What is the net power that a dog with surface area of 0.075 m2 radiates if his emissivity is 0.75, his skin temperature is 315 K, and he is in a room with a temperature of 290 K? The Stefan-Boltzmann constant is 5.67 x 10-8 W/(m2•K4)
A) 9.0 W
B) 6.0 W
C) 8.0 W
D) 15 W
E) 18 W
A
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Calculate the rate of heat loss per foot and the thermal resistance for a 15 cm schedule 40 steel pipe covered with a 7.5 cm thick layer of 85% magnesia. Superheated steam at 150°C flows inside the pipe [ ch = 170 W/(m2 K)] and still air at 16°C is on the outside [ ch = 30 W/(m2 K)].
GIVEN
A 6 in. standard steel pipe covered with 85% magnesia Magnesia thickness = 15 cm=0.15 m Superheated steam at Ts= 150°C flows inside the pipe Surrounding air temperature (T?) = 17°C Heat transfer coefficients
? Inside ( ci h ) = 170 W/(m2 K)
? Outside ( co h ) = 30 W/(m2 K)
FIND
(a) The thermal resistance (R) (b) The rate of heat loss per foot (q/L)
ASSUMPTIONS
Constant thermal conductivity The pipe is made of 1% carbon steel
SKETCH
PROPERTIES AND CONSTANTS
? Inside diameter (Di) = 6.065 in.=0.154 m
? Outside diameter (Do) = 6.625 in.=0.1683 m Thermal Conductivities
? 85% Magnesia (kI) = 0.059 W/(m K) at 20°C
? 1% Carbon steel (ks) = 43 W/(m K) at 20°C
The difference in the Moon's gravitational force on the near and far sides of the Earth produces a(n) ________
Fill in the blank(s) with correct word
A magnifying glass has a focal length of 7.0 cm. What is the angular magnification if the image is viewed by a person having a relaxed eye with the near point of 25 cm?
A) 1.6 B) 2.6 C) 3.6 D) 4.6
As a truck moves away from a person with its horn blowing, the person hears a frequency ______________ than that of the horn
Fill in the blank(s) with correct word