A 12-m-long and 5-m-high wall is constructed of two layers of 1 -cm-thick sheetrock ( k = 0.17 W/m .K ) and spaced 16 cm by wood studs ( k = 0.11 W/m .K ) and whose cross section is 16 cm × 5 cm . The studs are placed vertically 60 cm apart, and the space between them is filled with fiberglass insulation ( k = 0.034 W/m .K ) . and The house is maintained at 20°C and the ambient temperature outside is -9°C. Taking the heat transfer coefficients at the inner and outer surfaces of the house to be 8.3 and 34 W/m 2 -K, respectively, determine (a) the thermal resistance of the wall considering a representative section of it and (b) the rate of heat transfer through the wall.
A 12-m-long and 5-m-high wall is constructed of two layers of 1 -cm-thick sheetrock ( k = 0.17 W/m .K ) and spaced 16 cm by wood studs ( k = 0.11 W/m .K ) and whose cross section is 16 cm × 5 cm . The studs are placed vertically 60 cm apart, and the space between them is filled with fiberglass insulation ( k = 0.034 W/m .K ) . and The house is maintained at 20°C and the ambient temperature outside is -9°C. Taking the heat transfer coefficients at the inner and outer surfaces of the house to be 8.3 and 34 W/m 2 -K, respectively, determine (a) the thermal resistance of the wall considering a representative section of it and (b) the rate of heat transfer through the wall.
Solution Summary: The author explains the thermal resistance of the wall.
A 12-m-long and 5-m-high wall is constructed of two layers of 1 -cm-thick sheetrock
(
k
=
0.17
W/m
.K
)
and spaced 16 cm by wood studs
(
k
=
0.11
W/m
.K
)
and whose cross section is
16 cm
×
5 cm
. The studs are placed vertically 60 cm apart, and the space between them is filled with fiberglass insulation
(
k
=
0.034
W/m
.K
)
.
and The house is maintained at 20°C and the ambient temperature outside is -9°C. Taking the heat transfer coefficients at the inner and outer surfaces of the house to be 8.3 and 34 W/m2 -K, respectively, determine (a) the thermal resistance of the wall considering a representative section of it and (b) the rate of heat transfer through the wall.
Problem (17): water flowing in an open channel of a rectangular cross-section with width (b) transitions from a
mild slope to a steep slope (i.e., from subcritical to supercritical flow) with normal water depths of (y₁) and
(y2), respectively.
Given the values of y₁ [m], y₂ [m], and b [m], calculate the discharge in the channel (Q) in [Lit/s].
Givens:
y1 = 4.112 m
y2 =
0.387 m
b = 0.942 m
Answers:
( 1 ) 1880.186 lit/s
( 2 ) 4042.945 lit/s
( 3 ) 2553.11 lit/s
( 4 ) 3130.448 lit/s
Problem (14): A pump is being used to lift water from an underground
tank through a pipe of diameter (d) at discharge (Q). The total head
loss until the pump entrance can be calculated as (h₁ = K[V²/2g]), h
where (V) is the flow velocity in the pipe. The elevation difference
between the pump and tank surface is (h).
Given the values of h [cm], d [cm], and K [-], calculate the maximum
discharge Q [Lit/s] beyond which cavitation would take place at the
pump entrance. Assume Turbulent flow conditions.
Givens:
h = 120.31 cm
d = 14.455 cm
K = 8.976
Q
Answers:
(1) 94.917 lit/s
(2) 49.048 lit/s
( 3 ) 80.722 lit/s
68.588 lit/s
4
Problem (13): A pump is being used to lift water from the bottom
tank to the top tank in a galvanized iron pipe at a discharge (Q).
The length and diameter of the pipe section from the bottom tank
to the pump are (L₁) and (d₁), respectively. The length and
diameter of the pipe section from the pump to the top tank are
(L2) and (d2), respectively.
Given the values of Q [L/s], L₁ [m], d₁ [m], L₂ [m], d₂ [m],
calculate total head loss due to friction (i.e., major loss) in the
pipe (hmajor-loss) in [cm].
Givens:
L₁,d₁
Pump
L₂,d2
오
0.533 lit/s
L1 =
6920.729 m
d1 =
1.065 m
L2 =
70.946 m
d2
0.072 m
Answers:
(1)
3.069 cm
(2) 3.914 cm
( 3 ) 2.519 cm
( 4 ) 1.855 cm
TABLE 8.1
Equivalent Roughness for New Pipes
Pipe
Riveted steel
Concrete
Wood stave
Cast iron
Galvanized iron
Equivalent Roughness, &
Feet
Millimeters
0.003-0.03 0.9-9.0
0.001-0.01 0.3-3.0
0.0006-0.003 0.18-0.9
0.00085
0.26
0.0005
0.15
0.045
0.000005
0.0015
0.0 (smooth) 0.0 (smooth)
Commercial steel or wrought iron 0.00015
Drawn…
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