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Unformatted text preview: CHE/ME 109/03 Midterm Exam II, Spring 2004 Name § ‘9 l 09)“ 0V1 Problem I. 30 pts The pentium 4 processor has dimensions of 1.5 cm x 1.5 cm. Given the power output of the
processor is 36W, and counting ONLY ON NATURAL CONVECTION AND RADIATION, do
you expect, under steady state conditions, the surface temperature of the processor to be
closer to 900°C or 10000C? Assume the processor remains intact under these conditions '
and ignore the surface area of the sides of the processor. The orientation of the processor is
horizontal, as shown in the picture. The air temperature surrounding the processor is 20°C, as well as the surrounding surfaces. Show your calculations, guessing the temperature only is worth no credit. For radiation heat transfer, assume 8 = 0.95. ‘looac, mmm ms 4+. T = 880°C = 3345K
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QNﬁS'H EcbzcﬁaAJcha: * ﬁlial 23(45 Son/fact; CROW (000°C, Problem II. A heat sink is attached to the processor from problem I above. The heat sink has the
following dimensions:
Air Heat sink dimensions: 7 evenly spaced ﬁns, 5 cm long and 0.5 cm high in the
vertical direction, and each fin is 1 mm thick. All surfaces are 60°C i
10 pts. IIa. Determine the area for heat transfer. Ignore heat transfer from the bottom side of the heat sink assuming it is attached to a case containing the processor. "3 a?" Agni ALAan 105m XIOOSmX25i‘cUéxlﬁ.’qS r IOOBSML areA o—C .eAjC/S ‘5. E005 X’Z inogﬂool X'7‘QAS : «Lat—M cit/ea >7 cOog Cl W12, Rm: 109%.02/7L‘n52400i 1,000Q5 Problem II continued from previous page. 30 pts. IIb. Determine the minimum velocity of the air to maintain the surfaces at 60°C.
Ignore radiation for the calculation and recall the power of the processor is 36W and the air
temperature is 20°C. State whether the air ﬂow regime is laminar or turbulent and justify your claim.
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The heat sink is at 600C and the velocity of the
air is 0.8 m/s. Fins are 1 mm thick. Ignore Problem IV. I heat transfer from the back (ﬂat) surface of
the heat sink. Ignore radiation heat transfer
for this calculation. ' forced ﬂow ‘ I
of air at 015 m
200C IIIa. 15 pts. Can natural convection heat transfer be ignored for the steadystate heat
transfer analysis of this problem? For forced convection, 6 is the vertical height of the plate. 1:6 : 40% M=0.0ZQLZ R: 0.7254 7/: 1.?ozxzo‘5
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(TE—£72475??? ' (loom/mi héchCi‘ half/L C V1 ‘ IIIb. 15 pts. Determine the total rate of heat transfer from the heat sink. N s (0 {am 12596"; C .9024 (357Z)‘5(,?2§</)’?33 2364,10
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This note was uploaded on 11/08/2010 for the course ME 109 taught by Professor Staff during the Spring '08 term at San Jose State University .
 Spring '08
 Staff

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