWL’WMJ 709‘LF77L0‘LFWF X W7“?
:/942 fkﬂg> 82‘; +K><7I y3'0072‘. , 4h 35?5'@%‘ K) ...
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