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Unformatted text preview: ME 114 Homework Assignment 3
Due February 14, 2008 temperature of the furnace is estimated to be 1100 “C. The outer surfacebis exposed
to air at 30 “C with a convective heat transfer coefﬁcient of 10 tha1 “C. Estimate
the heat ﬂux across the wall and the temperature of the outer surface. 0) A boiler furnace is constructed with SOD-mm thick ﬁreclay brick. The inner surface In an experiment, an electrical heater is sandwiched between We stainless steel 7 - (type 347) plates. each ED—crn wide, 20-crn high, and l-ctn thick Air at 20 “C ﬂows
J f the inner surfaces of the
over the outer surfaces of the plates. The temperature o plate (adjacent to the heater) is 80 "C. If the power input to the heater'is 96 W".
determine the convective heat transfer coefﬁcient on the air side assuming that 1t is the same on hath sides; Insulated edges _Heati.ng element The inside diameter of a ﬁreplace chimney is 200 mm and made of very thin sheet @ steel (negligible conduction resistance) covered with 8-113m thick insulation mate-
rial (k = 0.05 With K). The outer surface of the chimney is exposed to air at — 10 “C
with a convective heat transfer coefﬁcient of 7 )anr1 “C. The convective heat transfer
coefﬁcient on the inside surface is 20 With1 “C. To avoid condensation, the inner
surface temperature should he more than 50 “C. What should he the minimum tern-
peraturecf the gases in the chhnney? Insulation Air at -10 ='C
h = 7 Wire2 “C rescue Hot gases Two 5-cm-diameter, 15-cm-long aluminum hers
(I: = 176 Wire - °C) with ground surfaces are pressed against
each other with a pressure of 20 aim. The bars are enclosed in .
an insulation sleeve andI thus, heat transfer from the lateral sur- ;
faces is negligible. If the top and bottom surfaces of the two- 5
bar system are maintained at temperatures of 150°C and 20°C, L
respectively. determine (a) the rate of heat transfer along the ‘
cylinders under steady conditions and (b) the temperature drop
at the interface. Answers: (a) 142.4 W. (b) 6.4“C A 4—m—high and 6-m—wide wall consists of along 3D—cm cross section of horizontal bricks (k = 0.72 ern separated by 3—ern-thiclt plaster layers (it = 0.22 Wire - There are also Z—cm-thick plaster layers on each side of the Will;
and a 2—om—thiclt rigid foam (it = 0.026 W/rn ‘ “C) on the
side of the wall. The indoor and the outdoor temperatures:
22°C and —4°C, and the convection heat transfer coefﬁcientségll
the inner and the outer sides are h, = 10 Vii/1nI - °C h1 = 20 W/m1 - “c. respectively. Assuming one-dimensionalhg " ulna- ” far and disrecrarding radiation d .
fer through m: wan. . etermme the rate of heat ...
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This homework help was uploaded on 04/15/2008 for the course ME 114 taught by Professor Okamoto during the Spring '08 term at San Jose State University .
- Spring '08
- Heat Transfer