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PROBLEM 4.29
KNOWN:
Dimensions and thermal conductivity of concrete duct.
Convection conditions of ambient
ir.
Inlet temperature of water flow through the duct.
a
FIND:
(a) Heat loss per duct length near inlet, (b) Minimum allowable flow rate corresponding to
aximum allowable temperature rise of water.
m
SCHEMATIC:
ASSUMPTIONS:
(1) Steady state, (2) Negligible waterside convection resistance, pipe wall
conduction resistance, and pipe/concrete contact resistance (temperature at inner surface of concrete
corresponds to that of water), (3) Constant properties, (4) Negligible flow work and kinetic and
otential energy changes.
p
A
NALYSIS:
(a) From the thermal circuit, the heat loss per unit length near the entrance is
()
ii
conv
cond 2D
TT
q
ln 1.08w / D
RR
1
2k
h4
w
π
∞∞
−−
′
==
′′
+
+
where
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This note was uploaded on 12/07/2010 for the course MAE Heat Trans taught by Professor Lee,j.s. during the Spring '10 term at Seoul National.
 Spring '10
 LEE,J.S.
 Heat Transfer

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