绗崄绔?/p>
瀵规祦鎹㈢儹
鑻辨枃涔犻
1. Finding convection coefficient from drag measurement
A 2 m脳
3 m flat plate is suspended in a room, and is subjected to air flow parallel to its
surfaces along its 3-m-long side. The free stream temperature and velocity of air are
20
鈩?/p>
and
7m/s.
The
total
drag
force
acting
on
the
plate
is
measured
to
be
0.86
N.
Determine the average convection heat transfer coefficient for the plate (Fig. 10-1).
2. Cooling of a hot block by forced air at high elevation
The local atmospheric pressure in Denver, Colorado (elevation 1610
m), is 83.4 kPa. Air at this pressure and 20
鈩?/p>
flows with a velocity of 8
m/s over a 1.5 m脳
6 m flat plate whose temperature is 140
鈩?/p>
(Fig. 10-2).
Determine
the
rate
of
heat
transfer
from
the
plate
if
the
air
flows
parallel to the (a) 6-m-long side and (b) the 1.5-m side.
3. Cooling of a steel ball by forced air
A 25-cm-diameter stainless steel ball (
蟻=8055 kg/m
3
, and C
p
=480 J/kg.
鈩?/p>
) is removed from the oven at
a uniform temperature of 300
鈩?/p>
. The ball is then subjected to the flow of air at 1 atm pressure and 25
鈩?/p>
with a velocity of 3 m/s. The surface temperature of the ball eventually
drops
to
200
鈩?/p>
.
Determine
the
average
convection
heat
transfer
coefficient
during
this
cooling
process
and
estimate
how
long
the
process will take.
4.
Flow
of
oil
in a
pipeline
through
the
icy
waters
of
a
lake
Consider
the
flow
of
oil
at
20
鈩?/p>
in
a
30-cm-diameter
pipeline
at
an
average velocity of 2 m/s (Fig.10-3). A 200-m-long section of the pipeline
passes through icy waters of a lake at 0
鈩?/p>
. Measurements indicate that
the
surface
temperature
of
the
pipe
is
very
nearly
0
鈩?/p>
.
disregarding
thermal resistance of the pipe material, determine (a) the temperature of
the oil when the pipe leaves the lake, (b) the rate of heat transfer from
the oil.
5. Heat loss through a double-pane window
The
vertical
0.8-m-high,
2-m-wide
double-pane
window
shown
in
Fig.10-3, consists of two sheets of glass separated by a 2-cm air gap at
atmospheric pressure. If the glass surface temperatures across the air
gap
are
measured
to
be
12
鈩?/p>
and
2
鈩?/p>
,
determine
the
rate
of
heat
transfer through the window.
FIGURE 10-1
FIGURE 10-2
FIGURE 10-3
FIGURE 10-4