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# solution2 - A composite wall is composed of two layers as...

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Unformatted text preview: A composite wall is composed of two layers as shown below. One layer whose thermal conductivity is 1.0 W/m 0C has a thickness of 30 cm. Another layer, 5 cm in thickness, which provides insulation to the wall, has the thermal conductivity of 0.05 W/m K. One side of the composite wall is exposed to air at 20°C with convection heat transfer coefﬁcient of 4.0 W/m 2 “C. The other side is exposed to air at 0°C with h z 6.0 W/m 2 0C. (1) Calculate the steady-state heat transfer rate per unit area through the composite wall. (2) If there were no insulating layer, what would be the steady-state heat transfer rate through the wall? £16.05 h=4W/rnz°C h:6W/m2°C Airat0°C Airat20°C Cl) S‘iﬁaria q” _ AT *— __ _7-ws—O ‘7 — —t—+£ﬁ)+'ﬂl)+_j_ " _I_+i<=i +ms "T he KA Lian ha + l 217;“; 7“ H ‘3‘ W/Mz. Q a.) “Ji'Hﬂ’er THSmG—a‘f'rvtcx' Layer. Br, (3T LO _ \ AI' _ “R ‘—" _ + ——- -—-l— _l 0.3 h; KJA+ inc 4+ + T + 4g Two separate experiments are performed on a small refrigerator. The refrigerator is placed in ambient air at 20°C. In one experiment, an electrical heater is suspended inside the refrigerator cavity with the door closed, while the reﬁigerator is unplugged. With the heater dissipating 20 W, a steady-state temperature of 90°C is recorded within the cavity. With the heater removed and the refrigerator now in operation, the second experiment involves maintaining a steady-state cavity temperature of 5°C for a ﬁxed time interval and recording the electrical energy consumption. In such an experiment, the input electrical energy is 125 kJ over 12—hour period. Determine the refrigerator’s coefﬁcient of performance (COP). First E‘q‘rtrlwcnf 71.,_ ,,,_ _,_. i T”: ao'(_ i 90 c, I mg l Zr i a. __,.,l inﬁlog Fir-52. l i l' w» FT“ “Dire we _ ‘ {go-«r A {"‘7‘ '“ p—ﬁ ._ H —7 H— J 3.“ : oACrs-r) _ 2 ‘ 7 < 1°45) 3"“ : gnvf Q94 7-: E‘s—t At 2 iii—c—S)x(l?_xggno) : “gs-gag J‘ : Qatar : lESca: : \ an 12.50:; ' ...
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